The Influence of Stress Triaxiality on the Damage Mechanisms in an Equiaxed α/β Ti-6Al-4V Alloy

摘要

Division Mecanique, Universite de Technologie de Compiegne, 60206 Compiegne Ccdex, France The influence of the stress triaxiality on void formation, void growth, and fracture was investigated for an equiaxed Ti-6Al-4V alloy. Void nucleation in the α phase was found to occur for a critical value of macroscopic plastic strain, whereas void nucleation at the α/β interface also depends on triaxiality. Under low triaxiality and important plastic strain, voids appear and grow in the area where the microshear bands develop, with an angle close to 45 deg to the stress axis in the α particles. In contrast, with high triaxiality, voids nucleate preferably at the α/β interfaces and grow perpendicular to the stress axis by a cleavage mechanism. In a middle range of triaxiality and plastic strain, voids nucleate in α because of the sufficient plastic strain and also at the α/β interfaces because of the sufficient triaxiality (χ). Void growth occurs with an angle of 60 deg to the stress axis, since χ is not high enough to create cleavage and ε_p is high enough to provide a ductile growth. Two types of fracture were identified and reported on a fracture map: under low triaxiality, failure appears by plastic instability, whereas for high triaxiality, the instability is induced by a void-growth process discussed with the help of Rice and Tracey's approach.