The Mechanics and Mechanical Behavior of High-Temperature Intermetallic Matrix Composites

Abstract : This program has examined mechanics analyses and mechanical behavior of advanced intermetallic matrix composites based on the matrix materials MoSi2. Nb5Si3, NiAl, and TiAl, including Ti-based metal matrix composites. There has been a major focus on determination of strength of interfaces in composites under simple and complex loading configurations involving constrained deformation. Interface strength properties have been determined by use of novel experiments (e.g., asymmetric-notch shear testing of model laminates), finite element simulations, homogenization analysis, and first- principles calculations. Additional focus involved investigation of crack growth, process zone formation, and damage accumulation processes during creep. fatigue. shear, tension, and compression of monolithic matrix materials and ductile phase toughened composites. These experiments have been developed in conjunction with methods of theoretical modeling, e.g.. by macroscopic mechanics of composite interfaces (finite elements, homogenization), analytical theory of eutectic microstructural evolution, and first-principles calculations of MoSi2-Mo and NiAl-Cr/Mo interfaces. Damage generation by thermal fatigue, thermal shock, and thermal misfit stresses has also been investigated experimentally and modeled analytically. The experimental program has included development of processing techniques to produce novel composites and microstructures for mechanical investigations: directional solidification of NiAl, Nb5Si3, and MoSi2-based alloy composites, powder processing of MoSi2 toughened with particulates and uniquely shaped (e.g., wire-mesh) second phase dispersoids, hot pressing methods to form macrolaminates of MoSi2, Nb5Si3, and NiAl-based composites. and physical vapor deposition to produce finer scale micro-laminates of TiAl.