Anisotropy of the hot plastic deformation of Ti–6Al–4V single-colony samples

Abstract

The critical resolved shear stresses (CRSSs) and flow curves for the seven possible slip systems in Ti–6Al–4V with a lamellar microstructure were determined via high-temperature uniaxial compression testing. For this purpose, samples with a rectangular cross section were cut from single colonies grown using a float-zone technique and then tested at 815 °C. Each sample was oriented for single slip along one of seven different slip systems in the alpha phase; i.e., one of the three 〈 1 1 2 ¯ 0 〉 { 1 0 1 ¯ 0 } (prism 〈 a〉), the three 〈 1 1 2 ¯ 0 〉 { 0 0 0 1 } (basal 〈 a〉), or the 〈 c + a〉 (pyramidal) systems was activated by orienting specific samples to have the highest Schmid factor on that particular system. Measurements of the CRSS at yielding and the subsequent flow behavior revealed a strong dependence of mechanical behavior on colony orientation/activated slip system. The anisotropy in the CRSS and the tendency for flow softening at large strains was rationalized on the basis of the Burgers orientation relationship between the alpha (hcp) lamellae and the beta (bcc) matrix and hence the orientation of alpha slip directions relative to those in the beta phase.