**Copper and Copper Alloys: Casting, Classification and Characteristic Microstructures**

Radomila Konečná and Stanislava Fintová *University of Žilina Slovak Republic* 

#### **1. Introduction**

#### **1.1 Copper**

Copper is non-polymorphous metal with face centered cubic lattice (FCC, Fig. 1). Pure copper is a reddish color (Fig. 2); zinc addition produces a yellow color, and nickel addition produces a silver color. Melting temperature is 1083 °C and density is 8900 kg.m-3, which is three times heavier than aluminum. The heat and electric conductivity of copper is lower compared to the silver, but it is 1.5 times larger compared to the aluminum. Pure copper

Fig. 1. FCC lattice (http://cst-www.nrl.navy.mil/lattice/struk/a1.html)

Fig. 2. Natural copper (http://jeanes.webnode.sk/prvky/med/)

Copper and Copper Alloys: Casting, Classification and Characteristic Microstructures 5

a) temperature influence on tensile strength, yield value and ductility

b) change properties due to the cold forming

Fig. 3. Copper mechanical properties (Skočovský et al., 2006).

surface cracking, porosity, and the formation of internal cavities are high.

Copper resists oxidation, however, it is reactive with sulphur and its chemical compounds, and during this reaction copper sulphide is created. Besides oxygen, the main contaminant, phosphor and iron are the significant copper contaminants. It is difficult to cast pure copper because large shrinkages during the solidification occur (1.5 %), and is the dissolving of a large amount of gasses at high temperatures disengaged during the solidification process and resulting in the melted metal gassing and the casting porosity (Fig. 4a, b). Cast copper microstructure is formed by non-uniform grains with very different sizes. Wrought copper microstructure consists of uniform polyhedral grains with similar grain size and it is also possible to observe annealing twins (Fig. 4c-e). Because of coppers reactivity, the dangers of

electric conductivity is used like a basic value for other metals evaluation and electric conductivity alloys characterization (Skočovský et al., 2000, 2006). Copper conductivity standard (IASC) is determined as 58 Mss-1. The pure metal alloying decreased its conductivity (Skočovský et al., 2000).

Before the copper products usage it has to pass through a number of stages. When recycled, it can pass through some stages over and over again. In nature, copper in its pure metal form occurs very often. Metallurgically from ores, where the chemical compound of copper with oxygen, sulphur or other elements occurs, copper is produced:


The beginning for all copper is to mine sulfide and oxide ores through digging or blasting and then crushing these to walnut-sized pieces. Crushed ore is ball or rod-milled in large, rotating, cylindrical machines until it becomes a powder, usually containing less than 1 % copper. Sulfide ores are moved to a concentrating stage, while oxide ores are routed to leaching tanks.

Minerals are concentrated into slurry that is about 15 % of copper. Waste slag is removed. Water is recycled. Tailings (left-over earth) containing copper oxide are routed to leaching tanks or are returned to the surrounding terrain. Once copper has been concentrated, it can be turned into pure copper cathode in two different ways: leaching & electrowinning or smelting and electrolytic refining.

Oxide ore and tailings are leached by a weak acid solution, producing a weak copper sulfate solution. The copper-laden solution is treated and transferred to an electrolytic process tank. When electrically charged, pure copper ions migrate directly from the solution to starter cathodes made from pure copper foil. Precious metals can be extracted from the solution.

Several stages of melting and purifying the copper content result, successively, in matte, blister and, finally, 99% pure copper. Recycled copper begins its journey to finding another use by being remelted. Anodes cast from the nearly pure copper are immersed in an acid bath. Pure copper ions migrate electrolytically from the anodes to "starter sheets" made from pure copper foil where they deposit and build up into a 300-pound cathode. Gold, silver and platinum may be recovered from the used bath.

Cathodes of 99.9% purity may be shipped as melting stock to mills or foundries. Cathodes may also be cast into wire rod, billets, cakes or ingots, generally, as pure copper or alloyed with other metals (http://www.mtfdca.szm.com/subory/med-zliatiny.pdf, http://www.copper.org/education/production.html).

Coppers mechanical properties (Fig. 3) depend on its state and are defined by its lattice structure. Copper has good formability and toughness at room temperature and also at reduced temperature. Increasing the temperature steadily decreases coppers strength properties. Also at around 500 °C the coppers technical plastic properties decrease. Due to this behavior, cold forming or hot forming at 800 to 900 °C of copper is proper. Cold forming increases the strength properties but results in ductility decreasing. In the as cast state, the copper has strength of 160 MPa. Hot rolling increases coppers strength to 220 MPa. Copper has a good ductility and by cold deformation it is possible to reach the strength values close to the strength values of soft steel (Skočovský et al., 2000, 2006).

electric conductivity is used like a basic value for other metals evaluation and electric conductivity alloys characterization (Skočovský et al., 2000, 2006). Copper conductivity standard (IASC) is determined as 58 Mss-1. The pure metal alloying decreased its

Before the copper products usage it has to pass through a number of stages. When recycled, it can pass through some stages over and over again. In nature, copper in its pure metal form occurs very often. Metallurgically from ores, where the chemical compound of copper


The beginning for all copper is to mine sulfide and oxide ores through digging or blasting and then crushing these to walnut-sized pieces. Crushed ore is ball or rod-milled in large, rotating, cylindrical machines until it becomes a powder, usually containing less than 1 % copper. Sulfide ores are moved to a concentrating stage, while oxide ores are routed to leaching tanks. Minerals are concentrated into slurry that is about 15 % of copper. Waste slag is removed. Water is recycled. Tailings (left-over earth) containing copper oxide are routed to leaching tanks or are returned to the surrounding terrain. Once copper has been concentrated, it can be turned into pure copper cathode in two different ways: leaching & electrowinning or

Oxide ore and tailings are leached by a weak acid solution, producing a weak copper sulfate solution. The copper-laden solution is treated and transferred to an electrolytic process tank. When electrically charged, pure copper ions migrate directly from the solution to starter cathodes made from pure copper foil. Precious metals can be extracted from the solution. Several stages of melting and purifying the copper content result, successively, in matte, blister and, finally, 99% pure copper. Recycled copper begins its journey to finding another use by being remelted. Anodes cast from the nearly pure copper are immersed in an acid bath. Pure copper ions migrate electrolytically from the anodes to "starter sheets" made from pure copper foil where they deposit and build up into a 300-pound cathode. Gold, silver and

Cathodes of 99.9% purity may be shipped as melting stock to mills or foundries. Cathodes may also be cast into wire rod, billets, cakes or ingots, generally, as pure copper or alloyed with other metals (http://www.mtfdca.szm.com/subory/med-zliatiny.pdf,

Coppers mechanical properties (Fig. 3) depend on its state and are defined by its lattice structure. Copper has good formability and toughness at room temperature and also at reduced temperature. Increasing the temperature steadily decreases coppers strength properties. Also at around 500 °C the coppers technical plastic properties decrease. Due to this behavior, cold forming or hot forming at 800 to 900 °C of copper is proper. Cold forming increases the strength properties but results in ductility decreasing. In the as cast state, the copper has strength of 160 MPa. Hot rolling increases coppers strength to 220 MPa. Copper has a good ductility and by cold deformation it is possible to reach the strength

values close to the strength values of soft steel (Skočovský et al., 2000, 2006).

with oxygen, sulphur or other elements occurs, copper is produced:


conductivity (Skočovský et al., 2000).


smelting and electrolytic refining.

platinum may be recovered from the used bath.

http://www.copper.org/education/production.html).

a) temperature influence on tensile strength, yield value and ductility

b) change properties due to the cold forming

Fig. 3. Copper mechanical properties (Skočovský et al., 2006).

Copper resists oxidation, however, it is reactive with sulphur and its chemical compounds, and during this reaction copper sulphide is created. Besides oxygen, the main contaminant, phosphor and iron are the significant copper contaminants. It is difficult to cast pure copper because large shrinkages during the solidification occur (1.5 %), and is the dissolving of a large amount of gasses at high temperatures disengaged during the solidification process and resulting in the melted metal gassing and the casting porosity (Fig. 4a, b). Cast copper microstructure is formed by non-uniform grains with very different sizes. Wrought copper microstructure consists of uniform polyhedral grains with similar grain size and it is also possible to observe annealing twins (Fig. 4c-e). Because of coppers reactivity, the dangers of surface cracking, porosity, and the formation of internal cavities are high.

Copper and Copper Alloys: Casting, Classification and Characteristic Microstructures 7

c) microstructure of wrought Cu with uniform polyhedral grains and annealing twins, white

d) the same microstructure of wrought Cu, polarized light

Fig. 4. Pure copper, chemically polished

light

a) microstructure of cast Cu; specimens edge on the right, where is different grain size due to high cooling rate on the surface

b) cast Cu; specimens middle part with big grains at low cooling rate Fig. 4. Pure copper, chemically polished

a) microstructure of cast Cu; specimens edge on the right, where is different grain size due

b) cast Cu; specimens middle part with big grains at low cooling rate

Fig. 4. Pure copper, chemically polished

to high cooling rate on the surface

c) microstructure of wrought Cu with uniform polyhedral grains and annealing twins, white light

d) the same microstructure of wrought Cu, polarized light Fig. 4. Pure copper, chemically polished

Copper and Copper Alloys: Casting, Classification and Characteristic Microstructures 9

The casting characteristics of copper can be improved by the addition of small amounts of elements like beryllium, silicon, nickel, tin, zinc, chromium, and silver. In copper based alloys 14 alloying elements, almost always in the solid solution dissolving area, are used. Most of the industrial alloys are monophasic and they do not show allotropic changes during heating or cooling. For some copper-base alloys precipitation hardening is possible. For the alloys with allotropic recrystallization heat treatment is possible. Single-phase copper alloys are strengthened by cold-working. The FCC copper has excellent ductility and

Copper and copper based alloys can be divided into 3 groups according to the chemical

The copper based alloys, according to the application can be divided into two groups, as copper alloys for casting and wrought alloys subsequently. Copper-base alloys are heavier

Although the yield strength of some alloys is high, their specific strength is typically less than that of aluminum or magnesium alloys. The alloys have better resistance to fatigue, creep, and wear than the lightweight aluminum and magnesium alloys. Many of the alloys have excellent ductility, corrosion resistance, and electrical and thermal conductivity, and they are easily joined or fabricated into useful shapes. The wide varieties of copper-based alloys take advantage of all of the straightening mechanisms on the mechanical properties

From the casting point of view, especially the solidification (freezing range) Cu cast alloys

*Group I alloys* - alloys that have a narrow freezing range, that is, a range of 50 °C between the liquidus and solidus curves. These are the yellow brasses, manganese and aluminum

*Group II alloys* – alloys that have an intermediate freezing range, that is, a freezing range of 50 to 110 °C between the liquidus and the solidus curves. These are the beryllium coppers,

*Group III alloys* – alloys that have a wide freezing range. These alloys have a freezing range of well over 110 °C, even up to 170 °C. These are the leaded red and semi-red brasses, tin and leaded tin bronzes, and high leaded tin bronze alloys (R. F. Schmidt, D. G. Schmidt &

According to the cast products quality the Cu based foundry alloys can be classified as highshrinkage or low-shrinkage alloys. The former class includes the manganese bronzes, aluminum bronzes, silicon bronzes, silicon brasses, and some nickel-silvers. They are more fluid than the low-shrinkage red brasses, more easily poured, and give high-grade castings

bronzes, nickel bronze, manganese bronze alloys, chromium copper, and copper.

a high strain-hardening coefficient.


than iron (Skočovský et al., 2006).

**1.2 Copper and copper alloys casting** 

silicon bronzes, silicon brass, and copper-nickel alloys.

can be divided into three groups:

(Skočovský et al., 2000).

Sahoo 1998).


composition:

e) detail of wrought Cu grains, white light

f) detail of wrought Cu grains, polarized light Fig. 4. Pure copper, chemically polished

The casting characteristics of copper can be improved by the addition of small amounts of elements like beryllium, silicon, nickel, tin, zinc, chromium, and silver. In copper based alloys 14 alloying elements, almost always in the solid solution dissolving area, are used. Most of the industrial alloys are monophasic and they do not show allotropic changes during heating or cooling. For some copper-base alloys precipitation hardening is possible. For the alloys with allotropic recrystallization heat treatment is possible. Single-phase copper alloys are strengthened by cold-working. The FCC copper has excellent ductility and a high strain-hardening coefficient.

Copper and copper based alloys can be divided into 3 groups according to the chemical composition:


8 Copper Alloys – Early Applications and Current Performance – Enhancing Processes

e) detail of wrought Cu grains, white light

f) detail of wrought Cu grains, polarized light

Fig. 4. Pure copper, chemically polished


The copper based alloys, according to the application can be divided into two groups, as copper alloys for casting and wrought alloys subsequently. Copper-base alloys are heavier than iron (Skočovský et al., 2006).

Although the yield strength of some alloys is high, their specific strength is typically less than that of aluminum or magnesium alloys. The alloys have better resistance to fatigue, creep, and wear than the lightweight aluminum and magnesium alloys. Many of the alloys have excellent ductility, corrosion resistance, and electrical and thermal conductivity, and they are easily joined or fabricated into useful shapes. The wide varieties of copper-based alloys take advantage of all of the straightening mechanisms on the mechanical properties (Skočovský et al., 2000).

#### **1.2 Copper and copper alloys casting**

From the casting point of view, especially the solidification (freezing range) Cu cast alloys can be divided into three groups:

*Group I alloys* - alloys that have a narrow freezing range, that is, a range of 50 °C between the liquidus and solidus curves. These are the yellow brasses, manganese and aluminum bronzes, nickel bronze, manganese bronze alloys, chromium copper, and copper.

*Group II alloys* – alloys that have an intermediate freezing range, that is, a freezing range of 50 to 110 °C between the liquidus and the solidus curves. These are the beryllium coppers, silicon bronzes, silicon brass, and copper-nickel alloys.

*Group III alloys* – alloys that have a wide freezing range. These alloys have a freezing range of well over 110 °C, even up to 170 °C. These are the leaded red and semi-red brasses, tin and leaded tin bronzes, and high leaded tin bronze alloys (R. F. Schmidt, D. G. Schmidt & Sahoo 1998).

According to the cast products quality the Cu based foundry alloys can be classified as highshrinkage or low-shrinkage alloys. The former class includes the manganese bronzes, aluminum bronzes, silicon bronzes, silicon brasses, and some nickel-silvers. They are more fluid than the low-shrinkage red brasses, more easily poured, and give high-grade castings

Copper and Copper Alloys: Casting, Classification and Characteristic Microstructures 11

The core type, better known as the channel furnace, and the coreless type of electric induction furnaces for Cu and its alloys melting are also used. Because core type furnaces are very efficient and simple to operate with lining life in the millions of pounds poured, they are best suited for continuous production runs in foundries making plumbing alloys of the leaded red and semi-red brasses, tin and leaded tin bronzes, and high leaded tin bronze alloys. They are not recommended for dross-forming alloys; yellow brasses, manganese and aluminum bronzes, nickel bronze, manganese bronze alloys, chromium copper, and copper. The channel furnace is at its best when an inert, floating, cover flux is used and charges of

Coreless type furnaces have become the most popular melting unit in the Cu alloy foundry

**Commercially pure copper and high copper alloys** are very difficult to melt and they are very susceptible to gassing. Chromium copper melting is negatively linked with oxidation loss of chromium. To prevent both oxidation and the pickup of hydrogen from the atmosphere copper and chromium copper should be melted under a floating flux cover. In the case of pure copper crushed graphite should cover the melt. In the case of chromium copper, the cover should be a proprietary flux made for this alloy. It is necessary to deoxidize the melted metal. For this reason the calcium boride or lithium should be plunged into the molten bath when the melted metal reaches 1260 °C. The metal should then be

**Beryllium coppers** can be very toxic and dangerous. This is caused by the beryllium content in cases where beryllium fumes are not captured and exhausted by proper ventilating equipment. To minimize beryllium losses beryllium coppers should be melted quickly under a slightly oxidizing atmosphere. They can be melted and poured successfully at

**Copper-nickel alloys** (90Cu-10Ni and 70Cu-30Ni) must also be carefully melted. Concern is caused by the presence of nickel in high percentages because this raises not only the melting point but also the susceptibility to hydrogen pickup. These alloys are melted in coreless electric induction furnaces, because the melting rate is much faster than it is with a fuel-fired furnace. The metal should be quickly heated to a temperature slightly above the pouring temperature and deoxidized either by the use of one of the proprietary degasifiers used with nickel bronzes or, better yet, by plunging 0.1 % Mg stick to the bottom of the ladle. This has to be done to prevent the of steam-reaction porosity from occurring by the oxygen removing. If the gates and risers are cleaned by shotblasting prior to melting there is a little

**Yellow Brasses** (containing 23 - 41 % of zinc) as the major alloying element and may contain up to 3 % of lead and up to 1.5 % of tin as additional alloying elements. Due to vaporization these alloys flare, ore lose zinc close to the melting point. The zinc vaporization can be minimized by the addition of aluminum (0.15 to 0.35 %) which also increases the melted

ingot, clean remelt, and clean and dry turnings are added periodically.

industry (R. F. Schmidt, D. G. Schmidt & Sahoo, 1988).

**1.2.3 Pure copper and high copper alloys** 

poured without removing the floating cover.

**1.2.4 Brasses** 

relatively low temperatures. They are very fluid and pour well.

need to use cover fluxes (R. F. Schmidt, D. G. Schmidt & Sahoo, 1988).

in the sand, permanent mold, plaster, die, and centrifugal casting processes. With highshrinkage alloys, careful design is necessary to promote directional solidification, avoid abrupt changes in cross section, avoid notches (by using generous fillets), and properly place gates and risers; all of these design precautions help avoid internal shrinks and cracks (R. F. Schmidt & D. G. Schmidt, 1997).

#### **1.2.1 Casting**

To obtain good results from the product quality point of view, the casting processes technological specifications are the most important factor. The lowest possible pouring temperature needed to suit the size and form of the solid metal should be used to encourage as small a grain size as possible, as well as to create a minimum of turbulence of the metal during pouring to prevent the casting defects formation (R. F. Schmidt, D. G. Schmidt & Sahoo, 1988). Liberal use of risers or exothermic compounds ensures adequate molten metal to feed all sections of the casting.

Many types of castings for Cu and its alloys casting, such as sand, shell, investment, permanent mold, chemical sand, centrifugal, and die, can be used (R. F. Schmidt, D. G. Schmidt & Sahoo, 1988). Of course each of them has its advantages and disadvantages. If only a few castings are made and flexibility in casting size and shape is required, the most economical casting method is sand casting. For tin, silicon, aluminum and manganese bronzes, and also yellow brasses, permanent mold casting is best suited. For yellow brasses die casting is well suited, but increasing amounts of permanent mold alloys are also being die cast. Definite limitation for both methods is the casting size, due to the reducing the mold life with larger castings.

All copper alloys can be cast successfully by the centrifugal casting process. Because of their low lead contents, aluminum bronzes, yellow brasses, manganese bronzes, low-nickel bronzes, and silicon brasses and bronzes are best adapted to plaster mold casting. Lead should be held to a minimum for most of these alloys because lead reacts with the calcium sulfate in the plaster, resulting in discoloration of the surface of the casting and increased cleaning and machining costs.

#### **1.2.2 Furnaces**

The copper based alloys are melted mainly in Fuel-Fired Furnaces and Electric Induction Furnaces.

From Fuel-Fired Furnaces, oil- and gas-fired furnaces are the most important. However openflame furnaces are able to melt large amounts of metal quickly; there is a need for operator skill to control the melting atmosphere within the furnace at present this kind of furnaces are not often used. Also, the refractory furnace walls become impregnated with the melting metal causing a contamination problem when switching from one alloy family to another.

When melting leaded red and semi-red brasses, tin and leaded tin bronzes, and high leaded tin bronze alloys, lead and zinc fumes are given off during melting and superheating. These harmful oxides emissions are much lower when the charge is melted in an induction furnace. This is caused by the duration of the melting cycle is only about 25 % of the cycle in a fuel-fired furnace.

The core type, better known as the channel furnace, and the coreless type of electric induction furnaces for Cu and its alloys melting are also used. Because core type furnaces are very efficient and simple to operate with lining life in the millions of pounds poured, they are best suited for continuous production runs in foundries making plumbing alloys of the leaded red and semi-red brasses, tin and leaded tin bronzes, and high leaded tin bronze alloys. They are not recommended for dross-forming alloys; yellow brasses, manganese and aluminum bronzes, nickel bronze, manganese bronze alloys, chromium copper, and copper. The channel furnace is at its best when an inert, floating, cover flux is used and charges of ingot, clean remelt, and clean and dry turnings are added periodically.

Coreless type furnaces have become the most popular melting unit in the Cu alloy foundry industry (R. F. Schmidt, D. G. Schmidt & Sahoo, 1988).

