Chapter 09979 - Intermetallic Matrix Composites

Abstract

Intermetallic matrix composites (IMCs) are distinguished from metal matrix composites (MMCs) by the fact that the matrix is an ordered intermetallic compound (IC) or a multiphase combination of ICs. In some cases, materials that possess a significant fraction of an ordered IC, or where the IC is the reinforcement, have also been referred to as intermetallic composites. As a distinct class of materials, IMCs have their origins in the two disciplines of MMCs and ordered ICs and alloys. A major objective of each of these two activities has been to develop structural aerospace materials for use at elevated temperatures, and IMCs are a product of collaboration between these parallel efforts. The extensive research and development of ICs has been motivated by the promise of good high temperature structural properties of these materials. Ordered compounds typically possess high melting temperatures and the ability to retain mechanical properties at a higher fraction of their melting point relative to disordered alloys. ICs also often possess a lower density than other candidate high temperature structural alloys. However, ICs typically suffer from inadequate fracture properties, with low tensile elongation-to-failure values and fracture toughness. In addition, single-phase intermetallic alloys often have poor creep resistance at projected use temperatures. Thus, the IC technical community has pursued the addition of a reinforcing phase to improve the high temperature creep response through a load-sharing mechanism with the (generally ceramic) reinforcement. Reinforcements have also been incorporated to increase the fracture resistance of ICs. Processing–microstructure–property relationships of IMCs will be discussed in this chapter.