Optimizing the microstructural and mechanical isotropy for the twin-wire directed energy deposition-arc fabricated Ti-48Al-2Cr-2Nb alloy via interpass remelting

Abstract

Twin-wire directed energy deposition-arc (TW-DED-arc) has demonstrated feasibility in fabricating TiAl alloys. Unfortunately, it is hard to simultaneously guarantee the effective product utilization, and suppress the anisotropy. To break the trade-offs, a novel depositing strategy of an interpass remelting (IR) process, a representative of low-carbon-friendly and easy-to-operate processing route, is designed to fabricate Ti-48Al-2Cr-2Nb (TiAl-4822) alloy without chemical adjustment. The results indicated that the IR process promoted high-fraction equiaxed grains of ∼90 %, much higher than that fabricated by constant process (CP). The IR process significantly increased the microstructural and mechanical isotropy of TW-DED-arc fabricated TiAl-4822 alloy. For microstructural isotropy, the IR process facilitated the growth of equiaxed grains with appropriate size, twin thickness refinement, and micro-segregation improvement. The IR process also strengthened the α₂/γ phase interface and γ/γ twinning boundaries. For mechanical isotropy, the IR process generated superior tensile properties along different directions of TW-DED-arc fabricated TiAl-4822 alloy wall compared to CP process and other fabricating techniques. Meanwhile, the exceptional strength retention of about 97 % at 650 °C was maintained. This work provides a new perspective to optimize microstructure and mechanical properties of TiAl-4822 alloys, facilitating further development of TW-DED-arc and its application in aerospace industry.