#### **1.2.3 Pure copper and high copper alloys**

10 Copper Alloys – Early Applications and Current Performance – Enhancing Processes

in the sand, permanent mold, plaster, die, and centrifugal casting processes. With highshrinkage alloys, careful design is necessary to promote directional solidification, avoid abrupt changes in cross section, avoid notches (by using generous fillets), and properly place gates and risers; all of these design precautions help avoid internal shrinks and cracks

To obtain good results from the product quality point of view, the casting processes technological specifications are the most important factor. The lowest possible pouring temperature needed to suit the size and form of the solid metal should be used to encourage as small a grain size as possible, as well as to create a minimum of turbulence of the metal during pouring to prevent the casting defects formation (R. F. Schmidt, D. G. Schmidt & Sahoo, 1988). Liberal use of risers or exothermic compounds ensures adequate molten metal

Many types of castings for Cu and its alloys casting, such as sand, shell, investment, permanent mold, chemical sand, centrifugal, and die, can be used (R. F. Schmidt, D. G. Schmidt & Sahoo, 1988). Of course each of them has its advantages and disadvantages. If only a few castings are made and flexibility in casting size and shape is required, the most economical casting method is sand casting. For tin, silicon, aluminum and manganese bronzes, and also yellow brasses, permanent mold casting is best suited. For yellow brasses die casting is well suited, but increasing amounts of permanent mold alloys are also being die cast. Definite limitation for both methods is the casting size, due to the reducing the

All copper alloys can be cast successfully by the centrifugal casting process. Because of their low lead contents, aluminum bronzes, yellow brasses, manganese bronzes, low-nickel bronzes, and silicon brasses and bronzes are best adapted to plaster mold casting. Lead should be held to a minimum for most of these alloys because lead reacts with the calcium sulfate in the plaster, resulting in discoloration of the surface of the casting and increased

The copper based alloys are melted mainly in Fuel-Fired Furnaces and Electric Induction

From Fuel-Fired Furnaces, oil- and gas-fired furnaces are the most important. However openflame furnaces are able to melt large amounts of metal quickly; there is a need for operator skill to control the melting atmosphere within the furnace at present this kind of furnaces are not often used. Also, the refractory furnace walls become impregnated with the melting metal

When melting leaded red and semi-red brasses, tin and leaded tin bronzes, and high leaded tin bronze alloys, lead and zinc fumes are given off during melting and superheating. These harmful oxides emissions are much lower when the charge is melted in an induction furnace. This is caused by the duration of the melting cycle is only about 25 % of the cycle in

causing a contamination problem when switching from one alloy family to another.

(R. F. Schmidt & D. G. Schmidt, 1997).

to feed all sections of the casting.

mold life with larger castings.

cleaning and machining costs.

**1.2.2 Furnaces** 

a fuel-fired furnace.

Furnaces.

**1.2.1 Casting** 

**Commercially pure copper and high copper alloys** are very difficult to melt and they are very susceptible to gassing. Chromium copper melting is negatively linked with oxidation loss of chromium. To prevent both oxidation and the pickup of hydrogen from the atmosphere copper and chromium copper should be melted under a floating flux cover. In the case of pure copper crushed graphite should cover the melt. In the case of chromium copper, the cover should be a proprietary flux made for this alloy. It is necessary to deoxidize the melted metal. For this reason the calcium boride or lithium should be plunged into the molten bath when the melted metal reaches 1260 °C. The metal should then be poured without removing the floating cover.

**Beryllium coppers** can be very toxic and dangerous. This is caused by the beryllium content in cases where beryllium fumes are not captured and exhausted by proper ventilating equipment. To minimize beryllium losses beryllium coppers should be melted quickly under a slightly oxidizing atmosphere. They can be melted and poured successfully at relatively low temperatures. They are very fluid and pour well.

**Copper-nickel alloys** (90Cu-10Ni and 70Cu-30Ni) must also be carefully melted. Concern is caused by the presence of nickel in high percentages because this raises not only the melting point but also the susceptibility to hydrogen pickup. These alloys are melted in coreless electric induction furnaces, because the melting rate is much faster than it is with a fuel-fired furnace. The metal should be quickly heated to a temperature slightly above the pouring temperature and deoxidized either by the use of one of the proprietary degasifiers used with nickel bronzes or, better yet, by plunging 0.1 % Mg stick to the bottom of the ladle. This has to be done to prevent the of steam-reaction porosity from occurring by the oxygen removing. If the gates and risers are cleaned by shotblasting prior to melting there is a little need to use cover fluxes (R. F. Schmidt, D. G. Schmidt & Sahoo, 1988).

#### **1.2.4 Brasses**

**Yellow Brasses** (containing 23 - 41 % of zinc) as the major alloying element and may contain up to 3 % of lead and up to 1.5 % of tin as additional alloying elements. Due to vaporization these alloys flare, ore lose zinc close to the melting point. The zinc vaporization can be minimized by the addition of aluminum (0.15 to 0.35 %) which also increases the melted

Copper and Copper Alloys: Casting, Classification and Characteristic Microstructures 13

because they are very fluid. The alloy superheating resulting in the zinc vaporization and

**Aluminum bronzes** must be melted carefully under an oxidizing atmosphere and heated to the proper furnace temperature. If needed, degasifiers removing the hydrogen and oxygen from the melted metal can be stirred into the melt as the furnace is being tapped. By pouring a blind sprue before tapping and examining the metal after freezing, it is possible to tell whether it shrank or exuded gas. If the sample purged or overflowed the blind sprue during solidification, degassing is necessary. For converting melted metal fluxes, are available, mainly in powder form, and usually fluorides. They are used for the elimination of oxides, which normally form on top of the melt during melting and superheating (R. F. Schmidt, D.

From the freezing range point of view, the manganese and aluminum bronzes are similar to steels. Their freezing ranges are quite narrow, about 40 and 14 °C, respectively. Large castings can be made by the same conventional methods used for steel. The attention has to be given to placement of gates and risers, both those for controlling directional solidification and those for feeding the primary central shrinkage cavity (R. F. Schmidt & D. G. Schmidt,

**Nickel bronzes***,* also known as nickel silver, are difficult to melt because nickel increases the hydrogen solubility, if the alloy is not melted properly it gases readily. These alloys must be melted under an oxidizing atmosphere and they have to be quickly superheated to the proper furnace temperature to allow for temperature losses during fluxing and handling. After the furnace tapping the proprietary fluxes should be stirred into the metal for the hydrogen and oxygen removing. These fluxes contain manganese, calcium, silicon,

**Silicon bronzes** are relatively easy to melt and should be poured at the proper pouring temperatures. In the case of overheating the hydrogen, picking up can occur. For degassing, one of the proprietary degasifiers used with aluminum bronze can be successfully used.

**Tin and leaded tin bronzes**, and **high-leaded tin bronzes**, are treated the same in regard to melting and fluxing. Their treatment is the same as in the case of the red brasses and leaded red brasses, because of the similar freezing range which is long (R. F. Schmidt, D. G.

**Tin bronzes** have practically no feeding range, and it is extremely difficult to get fully sound castings. Alloys with such wide freezing ranges form a mushy zone during solidification, resulting in interdendritic shrinkages or microshrinkages. In overcoming this effect, design and riser placement, plus the use of chills, are important and also the solidification speed, for better results the rapid solidification should be ensured. As in the case of leaded red brasses, tin bronzes also have problems with porosity. The castings contain 1 to 2 % of porosity and only small castings have porosity below 1 %. Directional solidification is best for relatively large, thick castings and for smaller, thin wall castings, uniform solidification is recommended. Sections up to 25 mm in thickness are routinely cast. Sections up to 50 mm thick can be cast, but only with difficulty and under carefully

the chemistry of the alloy is changed. Normally, no fluxes are used with these alloys.

G. Schmidt & Sahoo, 1988).

magnesium, and phosphorus.

Schmidt & Sahoo, 1988).

Normally no cover fluxes are used for these alloys.

controlled conditions (R. F. Schmidt & D. G. Schmidt, 1997).

1997).

metals fluidity. In the case of larger aluminum amount shrinkages take place during freezing; this has to be solved by use of risers. Except for aluminum problems, yellow brass melting is simple and no fluxing is necessary. Zinc lost during the melting should be readded before pouring.

**Silicon brasses** have excellent fluidity and can be poured slightly above their freezing range. If overheated, they can pick up hydrogen. In the case of the silicon brasses no cover fluxes are required.

**Red brasses and leaded red brasses** are copper alloys, containing 2 - 15 % of zinc as the major alloying element and up to 5 % of Sn and up to 8 % of Pb as additional alloying elements. Because of lengthy freezing range in the case of these alloys, chills and risers should be used in conjunction with each other. The best pouring temperature is the lowest one that will pour the molds without having misruns or cold shuts. For good casting, properties retaining these alloys should be melted from charges comprised of ingot and clean, sandfree gates and risers. The melting should be done quickly in a slightly oxidizing atmosphere. When at the proper furnace temperature to allow for handling and cooling to the proper pouring temperature, the crucible is removed or the metal is tapped into a ladle. At this point, a deoxidizer (15 % phosphorus copper) is added. The phosphorus is a reducing agent (deoxidizer) and must be carefully measured so that enough oxygen is removed, yet a small amount remains to improve fluidity. This residual level of phosphorus must be controlled by chemical analysis. Only amount in the range 0.010 and 0.020 % P is accepted, in the case of the larger phosphorus amount internal porosity may occur. Along with phosphorus copper pure zinc should also be added at the point at which skimming and temperature testing take place prior to pouring. This added zinc replaces the zinc lost during melting and superheating. With these alloys, cover fluxes are seldom used. In some foundries in which combustion cannot be properly controlled, oxidizing fluxes are added during melting, followed by final deoxidation by phosphor copper.

**Leaded red brasses** alloys have practically no feeding range, and it is extremely difficult to get fully sound castings. Leaded red brasses castings contain 1 to 2 % of porosity. Only small castings have porosity below 1 %. Experience has shown that success in achieving good quality castings depends on avoiding slow cooling rates. Directional solidification is the best for relatively large, thick castings and for smaller, thin wall castings, uniform solidification is recommended (R. F. Schmidt, D. G. Schmidt & Sahoo 1998).

#### **1.2.5 Bronzes**

**Manganese bronzes** are carefully compounded yellow brasses with measured quantities of iron, manganese, and aluminum. When the metal is heated at the flare temperature or to the point at which zinc oxide vapor can be detected, it should be removed from the furnace and poured. No fluxing is required with these alloys. The only required addition is zinc, which is caused by its vaporization. The necessary amount is the one which will bring the zinc content back to the original analysis. This varies from very little, if any, when an all-ingot heat is being poured, to several percent if the heat contains a high percentage of remelt.

**White manganese bronzes***.* There are two alloys in this family, both of which are copperzinc alloys containing a large amount of manganese and, in one case, nickel. They are manganese bronze type alloys, are simple to melt, and can be poured at low temperatures

metals fluidity. In the case of larger aluminum amount shrinkages take place during freezing; this has to be solved by use of risers. Except for aluminum problems, yellow brass melting is simple and no fluxing is necessary. Zinc lost during the melting should be re-

**Silicon brasses** have excellent fluidity and can be poured slightly above their freezing range. If overheated, they can pick up hydrogen. In the case of the silicon brasses no cover

**Red brasses and leaded red brasses** are copper alloys, containing 2 - 15 % of zinc as the major alloying element and up to 5 % of Sn and up to 8 % of Pb as additional alloying elements. Because of lengthy freezing range in the case of these alloys, chills and risers should be used in conjunction with each other. The best pouring temperature is the lowest one that will pour the molds without having misruns or cold shuts. For good casting, properties retaining these alloys should be melted from charges comprised of ingot and clean, sandfree gates and risers. The melting should be done quickly in a slightly oxidizing atmosphere. When at the proper furnace temperature to allow for handling and cooling to the proper pouring temperature, the crucible is removed or the metal is tapped into a ladle. At this point, a deoxidizer (15 % phosphorus copper) is added. The phosphorus is a reducing agent (deoxidizer) and must be carefully measured so that enough oxygen is removed, yet a small amount remains to improve fluidity. This residual level of phosphorus must be controlled by chemical analysis. Only amount in the range 0.010 and 0.020 % P is accepted, in the case of the larger phosphorus amount internal porosity may occur. Along with phosphorus copper pure zinc should also be added at the point at which skimming and temperature testing take place prior to pouring. This added zinc replaces the zinc lost during melting and superheating. With these alloys, cover fluxes are seldom used. In some foundries in which combustion cannot be properly controlled, oxidizing fluxes are added

**Leaded red brasses** alloys have practically no feeding range, and it is extremely difficult to get fully sound castings. Leaded red brasses castings contain 1 to 2 % of porosity. Only small castings have porosity below 1 %. Experience has shown that success in achieving good quality castings depends on avoiding slow cooling rates. Directional solidification is the best for relatively large, thick castings and for smaller, thin wall castings, uniform solidification

**Manganese bronzes** are carefully compounded yellow brasses with measured quantities of iron, manganese, and aluminum. When the metal is heated at the flare temperature or to the point at which zinc oxide vapor can be detected, it should be removed from the furnace and poured. No fluxing is required with these alloys. The only required addition is zinc, which is caused by its vaporization. The necessary amount is the one which will bring the zinc content back to the original analysis. This varies from very little, if any, when an all-ingot heat is being poured, to several percent if the heat contains a high percentage of remelt.

**White manganese bronzes***.* There are two alloys in this family, both of which are copperzinc alloys containing a large amount of manganese and, in one case, nickel. They are manganese bronze type alloys, are simple to melt, and can be poured at low temperatures

during melting, followed by final deoxidation by phosphor copper.

is recommended (R. F. Schmidt, D. G. Schmidt & Sahoo 1998).

added before pouring.

fluxes are required.

**1.2.5 Bronzes** 

because they are very fluid. The alloy superheating resulting in the zinc vaporization and the chemistry of the alloy is changed. Normally, no fluxes are used with these alloys.

**Aluminum bronzes** must be melted carefully under an oxidizing atmosphere and heated to the proper furnace temperature. If needed, degasifiers removing the hydrogen and oxygen from the melted metal can be stirred into the melt as the furnace is being tapped. By pouring a blind sprue before tapping and examining the metal after freezing, it is possible to tell whether it shrank or exuded gas. If the sample purged or overflowed the blind sprue during solidification, degassing is necessary. For converting melted metal fluxes, are available, mainly in powder form, and usually fluorides. They are used for the elimination of oxides, which normally form on top of the melt during melting and superheating (R. F. Schmidt, D. G. Schmidt & Sahoo, 1988).

From the freezing range point of view, the manganese and aluminum bronzes are similar to steels. Their freezing ranges are quite narrow, about 40 and 14 °C, respectively. Large castings can be made by the same conventional methods used for steel. The attention has to be given to placement of gates and risers, both those for controlling directional solidification and those for feeding the primary central shrinkage cavity (R. F. Schmidt & D. G. Schmidt, 1997).

**Nickel bronzes***,* also known as nickel silver, are difficult to melt because nickel increases the hydrogen solubility, if the alloy is not melted properly it gases readily. These alloys must be melted under an oxidizing atmosphere and they have to be quickly superheated to the proper furnace temperature to allow for temperature losses during fluxing and handling. After the furnace tapping the proprietary fluxes should be stirred into the metal for the hydrogen and oxygen removing. These fluxes contain manganese, calcium, silicon, magnesium, and phosphorus.

**Silicon bronzes** are relatively easy to melt and should be poured at the proper pouring temperatures. In the case of overheating the hydrogen, picking up can occur. For degassing, one of the proprietary degasifiers used with aluminum bronze can be successfully used. Normally no cover fluxes are used for these alloys.

**Tin and leaded tin bronzes**, and **high-leaded tin bronzes**, are treated the same in regard to melting and fluxing. Their treatment is the same as in the case of the red brasses and leaded red brasses, because of the similar freezing range which is long (R. F. Schmidt, D. G. Schmidt & Sahoo, 1988).

**Tin bronzes** have practically no feeding range, and it is extremely difficult to get fully sound castings. Alloys with such wide freezing ranges form a mushy zone during solidification, resulting in interdendritic shrinkages or microshrinkages. In overcoming this effect, design and riser placement, plus the use of chills, are important and also the solidification speed, for better results the rapid solidification should be ensured. As in the case of leaded red brasses, tin bronzes also have problems with porosity. The castings contain 1 to 2 % of porosity and only small castings have porosity below 1 %. Directional solidification is best for relatively large, thick castings and for smaller, thin wall castings, uniform solidification is recommended. Sections up to 25 mm in thickness are routinely cast. Sections up to 50 mm thick can be cast, but only with difficulty and under carefully controlled conditions (R. F. Schmidt & D. G. Schmidt, 1997).

Copper and Copper Alloys: Casting, Classification and Characteristic Microstructures 15

Alloys with Zn concentration from 32 % (point B, Fig. 5) to 36 % (point C) crystallize according to the peritectic reaction at temperature 902 °C. During this reaction the phase is created by the reaction of formed primary crystals and the liquid alloy. By decreasing the temperature in the solid state the ratio of both crystals is changed. This is caused by solubility changes and the resulting brass structure is created only by the solid solution crystals. In the case of alloys with the concentration of Zn from 36 to 56 % the phase exists after the solidification. phase has a body centered cubic (BCC) lattice. The atoms of Cu and Zn are randomly distributed in the lattice. phase has good ductility. By the next temperature decreasing the random phase is changed to the ordered hard and brittle ´ phase; temperatures from 454 to 468 °C. The 39 to 45 % Zn containing brass resulting structure is heterogeneous, consisting of the solid solution crystals and ´ phase crystals. Only the alloys containing less than 45 % of Zn in the technical praxis, apart from small exceptions, are used. Brasses with less than 40 % Zn form single-phase solid solution of zinc in copper. The mechanical properties, even elongation, increase with increasing zinc content. These alloys can be cold-formed into rather complicated yet corrosion-resistant components. Brasses with higher Zn concentration, created by the ´ phases, or ´ phase, are excessively brittle. Mechanical properties of the brasses used in the technical praxis are

shown in the Fig. 6 (Skočovský et al., 2000).

Fig. 6. Influence of the Zn content to the brass mechanical properties

Brasses used in technical praxis consist also of some other elements; impurities and alloying elements besides Zn, whose influence is the same as in the case of pure copper. Bismuth and sulphur, for example, decreases the ability of the metal to hot forming. Lead has a similar influence. On the other hand, lead improves the materials workability. For this reason, lead is used for heterogeneous brasses in an amount from 1 to 3 %. Homogenous brasses, for improving strength, contain tin, aluminum, silicon and nickel. Silicon improves the

**Brasses heat treatment.** Recrystallization annealing is brasses basic heat treatment process. Combination of recrystallization annealing and forming allows to change the materials grain

materials resistance against corrosion and nickel improves the materials ductility.

#### **2. Copper based alloys**

#### **2.1 Brasses**

Brasses are copper based alloys where zinc is the main alloying element. Besides zinc, also some amount of impurities and very often some other alloying elements are present in the alloys. The used alloying elements can improve some properties, depending on their application. Due to the treatment, brasses can be divided into two groups: wrought brasses and cast brasses. One special group of brasses is brazing solder.

The binary diagram of the Cu-Zn system is quite difficult, Fig. 5. For the technical praxis only the area between the 0 to 50 % of Zn concentration is important. Alloys with higher Zn concentration have not convenient properties, as they are brittle.

Fig. 5. Binary diagram copper-zinc

In the liquid state copper and zinc are absolutely soluble. In the solid state solubility is limited; copper has face centered cubic lattice and zinc has the hexagonal close-packed lattice (HCP). During solidification the andphases are released. Most of the phases are intermediary phases characterized by the relation of valence electrons and amount of atoms. Primary solid solution (Zn in Cu) has the same crystal lattice as pure copper and dissolves maximum 39 % of Zn at temperature 450 °C. Decreasing the temperature, also the zinc solubility in the solution decreases ~ 33 %. In the alloys with higher content of Zn concentration the supersaturated solid solution is retaining at room temperature. This is why alloys up to 39 % Zn concentration have homogenous structure consisting from the solid solution crystals. After the forming and annealing the brass structure consists of the solid solution polyhedral grains with annealed twins (Skočovský et al., 2000, 2006).

Brasses are copper based alloys where zinc is the main alloying element. Besides zinc, also some amount of impurities and very often some other alloying elements are present in the alloys. The used alloying elements can improve some properties, depending on their application. Due to the treatment, brasses can be divided into two groups: wrought brasses

The binary diagram of the Cu-Zn system is quite difficult, Fig. 5. For the technical praxis only the area between the 0 to 50 % of Zn concentration is important. Alloys with higher Zn

In the liquid state copper and zinc are absolutely soluble. In the solid state solubility is limited; copper has face centered cubic lattice and zinc has the hexagonal close-packed lattice (HCP). During solidification the andphases are released. Most of the phases are intermediary phases characterized by the relation of valence electrons and amount of atoms. Primary solid solution (Zn in Cu) has the same crystal lattice as pure copper and dissolves maximum 39 % of Zn at temperature 450 °C. Decreasing the temperature, also the zinc solubility in the solution decreases ~ 33 %. In the alloys with higher content of Zn concentration the supersaturated solid solution is retaining at room temperature. This is why alloys up to 39 % Zn concentration have homogenous structure consisting from the solid solution crystals. After the forming and annealing the brass structure consists of the solid solution polyhedral grains with annealed twins (Skočovský

and cast brasses. One special group of brasses is brazing solder.

concentration have not convenient properties, as they are brittle.

