**3. Sintering process of sulfide bronze as bimetal**

In this chapter, one of the conditions is the proposal of the copper alloy developed as the sliding member described below.

In the case of a Cu alloy containing a sulfide, sulfur may disappear from the Cu alloy by reacting with the reducing gas. Further, in the case of Cu-Sn-S, the mechanical properties of the sintered body have not been clarified. Therefore, hardness is evaluated as one of the mechanical properties.

#### **3.1 Materials**

*Design and Manufacturing*

tion material.

alloys [7].

friction properties are also discussed.

**2. Chemical component of sulfide-dispersed bronze**

atomized bronze keeps their metastable state including sulfide.

Bismuth and sulfides are well known as lead substitutes and are candidates for the development of solid lubricants. Bi-bronze castings were used as bimetallic bearings and showed good loading capacity [4]. Potential applications of these castings are pointed out in Ref. [4], and it has been shown that castability was improved using Bi. The machinability of bronze-containing sulfides (Cu2S and ZnS) was investigated. It was concluded that the mechanical properties and machinability of sand casting are the same as the mechanical properties and machinability of Pb-bronze castings [5]. For industrial, it is important that the manufacturing cost is low and that there is a stable supply of raw materials. Bi is far more expensive than S and Cu. Since Bi is a rare metal, the supply of sulfide seems to be superior to that of Bi. As a result, sulfide based on S and Cu is a promising alternative for lead substitu-

In this study, we will discuss how to influence bronze sulfide which is already atomized. Specifically, the strength of bronze matrix and the reaction between sulfide and hydrogen gas are drawing attention. We clarify composition and atmosphere effective for sintering bronze with sulfide dispersed. In the investigation, solid-state sintering and liquid-phase sintering are compared under reducing atmosphere and inert atmosphere. Hardness as one of the important mechanical properties was also investigated. Moreover, some other sintering conditions and

As shown in **Figure 1**, a phase diagram was calculated based on the calculation of phase diagrams (CALPHAD) method [6] of the Cu-Sn-Fe-S system in order to confirm the optimum content of the sulfide in the cast material. In the Cu-Sn alloy, since the crystallization of the α′ phase of Fe was suppressed, the Fe content was 1.3 mass% or less. The reason why the sulfide was dispersed in the Cu alloy is that crystallization of the sulfide (0.25 mass% or less) occurred after crystallization of the α-phase Cu. On the one hand, the sulfide in the matrix remained below 0.60% by mass experimentally. **Figure 2** shows the matrix and sulfides of casting

On the other hand, much amount of sulfide is able to disperse in the atomized bronze powders. Because of the rapid cooling of (gas and/or water) atomization,

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**Figure 1.**

*Calculated phase diagram of sulfide bronze [7].*

Atomized powders were prepared for comparison of sintering properties. As a feature of the sulfide-dispersed Cu-Sn system materials, the sulfide was pre-alloyed by water atomization manufacturing. As shown in **Figure 3a–e**, micro-sized small dots were observed by scanning electron microscopy (SEM). This image is a sectional view of one of the typically sintered bronze-containing sulfides (from irregular powders). Generally, sintered composite from premixed bronze and sulfides indicated lower mechanical properties. It was reported that mechanical properties become better to cover the MoS2 particles by copper [8]. However, this sulfide-dispersed bronze was made by atomizing as pre-alloyed material. So we can see that the pre-alloyed material shows better mechanical properties than the premixed material.

Energy-dispersive X-ray spectroscopy (EDS) was performed to determine the elements that make up the observed small dots. As a result, as shown in **Figure 1**, a ternary sulfide consisting of Cu, Fe, and S was detected. This sulfide is a kind of bornite (Cu5FeS4) detected by the X-ray diffraction (XRD) method [9] as shown in **Figure 4**. Only a small peak was observed as bornite (dot references). It may be metastable in the system because it is difficult to crystalize in the phase diagram as shown in **Figure 1**.

#### **3.2 Experimental method**

#### *3.2.1 Sintering and manufacturing process*

By preparing, bimetal specimens, these procedures are conducted as below. At first, powder was sprayed to a height of 1.0 mm (by leveling off) onto a 3.2-mm-thick steel plate (low-carbon steel). At this time, binding materials such

**Figure 3.**

*SEM image of and EDS mapping results for the sulfide-dispersed copper alloy [10].*

as oils or zinc stearate were not mixed. As the next step, the first sintering under reducing and/or inert atmosphere is performed.

The sample was heated to 1123 K for 1050 s in a mesh belt furnace. Next, the thickness of the bimetal was adjusted by a cold rolling mill. The thickness of the bimetal was controlled to flatten the entire surface on the Cu side of the bimetal in contact with the roll surface. Then, a second sintering under reducing and/or inert atmosphere is performed. The sample was heated to 1123 K for 1368 s in a mesh belt furnace.

