Precipitation behavior of α phase during post-deposition heat treatment of double-wire arc directed energy deposited TC17 alloy

Additive manufacturing has attracted considerable attention as an effective strategy for producing high-performance titanium alloy systems in both scientific research and industrial applications. The relationship between heat-treatment temperature, α-phase evolution, and mechanical performance was comprehensively evaluated in double-wire arc directed energy deposition (D-WADED) fabricated TC17 alloy (Ti–5Al–2Sn–2Zr–4Mo–4Cr), with particular emphasis on annealing and solution conditions. Annealing within the α + β phase region (600–700 °C) improved the homogeneity of the α phase; however, α phase coarsening led to a pronounced reduction in strength. High-temperature annealing in the β phase region (950 °C) induced severe α-phase coarsening and elemental segregation, resulting in a substantial decrease in ultimate tensile strength (UTS) to 798.69 MPa. High-temperature solution treatment (900–950 °C) followed by aging produced extremely coarse α phase and finely dispersed secondary α phase (α_S), accompanied by elemental segregation which compromised ductility and resulted in a UTS of 1042.28 MPa, hardness of 617.20 HV, and elongation (El) of only 5.75% for the specimen treated at 950 °C. In contrast, after solution treatment in the α + β phase region followed by aging, a dual-scale bimodal matrix comprising lath-shaped primary α phase (α_P) and finely dispersed α_S was obtained. The optimal combination of UTS and El was achieved at a solution temperature of 850 °C (1091.73 MPa and 12.60%, respectively), representing the most favorable heat-treatment window and a significant improvement over the as-deposited condition (1022.00 MPa and 11.16%, respectively).