Particle reinforced metals

Key words infiltration, particle reinforced metals, metal matrix composites, metal foams, microcellular aluminium... 

As the porous preform must be free-standing prior to infiltration, this process is restricted to a limited range of variation in phase volume fraction, which depends on the morphology of the reinforcing phase. It cannot, for example, produce low-volume fraction particle reinforced metals unless specific additional processing steps are used. 

A. Miserez Fracture and Toughening of High Volume Fraction Ceramic Particle Reinforced Metals, PhD thesis No. 2703, Ecole Polytechnique Federate de Lausanne (2002) -available on-line at < http //library.epfl.ch/theses/ display=detail nr=2703>. 

Y. C. Zhou, S. G. Long, and Y. W. Liu, Thermal failure mechanism and failure threshold of SiC particle reinforced metal matrix composites induced by laser beam, Mechanics of Materials, vol. 35, no. 10, pp. 1003—1020, 2003. 

There are three kinds of metal-matrix composites distinguished by type of reinforcement particle-reinforced MMCs, short fiber- or whisker-reinforced MMCs, and continuous fiber- or sheet-reinforced MMCs. Table 1 provides examples of some important reinforcements used in metal-matrix composites as well as their aspect (length/diameter) ratios and diameters. 

Particulate Composites. These composites encompass a wide range of materials. As the word particulate suggests, the reinforcing phase is often spherical or at least has dimensions of similar order ia all directions. Examples are concrete, filled polymers (18), soHd rocket propellants, and metal and ceramic particles ia metal matrices (1). 

Particulate Composites. Particulate composites encompass a wide range of materials, from cement reinforced with rock aggregates (concrete) to mixtures of ceramic particles in metals, called cermets. In all cases, however, the particulate composite consists of a reinforcement that has similar dimensions in all directions (roughly spherical), and all phases in the composite bear a proportion of an applied load. The percentage of particulates in this class of composites range from a few percent to 70%. 

Jin, Z-H., Batra, R.C. (1999), Thermal shock cracking in a metal-particle-reinforced ceramic matrix composite , Eng. Fract. Mech., 62, 339-350. 

Powder metallurgy was used to fabricate SiC particle-reinforced and unreinforced QE 22 alloy. The QE 22 + 15vol.%SiC composite was prepared from gas-atomized metal alloy powders of various sizes (ASTM sieve sizes 230 and 600 corresponding to mean particle diameters of 30 and 10 pm, respectively) and various shapes of the SiC particles (bulky particles - BL, rounded particles - HD). 

Metal/ceramic PBs are not only the most important feature in ceramic-reinforced metal-matrix composites, but they also occur when metals are oxidized or when oxides are reduced to the metal or when a metal film is grown on a ceramic substrate (or vice versa). In Figure 15.19 particles of W have grown on a single-crystal thin film of SiC. The... 

Gumprasad and workers [182] have described the production and properties of carbon fiber particle reinforced cast metal matrix composites. 

Large particle reinforced composite systems are utilised with all three types of materials (metals, ceramics and polymers). Concrete is a common large particle strengthened composite where both matrix and particulate phases are ceramic materials. 

Metal matrix composites (MMCs) are metals that are reinforced with fibers or particles that usually are stiff, strong, and lightweight. The fibers and particles can be metal (e.g., tungsten), nonmetal (e.g., carbon or boron), or ceramic (e.g., silicon carbide (SiC) or (alumina) AljOj). The purpose for reinforcing metals with fibers or particles is to create composites that have properties more useful than that of the individual constituents. For example, fibers and particles are used in MMCs to increase stiffness [/], strength [f ], and thermal conductivity [2], and to reduce weight [f], thermal expansion [3], fiiction [4], and wear [5]. 

Among the particle-reinforced materials are the cermets (a word created from ceramic and metal ) that comprise a metallic matrix containing ceramic particles. Very hard carbides, for example tungsten carbide or titanium carbide, are embedded in a cobalt matrix. These cermets are frequently used as cutting tools. The ceramic particles serve to improve the wear resistance, an effect similar to that already discussed in section 6.4.4 for the case of coarse particles in metals. 

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