**2. Copper based alloys** 

Fig. 5. Binary diagram copper-zinc

et al., 2000, 2006).

**2.1 Brasses** 

Alloys with Zn concentration from 32 % (point B, Fig. 5) to 36 % (point C) crystallize according to the peritectic reaction at temperature 902 °C. During this reaction the phase is created by the reaction of formed primary crystals and the liquid alloy. By decreasing the temperature in the solid state the ratio of both crystals is changed. This is caused by solubility changes and the resulting brass structure is created only by the solid solution crystals. In the case of alloys with the concentration of Zn from 36 to 56 % the phase exists after the solidification. phase has a body centered cubic (BCC) lattice. The atoms of Cu and Zn are randomly distributed in the lattice. phase has good ductility. By the next temperature decreasing the random phase is changed to the ordered hard and brittle ´ phase; temperatures from 454 to 468 °C. The 39 to 45 % Zn containing brass resulting structure is heterogeneous, consisting of the solid solution crystals and ´ phase crystals.

Only the alloys containing less than 45 % of Zn in the technical praxis, apart from small exceptions, are used. Brasses with less than 40 % Zn form single-phase solid solution of zinc in copper. The mechanical properties, even elongation, increase with increasing zinc content. These alloys can be cold-formed into rather complicated yet corrosion-resistant components. Brasses with higher Zn concentration, created by the ´ phases, or ´ phase, are excessively brittle. Mechanical properties of the brasses used in the technical praxis are shown in the Fig. 6 (Skočovský et al., 2000).

Fig. 6. Influence of the Zn content to the brass mechanical properties

Brasses used in technical praxis consist also of some other elements; impurities and alloying elements besides Zn, whose influence is the same as in the case of pure copper. Bismuth and sulphur, for example, decreases the ability of the metal to hot forming. Lead has a similar influence. On the other hand, lead improves the materials workability. For this reason, lead is used for heterogeneous brasses in an amount from 1 to 3 %. Homogenous brasses, for improving strength, contain tin, aluminum, silicon and nickel. Silicon improves the materials resistance against corrosion and nickel improves the materials ductility.

**Brasses heat treatment.** Recrystallization annealing is brasses basic heat treatment process. Combination of recrystallization annealing and forming allows to change the materials grain

Copper and Copper Alloys: Casting, Classification and Characteristic Microstructures 17

a) microstructure, polyhedral grains of α phase, chemically etched

b) size and orientation of grains, polarized light, etched K2Cr2O7

Fig. 7. Deep-drawing brass with 70 % Cu

structure and to influence the hardening state reached by the plastic deformation. The lower limit of the recrystallizing temperatures for binary Cu-Zn alloys is ~ 425 °C and the upper limit is limited by the amount of Zn in the alloy.

Stress-relief annealing is the second possible heat treatment used for brasses. This heat treatment process, at temperatures from 250 – 300 °C, decreases the danger of corrosion cracking (Skočovský et al., 2000).

#### **2.1.1 Wrought brasses**

Wrought brasses are supplied in the form of metal sheets, strips, bars, tubes, wires, etc. in the soft (annealed) state, or in the state (medium, hard state) after cold forming (Skočovský et al., 2000, 2006).

**Tombacs** are brasses containing more than 80 % of copper. They are similar to the pure copper by theirs chemical and physical properties, but they have better mechanical properties. Tombac with higher copper content is used for coins, memorial tablets, medals, etc. (after production the products are gold-plated before distribution). Tombacs with medium or lower copper content are light yellow colored, close to the color of gold. Because of this, brass films are used like the gold substituent in the case of decorative, artistic, fake jewelry, architecture, armatures, in electrical engineering, for manometers, flexible metal tubes, sieves etc. plating. Tombac with 80 % Zn has lower chemical resistance due to the higher Zn content, and so its usage (same like for other Tombacs) is dependent on the working conditions.

**Deep-drawing brasses** contain around 70 % of Cu (Fig. 7); for securing high ductility the impurities elements content has to be low. Cu-Zn alloys with the 32 % Zn content have the highest ductility at high strength which is why those alloys are used for deep-drawing. They are used, for example, for ball cartridges, musical equipment production and in the food industry (Skočovský et al., 2000).

**Brass with higher Zn content** (37 % of Zn) is quite cheap because of its lower Cu content. It is a heterogeneous alloy with small ´ phase content, with lower ductility and good ability for cold forming, Fig. 8. It is used for different not very hard loaded products; for example wiring material in electrical engineering, automotive coolers, etc. For improving the materials workability a small amount of lead is added to brasses with higher Zn content (Skočovský et al., 2000).

Brass with 40 % of Zn is heterogeneous alloy with (´) microstructure. Compared to other brasses it has higher strength properties, but lower ductility and cold forming ability. This is caused by the ´ presence. It is suitable for forging and die pressing at higher temperatures (700 – 800 °C). This kind of brass is used in architecture, for different ship forging products, for tubes and welding electrodes. For this brass type, with 60 % of Cu, the tendency to dezincification corrosion and to corrosion cracking is typical. The crack tendency increases with the increasing Zn content and it is largest at 40 % Zn content. In the case of zinc content below 15 % this tendency is not present. Brasses alloying elements do not improve the crack tendency. Some of the used alloying elements can decrease this disadvantage; Mg, Sn, Be, Mn. Grain refinement has the same influence (Skočovský et al., 2000).

structure and to influence the hardening state reached by the plastic deformation. The lower limit of the recrystallizing temperatures for binary Cu-Zn alloys is ~ 425 °C and the upper

Stress-relief annealing is the second possible heat treatment used for brasses. This heat treatment process, at temperatures from 250 – 300 °C, decreases the danger of corrosion

Wrought brasses are supplied in the form of metal sheets, strips, bars, tubes, wires, etc. in the soft (annealed) state, or in the state (medium, hard state) after cold forming (Skočovský

**Tombacs** are brasses containing more than 80 % of copper. They are similar to the pure copper by theirs chemical and physical properties, but they have better mechanical properties. Tombac with higher copper content is used for coins, memorial tablets, medals, etc. (after production the products are gold-plated before distribution). Tombacs with medium or lower copper content are light yellow colored, close to the color of gold. Because of this, brass films are used like the gold substituent in the case of decorative, artistic, fake jewelry, architecture, armatures, in electrical engineering, for manometers, flexible metal tubes, sieves etc. plating. Tombac with 80 % Zn has lower chemical resistance due to the higher Zn content, and so its usage (same like for other Tombacs) is dependent on the

**Deep-drawing brasses** contain around 70 % of Cu (Fig. 7); for securing high ductility the impurities elements content has to be low. Cu-Zn alloys with the 32 % Zn content have the highest ductility at high strength which is why those alloys are used for deep-drawing. They are used, for example, for ball cartridges, musical equipment production and in the food

**Brass with higher Zn content** (37 % of Zn) is quite cheap because of its lower Cu content. It is a heterogeneous alloy with small ´ phase content, with lower ductility and good ability for cold forming, Fig. 8. It is used for different not very hard loaded products; for example wiring material in electrical engineering, automotive coolers, etc. For improving the materials workability a small amount of lead is added to brasses with higher Zn content

Brass with 40 % of Zn is heterogeneous alloy with (´) microstructure. Compared to other brasses it has higher strength properties, but lower ductility and cold forming ability. This is caused by the ´ presence. It is suitable for forging and die pressing at higher temperatures (700 – 800 °C). This kind of brass is used in architecture, for different ship forging products, for tubes and welding electrodes. For this brass type, with 60 % of Cu, the tendency to dezincification corrosion and to corrosion cracking is typical. The crack tendency increases with the increasing Zn content and it is largest at 40 % Zn content. In the case of zinc content below 15 % this tendency is not present. Brasses alloying elements do not improve the crack tendency. Some of the used alloying elements can decrease this disadvantage; Mg, Sn, Be,

Mn. Grain refinement has the same influence (Skočovský et al., 2000).

limit is limited by the amount of Zn in the alloy.

cracking (Skočovský et al., 2000).

**2.1.1 Wrought brasses** 

et al., 2000, 2006).

working conditions.

industry (Skočovský et al., 2000).

(Skočovský et al., 2000).

a) microstructure, polyhedral grains of α phase, chemically etched

b) size and orientation of grains, polarized light, etched K2Cr2O7 Fig. 7. Deep-drawing brass with 70 % Cu

Copper and Copper Alloys: Casting, Classification and Characteristic Microstructures 19

Brass CuZn40Mn3Fe1 is an alloy with a two phase microstructure (Fig. 9); α phase is light (in black and white color) or blue (with polarized light) and β´ phase is dark or a different color depending on the grains orientation. The microstructure shows polyhedral grains with different size and color of β´ phase (Fig. 9a). A direction of α phase is different according to

**Leaded brass.** Brasses in this group contain ~ 60 % of copper and from 1 to 3 % of lead which improve the materials machinability (Skočovský et al., 2000). The microstructure is constituted by two phases, α and β´, where α phase is lighter than the second phase β´, (Fig.

Lead is not soluble in copper and so its influence is the same as in the case of leaded steels. Lead should be finely dispersed as isolated particles in the final brass structure (Fig. 10).

Brasses with 58 or 59 % of Cu and lead are suitable for metal sheets, strips, bands, bars production and different shaped tubes. At higher temperatures it is possible apply forging and pressing to these brasses. They are difficult to cold form, but it is possible to strike them. They are used for different stroked product for watchmakers and small machines, especially in electrical engineering production. Leaded brass with 58 % of Cu and is used for screw

The CuZn43Mn4Pb3Fe brass with higher content of Zn (43 %) has only one phase β´ microstructure (Fig. 11). This phase is constituted by polyhedral grains (different color according to the grains orientation) with very small black globular particles of the phase

Cast brasses are heterogeneous alloys ´) containing from 58 to 63 % of copper. For improving machinability they very often also contain lead (1 - 3 %). Cast brasses have good feeding, low tendency to chemical unmixing, but high shrinkage. Because of their structure cast brasses have lower mechanical properties compared to the mechanical properties of wrought brasses. These brasses are used mainly for low stressed castings; pumps parts, gas and water armatures, ironworks for furniture and building, etc.

This alloy family consists of copper, zinc and one or more elements in addition (aluminum, tin, nickel, manganese, iron, silicon). The name of the alloy is usually formed according to the additional element (for example silicon brass is the Cu-Zn-Si alloy). Other elements addition improves the materials mechanical properties, corrosion resistance, castability and workability increasing. The change in properties is dependant on the element type and on

According to production technology special brasses can be divided into two groups:

the orientation of grains, as is shown in a detail of the microstructure (Fig. 9b).

Smaller carburetor parts and seamless tubes are produced from leaded brasses.

production and for other in mass scale turned products (Skočovský et al., 2000).

with high content of iron, and light colored regularly distributed small Pb particles.

10).

**2.1.2 Cast brasses** 

(Skočovský et al., 2000, 2006).

its influence on the materials structure.

wrought and cast special brasses (Skočovský et al., 2000, 2006).

**2.1.3 Special brasses** 

a) (´) microstructure, chemically etched

b) α phase is violet, polarized light, etched K2Cr2O7 Fig. 8. Brass with 37 % of Zn

Brass CuZn40Mn3Fe1 is an alloy with a two phase microstructure (Fig. 9); α phase is light (in black and white color) or blue (with polarized light) and β´ phase is dark or a different color depending on the grains orientation. The microstructure shows polyhedral grains with different size and color of β´ phase (Fig. 9a). A direction of α phase is different according to the orientation of grains, as is shown in a detail of the microstructure (Fig. 9b).

**Leaded brass.** Brasses in this group contain ~ 60 % of copper and from 1 to 3 % of lead which improve the materials machinability (Skočovský et al., 2000). The microstructure is constituted by two phases, α and β´, where α phase is lighter than the second phase β´, (Fig. 10).

Lead is not soluble in copper and so its influence is the same as in the case of leaded steels. Lead should be finely dispersed as isolated particles in the final brass structure (Fig. 10). Smaller carburetor parts and seamless tubes are produced from leaded brasses.

Brasses with 58 or 59 % of Cu and lead are suitable for metal sheets, strips, bands, bars production and different shaped tubes. At higher temperatures it is possible apply forging and pressing to these brasses. They are difficult to cold form, but it is possible to strike them. They are used for different stroked product for watchmakers and small machines, especially in electrical engineering production. Leaded brass with 58 % of Cu and is used for screw production and for other in mass scale turned products (Skočovský et al., 2000).

The CuZn43Mn4Pb3Fe brass with higher content of Zn (43 %) has only one phase β´ microstructure (Fig. 11). This phase is constituted by polyhedral grains (different color according to the grains orientation) with very small black globular particles of the phase with high content of iron, and light colored regularly distributed small Pb particles.

#### **2.1.2 Cast brasses**

18 Copper Alloys – Early Applications and Current Performance – Enhancing Processes

a) (´) microstructure, chemically etched

b) α phase is violet, polarized light, etched K2Cr2O7

Fig. 8. Brass with 37 % of Zn

Cast brasses are heterogeneous alloys ´) containing from 58 to 63 % of copper. For improving machinability they very often also contain lead (1 - 3 %). Cast brasses have good feeding, low tendency to chemical unmixing, but high shrinkage. Because of their structure cast brasses have lower mechanical properties compared to the mechanical properties of wrought brasses. These brasses are used mainly for low stressed castings; pumps parts, gas and water armatures, ironworks for furniture and building, etc. (Skočovský et al., 2000, 2006).

#### **2.1.3 Special brasses**

This alloy family consists of copper, zinc and one or more elements in addition (aluminum, tin, nickel, manganese, iron, silicon). The name of the alloy is usually formed according to the additional element (for example silicon brass is the Cu-Zn-Si alloy). Other elements addition improves the materials mechanical properties, corrosion resistance, castability and workability increasing. The change in properties is dependant on the element type and on its influence on the materials structure.

According to production technology special brasses can be divided into two groups: wrought and cast special brasses (Skočovský et al., 2000, 2006).

Copper and Copper Alloys: Casting, Classification and Characteristic Microstructures 21

a) (´) microstructure with Pb particles showed as dark gray, etched K2Cr2O7

b) the same microstructure after chemical etching Fig. 10. Leaded brass, 42 % of Zn and 2 % of Pb

a) polyhedral microstructure, mag. 100 x

b) detail of two grains, mag. 500 x Fig. 9. Brass CuZn40Mn3Fe1, polarized light, etched K2Cr2O7

a) polyhedral microstructure, mag. 100 x

b) detail of two grains, mag. 500 x

Fig. 9. Brass CuZn40Mn3Fe1, polarized light, etched K2Cr2O7

a) (´) microstructure with Pb particles showed as dark gray, etched K2Cr2O7

b) the same microstructure after chemical etching Fig. 10. Leaded brass, 42 % of Zn and 2 % of Pb

Copper and Copper Alloys: Casting, Classification and Characteristic Microstructures 23

**Aluminum brasses.** Aluminum brasses contain from 69 to 79 % of copper; the aluminum additive content, in the case of wrought alloys, is below 3 to 3.5 % to keep the structure homogeneous. As well as this aluminum content, the structure is also formed by new phases as are γ phases, which improve the materials hardness and strength, but decrease its ductility. Aluminum brass containing 70 % of Cu and 0.6 to 1.6 % Al, with Sn and Mn addition, is very corrosion resistant and is used for condenser tubes production. Al brass with higher content of Cu (77 %) and with Al from 1.7 to 2.5 %, whose application is the same as that of the previous brass, its corrosion resistance against the see water is higher

The structure of cast aluminum brasses is heterogeneous. The copper content is in this case lower and the aluminum content is higher (below 7 %), which ensures good corrosion resistance of the material in sea water. They are used for very hard loaded cast parts;

**Manganese brasses.** Wrought manganese brasses contain from 3 to 4 % manganese and cast manganese brasses contain from 4 to 5 % manganese. This alloying family has high strength properties, and corrosion resistance. They are used usually in the heterogeneous structure. Wrought manganese brasses with 58 % of Cu or 57 % of Cu with addition of Al have quite good strength (in medium-hard state 400 to 500 MPa) at large toughness and corrosion resistance. They are used for armatures, valve seating, high-pressured tubes, etc. Mn brass with 58 % of Cu is also used for decorations (product surface is layered during hot oxidation process by attractive, durable brown verdigris). Cast manganese brasses have larger manganese and iron content and they are used for very hard loaded castings; weapons

**Tin brasses.** Tin brasses are mostly heterogeneous alloys containing tin below 2.5 %. Tin has a positive influence on mechanical properties and corrosion resistance. Some Sn alloys with 60 % of Cu have good acoustical properties and so they are used for the musical/sound instruments production. Sn brass alloy with 62 % of Cu is used for the strips, metal sheets

**Silicon brasses.** Silicon brasses contain maximum 5 % of Si at large copper content, from 79 to 81 %. As in the other brasses case, silicon brasses can be wrought (max. 4 % Si) or cast. They have very good corrosion resistance and mechanical properties also at low temperatures (- 183 °C). Over 230 °C their creeping is extensive, at a low stress level and at a temperature larger than 290 °C silicon brasses are also brittle. Lead addition, (3 to 3.5 %), positively affects the materials wear properties and so these alloys are suitable for bearings and bearings cases casting (Cu 80 %, Si 3 %, Pb 3 %). Silicon brasses are used in boats, locomotives and railway cars production. Silicon cast alloys with good feeding properties

**Nickel brasses.** Nickel brasses contain from 8 to 20 % nickel, which is absolutely soluble in homogeneous brasses and nickel enlarges area. Homogeneous alloys are good cold formed and are suitable for deep-drawing. Heterogeneous alloys () are good for hot forming. Nickel brasses have good mechanical properties, corrosion resistance and are easily polishable. One of the oldest alloys are alloys of 60 % of copper and from 14 to 18 % of nickel content; they were used for decorative and useful objects. These alloys have many different commercial names, for example "pakfong", "alpaca", "argentan" etc. they are used

are used for armatures, bearings cases, geared pinions and cogwheels production.

parts, screw propellers, turbine blades and armatures for the highest pressures.

because of the larger Al content.

armatures, screw-cutting wheel, bearings and bearings cases.

and profiles used in the ships or boat constructions.

a) polyhedral grains of β´phase, polarized light, mag. 100 x

b) detail, white light, mag. 500 x Fig. 11. Brass CuZn43Mn4Pb3Fe, etched K2Cr2O7

a) polyhedral grains of β´phase, polarized light, mag. 100 x

b) detail, white light, mag. 500 x

Fig. 11. Brass CuZn43Mn4Pb3Fe, etched K2Cr2O7

**Aluminum brasses.** Aluminum brasses contain from 69 to 79 % of copper; the aluminum additive content, in the case of wrought alloys, is below 3 to 3.5 % to keep the structure homogeneous. As well as this aluminum content, the structure is also formed by new phases as are γ phases, which improve the materials hardness and strength, but decrease its ductility. Aluminum brass containing 70 % of Cu and 0.6 to 1.6 % Al, with Sn and Mn addition, is very corrosion resistant and is used for condenser tubes production. Al brass with higher content of Cu (77 %) and with Al from 1.7 to 2.5 %, whose application is the same as that of the previous brass, its corrosion resistance against the see water is higher because of the larger Al content.

The structure of cast aluminum brasses is heterogeneous. The copper content is in this case lower and the aluminum content is higher (below 7 %), which ensures good corrosion resistance of the material in sea water. They are used for very hard loaded cast parts; armatures, screw-cutting wheel, bearings and bearings cases.

**Manganese brasses.** Wrought manganese brasses contain from 3 to 4 % manganese and cast manganese brasses contain from 4 to 5 % manganese. This alloying family has high strength properties, and corrosion resistance. They are used usually in the heterogeneous structure. Wrought manganese brasses with 58 % of Cu or 57 % of Cu with addition of Al have quite good strength (in medium-hard state 400 to 500 MPa) at large toughness and corrosion resistance. They are used for armatures, valve seating, high-pressured tubes, etc. Mn brass with 58 % of Cu is also used for decorations (product surface is layered during hot oxidation process by attractive, durable brown verdigris). Cast manganese brasses have larger manganese and iron content and they are used for very hard loaded castings; weapons parts, screw propellers, turbine blades and armatures for the highest pressures.

**Tin brasses.** Tin brasses are mostly heterogeneous alloys containing tin below 2.5 %. Tin has a positive influence on mechanical properties and corrosion resistance. Some Sn alloys with 60 % of Cu have good acoustical properties and so they are used for the musical/sound instruments production. Sn brass alloy with 62 % of Cu is used for the strips, metal sheets and profiles used in the ships or boat constructions.

**Silicon brasses.** Silicon brasses contain maximum 5 % of Si at large copper content, from 79 to 81 %. As in the other brasses case, silicon brasses can be wrought (max. 4 % Si) or cast. They have very good corrosion resistance and mechanical properties also at low temperatures (- 183 °C). Over 230 °C their creeping is extensive, at a low stress level and at a temperature larger than 290 °C silicon brasses are also brittle. Lead addition, (3 to 3.5 %), positively affects the materials wear properties and so these alloys are suitable for bearings and bearings cases casting (Cu 80 %, Si 3 %, Pb 3 %). Silicon brasses are used in boats, locomotives and railway cars production. Silicon cast alloys with good feeding properties are used for armatures, bearings cases, geared pinions and cogwheels production.

