Microstructure refinement via single-step heat treatment in LPBF-fabricated TA15 alloy for high strength and ductility

The Ti–6.5Al–2Zr–1Mo–1V (TA15) alloy fabricated by laser powder bed fusion (LPBF) generally exhibits high strength but limited ductility, mainly owing to the dominance of α′ martensite within coarse columnar prior-β grains. Achieving effective microstructure refinement via feasible and cost-effective heat treatment remains a critical goal for improving ductility. However, conventional heat treatment routines often lead to coarser α lath structures relative to the as-built martensite or require complicated processing routes. In this work, using a simple one-step annealing treatment, we successfully refined the microstructure of LPBF-fabricated TA15 alloy, significantly enhancing ductility with only a minor loss in strength. Following annealing at 800∼850 °C for 2 h and subsequent furnace cooling, a well-refined lamellar α+β microstructure was obtained. Compared with furnace cooling, water quenching further tailors the retained β phase into distinct layers of considerable thickness. This refined microstructure delivers an excellent strength–ductility synergy: a tensile strength of 1058 MPa accompanied by a ductility of 20.4%, far exceeding the 10.2% elongation of the as-built alloy. Such abnormal microstructure refinement during single-step annealing is attributed to the temperature-dependent competition between α′ martensite decomposition and thermal coarsening. Specifically, within 800∼850 °C, the decomposition of α′ martensite plays a dominant role in microstructure evolution, giving rise to lamellar refinement. This work demonstrates that a simple one-step annealing process can effectively regulate the as-built microstructure and achieve an outstanding mechanical balance, providing a practical and efficient approach for optimizing the mechanical performance of LPBF-manufactured TA15 components.