Microstructures in Heat Treated LPBF Ti-6Al-4V Alloys after α′ phase Decomposition and their Mechanical Properties

Alloys formed by laser power bed fusion (LPBF) contain high residual stress and strain due to the cyclic heating process, which decreases ductility. Therefore, many researchers have investigated heat treatments to improve ductility by removing residual stress and forming α + β phase structures. However, in this study the ductility of some heat-treated samples was found to decrease below that of as-built samples. This study investigated the heat treatment of LPBF at different temperatures to decompose α′ grains to α grains and understand the resulting microstructure and mechanical properties. Specifically, the influence of microstructural factors on ductility was examined. In the samples heat treated at 500°C, α′ was found to decompose into α with elevated strain and finer β grains, which increased yield strength at the cost of ductility. Meanwhile, in the samples heat treated at 700°C, coarser β phase was precipitated, and greater ductility was supported by the transfer of the slip deformation between α phase grains.