**Nickel brasses.** Nickel brasses contain from 8 to 20 % nickel, which is absolutely soluble in homogeneous brasses and nickel enlarges area. Homogeneous alloys are good cold formed and are suitable for deep-drawing. Heterogeneous alloys () are good for hot forming. Nickel brasses have good mechanical properties, corrosion resistance and are easily polishable. One of the oldest alloys are alloys of 60 % of copper and from 14 to 18 % of nickel content; they were used for decorative and useful objects. These alloys have many different commercial names, for example "pakfong", "alpaca", "argentan" etc. they are used

Copper and Copper Alloys: Casting, Classification and Characteristic Microstructures 25

Tin addition has a similar influence on bronzes properties as zinc addition in the case of brasses. For the forming, bronzes with around 9 % of Sn are used (it is possible to heat those alloys to single-phase state above 5 % Sn). Tin bronzes are used when bronzes are not sufficient in strength and corrosion resistance points of view. For casting, bronzes with higher Sn content are used; up to 20 % of Sn. Cast bronzes are used more often than wrought bronzes. Tin bronzes castings have good strength and toughness, high corrosion resistance and also good wear properties (the wear resistance is given by the heterogeneous structure ( Tin bronzes have small shrinkages during the solidification (1 %) but they have worst feeding properties and larger tendency to the creation of microshrinkages.

Bronze CuSn1 contains from 0.8 to 2 % of Sn. In the soft state this bronze has tensile strength 250 MPa and 33 % ductility. It has good corrosion resistance and electric conductivity; it is used in electrical engineering. Bronze CuSn3 with 2.5 to 4 % of Sn has in its soft state tensile strength 280 MPa and ductility 40 %. It is used for the chemical industry and electric engineering equipment production. Bronze CuSn6 with tensile strength 350 MPa and ductility 40 % (in soft state) is used for applications where β´, a higher corrosion resistance is required for good strength properties and ductility; for example corrosion environment springs. CuSn8 bronze has, from all wrought tin bronzes the highest strength (380 MPa) and ductility (40 %). It is suitable for bearing sleeves production and in the hard state also for

Bronze CuSn1 with low Sn content has sufficient electric conductivity and so it is used for the castings used in electric engineering. CuSn5 and CuSn10 bronzes have tensile strength 180 and 220 MPa, ductility 15 % and they have good corrosion resistance. They are used for the stressed parts of turbines, compressors, for armatures and for pumps runners' production. Bronze CuSn12 is used for parts used to large mechanical stress and wear frictional loading; spiral gears, gear rims. CuSn10 and CuSn12 bronzes are used in the same way as bearing bronzes. High Sn content (14 to 16 %) bronzes usage have been, because of their expense, replaced by lower Sn containing bronzes, around 6 %, with good sliding

Leaded tin bronzes and leaded bronzes are copper alloys where the Sn content is partially or absolutely replaced by Pb. The Pb addition to copper, improves the alloys sliding properties without the negative influence on their heat conductivity. Cu-Pb system is characteristic by only partial solubility in a liquid state and absolute insolubility in a solid state. The resulting structure, after solidification, consists of copper and lead crystals. At a high cooling rate both the alloy components are uniformly distributed and the alloys have very good sliding properties. Leaded bronzes are suitable for steel friction bearing shells casting. They endure high specific presses, quite high circumferential speeds and it is possible to use them at

Two types of bearing bronzes are produced. Bronzes with lower Pb content (from 10 to 20 %) and Sn addition (from 5 to 10 %) and also high-leaded bronzes (from 25 to 30 %) without

**Wrought tin bronzes** 

**Cast tin bronzes** 

springs which are resistant to fatigue corrosion.

properties (Skočovský et al., 2000, 2006).

elevated temperatures (around 300 °C).

**2.2.2 Leaded tin bronzes and leaded bronzes** 

in the building industry, precise mechanics, and medical equipment production and for stressed springs (high modulus of elasticity).

**Brazing solders.** Brazing solders are either basic or special brasses with melting temperature higher than 600 °C. They are used for soldering of metals and alloys with higher melting temperatures like copper and its alloys, steels, cast irons etc. In the case of binary alloys Cu-Zn with other element addition (Ag or Ni), the solders are marked like silver or nickel solders. Brasses solders with Cu content from 42 to 45 % have the melting temperature 840 to 880 °C and they are used for brasses soldering. Silver solders contain from 30 to 50 % of copper, from 25 to 52 % of Zn and from 4 to 45 % of Ag. Lower the Ag content; lower the melting temperature (to 720 °C). Silver solders have good feeding and give strong soldering joints. Nickel solders (38 % Cu, 50 % Zn and 12 % Ni) have a melting temperature of around 900 °C. They are used for steels and nickel alloys soldering.

Solder with a very low Ag content (0.2 to 0.4 %) with upper melting temperature 900 °C has good electric conductivity and for this reason is used in electrical engineering. Solder with an upper melting temperature of 850 °C (60 % Cu and low content of Si, Sn) has high strength and it is suitable for steels, grey cast iron, copper and brasses soldering (Skočovský et al., 2000, 2006).

#### **2.2 Bronzes**

Bronzes are copper based alloys with other alloying elements except zinc. The name of bronzes is defined according to the main alloying element; tin bronzes, aluminum bronzes, etc. (Skočovský et al., 2000, 2006).

#### **2.2.1 Tin bronzes**

Tin bronzes are alloys of copper and tin, with a minimal Cu-Sn content 99.3 %. Equilibrium diagram of Cu-Sn is one of the very difficult binary diagrams and in some areas (especially between 20 to 40 % of Sn) it is not specified till now. For the technical praxis only alloys containing less than 20 % of Sn are important. Tin bronzes with higher Sn content are very brittle due to the intermetallic phases' presence. Cu and Sn are absolutely soluble in the liquid state. In the solid state the Cu and Sn solubility is limited.

Normally, the technical alloys crystallize differently as compared to the equilibrium diagram. Until 5 % of Sn, the alloys are homogenous and consist only of the solid solution (solid solution of Sn in Cu) with face centered cubic lattice. In the cast state the alloy structure is dendritic and in the wrought and annealed state the structure is created by the regular polyhedral grains. The resulting structure of alloys with larger Sn content (from 5 to 20 %) is created by solid solution crystals and eutectic (). phase is an electron compound Cu31Sn8 (e/a = 21/13) with cubic lattice. phase is brittle phase, which has negative influence on the ductility and also decreases the materials strength in case of higher Sn content (above 20 %). Even though the solubility in the case of technical alloys decreases, the phase (Cu3Sn with hexagonal lattice; e/a = 7/4) is not created. The phases do not occur because the diffusion ability of Sn atoms below 350 °C is low. phase also does not occur at normal temperature with higher Sn content in bronze.

Tin addition has a similar influence on bronzes properties as zinc addition in the case of brasses. For the forming, bronzes with around 9 % of Sn are used (it is possible to heat those alloys to single-phase state above 5 % Sn). Tin bronzes are used when bronzes are not sufficient in strength and corrosion resistance points of view. For casting, bronzes with higher Sn content are used; up to 20 % of Sn. Cast bronzes are used more often than wrought bronzes. Tin bronzes castings have good strength and toughness, high corrosion resistance and also good wear properties (the wear resistance is given by the heterogeneous structure ( Tin bronzes have small shrinkages during the solidification (1 %) but they have worst feeding properties and larger tendency to the creation of microshrinkages.

#### **Wrought tin bronzes**

24 Copper Alloys – Early Applications and Current Performance – Enhancing Processes

in the building industry, precise mechanics, and medical equipment production and for

**Brazing solders.** Brazing solders are either basic or special brasses with melting temperature higher than 600 °C. They are used for soldering of metals and alloys with higher melting temperatures like copper and its alloys, steels, cast irons etc. In the case of binary alloys Cu-Zn with other element addition (Ag or Ni), the solders are marked like silver or nickel solders. Brasses solders with Cu content from 42 to 45 % have the melting temperature 840 to 880 °C and they are used for brasses soldering. Silver solders contain from 30 to 50 % of copper, from 25 to 52 % of Zn and from 4 to 45 % of Ag. Lower the Ag content; lower the melting temperature (to 720 °C). Silver solders have good feeding and give strong soldering joints. Nickel solders (38 % Cu, 50 % Zn and 12 % Ni) have a melting temperature of around

Solder with a very low Ag content (0.2 to 0.4 %) with upper melting temperature 900 °C has good electric conductivity and for this reason is used in electrical engineering. Solder with an upper melting temperature of 850 °C (60 % Cu and low content of Si, Sn) has high strength and it is suitable for steels, grey cast iron, copper and brasses soldering (Skočovský

Bronzes are copper based alloys with other alloying elements except zinc. The name of bronzes is defined according to the main alloying element; tin bronzes, aluminum bronzes,

Tin bronzes are alloys of copper and tin, with a minimal Cu-Sn content 99.3 %. Equilibrium diagram of Cu-Sn is one of the very difficult binary diagrams and in some areas (especially between 20 to 40 % of Sn) it is not specified till now. For the technical praxis only alloys containing less than 20 % of Sn are important. Tin bronzes with higher Sn content are very brittle due to the intermetallic phases' presence. Cu and Sn are absolutely soluble in the

Normally, the technical alloys crystallize differently as compared to the equilibrium diagram. Until 5 % of Sn, the alloys are homogenous and consist only of the solid solution (solid solution of Sn in Cu) with face centered cubic lattice. In the cast state the alloy structure is dendritic and in the wrought and annealed state the structure is created by the regular polyhedral grains. The resulting structure of alloys with larger Sn content (from 5 to 20 %) is created by solid solution crystals and eutectic (). phase is an electron compound Cu31Sn8 (e/a = 21/13) with cubic lattice. phase is brittle phase, which has negative influence on the ductility and also decreases the materials strength in case of higher Sn content (above 20 %). Even though the solubility in the case of technical alloys decreases, the phase (Cu3Sn with hexagonal lattice; e/a = 7/4) is not created. The phases do not occur because the diffusion ability of Sn atoms below 350 °C is low. phase also does not

stressed springs (high modulus of elasticity).

et al., 2000, 2006).

**2.2.1 Tin bronzes** 

etc. (Skočovský et al., 2000, 2006).

**2.2 Bronzes** 

900 °C. They are used for steels and nickel alloys soldering.

liquid state. In the solid state the Cu and Sn solubility is limited.

occur at normal temperature with higher Sn content in bronze.

Bronze CuSn1 contains from 0.8 to 2 % of Sn. In the soft state this bronze has tensile strength 250 MPa and 33 % ductility. It has good corrosion resistance and electric conductivity; it is used in electrical engineering. Bronze CuSn3 with 2.5 to 4 % of Sn has in its soft state tensile strength 280 MPa and ductility 40 %. It is used for the chemical industry and electric engineering equipment production. Bronze CuSn6 with tensile strength 350 MPa and ductility 40 % (in soft state) is used for applications where β´, a higher corrosion resistance is required for good strength properties and ductility; for example corrosion environment springs. CuSn8 bronze has, from all wrought tin bronzes the highest strength (380 MPa) and ductility (40 %). It is suitable for bearing sleeves production and in the hard state also for springs which are resistant to fatigue corrosion.

#### **Cast tin bronzes**

Bronze CuSn1 with low Sn content has sufficient electric conductivity and so it is used for the castings used in electric engineering. CuSn5 and CuSn10 bronzes have tensile strength 180 and 220 MPa, ductility 15 % and they have good corrosion resistance. They are used for the stressed parts of turbines, compressors, for armatures and for pumps runners' production. Bronze CuSn12 is used for parts used to large mechanical stress and wear frictional loading; spiral gears, gear rims. CuSn10 and CuSn12 bronzes are used in the same way as bearing bronzes. High Sn content (14 to 16 %) bronzes usage have been, because of their expense, replaced by lower Sn containing bronzes, around 6 %, with good sliding properties (Skočovský et al., 2000, 2006).

#### **2.2.2 Leaded tin bronzes and leaded bronzes**

Leaded tin bronzes and leaded bronzes are copper alloys where the Sn content is partially or absolutely replaced by Pb. The Pb addition to copper, improves the alloys sliding properties without the negative influence on their heat conductivity. Cu-Pb system is characteristic by only partial solubility in a liquid state and absolute insolubility in a solid state. The resulting structure, after solidification, consists of copper and lead crystals. At a high cooling rate both the alloy components are uniformly distributed and the alloys have very good sliding properties. Leaded bronzes are suitable for steel friction bearing shells casting. They endure high specific presses, quite high circumferential speeds and it is possible to use them at elevated temperatures (around 300 °C).

Two types of bearing bronzes are produced. Bronzes with lower Pb content (from 10 to 20 %) and Sn addition (from 5 to 10 %) and also high-leaded bronzes (from 25 to 30 %) without

Copper and Copper Alloys: Casting, Classification and Characteristic Microstructures 27

changed at lower temperatures the eutectic disappears and so its influence in the structure cannot be proven.) By decreasing the temperature the composition, of and crystals changes according to the time of solubility change. phase is a disordered solid solution of electron compound Cu3Al (e/a = 3/2) with face centered cubic lattice. It is a hard and brittle phase. phase, from which the solid solution is created at lower temperatures, is precipitated from liquid metal at the Al content from 9.5 to 12 % alloys during the crystallization process. During the slow cooling rate thephase is transformed at eutectoid temperature 565 °C to the lamellar eutectoid (). For this reason the eutectoid reaction of

Phase is solid solution of hard and brittle electron compound Cu9Al4 with complicated cubic lattice. After the recrystallization in solid state the slowly cooled alloys with Al content from 9.4 to 12 % are heterogeneous. Their structure is created with solid solution crystals

Because of the possibility to improve the mechanical properties by heat treatment heterogeneous alloys are used more often than homogeneous alloys. From 10 to 12 % Al content alloys can be heat treated with a similarly process as in the case of steels. The martensitic transformation can be reached in the case when the eutectoid transformation is limited by fast alloys cooling rate from the temperatures in the or () areas (Fig. 12). After this process the microstructure with very fine and hard needles phase with a body centered cubic lattice will be reached. By the phase undercooling below the martensitic transformation temperature Ms, a needle-like martensitic supersaturated disordered solid

Due to the chemical composition aluminum bronzes can be divided into two basic groups:

Iron is frequently an aluminum bronzes alloying element. It is dissolved in phase till 2 % and it improves its strength properties. With Al it creates FeAl3 intermetallic phase which

Manganese is added to the multicomponent alloys because it has deoxidizing effect in the melted metal. It is dissolved in phase, up to 12 % of Mn content, and it has an effect

Nickel is the most frequent alloying element in aluminum bronzes. It has positive influence on the corrosion resistance in aggressive water solutions and in sea water. Up to around 5 % nickel is soluble in phase. Nickel with aluminum creates Ni3Al intermetallic phase which

Homogeneous aluminum bronzes are tough and are suitable for cold and also hot forming. Heterogeneous alloys are stronger, harder, but they have lower cold forming properties compared to the homogeneous alloys. They are suitable for hot forming and have good cast properties. Aluminum bronzes are distinguished by good strength, even at elevated temperatures, and also very good corrosion resistance and wear resistance. Aluminum bronzes are used in the chemical and food industry for stressed components production.


alloying elements like Fe, Ni, Mg whose content does not exceeds 6 %.

phase is sometimes called "pearlitic transformation".

solution ´ phase with body centered cubic lattice is created.

and eutectoid ().

causes the structure fining.

has a precipitate hardening effect.

similar to iron.

tin. At present, specially leaded bronzes CuSn10Pb and CuSn10Pb10 like bearing bronzes are used (Skočovský et al., 2000, 2006). Lead (additive from 4 to 25 %) improves bearing sliding properties, and tin (from 4 to 10 %) improves strength and fatigue resistance. These alloys are used especially for bearings in dusty and corrosive environments. Second group binary alloys have lower strength and hardness and they are used for steel shells coatings. With small additions of Mn, Ni, Sn and Zn (in total 2 %) it is possible to refine the structure and to decrease the materials tendency to exsolution. These are very often used for steel shells coated by thin leaded bronze layer for the main and the piston rod bearings of internal-combustion engine (Skočovský et al., 2000).

#### **2.2.3 Aluminum bronzes**

Aluminum bronzes are alloys of copper, where aluminum is the main alloying element. For the technical praxis alloys with Al content below 12 % are important. Equilibrium diagram of Cu-Al is complicated and it is similar to Cu-Sn equilibrium diagram. One part of Cu-Al system for alloys containing up to 14 % of Al is shown on Fig. 12.

Fig. 12. Part of Cu-Al system equilibrium diagram

The solubility of Al in copper is maximum 7.3 % but it grows with temperature increasing to 9.4 % Al. Homogeneous alloys structure is created by solid solution crystals (substituted solid solution of Al in Cu) with body centered cubic lattice with similar properties as has the solid solution in brasses. It is relatively soft and plastic phase. In the real alloys the absolutely equilibrium state does not occur. In the case of Al content close to the solubility limit some portion of phase in the structure will occur. The upper limit of Al in homogeneous structure alloys is dependent on the cooling rate and it is in the range of 7.5 to 8.5 % of Al.

Alloys with Al content in the range of 7.3 to 9.4 % solidify at eutectic reaction () and close to the eutectic line they contain primary released phase or and eutectic. (After the

tin. At present, specially leaded bronzes CuSn10Pb and CuSn10Pb10 like bearing bronzes are used (Skočovský et al., 2000, 2006). Lead (additive from 4 to 25 %) improves bearing sliding properties, and tin (from 4 to 10 %) improves strength and fatigue resistance. These alloys are used especially for bearings in dusty and corrosive environments. Second group binary alloys have lower strength and hardness and they are used for steel shells coatings. With small additions of Mn, Ni, Sn and Zn (in total 2 %) it is possible to refine the structure and to decrease the materials tendency to exsolution. These are very often used for steel shells coated by thin leaded bronze layer for the main and the piston rod bearings of

Aluminum bronzes are alloys of copper, where aluminum is the main alloying element. For the technical praxis alloys with Al content below 12 % are important. Equilibrium diagram of Cu-Al is complicated and it is similar to Cu-Sn equilibrium diagram. One part of Cu-Al

The solubility of Al in copper is maximum 7.3 % but it grows with temperature increasing to 9.4 % Al. Homogeneous alloys structure is created by solid solution crystals (substituted solid solution of Al in Cu) with body centered cubic lattice with similar properties as has the solid solution in brasses. It is relatively soft and plastic phase. In the real alloys the absolutely equilibrium state does not occur. In the case of Al content close to the solubility limit some portion of phase in the structure will occur. The upper limit of Al in homogeneous structure alloys is dependent on the cooling rate and it is in the range of 7.5

Alloys with Al content in the range of 7.3 to 9.4 % solidify at eutectic reaction () and close to the eutectic line they contain primary released phase or and eutectic. (After the

internal-combustion engine (Skočovský et al., 2000).

Fig. 12. Part of Cu-Al system equilibrium diagram

to 8.5 % of Al.

system for alloys containing up to 14 % of Al is shown on Fig. 12.

**2.2.3 Aluminum bronzes**

changed at lower temperatures the eutectic disappears and so its influence in the structure cannot be proven.) By decreasing the temperature the composition, of and crystals changes according to the time of solubility change. phase is a disordered solid solution of electron compound Cu3Al (e/a = 3/2) with face centered cubic lattice. It is a hard and brittle phase. phase, from which the solid solution is created at lower temperatures, is precipitated from liquid metal at the Al content from 9.5 to 12 % alloys during the crystallization process. During the slow cooling rate thephase is transformed at eutectoid temperature 565 °C to the lamellar eutectoid (). For this reason the eutectoid reaction of phase is sometimes called "pearlitic transformation".

Phase is solid solution of hard and brittle electron compound Cu9Al4 with complicated cubic lattice. After the recrystallization in solid state the slowly cooled alloys with Al content from 9.4 to 12 % are heterogeneous. Their structure is created with solid solution crystals and eutectoid ().

Because of the possibility to improve the mechanical properties by heat treatment heterogeneous alloys are used more often than homogeneous alloys. From 10 to 12 % Al content alloys can be heat treated with a similarly process as in the case of steels. The martensitic transformation can be reached in the case when the eutectoid transformation is limited by fast alloys cooling rate from the temperatures in the or () areas (Fig. 12). After this process the microstructure with very fine and hard needles phase with a body centered cubic lattice will be reached. By the phase undercooling below the martensitic transformation temperature Ms, a needle-like martensitic supersaturated disordered solid solution ´ phase with body centered cubic lattice is created.

Due to the chemical composition aluminum bronzes can be divided into two basic groups:


Iron is frequently an aluminum bronzes alloying element. It is dissolved in phase till 2 % and it improves its strength properties. With Al it creates FeAl3 intermetallic phase which causes the structure fining.

Manganese is added to the multicomponent alloys because it has deoxidizing effect in the melted metal. It is dissolved in phase, up to 12 % of Mn content, and it has an effect similar to iron.

