Metal Matrix Composites

Metal Matrix Composites

The demand for materials having high strength and high toughness and capable of operating effectively under adverse conditions has led to the development of a new generation of materials known as Metal matrix composites. Attractive physical and mechanical properties that can be obtained with metal matrix composites (MMCs), such as high specific modulus, strength and thermal stability have made them the materials of the future and this fact has been documented extensively. MMCs combine metallic properties (high strength and high modulus), leading to greatest strength in shear and compression and higher service temperature capabilities. Interest in MMCs for aerospace, automotive and other structural applications has

The fibers and particles can be metal (e.g., C, B), or ceramic (e.g. SiC, AI2O3). One of the primary purposes for reinforcing metals with very stiff and strong constitutents is to Increase their stiffness / density and strength / density ratios. Metal matrix composites have application wherever it is advantageous to employ lightweight structural materials, such as in the aerospace, automotive, medical, and sports equipment industries. Other properties also make MMCs attractive. The coefficient of thermal expansion (CTE) of some MMCs can be tailored by selecting the appropriate type and amount of reinforcement constituent to be incorporated into the MMC. The reinforcement constituent can also improve thermal conductivity, reduce the coefficient of friction, and improve wear resistance. Metal matrix composites can be used at higher temperatures than organic matrix composites (OMCs). Many organic matrices will decompose at about 300’C and thus, metal matrices are required for applications at higher temperature. Metal matrix composites also do not expel moisture, as do some OMC, which can be critical for space

However, and as discussed in the previous section, since most ceramic materials are not wetted by the molten alloy, introduction and retention of the particulate necessitate either adding wetting agents to the melt or coating the ceramic particulate prior to mixing. Basically, all methods in this category involve liquid metal matrix infiltration of fibred perform. The infiltration may be carried out under atrnospheric or inert gas pressure or under vacuum. In most of these techniques, the long continuous fibres must be properly aligned and distributed before infiltration by tile matrix. Oiscontinuo~s fibres must be properly stirred and mixed with the molten metal. The liquid state penetration around the fibre bundles can occur by capillary action, vaccum infiltration, or pressure infiltration. Clearly, the molten metal must wet the fibre