**4. Metal matrix composite — MMC with ceramic reinforcement**

Metal matrix composites significantly evolved from the 20's. This composite was first used in the aerospace industry. More recently, various areas of industry have increasingly studied this type of material, for example, automotive, electronic, and nuclear, among others. MMCs attract many researchers and engineers as a good alternative to develop materials with high techno‐ logical potential.

Generally, the aim is to create material with the hardness of ceramics, combined with metal that has high toughness compared to ceramics. Thus, they form a family of materials called metal-ceramic materials. Nucleation and precipitation of carbides in steel to obtain good mechanical strength coupled with high toughness or the manufacture of hard metals contain‐ ing high amount of carbides and / or nitrides, in which, when processed by powder metallurgy form a continuous ceramic skeleton, are classical examples of these materials (Breval, 1995).

In principle, forged steel and most conventional steels can be treated as metal matrix compo‐ sites since this forged matrix has a dispersed phase. The dispersed phase may be composed of oxide, sulfide, nitride, carbide, etc. In addition, many metal alloys should be included as MMC if the microstructural definition is considered. Although the definition of a composite material is very comprehensive, there is a strong tendency to believe that the solidification direction of eutectic microstructure is within the possible definitions of MMC (Ralph, *et al*, 1997).

Different applications are found when a metal is reinforced. The reinforcement of light metals, for example, opens the possibility of their use in areas where weight reduction is a priority. The main objectives of reinforcing steel (not limited to only these) are:


activity, increased fluency and decrease in the ductile-brittle transition temperature after radioactive damage remain under constant growth, evolving thus to EUROFER 2 and 3. The aim is that EUROFER 3 becomes a residue of low level of radiation after 80 or 100 years when applied to the DEMO demonstration reactor (Daum and Fischer, 2000; Huang *et al*, 2007).

The mechanical and corrosion resistance properties of martensitic stainless steels can be seriously impaired particularly in function to the precipitation of complex phases, generally rich in chromium, operating temperature, or even during processing; thus, the thermal cycles

To provide the steel mechanical strength, hardness and toughness needed, the most common heat treatments consist of tempering followed by single or double thermal treatment. The main parameters involved in this case are: heating and cooling rate, austenitization temperature and

In the specific case of Eurofer steel, the improvement of its chemical composition aiming at reduced activity was achieved by replacing niobium by tantalum and molybdenum by tungsten. Nb, Mo, Ni, Cu, Al and Co were restricted to ppm values. Calculations aided by computer simulation programs indicate that Eurofer is a very promising reduced-activity

The mechanical properties of ferritic-martensitic steels restricted their use to temperatures above 550°C. Subsequently, the addition of fine and homogeneously dispersed particles allowed their use at higher temperatures (650°C) to give origin to ferritic-martensitic alloys hardened by oxide dispersion (ODS) (Lindau, 2005). To date, the most promising of this series is the ODS-EUROFER alloy. This reduced-activity alloy was developed by the Karlsruhe Research Center (Forschungszentrum Karlsruhe, FZK), in cooperation with France and Russia

EUROFER steel (9Cr-1W) can be used in turbines for power generation, pressure vessels, nuclear reactors or applications where the material is submitted to temperatures between 250 and 550°C. One way to improve the properties of steel, so that it works at higher temperature or become more stable is to add second-phase particles into the matrix. These particles can be in the form of oxides, carbides, nitrides, or even in solid solution when certain chemicals are

Metal matrix composites significantly evolved from the 20's. This composite was first used in the aerospace industry. More recently, various areas of industry have increasingly studied this type of material, for example, automotive, electronic, and nuclear, among others. MMCs attract many researchers and engineers as a good alternative to develop materials with high techno‐

Generally, the aim is to create material with the hardness of ceramics, combined with metal that has high toughness compared to ceramics. Thus, they form a family of materials called

**4. Metal matrix composite — MMC with ceramic reinforcement**

to which these steels are submitted should be conducted under absolute control.

time and tempering thermal cycles (Mariano, 2007).

alloy.

110 Sintering Techniques of Materials

aiming nuclear applications.

added to the material.

logical potential.

Therefore, composites are versatile in their applications because they combine the distinctive properties of each material that composes them.

Metal matrix composites can be obtained with continuous fiber reinforcement and the use of particulate reinforcements. However, particulate reinforcements have significant advantages because the cost of manufacture of such composite is reduced and conventional metallurgical processes such as powder metallurgy and casting, followed by post-processing steps such as lamination, forging and extrusion can be used. Depending on the type of particulate rein‐ forcement, the composites obtained may have higher use temperature compared to the matrix material, improved thermal stability and wear resistance, such as Al (matrix) / Si (fiber) composites. Therefore, research efforts have been directed to obtain metal matrix composites and partic‐ ulate reinforcement (Levy and Pardini, 2006).