Nickel is the most frequent alloying element in aluminum bronzes. It has positive influence on the corrosion resistance in aggressive water solutions and in sea water. Up to around 5 % nickel is soluble in phase. Nickel with aluminum creates Ni3Al intermetallic phase which has a precipitate hardening effect.

Homogeneous aluminum bronzes are tough and are suitable for cold and also hot forming. Heterogeneous alloys are stronger, harder, but they have lower cold forming properties compared to the homogeneous alloys. They are suitable for hot forming and have good cast properties. Aluminum bronzes are distinguished by good strength, even at elevated temperatures, and also very good corrosion resistance and wear resistance. Aluminum bronzes are used in the chemical and food industry for stressed components production.

Copper and Copper Alloys: Casting, Classification and Characteristic Microstructures 29

Beryllium is in copper limitedly soluble (max. 2.7 %) and in the solid state the solubility decreases (0.2 % at room temperature). The binary alloys with low beryllium content (0.25 to 0.7 %) have good electric conductivity, but lower mechanical properties, they are used rarely. More often alloys with higher Be content and other alloying elements as Ni, Co, Mn and Ti are produced. Cobalt (0.2 to 0.3 %) improves heat resistance and creep properties; nickel improves toughness and titanium affects like grain finer. The main group of this alloy family is the beryllium bronzes with 2 % of Be content due to the highest mechanical

Beryllium bronzes thermal treatment consists of dissolved annealing (700 to 800 °C/1h) and water quenching. The alloy after heat treatment is soft, formable and it can be improved only by artificial aging. Hardening is in progress at temperature from 280 to 300 °C. After the hardening the tensile strength of the alloy is more than 1200 MPa and the hardness 400 HB. By cold forming, applied after the cooling from the annealing temperature, the materials tensile strength can be improved. Beryllium bronzes usage is given by their high tensile strength, hardness, and corrosion resistance which those alloys do not lose, even not in the hardened state. They are used for the good electric conductive springs production; for the equipment which should not sparkling in case of bumping (mining equipment)

Copper and nickel are absolutely soluble in the liquid and in the solid state. Binary alloys are produced with minimal alloying elements content. Complex alloys, ternary or multi components, are suitable for hardening. Nickel bronzes have good strength at normal and also at elevated temperatures; good fatigue limit, they are resistant against corrosion and also against stress corrosion, and they have good wear resistance and large electric resistance.

Binary alloys Cu-Ni with low Ni content (bellow 10 %) are used only limitedly. They are replaced by cheaper Cu alloys. Alloys with middle Ni content (15 to 30 %) have good corrosion resistance and good cold formability. 15 to 20 % Ni containing alloys are used for deep-drawing. Alloys with 25 % Ni are used for coin production and alloys with 30 % Ni are

Complex Cu-Ni alloys have a wider usage in the technical praxis compared to the binary alloys. CuNi30Mn with Ni content from 27 to 30 %, Mn content from 2 to 3 % and impurities content bellow 0.6 % is characterized by high strength and corrosion resistance also at elevated temperatures. Because of its electric resistance this alloy is suitable for usage as resistive material till 400 °C. CuNi45Mn constantan is alloy with Ni content form 40 to 46 %, Mn content from 1 to 3 % and impurities content below 0.5 %. From the Cu-Ni alloys, this one has the largest specific electric resistance and it is used for resistive and thermal element material. Most often the Cu-Ni-Fe-Mn alloys are used. Iron and manganese addition improve the corrosion properties markedly, especially in the seas water and overheated water steam. CuNi30 alloy with iron content in the range from 0.4 to 1.5 % and manganese content from 0.5 to 1.5 % is used for seagoing ships condensers and condensers pipes production. In the new alloys also the niobium as an alloying element is used and the nickel content tends to

production; form dies, bearings, etc. (Skočovský et al., 2000, 2006).

**2.2.5 Beryllium bronzes** 

**2.2.6 Nickel bronzes** 

properties after the precipitin hardening.

used in the chemical and food industry.

These alloys are used in the mechanical engineering for much stressed gearwheels and worm wheels, armatures working at elevated temperatures etc. Production due to the treatment the aluminum bronzes are divided into two groups; cast and wrought aluminum bronzes.

Aluminum bronzes with Al content from 4.5 to 11 % are used for forming elementary or complex. Al content from 7.5 to 12 % are used for casting only complex aluminum bronzes

CuAl15 bronze is used for cold forming. It is supplied in the form of sheets, strips, bars, wires and pipes. In the soft state this alloy can reach the tensile strength 380 MPa, ductility 40 % and hardness 70 to 110 HB. It is used in the boats building, chemical, food and paper making industry.

Complex aluminum bronzes are normally used for hot forming. CuAl9Mn2 is used for the armatures (bellow 250 °C) production. CuAl9Fe3 is used for the bearings shells, valve seats production, etc. CuAl10Fe3Mn1.5 alloy has heightened hardness and strength; it is suitable for shells and bearings production; it is replacing leaded bronzes up to temperature 500 °C, sometimes also till 600 °C, the CuAl10Fe4Ni4 where Ni is replacing Mn is used. Nickel positively affects materials mechanical and corrosion properties. After the heat treatment the alloy has the tensile strength of 836 MPa and ductility 13.4 %. In the sea water corrosion environment this bronze reached better results compared to chrome-nickel corrosion steels. It is resistant against cavitational corrosion and stress corrosion. CuAl10Fe4Ni4 is used for castings, also used for water turbines and pumps construction, for valve seats, exhaust valves and other components working at elevated temperatures and also in the chemical industry. Besides CuAl19Ni5Fe1Mn1 the nickel alloy consists also a higher content of manganese. It is suitable for cars worm wheels, compressing rings of friction bearings for high pressures etc. (Skočovský et al., 2000, 2006).

#### **2.2.4 Silicon bronzes**

The silicon content in this type of alloys is in the range from 0.9 to 3.5 %. The Si content should not exceed 1 % when higher electric conductivity is required. Silicon bronzes more often in the form of complex alloys Cu-Si-Ni-Mn-Zn-Pb are produced; binary alloys Cu-Si only rarely are used. Manganese is dissolved in the solid solution; improving strength, hardness and corrosion properties. Zinc improves the casting properties and mechanical properties, as same as Mn. Nickel is dissolved in the solid solution but it also creates Ni2Si phase with silicon, which has a positive influence on the materials warm strength properties. Lead addition secure sliding properties.

Silicon bronzes have good cold and hot forming properties and are also used for castings production. They are resistant against sulphuric acid, hydrochloric acid and against some alkalis. Because of their good mechanical, chemical and wear properties, silicon bronzes are used for tin bronzes replacing; they outperform tin bronzes with higher strength and higher working temperatures interval. Formed CuSi3Mn alloy has in the soft state tensile strength 380 MPa and ductility 40 %. It is used for bars, wires, sheets, strips, forgings and stampings production. Casting alloys have normally higher alloying elements content and Si content reaches 5 % very often (Skočovský et al., 2000).

#### **2.2.5 Beryllium bronzes**

28 Copper Alloys – Early Applications and Current Performance – Enhancing Processes

These alloys are used in the mechanical engineering for much stressed gearwheels and worm wheels, armatures working at elevated temperatures etc. Production due to the treatment the aluminum bronzes are divided into two groups; cast and wrought

Aluminum bronzes with Al content from 4.5 to 11 % are used for forming elementary or complex. Al content from 7.5 to 12 % are used for casting only complex aluminum bronzes CuAl15 bronze is used for cold forming. It is supplied in the form of sheets, strips, bars, wires and pipes. In the soft state this alloy can reach the tensile strength 380 MPa, ductility 40 % and hardness 70 to 110 HB. It is used in the boats building, chemical, food and paper

Complex aluminum bronzes are normally used for hot forming. CuAl9Mn2 is used for the armatures (bellow 250 °C) production. CuAl9Fe3 is used for the bearings shells, valve seats production, etc. CuAl10Fe3Mn1.5 alloy has heightened hardness and strength; it is suitable for shells and bearings production; it is replacing leaded bronzes up to temperature 500 °C, sometimes also till 600 °C, the CuAl10Fe4Ni4 where Ni is replacing Mn is used. Nickel positively affects materials mechanical and corrosion properties. After the heat treatment the alloy has the tensile strength of 836 MPa and ductility 13.4 %. In the sea water corrosion environment this bronze reached better results compared to chrome-nickel corrosion steels. It is resistant against cavitational corrosion and stress corrosion. CuAl10Fe4Ni4 is used for castings, also used for water turbines and pumps construction, for valve seats, exhaust valves and other components working at elevated temperatures and also in the chemical industry. Besides CuAl19Ni5Fe1Mn1 the nickel alloy consists also a higher content of manganese. It is suitable for cars worm wheels, compressing rings of friction bearings for

The silicon content in this type of alloys is in the range from 0.9 to 3.5 %. The Si content should not exceed 1 % when higher electric conductivity is required. Silicon bronzes more often in the form of complex alloys Cu-Si-Ni-Mn-Zn-Pb are produced; binary alloys Cu-Si only rarely are used. Manganese is dissolved in the solid solution; improving strength, hardness and corrosion properties. Zinc improves the casting properties and mechanical properties, as same as Mn. Nickel is dissolved in the solid solution but it also creates Ni2Si phase with silicon, which has a positive influence on the materials warm strength

Silicon bronzes have good cold and hot forming properties and are also used for castings production. They are resistant against sulphuric acid, hydrochloric acid and against some alkalis. Because of their good mechanical, chemical and wear properties, silicon bronzes are used for tin bronzes replacing; they outperform tin bronzes with higher strength and higher working temperatures interval. Formed CuSi3Mn alloy has in the soft state tensile strength 380 MPa and ductility 40 %. It is used for bars, wires, sheets, strips, forgings and stampings production. Casting alloys have normally higher alloying elements content and Si content

aluminum bronzes.

making industry.

**2.2.4 Silicon bronzes** 

high pressures etc. (Skočovský et al., 2000, 2006).

properties. Lead addition secure sliding properties.

reaches 5 % very often (Skočovský et al., 2000).

Beryllium is in copper limitedly soluble (max. 2.7 %) and in the solid state the solubility decreases (0.2 % at room temperature). The binary alloys with low beryllium content (0.25 to 0.7 %) have good electric conductivity, but lower mechanical properties, they are used rarely. More often alloys with higher Be content and other alloying elements as Ni, Co, Mn and Ti are produced. Cobalt (0.2 to 0.3 %) improves heat resistance and creep properties; nickel improves toughness and titanium affects like grain finer. The main group of this alloy family is the beryllium bronzes with 2 % of Be content due to the highest mechanical properties after the precipitin hardening.

Beryllium bronzes thermal treatment consists of dissolved annealing (700 to 800 °C/1h) and water quenching. The alloy after heat treatment is soft, formable and it can be improved only by artificial aging. Hardening is in progress at temperature from 280 to 300 °C. After the hardening the tensile strength of the alloy is more than 1200 MPa and the hardness 400 HB. By cold forming, applied after the cooling from the annealing temperature, the materials tensile strength can be improved. Beryllium bronzes usage is given by their high tensile strength, hardness, and corrosion resistance which those alloys do not lose, even not in the hardened state. They are used for the good electric conductive springs production; for the equipment which should not sparkling in case of bumping (mining equipment) production; form dies, bearings, etc. (Skočovský et al., 2000, 2006).

#### **2.2.6 Nickel bronzes**

Copper and nickel are absolutely soluble in the liquid and in the solid state. Binary alloys are produced with minimal alloying elements content. Complex alloys, ternary or multi components, are suitable for hardening. Nickel bronzes have good strength at normal and also at elevated temperatures; good fatigue limit, they are resistant against corrosion and also against stress corrosion, and they have good wear resistance and large electric resistance.

Binary alloys Cu-Ni with low Ni content (bellow 10 %) are used only limitedly. They are replaced by cheaper Cu alloys. Alloys with middle Ni content (15 to 30 %) have good corrosion resistance and good cold formability. 15 to 20 % Ni containing alloys are used for deep-drawing. Alloys with 25 % Ni are used for coin production and alloys with 30 % Ni are used in the chemical and food industry.

Complex Cu-Ni alloys have a wider usage in the technical praxis compared to the binary alloys. CuNi30Mn with Ni content from 27 to 30 %, Mn content from 2 to 3 % and impurities content bellow 0.6 % is characterized by high strength and corrosion resistance also at elevated temperatures. Because of its electric resistance this alloy is suitable for usage as resistive material till 400 °C. CuNi45Mn constantan is alloy with Ni content form 40 to 46 %, Mn content from 1 to 3 % and impurities content below 0.5 %. From the Cu-Ni alloys, this one has the largest specific electric resistance and it is used for resistive and thermal element material.

Most often the Cu-Ni-Fe-Mn alloys are used. Iron and manganese addition improve the corrosion properties markedly, especially in the seas water and overheated water steam. CuNi30 alloy with iron content in the range from 0.4 to 1.5 % and manganese content from 0.5 to 1.5 % is used for seagoing ships condensers and condensers pipes production. In the new alloys also the niobium as an alloying element is used and the nickel content tends to

**2** 

*Spain* 

**Interaction of Copper Alloys with Hydrogen** 

Copper alloys are well known for their electrical and thermal conductivity, good resistance to corrosion, ease of fabrication and good strength and fatigue resistance. These properties make copper alloys suitable for several electrical and heat-conduction industrial applications. However, many of these industrial processes deal with hydrogen, and the interaction of this gas with copper alloys may affect to their mechanical features. Hydrogen dissolves in all metals to some extent. The dissolved hydrogen in the bulk of the material may change its mechanical properties assisting in its fracture, for example, and leading the material to the so-called hydrogen embrittlement. Therefore, it becomes important to characterise the transport properties of hydrogen in copper alloys as well as their ability to migrate by diffusion through structural walls by interstitial dissolution and trapping. This characterisation allows the improvement of the aforementioned industrial applications.

Lately, copper alloys are being considered as a technical option to construct a pipeline to transport any gaseous fuel including those of high hydrogen content or even pure hydrogen. In relation to this matter, the evaluation of hydrogen migration through the wall of the pipeline and the definition of related fundamental physics are key-issues when performing any risk evaluation because of hydrogen leak capacity. Apart from this question, it is well known the ability of hydrogen to damage copper alloys at high temperatures when they contain oxygen, this problem being directly connected to the ability of hydrogen to

The research in nuclear fusion technology is also highly interested in copper materials. In fact, copper alloys have been selected as structural/heat sink materials that may be used in future fusion reactors like ITER because of their high thermal conductivity, good mechanical properties, thermal stability at high temperature and good resistance to irradiation-induced embrittlement and swelling. In this research area, heat sink/structural materials are subjected to high heat flux and, therefore, must possess a combination of high thermal conductivity and high mechanical strength. Apart from the previous properties, the interaction of hydrogen isotopes with copper alloys that could be part of the in-vessel components of a fusion reactor is of primary importance because it affects to the fuel

**1. Introduction** 

migrate through the solid material.

I. Peñalva1, G. Alberro1, F. Legarda1, G. A. Esteban1 and B. Riccardi2

> *Faculty of Engineering, Bilbao, 2Fusion for Energy, Barcelona,*

*1University of the Basque Country (UPV/EHU), Dept. Nuclear Engineering & Fluid Mechanics,* 

be decreased because of its deficit. An alloy CuNi10Ge with nickel content from 9 to 10 % and Fe content from 1 to 1.75 % and maximally 0.75 % of Mn, which is used as the material for seagoing ships condensers (Skočovský et al., 2000, 2006).

#### **3. References**


http://www.mtfdca.szm.com/subory/med-zliatiny.pdf

http://www.copper.org/education/production.html

http://cst-www.nrl.navy.mil/lattice/struk/a1.html

http://jeanes.webnode.sk/prvky/med/

### **Interaction of Copper Alloys with Hydrogen**

I. Peñalva1, G. Alberro1, F. Legarda1, G. A. Esteban1 and B. Riccardi2 *1University of the Basque Country (UPV/EHU), Dept. Nuclear Engineering & Fluid Mechanics, Faculty of Engineering, Bilbao, 2Fusion for Energy, Barcelona, Spain* 

#### **1. Introduction**

30 Copper Alloys – Early Applications and Current Performance – Enhancing Processes

be decreased because of its deficit. An alloy CuNi10Ge with nickel content from 9 to 10 % and Fe content from 1 to 1.75 % and maximally 0.75 % of Mn, which is used as the material

Skočovský, P. et al. (2000). *Designing materials* [in Slovak] (1st edition), EDIS, ISBN 80-7100-

Skočovský, P. et al. (2006). *Material sciences for the fields of mechanical engineering* [in Slovak]

Schmidt, R. F. & Schmidt, D. G. (1997) Selection and Application of Copper Alloy Casting,

Schmidt, R. F., Schmidt, D. G. & Sahoo, M. (1998) Copper and Copper Alloys, In: *ASM* 

In: *ASM Handbook Volume 2: Properties and Selection: Nonferrous Alloys and Special-Purpose Materials*, pp. 1150-1180, ASM International, ISBN 0-87170-378-5 (v. 2),

*Handbook Volume 15: Casting,* pp. 1697-1734, ASM International, ISBN 0-87170-007-7

(2nd edition), EDIS, ISBN 80-8070-593-3, Žilina, Slovak republic.

for seagoing ships condensers (Skočovský et al., 2000, 2006).

http://www.mtfdca.szm.com/subory/med-zliatiny.pdf http://www.copper.org/education/production.html http://cst-www.nrl.navy.mil/lattice/struk/a1.html

608-4, Žilina, Slovak republic.

**3. References** 

USA.

(v. 1), USA.

http://jeanes.webnode.sk/prvky/med/

Copper alloys are well known for their electrical and thermal conductivity, good resistance to corrosion, ease of fabrication and good strength and fatigue resistance. These properties make copper alloys suitable for several electrical and heat-conduction industrial applications. However, many of these industrial processes deal with hydrogen, and the interaction of this gas with copper alloys may affect to their mechanical features. Hydrogen dissolves in all metals to some extent. The dissolved hydrogen in the bulk of the material may change its mechanical properties assisting in its fracture, for example, and leading the material to the so-called hydrogen embrittlement. Therefore, it becomes important to characterise the transport properties of hydrogen in copper alloys as well as their ability to migrate by diffusion through structural walls by interstitial dissolution and trapping. This characterisation allows the improvement of the aforementioned industrial applications.

Lately, copper alloys are being considered as a technical option to construct a pipeline to transport any gaseous fuel including those of high hydrogen content or even pure hydrogen. In relation to this matter, the evaluation of hydrogen migration through the wall of the pipeline and the definition of related fundamental physics are key-issues when performing any risk evaluation because of hydrogen leak capacity. Apart from this question, it is well known the ability of hydrogen to damage copper alloys at high temperatures when they contain oxygen, this problem being directly connected to the ability of hydrogen to migrate through the solid material.

The research in nuclear fusion technology is also highly interested in copper materials. In fact, copper alloys have been selected as structural/heat sink materials that may be used in future fusion reactors like ITER because of their high thermal conductivity, good mechanical properties, thermal stability at high temperature and good resistance to irradiation-induced embrittlement and swelling. In this research area, heat sink/structural materials are subjected to high heat flux and, therefore, must possess a combination of high thermal conductivity and high mechanical strength. Apart from the previous properties, the interaction of hydrogen isotopes with copper alloys that could be part of the in-vessel components of a fusion reactor is of primary importance because it affects to the fuel

Interaction of Copper Alloys with Hydrogen 33

A schematic view of a permeation facility is shown in *Figure 2*. The physical principle of the experimental technique entails the gas flux recording that passes through a thin membrane of the material of interest from a high gas pressure region to a low-pressure region at initial

The hydrogen migration through the specimen is measured by recording the pressure increase with time in the low-pressure region with two capacitance manometers (Baratron MKS Instr.-USA) P1 and P2 with full scale range of 1000 Pa and 13.33 Pa respectively. An electrical resistance furnace (F) regulated by a PID controller allows to establish the sample temperature within a +/- 1 K precision. The temperature of the specimen is measured by a Ni-Cr/Ni thermocouple inserted into a well drilled in one of the two flanges where the specimen is mounted. The pressure controller (PC) allows the instant exposure of the highpressure face of the specimen to any desired gas driving pressure, which is measured by

Before any experimental test is performed with high purity hydrogen (99.9999%), ultrahigh vacuum state is reached inside the experimental volumes (up to 10-7 Pa) in order to assure the absence of any deleterious species (such as oxygen or water vapour) that may provoke surface oxidation of the specimen (S). There are three ultra-high vacuum pumping units, UHV, composed by a hybrid turbomolecular pump and a primary pump; they pump down the inner volumes of the rig to the desired vacuum level with the help of heating tapes. The vacuum state is checked with three Penning gauges PG in different zones of the facility. A quadrupole mass spectrometer (QMS) is available to check the purity of the gas before and after any experimental test and as an alternative means of

Fig. 1. CuCrZr microstructure.

vacuum conditions.

