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Metal Matrix Composites | High Speed Machining | Engines
Metal Matrix CompositesA MMC material consists of a combination of metal and ceramics where the metal provides the toughness and the ceramics are adding strength (Young’s modulus), hardness and wear resistance. The most common MMCs are aluminium reinforced with silicon carbide particles. The properties of the MMC can be tailor made by adjusting the amount of particles added (15-70 vol%). To the right some typical properties of aluminium based MMC are listed. The material characteristics are also much dependent on the manufacturing process. There are three common ways, powder metallurgy, stir casting and infiltration. The most high performance MMC is manufactured by powder metallurgy where the aluminium powder is blended with the silicon carbide particles in a high energy mixing process, compacted to a billet through Hot Isostatic Pressing (HIP) and then extruded, forged or rolled to a bar, plate or sheet. The high specific stiffness (the Young’s modulus in relation to the density) is the really interesting characteristics of MMC. It makes it possible to substantially lower the weight and still retain high strength. The specific stiffness is constant at 25 in a conventional metal alloy compared to 30 or more depending on the reinforcement ratio for MMC. To conclude, MMC offers increased design freedom obtained by the superior qualities described above. |
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