Effect of microstructure evolution on tensile properties of arc wire directed energy deposited Ti-6.5Al-3.5Mo-1.5Zr-0.3Si titanium alloy

In this study, the static globularization and static coarsening behavior of arc wire directed energy deposited (AW-DEDed) Ti-6.5Al-3.5Mo-1.5Zr-0.3Si (TC11) alloy and their affected on tensile properties were studied. The as-deposited sample and the 550-AC (550 °C/4h/air cooling) sample showed columnar prior-β grains, while the microstructure showed the continuous αGB grew up through the colony microstructure and the basket-weave microstructure. The driving force in the α/β interface was enough for static globularization and static coarsening, which formed crack-like primary α (crab-like αP), αG (globularized α), and the αs (secondary α) during 970-AA (970 °C/2h/air cooling+550 °C/4h/air cooling) or 990-AA (990 °C/2h/air cooling+550 °C/4h/air cooling). The microstructure evolution and formation mechanism of the crab-like αP, the αG, and the αs were discussed. The formation of the αG was mainly via grain boundary splitting, and the formation of the crab-like αP was mainly via terminal migration with different interchanged interfaces. The ultrafine lamellae α nucleated with the sympathetic mechanism grew until lost burgers orientation relationships with adjacent grain boundaries and formed αS. The 550-AC sample showed the highest yield strength (YS, 905MPa) and the highest anisotropic ductility (ΔEL, 7.9) than those in the 970-AA sample and the 990-AA ample. It was because the crab-like αP, the αG, and the αs decreased the fracture resistance in the 970-AA sample and the 990-AA sample.