**2.2 Gas evolution permeation technique** 

means of a high-pressure transducer (HPT).

testing the quality of the vacuum.

economy, the plasma stability and the radiological safety of the facility. There are various examples of predictive works trying to establish the time dependant evolution of migration fluxes and fuel inventory within fusion reactor components (Esteban et al., 2004; Meyder et al., 2006) by means of numerical simulation codes that use the hydrogen transport and trapping properties as the main input parameters. Trapping is the process by which dissolved hydrogen atoms remain bound to some specific centres known as "traps" (e.g. inclusions, dislocations, grain boundaries and precipitates). Hence, hydrogen isotopes may be dissolved in trapping or lattice sites of the material. The effect of trapping on hydrogen transport affects to the transport parameters and also to the physical and mechanical properties of the copper alloys involved.

Two of the most promising copper alloys at the present time in several specialised research areas are oxide dispersion strengthened (DS) copper alloys and precipitation hardened (PH) copper alloys (Barabash et al., 2007; Fabritsiev & Pokrovsky, 2005; ITER, 2001; Lorenzetto et al., 2006; Zinkle & Fabritsiev, 1994). This chapter will analyse and compare the experimental hydrogen transport parameters of diffusivity, permeability and Sieverts' constant for the diffusive regime of these kinds of copper alloys. Results can then be extrapolated as general behaviour for similar copper alloys. Trapping properties will also be discussed. Data shown in the chapter will refer to real experimental values for copper alloys obtained by means of the gas evolution permeation technique.

#### **2. Experimental**

The gas evolution permeation technique is widely used to characterize the hydrogen transport in metallic materials and, therefore, it turns out to be a suitable technique for the analysis of hydrogen transport in specimens made of different copper alloys. Oxide dispersion strengthened (DS) copper alloys and precipitation hardened (PH) copper alloys have been characterized by means of this experimental method. More precisely, experimental hydrogen transport data are available for a DS copper alloy named GlidCop® Al25 and for a PH-CuCrZr copper alloy named ELBRODUR®.

#### **2.1 Dispersion strengthened and precipitation hardened copper alloys**

The GlidCop® Al25 copper alloy is produced by OMG America and contains wt. 0.25 % Al in the form of Al2O3 particles. The material is manufactured by means of powder metallurgy using Cu-Al alloy and copper oxide powders. These are mixed and heated to form alumina and then consolidated by hot extrusion. This fabrication method derives in a high density of homogeneously distributed Al2O3 nanometric particles within the elongated grain substructure of the material, which are thermally stable and resistant to coarsening so that the grain substructure is resistant to thermal annealing effects (Esteban et al., 2009).

The ELBRODUR® copper alloy is produced by KME-Germany AG. The alloy composition is wt. 0.65 % Cr, wt. 0.05 % Zr and the rest Cu. The fabrication process and the heat treatment consisting of solution annealing (1253 K, 1 h), water quenching and aging (748 K, 2 h) makes possible the presence of nanometric Guinier-Preston zones and incoherent pure Cr particles that provide the material with the high mechanical strength by dislocation motion inhibition. An image of the CuCrZr microstructure is shown in *Figure 1*.

economy, the plasma stability and the radiological safety of the facility. There are various examples of predictive works trying to establish the time dependant evolution of migration fluxes and fuel inventory within fusion reactor components (Esteban et al., 2004; Meyder et al., 2006) by means of numerical simulation codes that use the hydrogen transport and trapping properties as the main input parameters. Trapping is the process by which dissolved hydrogen atoms remain bound to some specific centres known as "traps" (e.g. inclusions, dislocations, grain boundaries and precipitates). Hence, hydrogen isotopes may be dissolved in trapping or lattice sites of the material. The effect of trapping on hydrogen transport affects to the transport parameters and also to the physical and mechanical

Two of the most promising copper alloys at the present time in several specialised research areas are oxide dispersion strengthened (DS) copper alloys and precipitation hardened (PH) copper alloys (Barabash et al., 2007; Fabritsiev & Pokrovsky, 2005; ITER, 2001; Lorenzetto et al., 2006; Zinkle & Fabritsiev, 1994). This chapter will analyse and compare the experimental hydrogen transport parameters of diffusivity, permeability and Sieverts' constant for the diffusive regime of these kinds of copper alloys. Results can then be extrapolated as general behaviour for similar copper alloys. Trapping properties will also be discussed. Data shown in the chapter will refer to real experimental values for copper alloys obtained by means of

The gas evolution permeation technique is widely used to characterize the hydrogen transport in metallic materials and, therefore, it turns out to be a suitable technique for the analysis of hydrogen transport in specimens made of different copper alloys. Oxide dispersion strengthened (DS) copper alloys and precipitation hardened (PH) copper alloys have been characterized by means of this experimental method. More precisely, experimental hydrogen transport data are available for a DS copper alloy named GlidCop®

The GlidCop® Al25 copper alloy is produced by OMG America and contains wt. 0.25 % Al in the form of Al2O3 particles. The material is manufactured by means of powder metallurgy using Cu-Al alloy and copper oxide powders. These are mixed and heated to form alumina and then consolidated by hot extrusion. This fabrication method derives in a high density of homogeneously distributed Al2O3 nanometric particles within the elongated grain substructure of the material, which are thermally stable and resistant to coarsening so that

The ELBRODUR® copper alloy is produced by KME-Germany AG. The alloy composition is wt. 0.65 % Cr, wt. 0.05 % Zr and the rest Cu. The fabrication process and the heat treatment consisting of solution annealing (1253 K, 1 h), water quenching and aging (748 K, 2 h) makes possible the presence of nanometric Guinier-Preston zones and incoherent pure Cr particles that provide the material with the high mechanical strength by dislocation motion

properties of the copper alloys involved.

the gas evolution permeation technique.

Al25 and for a PH-CuCrZr copper alloy named ELBRODUR®.

**2.1 Dispersion strengthened and precipitation hardened copper alloys** 

the grain substructure is resistant to thermal annealing effects (Esteban et al., 2009).

inhibition. An image of the CuCrZr microstructure is shown in *Figure 1*.

**2. Experimental** 

Fig. 1. CuCrZr microstructure.

#### **2.2 Gas evolution permeation technique**

A schematic view of a permeation facility is shown in *Figure 2*. The physical principle of the experimental technique entails the gas flux recording that passes through a thin membrane of the material of interest from a high gas pressure region to a low-pressure region at initial vacuum conditions.

The hydrogen migration through the specimen is measured by recording the pressure increase with time in the low-pressure region with two capacitance manometers (Baratron MKS Instr.-USA) P1 and P2 with full scale range of 1000 Pa and 13.33 Pa respectively. An electrical resistance furnace (F) regulated by a PID controller allows to establish the sample temperature within a +/- 1 K precision. The temperature of the specimen is measured by a Ni-Cr/Ni thermocouple inserted into a well drilled in one of the two flanges where the specimen is mounted. The pressure controller (PC) allows the instant exposure of the highpressure face of the specimen to any desired gas driving pressure, which is measured by means of a high-pressure transducer (HPT).

Before any experimental test is performed with high purity hydrogen (99.9999%), ultrahigh vacuum state is reached inside the experimental volumes (up to 10-7 Pa) in order to assure the absence of any deleterious species (such as oxygen or water vapour) that may provoke surface oxidation of the specimen (S). There are three ultra-high vacuum pumping units, UHV, composed by a hybrid turbomolecular pump and a primary pump; they pump down the inner volumes of the rig to the desired vacuum level with the help of heating tapes. The vacuum state is checked with three Penning gauges PG in different zones of the facility. A quadrupole mass spectrometer (QMS) is available to check the purity of the gas before and after any experimental test and as an alternative means of testing the quality of the vacuum.

Interaction of Copper Alloys with Hydrogen 35

between the flux and the concentration gradient is called diffusivity (*D*) and is directly related to the kinetics of the system in order to reach the equilibrium by means of diffusion. Finally, Sieverts´ constant (*K*S) is directly related to the solubility of the gas in the solid and

Transitory permeation regime Steady-state permeation regime

Fig. 3. Experimental permeation curve: transitory permeation regime and steady-state

(time-lag) *t* (s)

Typical bulk parameters for the study of hydrogen transport in metal lattices are the diffusivity (*D*), the Sieverts´ constant, (*K*S), and the permeability (*Φ*) (Alberici & Tominetti, 1995). The diffusivity is related to the diffusing flux in a metallic matrix, *J*, and the gradient

0 400 800 1200

where is easy to see that *D* is linked to the migration velocity of the gas in the material.

In this equation, taking into account a homogeneous bulk, *D* will be supposed to be uniform and constant throughout the material volume and it only depends on the absolute

*J Dc* (1)

permeation regime. Definition of the time-lag.

0,0

0,5

1,0

*p* (Pa)

1,5

2,0

2,5

temperature, *T*, by an Arrhenius relationship:

of the gas concentration in the matrix, *c* , by the first Fick's law:

t L

*τ*L

**3. Theory** 

can be derived from the values of diffusivity and permeability.

Fig. 2. Schematic view of the permeation facility. PG – Penning gauge; F – furnace; PC – pressure controller; HPT – high-pressure transducer; QMS – quadrupole mass spectrometer; S – specimen; T1, T2 – nickel/chromium-nickel thermocouples; P1, P2 – capacitance manometers; UHV – ultra-high vacuum pumping units, V1 – calibrated volume.

In an individual experimental test, the high driving pressure starts forcing permeation through the high-pressure face of the specimen towards the low-pressure region, where the hydrogen permeation flux rises progressively with time until a steady-state permeation flux is reached. After every experimental permeation run, an expansion of the gas in the lowpressure region is performed to a calibrated volume (V1) in order to convert pressure values into permeated gas amount, or alternatively, the speed of pressure increase into permeation flux. The modelling of the pressure increase *p*(*t*) due to the gas permeation towards the lowpressure region (a typical experimental permeation curve is shown in *Figure 3*) makes possible to obtain the hydrogen transport properties of the copper alloy: permeability (*Φ*), diffusivity (*D*) and Sieverts´ constant (*K*S).

The permeated flux under diffusive regime for every temperature depends on the thickness of the sample, the values of the loading pressure and the permeability of the gas (*Φ*). This transport parameter defines the gas-material interaction. Diffusion is a physical property that allows the flux of a gas through the bulk of a solid material due to, in this case, a concentration gradient of the dissolved hydrogen. The gas flux in the bulk of the material depends on the concentration gradient and on the temperature. The proportionality

Fig. 2. Schematic view of the permeation facility. PG – Penning gauge; F – furnace; PC – pressure controller; HPT – high-pressure transducer; QMS – quadrupole mass spectrometer;

In an individual experimental test, the high driving pressure starts forcing permeation through the high-pressure face of the specimen towards the low-pressure region, where the hydrogen permeation flux rises progressively with time until a steady-state permeation flux is reached. After every experimental permeation run, an expansion of the gas in the lowpressure region is performed to a calibrated volume (V1) in order to convert pressure values into permeated gas amount, or alternatively, the speed of pressure increase into permeation flux. The modelling of the pressure increase *p*(*t*) due to the gas permeation towards the lowpressure region (a typical experimental permeation curve is shown in *Figure 3*) makes possible to obtain the hydrogen transport properties of the copper alloy: permeability (*Φ*),

The permeated flux under diffusive regime for every temperature depends on the thickness of the sample, the values of the loading pressure and the permeability of the gas (*Φ*). This transport parameter defines the gas-material interaction. Diffusion is a physical property that allows the flux of a gas through the bulk of a solid material due to, in this case, a concentration gradient of the dissolved hydrogen. The gas flux in the bulk of the material depends on the concentration gradient and on the temperature. The proportionality

S – specimen; T1, T2 – nickel/chromium-nickel thermocouples; P1, P2 – capacitance manometers; UHV – ultra-high vacuum pumping units, V1 – calibrated volume.

diffusivity (*D*) and Sieverts´ constant (*K*S).

between the flux and the concentration gradient is called diffusivity (*D*) and is directly related to the kinetics of the system in order to reach the equilibrium by means of diffusion. Finally, Sieverts´ constant (*K*S) is directly related to the solubility of the gas in the solid and can be derived from the values of diffusivity and permeability.

Fig. 3. Experimental permeation curve: transitory permeation regime and steady-state permeation regime. Definition of the time-lag.

#### **3. Theory**

Typical bulk parameters for the study of hydrogen transport in metal lattices are the diffusivity (*D*), the Sieverts´ constant, (*K*S), and the permeability (*Φ*) (Alberici & Tominetti, 1995). The diffusivity is related to the diffusing flux in a metallic matrix, *J*, and the gradient of the gas concentration in the matrix, *c* , by the first Fick's law:

$$J = -D \cdot \nabla \mathcal{L} \tag{1}$$

where is easy to see that *D* is linked to the migration velocity of the gas in the material.

In this equation, taking into account a homogeneous bulk, *D* will be supposed to be uniform and constant throughout the material volume and it only depends on the absolute temperature, *T*, by an Arrhenius relationship:

$$D = D\_0 \cdot \exp(-E\_d / \mathbb{R} \cdot T) \tag{2}$$

Interaction of Copper Alloys with Hydrogen 37

Hydrogen isotope transport through material may be limited either by gas interstitial diffusion through the bulk (diffusion-limited regime) or by the physical-chemical reactions of adsorptive dissociation and desorptive recombination occurring on the surface of the solid material (surface-limited regime). The objective of this experimental task is usually to characterize the diffusion-limited regime instead of the surface-limited regime, the second one being only relevant when any kind of impurities or oxides are present on the surface of

"Trapping" is the process by which dissolved hydrogen atoms remain bound to some specific centres known as "traps" (e.g. inclusions, dislocations, grain boundaries and precipitates). Hence, hydrogen isotopes may be dissolved in trapping or lattice sites of the material. The effect of trapping on hydrogen transport is, on the one hand, the increase in the gas absorbed inventory, i.e. the increase in the effective Sieverts' constant (*K*S,eff) with respect to the aforementioned lattice Sieverts' constant (*K*S). On the other hand, the dynamics of transport becomes slower, i.e. the decrease of the effective diffusivity (*D*eff) with respect to the aforementioned lattice diffusivity (*D*). As a result, the Arrhenius temperature dependence of the parameters remains modified as follows, according to Eqs. (2) and (4) for

> eff <sup>t</sup> <sup>t</sup> l

<sup>t</sup> S,eff S <sup>t</sup>

1 exp( /R ) *<sup>D</sup> <sup>D</sup> <sup>N</sup> E T N*

 

l 1 exp( /R ) *<sup>N</sup> KK ET N*

 

(7)

(8)

Fig. 4. Potential energy distribution in a metal (Möller, 1984).

the material.

diluted solutions (Oriani R.A., 1970):

where *E*d is the diffusion activation energy, which is always positive.

Experimentally it is found that hydrogen dissolves atomically in metal lattices; the proportionality between the atomic gas concentration in the bulk volume, *c*, and the square root of the equilibrium gas pressure outside the bulk, p1/2, is known as the Sieverts´ constant:

$$K\_{\rm S} = c \;/\sqrt{p} \tag{3}$$

It is interesting to note that Sieverts´ constant also shows an Arrhenius dependence on the temperature:

$$K\_{\rm S} = K\_{\rm S,0} \cdot \exp(-E\_{\rm s} \,/\, \text{R} \cdot T) \tag{4}$$

where *E*S is the activation energy for solution, which can be either positive or negative.

Permeability (*Φ*) is given by means of Richardson's law that states a linear relation between *D* and *K*S:

$$
\phi = \mathbf{K}\_{\mathbb{S}} \cdot D \tag{5}
$$

From Eq. 5, it is obvious that permeability also follows an Arrhenius behaviour like *D* and *K*S, with an activation energy of permeation which is the sum of *E*d and *E*s:

$$\phi = \phi\_0 \cdot \exp\left(-(E\_d + E\_s) / R \cdot T\right) \tag{6}$$

All the processes involved in the interaction between hydrogen and the metallic material, either on the surface or in the bulk, may be explained by the analysis of the different potential energy levels acquired by the hydrogen atom/molecule in the immediacy of, and within the metal (Esteban et al., 1999). These energy levels are summarised in *Figure 4* (Möller, 1984). Out of the material, hydrogen is in the molecular form: the solid line refers to atomic hydrogen and the broken line to molecular hydrogen. All the energy increments and decrements depicted in *Figure 4* define the hydrogen behaviour within, and in the vicinity of the solid metal and explain observed physical processes. The dissociation energy, *E*di, is the amount of energy needed for splitting a hydrogen molecule into two atoms. The chemisorption energy, *E*ch, refers to the chemical binding established between atomic hydrogen and metallic atoms. The adsorption energy, *E*ad, is the energy barrier hydrogen has to surmount in order to access to a chemisorption site and it depends on the surface condition. The solution energy, *E*s, is the energy difference between a free atom and a dissolved one and depending on the sign of this energy the material is characterised as endothermic, *E*s > 0, or exothermic, *E*s < 0. The diffusion energy, *E*d, is the barrier the diffusing atom has to surmount in order to pass, within the lattice, from one solution site to another. The trapping energy, *E*t, is the potential well to which a hydrogen atom remains bound when interacting with the potential trapping sites. ∆*E* states for the energy difference between a normal solution site and a trapping site, (*E*s – *E*t). Finally, *E*c states for the energy difference when comparing potential barriers between normal solution sites and a trapping site.

Experimentally it is found that hydrogen dissolves atomically in metal lattices; the proportionality between the atomic gas concentration in the bulk volume, *c*, and the square root of the equilibrium gas pressure outside the bulk, p1/2, is known as the Sieverts´

It is interesting to note that Sieverts´ constant also shows an Arrhenius dependence on the

Permeability (*Φ*) is given by means of Richardson's law that states a linear relation between

From Eq. 5, it is obvious that permeability also follows an Arrhenius behaviour like *D* and

All the processes involved in the interaction between hydrogen and the metallic material, either on the surface or in the bulk, may be explained by the analysis of the different potential energy levels acquired by the hydrogen atom/molecule in the immediacy of, and within the metal (Esteban et al., 1999). These energy levels are summarised in *Figure 4* (Möller, 1984). Out of the material, hydrogen is in the molecular form: the solid line refers to atomic hydrogen and the broken line to molecular hydrogen. All the energy increments and decrements depicted in *Figure 4* define the hydrogen behaviour within, and in the vicinity of the solid metal and explain observed physical processes. The dissociation energy, *E*di, is the amount of energy needed for splitting a hydrogen molecule into two atoms. The chemisorption energy, *E*ch, refers to the chemical binding established between atomic hydrogen and metallic atoms. The adsorption energy, *E*ad, is the energy barrier hydrogen has to surmount in order to access to a chemisorption site and it depends on the surface condition. The solution energy, *E*s, is the energy difference between a free atom and a dissolved one and depending on the sign of this energy the material is characterised as endothermic, *E*s > 0, or exothermic, *E*s < 0. The diffusion energy, *E*d, is the barrier the diffusing atom has to surmount in order to pass, within the lattice, from one solution site to another. The trapping energy, *E*t, is the potential well to which a hydrogen atom remains bound when interacting with the potential trapping sites. ∆*E* states for the energy difference between a normal solution site and a trapping site, (*E*s – *E*t). Finally, *E*c states for the energy difference when comparing potential barriers between normal solution

0 ds

where *E*S is the activation energy for solution, which can be either positive or negative.

*K*S, with an activation energy of permeation which is the sum of *E*d and *E*s:

 

where *E*d is the diffusion activation energy, which is always positive.

constant:

temperature:

*D* and *K*S:

sites and a trapping site.

0 d *DD E T* exp( /R ) (2)

*Kc p* <sup>S</sup> / (3)

*K D* <sup>S</sup> (5)

exp( ( ) /R ) *EE T* (6)

S S,0 <sup>s</sup> *KK E T* exp( /R ) (4)

$$\text{Fig. 4. Potential energy distribution in a metal (Möller, 1984).}$$

Hydrogen isotope transport through material may be limited either by gas interstitial diffusion through the bulk (diffusion-limited regime) or by the physical-chemical reactions of adsorptive dissociation and desorptive recombination occurring on the surface of the solid material (surface-limited regime). The objective of this experimental task is usually to characterize the diffusion-limited regime instead of the surface-limited regime, the second one being only relevant when any kind of impurities or oxides are present on the surface of the material.

"Trapping" is the process by which dissolved hydrogen atoms remain bound to some specific centres known as "traps" (e.g. inclusions, dislocations, grain boundaries and precipitates). Hence, hydrogen isotopes may be dissolved in trapping or lattice sites of the material. The effect of trapping on hydrogen transport is, on the one hand, the increase in the gas absorbed inventory, i.e. the increase in the effective Sieverts' constant (*K*S,eff) with respect to the aforementioned lattice Sieverts' constant (*K*S). On the other hand, the dynamics of transport becomes slower, i.e. the decrease of the effective diffusivity (*D*eff) with respect to the aforementioned lattice diffusivity (*D*). As a result, the Arrhenius temperature dependence of the parameters remains modified as follows, according to Eqs. (2) and (4) for diluted solutions (Oriani R.A., 1970):

$$D\_{\rm eff} = \frac{D}{1 + \frac{N\_{\rm t}}{N\_{\rm l}} \exp(E\_{\rm t} / \mathbb{R} \cdot T)} \cdot \tag{7}$$

$$K\_{\rm S,eff} = K\_{\rm S} \cdot \left(1 + \frac{N\_{\rm t}}{N\_{\rm l}} \exp(E\_{\rm t} / \mathbb{R} \cdot T)\right) \tag{8}$$

*D*0 and *K*S,0 being the pre-exponential lattice diffusivity and pre-exponential lattice Sieverts' constant, and *E*d, *E*s the diffusion and solution energies, respectively. *N*t (m–3) is the trap sites concentration, *N*l (m–3) is the lattice dissolution sites concentration and *E*t the trapping energy.

