Effect of heat treatments on the microstructure and mechanical properties of a laser powder fused Ti–6Al–2Sn–4Zr–6Mo alloy at room and elevated temperatures: a preliminary study

Ti–6Al–2Sn–4Zr–6Mo (Ti6246) is a titanium alloy designed to outperform the widely used Ti–6Al–4V, particularly in high-temperature applications. Combined with additive manufacturing technologies, such as Laser Powder Bed Fusion, 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 laser powder bed-fused Ti6246. The as-built samples exhibit an ultrafine orthorhombic α″ martensite microstructure, resulting in a high mechanical strength (yield strength ~ 1270 MPa) but poor ductility (~ 5% elongation to failure). To improve functional characteristics of the printed alloy, it is subjected to two heat treatment protocols: 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 reveal the transformation of α″ martensite into a stable α + β microstructure, with coarsening of α-laths and chemical partitioning between Al-rich α and Mo-rich β phases. Both treatments significantly enhance the room temperature ductility (elongation up to ~ 14%) but reduce the mechanical resistance (yield strength down to ~ 970 MPa), with more pronounced softening after the supertransus annealing. At 480 °C, the post-treated samples maintain a good strength-ductility balance (567–577 MPa and 10–12%), but their as-built counterparts show a higher combination of the mechanical properties, with a yield strength of ~ 958 MPa and an elongation to failure of 13%. The results obtained point to a trade-off between strength and ductility induced by heat treatments and highlight the need for their further optimization—to match or exceed the performance of conventionally processed Ti6246 for elevated-temperature applications.