Influence of heat treatment and loading direction on compressive deformation behaviour of Ti–6Al–4V ELI fabricated by powder bed fusion additive manufacturing

Abstract

In this study, we have investigated the effects of heat treatment and loading direction on anisotropic compressive behaviour of additively manufactured (AM) Ti–6Al–4V ELI (extra low interstitials). AM samples were fabricated by powder bed fusion (PBF) processing, heat-treated between 800 °C and 950 °C, and compressed along two directions (i.e. parallel and perpendicular to the building direction) with a strain rate of 10−3 s−1 at room temperature. The heat treatment effectively leads to increasing ductility of as-built by decomposing the α′ phase to α and β phases. The heat-treated samples show a significantly lower yield strength than the as-built sample, which has a higher pre-existing dislocation density. As the annealing temperature increases, the yield strength decreased with a broadening of α lath thickness. Furthermore, perpendicular loaded samples have significantly higher strain hardening rate and ductility than parallel loaded samples. However, most of these anisotropic responses disappeared with indistinct morphologies. Anisotropic properties can be ascribed to the directional features of the microstructure resulting from the additive manufacturing process.