METAL MATRIX COMPOSITE BODY HAVING A SURFACE OF INCREASED MACHINABILITY AND DECREASED ABRASIVENESS

摘要

Often, metal matrix composites (MMC's) lack adequate machinability and possess excessive abrasiveness because hard ceramic materials, such as silicon carbide, are used as the reinforcement phase. To make a metal matrix composite body having a more machinable and less abrasive surface, an MMC comprising an aluminum nitride reinforcement is formed on the surface of the body. In one embodiment, a layer is provided to a permeable mass or preform at the surface at issue, the layer featuring at least a reduced loading of ceramic filler material, and sometimes no ceramic material at all. The reduced loading is achieved by incorporating a fugitive material into the coating layer. Molten matrix metal is caused to infiltrate the permeable mass or preform and the coating layer to produce a macrocomposite body comprising a metal matrix composite coating and substrate. The metal matrix composite coating layer is distinguishable from the metal matrix composite substrate material, both compositionally and in terms of resulting properties. Under spontaneous infiltration conditions, as defined herein, aluminum nitride forms in-situ in the infiltrated body, including the surface layer. The present coating technique, however, permits a thicker MMC surface layer to be produced than could be produced previously. The present MMC surface layer can be applied to virtually any reinforced or unreinforced aluminum or aluminum alloy body.