Commercial processing of metal matrix composites

Discontinuously reinforced metal matrix composites are a class of materials that exhibit a blending of properties of the reinforcement and the matrix. The reinforcement can be ultra-high strength whiskers, short or chopped fibers or particles. Each of the reinforcements has property or cost attributes that dictate its use in a given situation. Commercial producers have concentrated on composites with particulate reinforcement because of cost issues. These composites have been made by a number of manufacturing techniques. These include powder metallurgy, casting and spray deposition. The technique that has consistently produced higher property composites has been powder metallurgy. This paper concentrates on the commercial production of metal matrix composites. There have been many laboratory scale manufacturing methods developed for creating metal matrix composites. These will not be addressed in this paper. Recent work in this area has focused upon refining techniques that offer lower cost manufacturing. Scale-up of facilities to produce vacuum–hot pressed composite billets has been completed with the help of DOD funds through a Defense Production Act Title III program. Several companies have been working with a cold isostatic pressing–vacuum sintering process (CIP–sinter), to produce lower cost billet stock. In July 1996, the Alyn Corporation used private capitol to put in a scaled-up CIP–sinter facility. This paper will review the recent test data generated from aluminum composites made by the CIP–sinter manufacture method. These data will be compared with data generated by the Title III program that represent state-of-the-art processing. This comparison will demonstrate that both manufacturing methods produce composites with similar properties.