Effect of heat treatments on the structure and mechanical properties of a laser powder fused Ti-6Al-2Sn-4Zr-6Mo alloy at room and elevated temperatures

Ti-6Al-2Sn-4Zr-6Mo (Ti6246) is a new generation titanium alloy designed to outperform the widely used Ti-6Al-4V (Ti64), particularly in high-temperature applications. Combined with additive manufacturing (AM) technologies, such as Laser Powder Bed Fusion (LPBF), Ti6246 offers the potential to produce complex geometries and expand their application range. This study investigates the influence of post-processing heat treatments on the microstructure and mechanical performance of LPBF-processed Ti6246. It is observed that as-built specimens exhibit an ultrafine orthorhombic α″ martensite microstructure, resulting in a high mechanical strength (yield strength ~ 1270 MPa) but poor ductility (~ 5% elongation). Two heat-treatment protocols were applied to the printed alloy to improve its applicability: low temperature annealing at 600°C, followed by either a) subtransus (875°C) or b) supertransus (950°C) annealing. In both cases, structural analyses of the heat-treated alloy revealed the transformation of α″ martensite into a stable α + β duplex microstructure, with coarsening of α-laths and chemical partitioning between Al-rich α and Mo-rich β phases. Both treatments significantly enhanced the room temperature ductility (elongation up to ~ 14%) but reduced the strength (yield strength down to ~ 970 MPa), with more pronounced softening after the supertransus annealing. At 480°C, the post-treated samples maintained a good strength-ductility balance (567–577 MPa and 10–12%), but the as-built samples showed the best performance, with a strength of ~ 958 MPa and a ductility of 13%.The results underscore a trade-off between strength and ductility induced by heat treatments and highlight the need for further optimization to match or exceed the performance of conventionally processed Ti6246 for elevated temperature applications.