Metal matrix composites properties

Two approaches have been taken to produce metal-matrix composites (qv) incorporation of fibers into a matrix by mechanical means and in situ preparation of a two-phase fibrous or lamellar material by controlled solidification or heat treatment. The principles of strengthening for alloys prepared by the former technique are well estabUshed (24), primarily because yielding and even fracture of these materials occurs while the reinforcing phase is elastically deformed. Under these conditions both strength and modulus increase linearly with volume fraction of reinforcement. However, the deformation of in situ, ie, eutectic, eutectoid, peritectic, or peritectoid, composites usually involves some plastic deformation of the reinforcing phase, and this presents many complexities in analysis and prediction of properties. 

Electronic-Grade MMCs. Metal-matrix composites can be tailored to have optimal thermal and physical properties to meet requirements of electronic packaging systems, eg, cotes, substrates, carriers, and housings. A controUed thermal expansion space tmss, ie, one having a high precision dimensional tolerance in space environment, was developed from a carbon fiber (pitch-based)/Al composite. Continuous boron fiber-reinforced aluminum composites made by diffusion bonding have been used as heat sinks in chip carrier multilayer boards. 

Advanced Structural and Heating Materials. Molybdenum siHcide [12136-78-6] and composites of MoSi2 and siHcon carbide, SiC, have properties that allow use as high temperature stmctural materials that are stable in oxidizing environments (see Composite materials Metal-matrix composites). Molybdenum disiHcide also finds use in resistance heating elements (87,88). 

Let s address the issue of nonlinear material behavior, i.e., nonlinear stress-strain behavior. Where does this nonlinear material behavior come from Generally, any of the matrix-dominated properties will exhibit some degree of material nonlinearity because a matrix material is generally a plastic material, such as a resin or even a metal in a metal-matrix composite. For example, in a boron-aluminum composite material, recognize that the aluminum matrix is a metal with an inherently nonlinear stress-strain curve. Thus, the matrix-dominated properties, 3 and Gj2i generally have some level of nonlinear stress-strain curve. 

Electroplating of metal matrix composites by codeposition of suspended particles, a process that has improved physical and electrochemical properties. 

Ghosn, L. and Lerch, B.A. (1989). Optimum interface properties for metal matrix composites. NASA TM-102295. 

The amount of incorporated particles is the parameter characterizing a metal matrix composite. As discussed in the previous section it largely determines the composite properties. In order to obtain a composite exhibiting certain properties, the effect of process parameters on the particle composite content has therefore to be known. Apart from the practical significance knowledge of these effects is also a prerequisite for the understanding of the mechanism underlying particle codeposition. 

Finally, in chapter 6, another direction of applied electrochemistry is treated by Hovestad and Janssen Electroplating of Metal Matrix Composites by Codeposition of Suspended Particles. This is another area of metals materials-science where electroplating of a given metal is conducted in the presence of suspended particles, e.g. of A1203, BN, WC, SiC or TiC, which become electrodeposited as firmly bound occlusions. Such composite deposits have improved physical and electrochemical properties. Process parameters, and mechanisms and models of the codeposition processes are described in relation to bath... 

In recent years, there has been a growing interest in the electrochemical synthesis of composite materials consisting of metal matrix with embedded particles of oxides, carbides, borides, etc. Metal-matrix composites offer new possibilities in fabrication of ftmctional coatings with radically improved durability and performance [1], However, in spite of the efforts of many researches, the overall picture of the processes occurring during co-deposition of metal with dispersed phase and mechanism of particle-induced modification of mechanical and chemical properties still remain unclear. In this study, we focused on the kinetics and mechanism of the electrochemical co-deposition of nickel with highly dispersed oxide phases of different nature and morphology. 

In some applications the lack of toughness of ceramics or CMCs prohibits their use. In cases where enhanced stiffness, wear resistance, or elevated temperature capabilities greater than those provided by metals are necessary, metal matrix composites (MMCs) offer a reasonable compromise between ceramics or CMCs and metals. Typically, MMCs have discrete ceramic particulate or fiber reinforcement contained within a metal matrix. In comparison to CMCs, MMCs tend to be more workable and more easily formed, less brittle, and more flaw tolerant. These gains come primarily at the expense of a loss of high-temperature mechanical properties and chemical stability offered by CMCs. These materials thus offer an intermediate set of properties between metals and ceramics, though somewhat closer to metals than ceramics or CMCs. Nonetheless, like ceramic matrix composites, they involve physical mixtures of different materials that are exposed to elevated temperature processes, and therefore evoke similar thermodyamic considerations for reinforcement stability. 

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