When the individual effective parameters for each experimental temperature have been obtained, another fitting routine is separately run with Eqs. (2), (4), (7) and (8) for the lattice parameters *D*0, *E*d, *K*S,0 and *E*s and trapping parameters *E*t and *N*t over the correspondent temperature range of influence. The value of 8.5 1028 m–3 is taken for the density of solution sites into the lattice *N*l, assuming that the copper alloy is close to a fcc structure where hydrogen occupies only the octahedral interstitial positions (Vykhodets et al., 1972).

The effective transport parameters of diffusivity (*D*eff) and permeability (*Φ*) are evaluated for each temperature by modelling the experimental permeation curves obtained for every individual test. The Sieverts' constant (*K*S,eff) is derived from the definition of permeability that states the relationship amongst the three transport parameters:

$$\mathbf{OP} = \mathbf{D}\_{\text{eff}} \cdot \mathbf{K}\_{\text{S,eff}} \tag{9}$$

Interaction of Copper Alloys with Hydrogen 39

A scheme of the gas transport through a sheet of material with a certain thickness (*d*) is shown in *Figure 5*. That specimen is exposed on one side to a certain gas driving pressure (*p*h), whereas the other side is left under vacuum conditions (i.e. very low pressure *p*l).

The hydrogen concentration (*c*(*x*,*t*)) at each position (*x* coordinate) and each time (*t*) may be

( ,) ( ,) *eff cxt cxt <sup>D</sup> t x*

 1st condition: h *cx t c* ( 0, ) , from the beginning, in the region closest to the surface, the gas concentration acquires the final equilibrium value in the saturation state given by

2nd condition: *cx dt* ( ,) 0 , the gas concentration in the low-pressure side is negligible

The initial condition is *cx t* ( 0, 0) 0 ; at the beginning of the test, the specimen is under

The analytical solution of the Eq. (10) with the previous boundary and initial conditions is

2 1 π π , 1 sin exp

*d nd d*

*t d d*

(14)

(13)

1

0.5 0.5

*d D*

*x c nx n c xt c D t*

eff S,eff h

The total gas inventory (*I*(*t*)) permeated to the low-pressure region is evaluated by accounting for all the gas flux released during the considered time period (*t*) and taking into

h h s s s 0 eff

,´ ´ <sup>6</sup>

*<sup>Φ</sup> <sup>p</sup> <sup>Φ</sup> p d I t A J d t dt A t <sup>A</sup>*

2 2 eff

, <sup>π</sup> , 1 2 1 exp *<sup>n</sup> x d n c xt DK p <sup>n</sup> J x dt D D t*

vacuum conditions without any amount of hydrogen dissolved into the material.

h

π

The resultant flux to the low-pressure region can be evaluated as:

*t*

eff 1

exp <sup>6</sup>

*s n*

h

1

*n*

2 1 π

0.5 2 2

*n*

*<sup>Φ</sup> p d <sup>n</sup> A Dt D n d*

2 2

0.5

0.5

(10)

h S,eff h *cK p* (11)

0 S,eff l *cK p* (12)

2 2

2

(15)

eff 2

0.5 2 2

determined by solving the second Fick's law in the one dimension slab:

in comparison to *c*h; i.e. *p*l negligible in comparison to *p*h,

The boundary conditions being the following:

Sieverts' law,

(Carslaw & Jaeger, 1959):

account the surface area of the specimen (*A*s):

*h*

A subsequent analysis of the Arrhenius dependence of these transport parameters with temperature enables the obtaining of the characteristic transport parameters of trapping energy (*E*t) and density of traps (*N*t).

The obtaining of the theoretical expression for the pressure increase with time in the low-pressure region as a function of the previous transport parameters is briefly explained hereafter.

The specimens are thin discs with a very high ratio of the circular surface exposed to the gas in relation to the length of the diffusion path through the bulk of material. This is the reason why the problem can be modelled by an infinite slab with gas diffusion occurring in the direction perpendicular to the surface of the specimen.

Fig. 5. Scheme of the permeation process through a 1-D slab. *p*h – high-pressure; *p*l – lowpressure; *d* – thickness of the slab; *J*d (*x*,*t*) – diffusive flux; *c*(*x*,*t*) – gas concentration.

*D*0 and *K*S,0 being the pre-exponential lattice diffusivity and pre-exponential lattice Sieverts' constant, and *E*d, *E*s the diffusion and solution energies, respectively. *N*t (m–3) is the trap sites concentration, *N*l (m–3) is the lattice dissolution sites concentration and *E*t the trapping energy. When the individual effective parameters for each experimental temperature have been obtained, another fitting routine is separately run with Eqs. (2), (4), (7) and (8) for the lattice parameters *D*0, *E*d, *K*S,0 and *E*s and trapping parameters *E*t and *N*t over the correspondent temperature range of influence. The value of 8.5 1028 m–3 is taken for the density of solution sites into the lattice *N*l, assuming that the copper alloy is close to a fcc structure where

hydrogen occupies only the octahedral interstitial positions (Vykhodets et al., 1972).

that states the relationship amongst the three transport parameters:

energy (*E*t) and density of traps (*N*t).

High-pressure region

*txc Dtx <sup>d</sup> <sup>J</sup>*

),( ,

direction perpendicular to the surface of the specimen.

*x*

*c*h

*<sup>p</sup>***h** *p***<sup>l</sup> <<** *<sup>p</sup>***<sup>h</sup>** *<sup>c</sup>*(*x*,*t*)

hereafter.

The effective transport parameters of diffusivity (*D*eff) and permeability (*Φ*) are evaluated for each temperature by modelling the experimental permeation curves obtained for every individual test. The Sieverts' constant (*K*S,eff) is derived from the definition of permeability

A subsequent analysis of the Arrhenius dependence of these transport parameters with temperature enables the obtaining of the characteristic transport parameters of trapping

The obtaining of the theoretical expression for the pressure increase with time in the low-pressure region as a function of the previous transport parameters is briefly explained

The specimens are thin discs with a very high ratio of the circular surface exposed to the gas in relation to the length of the diffusion path through the bulk of material. This is the reason why the problem can be modelled by an infinite slab with gas diffusion occurring in the

*c*<sup>0</sup> ≈ 0

**x**

Fig. 5. Scheme of the permeation process through a 1-D slab. *p*h – high-pressure; *p*l – lowpressure; *d* – thickness of the slab; *J*d (*x*,*t*) – diffusive flux; *c*(*x*,*t*) – gas concentration.

x = 0 x = d

*<sup>Φ</sup> D K* eff S,eff (9)

Low-pressure region

A scheme of the gas transport through a sheet of material with a certain thickness (*d*) is shown in *Figure 5*. That specimen is exposed on one side to a certain gas driving pressure (*p*h), whereas the other side is left under vacuum conditions (i.e. very low pressure *p*l).

The hydrogen concentration (*c*(*x*,*t*)) at each position (*x* coordinate) and each time (*t*) may be determined by solving the second Fick's law in the one dimension slab:

$$\frac{\partial \mathbf{c}(\mathbf{x},t)}{\partial t} = D\_{\text{eff}} \frac{\partial^2 \mathbf{c}(\mathbf{x},t)}{\partial \mathbf{x}^2} \tag{10}$$

The boundary conditions being the following:

 1st condition: h *cx t c* ( 0, ) , from the beginning, in the region closest to the surface, the gas concentration acquires the final equilibrium value in the saturation state given by Sieverts' law,

$$\mathbf{c}\_{\mathbf{h}} = \mathbf{K}\_{\text{S,eff}} \cdot \mathbf{p}\_{\mathbf{h}}^{0.5} \tag{11}$$

 2nd condition: *cx dt* ( ,) 0 , the gas concentration in the low-pressure side is negligible in comparison to *c*h; i.e. *p*l negligible in comparison to *p*h,

$$\mathbf{c}\_0 = \mathbf{K}\_{\text{S,eff}} \cdot \mathbf{p}\_{\text{l}}^{0.5} \tag{12}$$

The initial condition is *cx t* ( 0, 0) 0 ; at the beginning of the test, the specimen is under vacuum conditions without any amount of hydrogen dissolved into the material.

The analytical solution of the Eq. (10) with the previous boundary and initial conditions is (Carslaw & Jaeger, 1959):

$$\mathcal{L}\left(\mathbf{x},t\right) = c\_h \left(1 - \frac{\mathbf{x}}{d}\right) - \frac{2c\_h}{\mathbf{n}} \sum\_{n=1}^{n} \frac{1}{n} \sin\left(\frac{n \cdot \mathbf{n} \cdot \mathbf{x}}{d}\right) \exp\left(-D\_{\mathrm{eff}} \frac{n^2 \cdot \mathbf{n}^2}{d^2} t\right) \tag{13}$$

The resultant flux to the low-pressure region can be evaluated as:

$$f(\mathbf{x} = d, t) = -D \frac{\partial c(\mathbf{x}, t)}{\partial t} \bigg|\_{\mathbf{x} = d} = \frac{D\_{\text{eff}} \cdot K\_{\text{S,eff}} \cdot p\_{\text{h}}^{0.5}}{d} \left[ 1 + 2 \sum\_{n=1}^{\infty} (-1)^n \exp\left( -D \frac{n^2 \cdot \mathbf{n}^2}{d^2} t \right) \right] \tag{14}$$

The total gas inventory (*I*(*t*)) permeated to the low-pressure region is evaluated by accounting for all the gas flux released during the considered time period (*t*) and taking into account the surface area of the specimen (*A*s):

$$\begin{aligned} I(t) &= A\_{\sf s} \Big|\_{0}^{t} J(d, t') \, dt' = \frac{\clubsuit \cdot p\_{\sf h}^{0.5}}{d} A\_{\sf s} \cdot t - \frac{\clubsuit \cdot p\_{\sf h}^{0.5} \cdot d}{6 \cdot D\_{\sf eff}} A\_{\sf s} -\\ &\frac{2 \cdot \clubsuit \cdot p\_{\sf h}^{0.5} \cdot d}{6 \cdot D\_{\sf eff}} A\_{\sf s} \sum\_{n=1}^{o} \frac{\left(-1\right)^{n}}{n^{2}} \exp\left(-D\_{\sf eff} \frac{n^{2} \cdot \mathbf{n}^{2}}{d^{2}} t\right) \end{aligned} \tag{15}$$

Interaction of Copper Alloys with Hydrogen 41

where *σk*1 is the adsorption rate constant. The experimental confirmation of one of these relationships is a method to decide the type of transport regime for modelling the

This section reviews the available data in literature for oxide dispersion strengthened (DS) copper alloys and precipitation hardened (PH) copper alloys. Results regarding interaction of these alloys with hydrogen are compared in relation to base material, Cu. Punctual experimental values are shown only for the ELBRODUR® alloy (not published), whereas

Individual permeation tests have been carried out for the aforementioned copper alloys, GlidCop® Al25 (Esteban et al., 2009) and ELBRODUR®, with temperatures ranging from 573 K to 793 K and using loading pressures ranging from 103 Pa to 1.0 105 Pa. Additionally, data for base material, Cu, (Reiter et al., 1993) and for a similar PH-CuCrZr alloy (Serra & Perujo, 1998) named ELBRODUR-II hereafter to distinguish from the material analysed, are also available. These results for the hydrogen transport parameters in copper alloys are

In relation to the permeation tests carried out for GlidCop® Al25 and ELBRODUR® copper alloys, the evaluation of the diffusive transport parameters has been assured because no surface effect has become relevant within the whole group of individual tests. This fact has been proved by studying the evolution of the experimental steady-state flux (*J*∞) with

In the case of the ELBRODUR® copper alloy, a set of 9 permeation tests has been performed at the same temperature (688 K) with different loading pressures (*p*h) in order to study the type of hydrogen transport regime. These results are shown in *Figure 6*. The exponential relationship between the steady-state hydrogen flux (*J*∞) and the loading pressure (*p*h) has a power of *n* = 0.52, which is close to 0.5 (pure diffusion-limited regime) and far from 1.0

Individual transport parameters of effective diffusivity (*D*eff), permeability (*Φ*) and effective Sieverts' constant (*K*S,eff) have been obtained at different temperatures by modelling the corresponding individual permeation tests, both for GlidCop® Al25 (Esteban et al., 2009)

The dependence of the transport parameters on temperature for the ELBRODUR® copper alloy is shown in *Figure 7* (permeability), *Figure 8* (diffusivity) and *Figure 9* (Sieverts´ constant), together with the results obtained for the aforementioned reference copper alloys (Esteban et al., 2009; Reiter et al., 1993; Serra & Perujo, 1998). The Arrhenius parameters are obtained by fitting the individual experimental values to the tendencies given by Eqs. (2),


2 -1 <sup>5</sup> <sup>1</sup> *D T* (m s ) 3.55 10 exp( 65.5 (kJ mol ) /R )

Arrhenius regressions of the transport parameters are compiled for all the alloys.

experimental tests.

and ELBRODUR®.

(4), (7) and (8), resulting:

**4. Results and discussion** 

summarised and discussed in the next paragraphs.

driving pressure (*p*h) at the same temperature.

(pure surface-limited regime) (Eqs. (20) and (21), respectively).

Taking into account the ideal gas approximation, pressure increment with time in the lowpressure region due to this amount of gas is:

$$p(t) = \frac{\mathbf{R} \cdot T\_{\rm eff}}{V\_{\rm eff}} \left[ \frac{\boldsymbol{\Phi} \cdot p\_{\rm h}^{0.5}}{d} \, A\_{\rm s} \cdot t - \frac{\boldsymbol{\Phi} \cdot p\_{\rm h}^{0.5} \cdot d}{6 \cdot D\_{\rm eff}} A\_{\rm s} - \frac{2 \cdot \boldsymbol{\Phi} \cdot p\_{\rm h}^{0.5} \cdot d}{6 \cdot D\_{\rm eff}} A\_{\rm s} \sum\_{n=1}^{n} \frac{\left(-1\right)^{n}}{n^{2}} \exp\left( -D\_{\rm eff} \frac{n^{2} \cdot \mathbf{n}^{2}}{d^{2}} t \right) \right] (16)$$

Where the *V*eff is the effective volume where the permeated gas is retained, *T*eff is the temperature of the volume and R is the ideal gas constant (8.314 J K–1 mol–1). The volume *V*eff is precisely measured in each experimental permeation test by performing gas expansion to a calibrated volume.

When imposing a very large period of time ( *t* ) in the previous expression the evolution of pressure with time for the steady-state permeation regime is obtained:

$$p\_{\text{ev}}(t) = \frac{\mathbf{R} \cdot T\_{\text{eff}}}{V\_{\text{eff}}} \left( \frac{\boldsymbol{\Phi} \cdot \boldsymbol{p}\_{\text{h}}^{0.5}}{d} \boldsymbol{A}\_{\text{s}} \cdot \boldsymbol{t} - \frac{\boldsymbol{\Phi} \cdot \boldsymbol{p}\_{\text{h}}^{0.5} \cdot d}{\boldsymbol{\Phi} \cdot \boldsymbol{D}\_{\text{eff}}} \boldsymbol{A}\_{\text{s}} \right) \tag{17}$$

This expression corresponds to the steady-state flux,

$$J\_{\rm co} = \frac{\bigoplus \cdot p\_{\rm h}^{0.5}}{d} \tag{18}$$

obtained from Eq. (17); this is the linear tendency shown in *Figure 3* on the right-hand side. When the straight line is extended down to cross the abscise axis in the time co-ordinate a characteristic time known as time-lag is obtained:

$$
\tau\_{\rm L} = \frac{d^2}{6 \cdot D\_{\rm eff}} \tag{19}
$$

The value of permeability (*Φ*) can be derived from the slope of the straight line in steadystate permeation regime (Eq. (17)) and the effective diffusivity (*D*eff) can be derived from the value of the time-lag. Nevertheless, a non-linear least-squares fitting to all the experimental points of each single test has been preferred with the general expression (Eq. (16)) in both the steady-state region and the transitory region by considering the permeability (*Φ*) and the diffusivity (*D*eff) as the fitting parameters.

In any individual permeation test, the gas is on contact with a solid surface and the hydrogen concentration profile through the sample thickness rises, becoming linear and stable after certain period of time. In that final permeation process the relationship between steady-state flux (*J*∞) and the loading pressure (*p*h) will be different depending whether the transport regime is diffusion-limited or surface-limited (Esteban et al., 2002):

$$J\_{\infty} = \frac{\Phi}{d} \cdot p\_{\text{h}}^{0.5} \text{ (diffusion-limited)} \tag{20}$$

$$J\_{\boldsymbol{\sigma}} = \frac{1}{2} \cdot \boldsymbol{\sigma} \cdot k\_1 \cdot p\_{\text{h}} \text{ (surface-limited)}\tag{21}$$

Taking into account the ideal gas approximation, pressure increment with time in the low-

0.5 0.5 0.5 2 2

*eff n*

of pressure with time for the steady-state permeation regime is obtained:

R

This expression corresponds to the steady-state flux,

characteristic time known as time-lag is obtained:

diffusivity (*D*eff) as the fitting parameters.

R 2 1 π

*T Φ p Φ p d Φ p d n p t A t A A Dt Vd D D n d*

Where the *V*eff is the effective volume where the permeated gas is retained, *T*eff is the temperature of the volume and R is the ideal gas constant (8.314 J K–1 mol–1). The volume *V*eff is precisely measured in each experimental permeation test by performing gas

When imposing a very large period of time ( *t* ) in the previous expression the evolution

eff h h eff eff

*<sup>T</sup> <sup>Φ</sup> <sup>p</sup> <sup>Φ</sup> p d <sup>p</sup> t A t A Vd D*

0.5 *<sup>Φ</sup>* <sup>h</sup>*<sup>p</sup> <sup>J</sup> <sup>d</sup>*

obtained from Eq. (17); this is the linear tendency shown in *Figure 3* on the right-hand side. When the straight line is extended down to cross the abscise axis in the time co-ordinate a

L

transport regime is diffusion-limited or surface-limited (Esteban et al., 2002):

1 <sup>2</sup> *J kp* 

0.5 h

1 h

2

eff 6 *d D*

The value of permeability (*Φ*) can be derived from the slope of the straight line in steadystate permeation regime (Eq. (17)) and the effective diffusivity (*D*eff) can be derived from the value of the time-lag. Nevertheless, a non-linear least-squares fitting to all the experimental points of each single test has been preferred with the general expression (Eq. (16)) in both the steady-state region and the transitory region by considering the permeability (*Φ*) and the

In any individual permeation test, the gas is on contact with a solid surface and the hydrogen concentration profile through the sample thickness rises, becoming linear and stable after certain period of time. In that final permeation process the relationship between steady-state flux (*J*∞) and the loading pressure (*p*h) will be different depending whether the

hh h s e 2 2 ff eff eff 1

*n*

(18)

(19)

*<sup>Φ</sup> J p <sup>d</sup>* (diffusion-limited) (20)

(surface-limited) (21)

(16)

(17)

exp 6 6

0.5 0.5

6 *s s*

*s s*

pressure region due to this amount of gas is:

*eff*

expansion to a calibrated volume.

where *σk*1 is the adsorption rate constant. The experimental confirmation of one of these relationships is a method to decide the type of transport regime for modelling the experimental tests.

#### **4. Results and discussion**

This section reviews the available data in literature for oxide dispersion strengthened (DS) copper alloys and precipitation hardened (PH) copper alloys. Results regarding interaction of these alloys with hydrogen are compared in relation to base material, Cu. Punctual experimental values are shown only for the ELBRODUR® alloy (not published), whereas Arrhenius regressions of the transport parameters are compiled for all the alloys.

Individual permeation tests have been carried out for the aforementioned copper alloys, GlidCop® Al25 (Esteban et al., 2009) and ELBRODUR®, with temperatures ranging from 573 K to 793 K and using loading pressures ranging from 103 Pa to 1.0 105 Pa. Additionally, data for base material, Cu, (Reiter et al., 1993) and for a similar PH-CuCrZr alloy (Serra & Perujo, 1998) named ELBRODUR-II hereafter to distinguish from the material analysed, are also available. These results for the hydrogen transport parameters in copper alloys are summarised and discussed in the next paragraphs.

In relation to the permeation tests carried out for GlidCop® Al25 and ELBRODUR® copper alloys, the evaluation of the diffusive transport parameters has been assured because no surface effect has become relevant within the whole group of individual tests. This fact has been proved by studying the evolution of the experimental steady-state flux (*J*∞) with driving pressure (*p*h) at the same temperature.

