Influence of heat treatment parameters on microstructure and mechanical performance of titanium alloy in LPBF: A brief review

In Laser Powder Bed Fusion (LPBF), residual stress in as-built 3D parts may require post-processing treatments to prevent the formation of cracks and voids, where heat treatment is commonly applied to overcome such issues. The selection of heat treatment parameters is critical in achieving suitable microstructure and mechanical properties in the final 3D-printed parts. For the past decade, less review on the effect of heat treatment parameters on the microstructure and mechanical performance of Ti6Al4V parts additively manufactured by LPBF has been reported. In this paper, the effect of heat treatment parameters such as heating temperature, heating rate, cooling rate, and holding time on the microstructure and mechanical properties of Ti6Al4V, namely microhardness and tensile strength, are discussed. In addition, the effectiveness of heat treatment in resolving LPBF issues for Ti6Al4V parts is also addressed. It has been reported that the common microstructure in as-built parts is acicular α′-martensite which, after heat treatment, transforms into an α+β bimodal structure. Microstructure development is reported to be significantly dependent on heating temperature as compared to holding time and cooling rate. Meanwhile, the effect of the heating rate has received little attention in previous reports. In general, heat treatment improves ductility (εb = 9–15%) but reduces strength (UTS = 1184 MPa–946 MPa) for LPBF parts. Additionally, heat treatment is found to be effective in improving porosity and residual stress in LPBF materials. Future work will involve focusing on optimising heat treatment.