Towards isotropic behaviour in Ti–6Al–4V fabricated with laser powder bed fusion and super transus hot isostatic pressing

Abstract

Super β-transus hot isostatic pressing (HIPing) has been shown to be able to transfer columnar to equiaxed grains in additively manufactured Ti–6Al–4V. Although pores in the additively manufactured parts have been found to play a role in such grain transformation, it remains unclear whether super β-transus HIPing can also generate isotropic microstructure and mechanical properties in relatively high-density additively manufactured Ti–6Al–4V. In the present study, super β-transus HIPing (1030 °C, 175 MPa) was applied to high density Ti–6Al–4V manufactured by laser powder bed fusion (L-PBF). As comparison, specimens were subjected to conventional heat treatment under identical conditions to the HIPing cycle except at standard atmospheric pressure. The results showed that the conventional heat-treated sample maintained columnar grains. In contrast, the super β-transus HIPed sample showed equiaxed grains. In respect of mechanical properties, both the as-built and heat-treated samples showed anisotropic tensile strength and ductility between horizontal and vertical building directions whereas HIPed samples achieved isotropic strength and ductility.