Tailoring microstructure and mechanical properties of Ti–5Al–2Sn–2Zr–4Mo–4Cr alloy via thermally controlled double-wire arc directed energy deposition

TC17 titanium alloy (Ti–5Al–2Sn–2Zr–4Mo–4Cr) is extensively utilized in aero-engine components owing to its high strength-to-weight ratio and excellent mechanical properties at elevated temperatures. However, additive manufacturing (AM) of this alloy is prone to producing coarse prior-β columnar grains and strong crystallographic texture, resulting in pronounced microstructural heterogeneity and mechanical anisotropy. In this work, a TC17 titanium alloy was deposited using double-wire arc directed energy deposition (D-WADED). The influence of thermal cycling on its microstructure and mechanical response was then systematically evaluated. The double-wire configuration not only increased the wire feeding capacity—lifting the wire feeding speed (WFS) limit by 50%—but also lowered the peak temperature and accelerated solidification through redistributed arc heat input and enhanced melt pool convection. Consequently, the growth of coarse β columnar grains was effectively suppressed, with distinct grain refinement observed along the sidewalls of the deposits. Without interlayer cooling, severe thermal accumulation led to grain coarsening (5.305 mm²) and excessive precipitate coarsening, which degraded mechanical properties and increased anisotropy. In contrast, D-WADED with a high WFS refined grains to 0.170 mm², promoted the columnar-to-equiaxed transition (CET), and resulted in more uniform α-phase precipitation. As a result, the hardness distribution became more homogeneous. The ultimate tensile strength in the building and travelling directions reached 1159 ± 52 MPa and 1113 ± 25 MPa, respectively, with corresponding elongations of 11.89 ± 0.72% and 7.56 ± 0.35%, significantly reducing mechanical anisotropy. This study demonstrates an effective strategy for producing fine-grained, high-performance titanium alloys via AM.