Metal-matrix structural composite

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). 

Nanocarbon structures such as fullerenes, carbon nanotubes and graphene, are characterized by their weak interphase interaction with host matrices (polymer, ceramic, metals) when fabricating composites [99,100]. In addition to their characteristic high surface area and high chemical inertness, this fact turns these carbon nanostructures into materials that are very difficult to disperse in a given matrix. However, uniform dispersion and improved nanotube/matrix interactions are necessary to increase the mechanical, physical and chemical properties as well as biocompatibility of the composites [101,102]. 

There are many ways to classify composites, including schemes based upon (1) materials combinations, such as metal-matrix, or glass-fiber-reinforced composites (2) bulk-form characteristics, such as laminar composites or matrix composites (3) distribution of constituents, such as continuous or discontinuous or (4) function, like structural or electrical composites. Scheme (2) is the most general, so we will utilize it here. We will see that other classification schemes will be useful in later sections of this chapter. 

Most fiber-matrix composites (FMCs) are named according to the type of matrix involved. Metal-matrix composites (MMCs), ceramic-matrix composites (CMCs), and polymer-matrix composites (PMCs) have completely different structures and completely different applications. Oftentimes the temperatnre at which the composite mnst operate dictates which type of matrix material is to be nsed. The maximum operating temperatures of the three types of FMCs are listed in Table 1.27. 

Finally, metal- and resin-bonded composites are also classified as particulate composites. Metal-bonded composites included structural parts, electrical contact materials, metal-cutting tools, and magnet materials and are formed by incorporating metallic or ceramic particulates such as WC, TiC, W, or Mo in metal matrixes through traditional powder metallurgical or casting techniques. Resin-bonded composites are composed of particulate fillers such as silica flour, wood flour, mica, or glass spheres in phenol-formaldehyde (Bakelite), epoxy, polyester, or thermoplastic matrixes. 

Dispersion hardening or strengthening of a material means an increased resistance to deformation. The movement of dislocations in the metal facilitates metal deformation. Incorporated particles block the dislocation movement and thus strengthen the metal.4,11 12,21 Grain refinement of the metal due to the codeposition of particles has also been thought to contribute to the hardening effect, but this is not supported by experimental evidence. For several composites it was found that the grain structure of the metal matrix was not altered by the codeposition of particles. 

These fibers are, due to their high thermal stability, particularly suitable for applications in high temperature thermal insulation and for the manufacture of metal matrix and ceramic matrix composites. They arc clearly superior to metal materials due to their lower weight, particularly in the lightweight construction of accelerated structure elements for which the basic material should represent an improve-... 

Aboudi, J., Pindera, M-J., and Arnold, S. M., "Elastic Response of Metal Matrix Composites with Tailored Microstructures to Thermal Gradients," Int. J. Solids and Structures, Vol. 31 (10), pp. 1393-1428,1994. 

Key words structural efficiency metal matrix composite amorphous metals, superhigh strength Al, nanocrystalline metals, Ti-B alloys... 

Opportunities for application of new materials as components in electrochemical cells (electrodes, electrolytes, membranes, and separators) are discussed in this section. In addition, electrochemical processing is considered in the sense that it presents opportunities for the synthesis of new materials such as electroepitaxial GaAs, graded alloys, and superlattices. Finally, attention is focused on the evolution of new engineering materials that were developed for reasons other than their electrochemical properties but that in some cases are remarkably inert (glassy alloys). Others that are susceptible to corrosion (some metal-matrix composites) and more traditional materials that are finding service in new applications (structural ceramics in aqueous media, for example) are also considered briefly. 

ZN-7. [Advanced Refracteny Tech.] Zir-crniiumdibcxide foroxid on-resistant conposhes, burnable sd>s(xba of neutrons, elec, contacts, molten metal crucibles, refractory toughener, cutting tool conq>osites, structural comnics, wear conq>onents, metal matrix composites. 

ZS-7. [Advanced Refractory Tech.] Zirconium diboride for oxidation-resistant ctxnposites, burble absorber of neutrons, elec, contacts, mdten metal crucibles, refractory roughener, cutting tool composites, structural ceramics, wear conqxxients, metal matrix omi-posites. 

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