Intermetallic-matrix composites: An overview

Abstract

Progress in the processing and characterization of intermetallic-matrix composites is reviewed. Issues related to reinforcement selection are highlighted and include availability, mismatch in thermal expansion coefficients and chemical compatibility with the matrix. A multitude of innovative processing techniques are currently being evaluated to produce continuously- and discontinuously-reinforced composites and these have been described. Process models are being formulated and coupled with state-of-the-art sensors technology to optimize parameters to produce composite materials of high integrity. Significant advances in characterization have been made in continuously-reinforced Ti 3Al-based alloys (SCS6 fibers in Ti 3Al + Nb alloys) and particle-reinforced TiAl alloys (TiAl + TiB 2 particulates), in directionally-solidified (DS) eutectics of NiAl, and in discontinuously-reinforced MoSi 2. In most cases, the major emphasis has been on obtaining a desirable balance between creep resistance and low-temperature fracture toughness. In this endeavour, micromechanical modeling has been used to identify, understand and quantify the critical material parameters that control these properties, thereby permitting microstructural design to obtain the desired combinations of these properties. Some of the recent models are presented together with graphical and/or numerical solutions that can be appropriately adapted to several practical situations. In the final section, potential areas for future research are outlined and include the need for viable machining and joining techniques and novel but reliable non-destructive evaluation methods.