THE FATIGUE AND FRACTURE-BEHAVIOR OF A GAMMA-TITANIUM ALUMINIDE INTERMETALLIC - INFLUENCE OF DUCTILE-PHASE REINFORCEMENT

This paper presents the results of recent studies on the ambient tempe rature fracture toughness and cyclic crack growth characteristics of a ductile-phase toughened gamma-titanium aluminide intermetallic alloy reinforced with TiNb particles. Under monotonic loading, substantial t oughening is achieved in the composite microstructure and is ascribed to bridging of the crack by uncracked TiNb particle reinforcements in the wake of the crack tip. Crack-particle interactions such as crack b ridging, bifurcation, deflection and crack renucleation contribute to an enhancement in toughness. Under cyclic loading, ductile phase tough ening was found to be less effective resulting in an inferior fatigue crack growth resistance of the composite when compared to the monolith ic counterpart. The lower cyclic fatigue resistance is attributed to a n increased susceptibility of the ductile phase to fatigue failure, co upled with the mutually interactive influences of an absence of bridgi ng contributions to crack-tip shielding, higher crack-tip opening disp lacements and the intrinsic effects of inelastic strains that are deve loped in the ductile phase-reinforced composite matrix. Copyright (C) 1996 Elsevier Science Ltd