MORPHOLOGICAL EFFECT ON THE MECHANICAL-BEHAVIOR OF A 2-PHASE TI3AL-NB ALLOY

Abstract

A study has been made on the deformation and fracture behavior of a two-phase (alpha2 + beta) Ti3Al-Nb alloy, with particular emphasis on the effect of morphologies. The coarse colony structure obtained by continuously annealing in the two-phase region directly from the beta region results in poor elongation ductility. The fine colony structure obtained by two-phase annealing the beta-quenched specimen also results in poor elongation ductility. However, upon obtaining fine equiaxed or basket-weave structures by following different transformation paths, improvements occur in elongation ductility without any sacrifice in strength. For the fine equiaxed structure, maximum elongation is obtained at the intermediate volume fraction of alpha2, while for the basket-weave structure, an increase in the volume fraction of alpha2 increases the elongation. Detailed fracture analysis shows that different fracture mechanisms operate for different morphologies, and the critical microstructural unit for arresting fracture also varies, depending on the morphologies.