YIELD STRESS ANOMALIES, DISLOCATION CORE STRUCTURES AND SUBSTITUTIONAL ALLOYING IN MOLYBDENUM DISILICIDE

A brief overview of the temperature dependence of yield strength for the different slip systems of MoSi{sub 2} is presented and mechanisms for the yield stress anomaly are discussed. Recent results on the atomistic simulation of the dislocation core structures and mobility are presented next. Finally, we present experimental results on substitutional alloying of polycrystalline MoSi{sub 2} with 1-2 at.% Re, Nb and Al. Re resulted in an order of magnitude increase in compressive strength at 1600 C, Al caused solution softening at near-ambient temperatures, and Nb caused softening at low temperatures and hardening at high temperatures. The quaternary MoSi{sub 2}-Re-Al alloys showed strengthening at elevated temperatures and reduction in flow stress with enhanced plasticity at near-ambient temperatures. The mechanisms of solution hardening and softening are discussed using insight from transmission electron microscopy observations of the dislocation substructures and atomistic simulation results