After these procedures, to the analysis of mechanical properties, hardness tests were conducted because the bimetals and sintered copper alloy specimens were too thin to be subjected to tensile tests. The hardness of the sintered copper alloy specimens was evaluated using a Vickers hardness meter. This testing machine uses

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**Table 1.**

*Effects of Dispersed Sulfides in Bronze During Sintering DOI: http://dx.doi.org/10.5772/intechopen.86385*

pyramid-shaped hollow on the test surface.

*XRD of sulfide-dispersed bronze powders.*

*3.2.2 Test specimens*

**Figure 4.**

a regular square pyramid diamond indenter with a face-to-face angle of 136° and a

copper alloy and the steels under an applied load of 0.98 N for 10 s.

concentration, all sulfur was assumed to exist as bornite.

process was tried experimentally to improve sintering [10].

*Chemical composition of powders primary elements (mass%) [10].*

The hardness represented by a value obtained by dividing the load at that time by the surface area obtained from the length of the diagonal line of the permanent indentation is the Vickers hardness. The indenter was pushed into the matrix of the

Six test specimens were prepared for observation of the sintering process, as shown in **Table 1**. In the table, the chemical components are described only for the primary element (i.e., Cu, Sn, Fe, S, and sulfide). Here, with respect to the sulfide

As preliminary alloy powders for solid-phase sintering at the time of initialstage sintering, SB8 (sulfide bronze containing 8 mass% Sn), SB10, and SB12 were used. However, SBP8 (sulfide bronze using a premix containing 8% by mass Sn), SBP10, and SBP12 are the same pre-alloyed powders as used in the first sintering (SB8, SB10, SB) (prepared as a mixture of 12). Bronze (containing 20% by mass Sn) powder. These mixed powders are prepared for liquid sintering at the time of primary sintering. The addition of low-melting Cu-Sn powder during the sintering

**Materials Cu Sn Fe S Sulfide** SB 8 Bal. 7.90 0.18 0.31 1.21

SBP 8 Bal. 8.00 0.13 0.20 0.78

10 Bal. 9.52 0.38 0.48 1.88 12 Bal. 12.00 0.41 0.58 2.27

10 Bal. 10.00 0.15 0.26 1.02 12 Bal. 12.00 0.29 0.37 1.45 *Design and Manufacturing*

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furnace.

**Figure 3.**

as oils or zinc stearate were not mixed. As the next step, the first sintering under

The sample was heated to 1123 K for 1050 s in a mesh belt furnace. Next, the thickness of the bimetal was adjusted by a cold rolling mill. The thickness of the bimetal was controlled to flatten the entire surface on the Cu side of the bimetal in contact with the roll surface. Then, a second sintering under reducing and/or inert atmosphere is performed. The sample was heated to 1123 K for 1368 s in a mesh belt

After these procedures, to the analysis of mechanical properties, hardness tests were conducted because the bimetals and sintered copper alloy specimens were too thin to be subjected to tensile tests. The hardness of the sintered copper alloy specimens was evaluated using a Vickers hardness meter. This testing machine uses

reducing and/or inert atmosphere is performed.

*SEM image of and EDS mapping results for the sulfide-dispersed copper alloy [10].*

**Figure 4.** *XRD of sulfide-dispersed bronze powders.*

a regular square pyramid diamond indenter with a face-to-face angle of 136° and a pyramid-shaped hollow on the test surface.

The hardness represented by a value obtained by dividing the load at that time by the surface area obtained from the length of the diagonal line of the permanent indentation is the Vickers hardness. The indenter was pushed into the matrix of the copper alloy and the steels under an applied load of 0.98 N for 10 s.

### *3.2.2 Test specimens*

Six test specimens were prepared for observation of the sintering process, as shown in **Table 1**. In the table, the chemical components are described only for the primary element (i.e., Cu, Sn, Fe, S, and sulfide). Here, with respect to the sulfide concentration, all sulfur was assumed to exist as bornite.

As preliminary alloy powders for solid-phase sintering at the time of initialstage sintering, SB8 (sulfide bronze containing 8 mass% Sn), SB10, and SB12 were used. However, SBP8 (sulfide bronze using a premix containing 8% by mass Sn), SBP10, and SBP12 are the same pre-alloyed powders as used in the first sintering (SB8, SB10, SB) (prepared as a mixture of 12). Bronze (containing 20% by mass Sn) powder. These mixed powders are prepared for liquid sintering at the time of primary sintering. The addition of low-melting Cu-Sn powder during the sintering process was tried experimentally to improve sintering [10].


**Table 1.** *Chemical composition of powders primary elements (mass%) [10].*
