Revealing the intensified preferred orientation and factors dominating the anisotropic mechanical properties of laser powder bed fusion Ti‐6Al‐4V alloy after heat treatment

Abstract

Heat treatment is a general process to modify the unsatisfactory microstructure and properties of laser powder bed fusion (LPBF) Ti‐6Al‐4V. However, the effects of heat treatment on the preferred orientation and anisotropic mechanical properties have not been clarified yet. The main objective of this study was to identify the roles of heat treatment in the preferred orientation and mechanical properties of LPBF Ti‐6Al‐4V. The results indicated that α′-martensite with a weak {112̅0}α′ preferred orientation and minor retained β phase with a strong {100}β preferred orientation along the prior columnar β grains existed in the as-built specimen. After 750 °C heat treatment, α′-martensite was fully decomposed to α + β phases, and the {112̅0}α preferred orientation gradually intensified with increases in the heat treatment temperature, particularly after 950 °C heat treatment. The mechanism of the intensified {112̅0}α preferred orientation was proposed and verified by the Burgers orientation relationship and parent phase reconstruction using electron backscatter diffraction.Furthermore, the factors dominating the anisotropic mechanical properties of LPBF Ti‐6Al‐4V after heat treatment were investigated in this study. The results showed that, in the as-built, 750 °C, and 850 °C heat-treated conditions, the ultimate tensile strength and elongation of the horizontally-built specimens were slightly higher than those of the vertically-built ones due to the large spatter-induced disk-shaped pores. However, after 950 °C heat treatment, the elongation of the vertically-built samples exceeded that of the horizontally-built ones. This trend can be attributed to the significant intensification of the preferred orientation by the 950 °C heat treatment, which contributed to the higher Schmid factor and ductility of the vertically-built specimens.