In the case of the ELBRODUR® copper alloy, a set of 9 permeation tests has been performed at the same temperature (688 K) with different loading pressures (*p*h) in order to study the type of hydrogen transport regime. These results are shown in *Figure 6*. The exponential relationship between the steady-state hydrogen flux (*J*∞) and the loading pressure (*p*h) has a power of *n* = 0.52, which is close to 0.5 (pure diffusion-limited regime) and far from 1.0 (pure surface-limited regime) (Eqs. (20) and (21), respectively).

Individual transport parameters of effective diffusivity (*D*eff), permeability (*Φ*) and effective Sieverts' constant (*K*S,eff) have been obtained at different temperatures by modelling the corresponding individual permeation tests, both for GlidCop® Al25 (Esteban et al., 2009) and ELBRODUR®.

The dependence of the transport parameters on temperature for the ELBRODUR® copper alloy is shown in *Figure 7* (permeability), *Figure 8* (diffusivity) and *Figure 9* (Sieverts´ constant), together with the results obtained for the aforementioned reference copper alloys (Esteban et al., 2009; Reiter et al., 1993; Serra & Perujo, 1998). The Arrhenius parameters are obtained by fitting the individual experimental values to the tendencies given by Eqs. (2), (4), (7) and (8), resulting:

$$\begin{aligned} \, \, \, \Phi \text{ (mol} \cdot \text{m}^{-1} \cdot \text{Pa}^{-0.5} \cdot \text{s}^{-1}) &= 2.38 \cdot 10^{-7} \cdot \exp(-73.9 \text{ (kJ} \cdot \text{mol}^{-1}) / \text{R} \cdot T) \\\\ \, \, \, \, \, D \, \, \text{(m}^2 \cdot \text{s}^{-1}) &= 3.55 \cdot 10^{-5} \cdot \exp(-65.5 \text{ (kJ} \cdot \text{mol}^{-1}) / \text{R} \cdot T) \end{aligned}$$

Interaction of Copper Alloys with Hydrogen 43

There exists a marked difference between the transport parameters obtained in the PH-CuCrZr alloy (ELBRODUR®) in relation to the corresponding ones for the base material (Cu) (Reiter et al, 1993), DS copper alloy GlidCop® Al25 (Esteban et al., 2009), and a similar PH-CuCrZr alloy (Serra & Perujo, 1998) named ELBRODUR-II. There is a different metallurgical composition in the Zr content and a slight difference in the thermal treatment of both the ELBRODUR alloys. Moreover, in the work performed with ELBRODUR-II (Serra & Perujo,

In the case of the transport property of permeability (*Figure 7*) the result obtained for the PHCuCrZr alloy ELBRODUR® is congruent with the results obtained in other reference Cu alloys. The permeation energy, 73.9 kJ/mol, preserves a similar value to those of the other Cu alloys (80.6 kJ/mol in GlidCop® Al25 and 79.8 kJ/mol in ELBRODUR-II) and it is slightly

The aforementioned similar results in the four different materials are reasonable because permeability is a property describing the steady-state hydrogen migration through lattice with no influence of the trapping effect and the particular microstructural defects of each material; i.e. when enough period of time passes, hydrogen concentration dependence on depth adopts the final linear profile (see *Figure 5*) when trapping and detrapping (the

10-11 <sup>I</sup> <sup>I</sup> <sup>I</sup> <sup>I</sup> <sup>I</sup> <sup>I</sup>

550 500 400 350 300 ºC

1000/*T* (K-1) 1,2 1,4 1,6 1,8

Fig. 7. Hydrogen permeability in PH-CuCrZr ELBRODUR® alloy compared with reference copper alloys: (1) ELBRODUR®, (2) GlidCop® Al25, (3) ELBRODUR-II, (4) pure Cu.

(4)

(3) (2)

(1)

inverse process) have reached equal equilibrium rates that cancel each other.

450

1998) the effect of hydrogen trapping was not envisaged.

lower than that of the pure Cu (92.6 kJ/mol).

(mol m-1Pa-1/2s-1)

10-14

10-13

10-12

$$K\_{\rm S} \text{ (mol} \cdot \text{m}^{\cdot 3} \cdot \text{Pa}^{\cdot 0.5}) = 6.71 \cdot 10^{-3} \cdot \exp(-8.4 \text{ (kJ} \cdot \text{mol}^{\cdot 1})/\text{R} \cdot T)$$

The trapping parameters are *N*t = 3.7 1024 m–3 and *E*t = 51.2 kJ mol–1.

Fig. 6. Experimental hydrogen permeation steady-state flux in PH-CuCrZr alloy (ELBRODUR®) at 688 K and different driving pressures ranging from 103 to 1.5 105 Pa.

The Arrhenius pre-exponentials and the activation energies of hydrogen transport parameters together with the trapping parameters that have been plotted in *Figs. 7-9* are shown in *Table 1*.


Table 1. Experimental hydrogen transport parameters for reference copper alloys; *Φ*0 in molm–1Pa –0.5s–1, *E<sup>Φ</sup>*, *Ed*, *Es* and *E*<sup>t</sup> in kJ mol–1, *D*0 in m2s–1, *K*S0 in mol m–3Pa–0,5, *N*t in m–3 and *T* in K.

The trapping parameters are *N*t = 3.7 1024 m–3 and *E*t = 51.2 kJ mol–1.

*J* (mol s-1)

10-7

10-6

10-8

shown in *Table 1*.

GlidCop® Al-25 (2)

ELBRODUR-II (3)

Cu (4)

and *T* in K.


*p*h (Pa)

The Arrhenius pre-exponentials and the activation energies of hydrogen transport parameters together with the trapping parameters that have been plotted in *Figs. 7-9* are

Material (curve) *Φ***<sup>0</sup>** *EΦ D***<sup>0</sup>** *E***<sup>d</sup>** *K***S0** *E***<sup>S</sup>** *N***<sup>t</sup>** *E***<sup>t</sup>** *T* ELBRODUR (1) 2.3810-7 73.9 3.5510-5 65.5 6.7110-3 8.4 3.71024 51.2 593-773

(Esteban et al., 2009) 5.8710-7 80.6 5.7010-5 76.8 0.006 3.7 3.1<sup>1022</sup> 75.4 573-793

(Serra & Perujo, 1998) 5.1310-7 79.8 5.7010-7 41.2 0.90 38.6 - - 553-773

(Reiter et al, 1993) 6.6010-6 92.6 6.6010-7 37.4 5.19 55.2 - - 470-1200

Table 1. Experimental hydrogen transport parameters for reference copper alloys; *Φ*0 in molm–1Pa –0.5s–1, *E<sup>Φ</sup>*, *Ed*, *Es* and *E*<sup>t</sup> in kJ mol–1, *D*0 in m2s–1, *K*S0 in mol m–3Pa–0,5, *N*t in m–3

Fig. 6. Experimental hydrogen permeation steady-state flux in PH-CuCrZr alloy (ELBRODUR®) at 688 K and different driving pressures ranging from 103 to 1.5 105 Pa.

102 103 104 105 106

*J p*<sup>h</sup>

0.52 (*T* = 415 ºC)

There exists a marked difference between the transport parameters obtained in the PH-CuCrZr alloy (ELBRODUR®) in relation to the corresponding ones for the base material (Cu) (Reiter et al, 1993), DS copper alloy GlidCop® Al25 (Esteban et al., 2009), and a similar PH-CuCrZr alloy (Serra & Perujo, 1998) named ELBRODUR-II. There is a different metallurgical composition in the Zr content and a slight difference in the thermal treatment of both the ELBRODUR alloys. Moreover, in the work performed with ELBRODUR-II (Serra & Perujo, 1998) the effect of hydrogen trapping was not envisaged.

In the case of the transport property of permeability (*Figure 7*) the result obtained for the PHCuCrZr alloy ELBRODUR® is congruent with the results obtained in other reference Cu alloys. The permeation energy, 73.9 kJ/mol, preserves a similar value to those of the other Cu alloys (80.6 kJ/mol in GlidCop® Al25 and 79.8 kJ/mol in ELBRODUR-II) and it is slightly lower than that of the pure Cu (92.6 kJ/mol).

The aforementioned similar results in the four different materials are reasonable because permeability is a property describing the steady-state hydrogen migration through lattice with no influence of the trapping effect and the particular microstructural defects of each material; i.e. when enough period of time passes, hydrogen concentration dependence on depth adopts the final linear profile (see *Figure 5*) when trapping and detrapping (the inverse process) have reached equal equilibrium rates that cancel each other.

Fig. 7. Hydrogen permeability in PH-CuCrZr ELBRODUR® alloy compared with reference copper alloys: (1) ELBRODUR®, (2) GlidCop® Al25, (3) ELBRODUR-II, (4) pure Cu.

Interaction of Copper Alloys with Hydrogen 45

The hydrogen Sieverts' constants for the PH-CuCrZr ELBRODUR® alloy and the DS-GlidCop® Al25 alloy are shown in *Figure 9* in comparison to the base material, Cu. All over again, a marked trapping effect in hydrogen Sieverts' constant (i.e. solubility) has been observed throughout the whole temperature range for both alloys (curves 1 and 2). At low temperatures, hydrogen remains trapped into the defects of material exceeding the prediction made by the consideration of normal interstitial lattice sites of the base material Cu (curve 4). The interstitial lattice dissolution remains endothermic but with a low value of the dissolution energy for both alloys (8.4 kJ/mol and 3.7 kJ/mol). The trapped hydrogen specie becomes so important at low temperature that the effective Sieverts' constant behaves

10-1 <sup>I</sup> <sup>I</sup> <sup>I</sup> <sup>I</sup> <sup>I</sup> <sup>I</sup>

550 500 450 400 350 300 ºC

1000/*T* (K-1) 1,2 1,4 1,6 1,8

(3)

(2)

(1)

(4)

Fig. 9. Hydrogen Sieverts´ constant in PH-CuCrZr ELBRODUR® alloy compared with reference copper alloys: (1) ELBRODUR®, (2) GlidCop® Al25, (3) ELBRODUR-II, (4) pure Cu.

The explanation of these particular tendencies may be found in the presence of high density nanosized defects in the materials. In the case of PH-CuCrZr ELBRODUR® alloy, the hydrogen interstitial atoms may remain trapped in the interface of the Guinier-Preston zones, incoherent Cr particles or precipitates, increasing the solubility and slowing down the transport through the lattice of the material (i.e. a lower effective diffusivity). In the case of the DS-GlidCop® Al25 alloy, the same effect can be attributed to the hydrogen inventory trapped in the nanosized Al2O3 particles. Furthermore, this phenomenon has been

as an effective endothermic tendency.

*K*S,eff (mol m-3Pa-1/2)

10-4

10-3

10-2

The influence of microstructural defects of the material acting as strong trapping sites for hydrogen absorption, can be observed in transport properties such as diffusivity (*D*eff) and Sieverts' constant (*K*S,eff). The dependence of the hydrogen diffusivity in PH-CuCrZr ELBRODUR® alloy and DS-GlidCop® Al25 alloy with temperature (shown in *Figure 8*) evidences the influence of trapping that provokes a general decrease in the diffusivity; i.e. the kinetics of migration becomes slower because trapping and detrapping processes impede the free flow of interstitial atoms through lattice solution sites. This effect becomes more pronounced as the temperature is lower (the vibration state of the hydrogen atom is weaker and the high trapping energy well is more effective for hydrogen trapping). At high temperatures, the diffusivity tends to approximate asymptotically to the behaviour of the base material Cu (curve 4) when the trapping effect becomes negligible. The alloys exhibit high values of diffusion energy (65.5 kJ/mol and 76,8 kJ/mol) and a marked influence of the trapping phenomenon with high values of trapping energies (51.2 kJ/mol and 75.4 kJ/mol). In the case of the in PH-CuCrZr ELBRODUR® alloy, the abundant hydrogen trapping sites in this material may be identified with the nanometric Guinier-Preston zones, incoherent pure Cr particles or extensive precipitates like Cu4Zr characteristic of this kind of alloy (Edwards et al., 2007). This behaviour is analogous to the trapping phenomena described in Gildcop Al25 (Esteban et al, 2009), where the presence of nanometric Al2O3 provoked a massive hydrogen trapping phenomenon even more effective than in the PH-CuCrZr alloy.

Fig. 8. Hydrogen diffusivity in PH-CuCrZr ELBRODUR® alloy compared with reference copper alloys: (1) ELBRODUR®, (2) GlidCop® Al25, (3) ELBRODUR-II, (4) pure Cu.

The influence of microstructural defects of the material acting as strong trapping sites for hydrogen absorption, can be observed in transport properties such as diffusivity (*D*eff) and Sieverts' constant (*K*S,eff). The dependence of the hydrogen diffusivity in PH-CuCrZr ELBRODUR® alloy and DS-GlidCop® Al25 alloy with temperature (shown in *Figure 8*) evidences the influence of trapping that provokes a general decrease in the diffusivity; i.e. the kinetics of migration becomes slower because trapping and detrapping processes impede the free flow of interstitial atoms through lattice solution sites. This effect becomes more pronounced as the temperature is lower (the vibration state of the hydrogen atom is weaker and the high trapping energy well is more effective for hydrogen trapping). At high temperatures, the diffusivity tends to approximate asymptotically to the behaviour of the base material Cu (curve 4) when the trapping effect becomes negligible. The alloys exhibit high values of diffusion energy (65.5 kJ/mol and 76,8 kJ/mol) and a marked influence of the trapping phenomenon with high values of trapping energies (51.2 kJ/mol and 75.4 kJ/mol). In the case of the in PH-CuCrZr ELBRODUR® alloy, the abundant hydrogen trapping sites in this material may be identified with the nanometric Guinier-Preston zones, incoherent pure Cr particles or extensive precipitates like Cu4Zr characteristic of this kind of alloy (Edwards et al., 2007). This behaviour is analogous to the trapping phenomena described in Gildcop Al25 (Esteban et al, 2009), where the presence of nanometric Al2O3 provoked a massive hydrogen trapping phenomenon even more effective than in the PH-CuCrZr alloy.

10-8 <sup>I</sup> <sup>I</sup> <sup>I</sup> <sup>I</sup> <sup>I</sup> <sup>I</sup>

550 500 450 400 350 300 ºC

1000/*T* (K-1) 1,2 1,4 1,6 1,8

Fig. 8. Hydrogen diffusivity in PH-CuCrZr ELBRODUR® alloy compared with reference copper alloys: (1) ELBRODUR®, (2) GlidCop® Al25, (3) ELBRODUR-II, (4) pure Cu.

(4)

(3)

(1)

(2)

*D*eff (m2

10-12

10-11

10-10

10-9

s


The hydrogen Sieverts' constants for the PH-CuCrZr ELBRODUR® alloy and the DS-GlidCop® Al25 alloy are shown in *Figure 9* in comparison to the base material, Cu. All over again, a marked trapping effect in hydrogen Sieverts' constant (i.e. solubility) has been observed throughout the whole temperature range for both alloys (curves 1 and 2). At low temperatures, hydrogen remains trapped into the defects of material exceeding the prediction made by the consideration of normal interstitial lattice sites of the base material Cu (curve 4). The interstitial lattice dissolution remains endothermic but with a low value of the dissolution energy for both alloys (8.4 kJ/mol and 3.7 kJ/mol). The trapped hydrogen specie becomes so important at low temperature that the effective Sieverts' constant behaves as an effective endothermic tendency.

Fig. 9. Hydrogen Sieverts´ constant in PH-CuCrZr ELBRODUR® alloy compared with reference copper alloys: (1) ELBRODUR®, (2) GlidCop® Al25, (3) ELBRODUR-II, (4) pure Cu.

The explanation of these particular tendencies may be found in the presence of high density nanosized defects in the materials. In the case of PH-CuCrZr ELBRODUR® alloy, the hydrogen interstitial atoms may remain trapped in the interface of the Guinier-Preston zones, incoherent Cr particles or precipitates, increasing the solubility and slowing down the transport through the lattice of the material (i.e. a lower effective diffusivity). In the case of the DS-GlidCop® Al25 alloy, the same effect can be attributed to the hydrogen inventory trapped in the nanosized Al2O3 particles. Furthermore, this phenomenon has been

Interaction of Copper Alloys with Hydrogen 47

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experimentally identified in other kind of materials like oxide dispersion strengthened (ODS) reduced activation ferritic martensitic (RAFM) steels where nanoparticles of yttria Y2O3 provoked an analogous effect (Esteban et al., 2007).

The effect of nanosized inclusions has an obvious successful effect in the improvement of thermal-mechanical properties of copper alloys. However, the effect of the increase of hydrogen isotope inventory retention needs to be taken into account. This effect can be extremely important in particular cases. In fusion reactor materials, for example, it should be taken into account when choosing the structural and heat-sink materials of the fusion reactor where the hydrogen isotope inventory has to be controlled with special attention when considering fuel balance economy or radiological safety issues. When choosing materials for pipelines that will transport gaseous fuels including those with high hydrogen content or even pure hydrogen, the observed hydrogen trapping should be taken into account as long as it may degrade its mechanical properties. On the other hand, electrical characteristics may also be affected by hydrogen trapping phenomenon (Lee K. & Lee Y.K., 2000).

#### **5. Conclusion**

The gas permeation technique has been used in order to characterise two copper alloys proposed for high heat flux components: an oxide dispersion strengthened (DS) copper alloy named GlidCop® Al25, and a precipitation hardened (PH) copper alloy named ELBRODUR®. The hydrogen diffusive transport parameters have been obtained and discussed in relation to the particular microstructure of each copper alloy. The hydrogen trapping phenomenon has resulted to be present throughout the whole experimental temperature provoking an increase of hydrogen Sieverts' constant and decrease of diffusivity. The permeability values remained close to the values of the base material, i.e. pure Cu, and the other reference copper alloys. The analogy of the experimental results obtained with other materials with nanosized inclusions, confirms the high ability of these kinds of material to trap hydrogen isotopes at low temperatures. This should be monitored with special care for applications where hydrogen trapping may modify the physical properties of copper alloys.

#### **6. Acknowledgment**

This work has been funded by the Spanish Ministry of Science and Education (Ref. ENE2005-03811) with an ERDF proportion. The authors would also like to thank the FEMaS Coordinated Action project for the support in knowledge exchange among different research groups.

#### **7. References**

Barabash V., (the ITER International Team), Peacock, A., Fabritsiev, S., Kalinin, G., Zinkle S., Rowcliffe, A., Rensman, J.-W., Tavassoli, A.A., Marmy, P., Karditsas P.J., Gillemot, F. & Akiba, M. (2007). Materials Challenges for ITER – Current Status and Future Activities. *Journal of Nuclear Materials*, Vol. 367-370, Part 1 (August 2007), pp. 31-32, ISSN-0022-3115

experimentally identified in other kind of materials like oxide dispersion strengthened (ODS) reduced activation ferritic martensitic (RAFM) steels where nanoparticles of yttria

The effect of nanosized inclusions has an obvious successful effect in the improvement of thermal-mechanical properties of copper alloys. However, the effect of the increase of hydrogen isotope inventory retention needs to be taken into account. This effect can be extremely important in particular cases. In fusion reactor materials, for example, it should be taken into account when choosing the structural and heat-sink materials of the fusion reactor where the hydrogen isotope inventory has to be controlled with special attention when considering fuel balance economy or radiological safety issues. When choosing materials for pipelines that will transport gaseous fuels including those with high hydrogen content or even pure hydrogen, the observed hydrogen trapping should be taken into account as long as it may degrade its mechanical properties. On the other hand, electrical characteristics may also

The gas permeation technique has been used in order to characterise two copper alloys proposed for high heat flux components: an oxide dispersion strengthened (DS) copper alloy named GlidCop® Al25, and a precipitation hardened (PH) copper alloy named ELBRODUR®. The hydrogen diffusive transport parameters have been obtained and discussed in relation to the particular microstructure of each copper alloy. The hydrogen trapping phenomenon has resulted to be present throughout the whole experimental temperature provoking an increase of hydrogen Sieverts' constant and decrease of diffusivity. The permeability values remained close to the values of the base material, i.e. pure Cu, and the other reference copper alloys. The analogy of the experimental results obtained with other materials with nanosized inclusions, confirms the high ability of these kinds of material to trap hydrogen isotopes at low temperatures. This should be monitored with special care for applications where hydrogen trapping may modify the physical

This work has been funded by the Spanish Ministry of Science and Education (Ref. ENE2005-03811) with an ERDF proportion. The authors would also like to thank the FEMaS Coordinated Action project for the support in knowledge exchange among different

Barabash V., (the ITER International Team), Peacock, A., Fabritsiev, S., Kalinin, G., Zinkle S.,

Rowcliffe, A., Rensman, J.-W., Tavassoli, A.A., Marmy, P., Karditsas P.J., Gillemot, F. & Akiba, M. (2007). Materials Challenges for ITER – Current Status and Future Activities. *Journal of Nuclear Materials*, Vol. 367-370, Part 1 (August 2007), pp. 31-32,

Y2O3 provoked an analogous effect (Esteban et al., 2007).

**5. Conclusion** 

properties of copper alloys.

ISSN-0022-3115

**6. Acknowledgment** 

research groups.

**7. References** 

be affected by hydrogen trapping phenomenon (Lee K. & Lee Y.K., 2000).


**Part 2** 

**Development of High-Performance** 

**Current Copper Alloys** 

