STRENGTH, FRACTURE, AND FATIGUE BEHAVIOR OF ADVANCED HIGH-TEMPERATURE INTERMETALLICS REINFORCED WITH DUCTILE PHASES

The results of recent studies on the fatigue and fracture behavior of extruded Ti-48Al + 20 vol pct TiNb and hot-isostatically pressed (''hipped'') MoSi2 + 20 vol pct Nb are presented (compositions in atomic percent unless stated otherwise). The effects of ductile phase reinforcement of Ti-48Al and MoSi2 on the micromechanisms of fracture under monotonic and cyclic loading are elucidated. Micromechanics models are applied to the prediction of crack-tip shielding components, and the effects of temperature on tensile/compressive/flexure strengths are discussed. Ductile phase toughening under monotonic loading conditions is shown to be associated with lower fatigue crack growth resistance. The lower fatigue resistance is attributed to the absence' of crack-tip shielding, higher crack opening displacements, and the effects of inelastic strains that are developed in ductile phase-reinforced composites under cyclic loading conditions.