Flow softening mechanism in isothermal compression of β-solidifying γ-TiAl alloy

Abstract

Flow softening mechanism in the isothermal compression of Ti-42.9Al-4.6Nb-2Cr with duplex structure was investigated. True stress-strain curves of Ti-42.9Al-4.6Nb-2Cr exhibited evident flow softening behavior when isothermal compression was conducted at the strain rate of 0.001–1.0 s−1, and the flow softening effect was assessed via flow softening index. Results show that kinking of α2/γ lamellar colonies and periodic morphology variation of β0 phase mainly contributed to the initial flow softening, while DRX of γ phase and periodic morphology variation of β0 phase contributed to the lateral flow softening of Ti-42.9Al-4.6Nb-2Cr with duplex structure. Kinking of lamellar colonies was caused by appearance of stacking faults pairs in γ lamellae and fracture of α2 lamellae. Lamellar colonies were decomposed by DRX of γ phase and growth of adjacent lamellae in the kinked area. Additionally, periodic morphology variation of β0 phase was related to intensive deformation systems, which can be easily-activated, and fast DRX behavior via rotation of subgrains during isothermal compression. Keywords: Titanium aluminides, Thermomechanical processing, Flow softening, Microstructure