Severe plastic deformation of an additively manufactured Ti–6%Al–4%V alloy: Effect of post-processing heat treatment and hot isostatic pressing on the behavior over a wide range of strain

Ti-6Al-4V (wt.%) alloy containing 0.14 wt.% trace Fe and 1 wt.% yttria-stabilized zirconia (YSZ) was manufactured by laser powder bed fusion. In addition to the as-built samples (AB), some samples received post-heat treatments, either by conventional heat treatment (HT) alone or by a combination of HT and hot isostatic pressing (HIP). The HT and HIP processing increased the grain size and the secondary β-phase fraction, and decreased the as-grown dislocation density, leading to a decrease in hardness from about 4500 to 4100 MPa. All three sample types were severely deformed by high-pressure torsion (HPT) to an equivalent strain of ∼208. The differences in the initial microstructures of the three states gradually disappeared as strain increased. The dislocation density increased with plastic deformation, leading to a decrease in the crystallite size and the β-phase fraction. The saturation values of the crystallite size and the dislocation density were about 20 nm and 10 16 m -2 , respectively, while the β phase practically disappeared at a strain of about 26. Instead, V/Fe-rich regions developed at the grain boundaries of the α phase. The strong initial texture components of and changed to an almost random texture with a weak component during HPT. Due to these changes in the microstructure, the hardness of the three types of samples saturated at similar values within the range of 4500-4700 MPa. The low hardness increase of 5-12% after HPT can be attributed to texture softening which moderated the hardening caused by the defects and small grain size.