Innovative Processing Techniques for Intermetallic Matrix Composites

Abstract

Although intermetallics based on aluminum or silicon tend to have a very attractive combination of low density and excellent oxidation resistance, they suffer from lack of adequate creep strength and, in most cases, from inadequate ductility and toughness. It has been recognized for several years that an approach which could simultaneously solve both problems, without degrading other properties, is to utilize the intermetallics as matrices for composite materials. The consequence has been an explosion of interest in two-phase intermetallic-based alloys. With the exception of some early work by Seybolt, intermetallic matrices have been utilized for composites only for the past five to six years; the first published reference to systematic studies of fibrous composites dates from the proceedings of an MRS meeting in December 1986. The published literature is much sparser than, for example, that on ceramic matrix composites, which have been under development for a much longer period. Nevertheless, an appreciable number of intermetallic matrices have been reinforced with fibers or particles. Because of the relatively high melting points and extreme brittleness of most intermetallic compounds utilized as matrices, as well as other significant advantages, enormous effort has been devoted to powder metallurgical techniques. In this category we include reactive sintering of elemental or elemental plus prealloyed powders, reactive hot pressing, reactive HIPing, injection molding, the XD process, dynamic compaction of powders, mechanical alloying, the powder cloth method, and, of course, traditional hot pressing techniques.