Dynamic Globularization Behavior of O-phase Lamellae in Ti-22Al-25Nb (at%) Alloy during Deformation at Elevated Temperatures

To clarify the globularization mechanism and model of the O-phase lamellae of Ti₂AlNb-based alloys during deformation at elevated temperatures, the hot deformation behavior and microstructure evolution of Ti-22Al-25Nb (at%) alloy during hot compression deformation in (α₂+O+B2) region were investigated. The results show that the flow softening is relevant to the dynamic globularization of O-phase lamellae and the flow instability including 45° shear deformation, 45° shear cracking and micro-cracks. The deformation constitutive model based on the exponential law was established and the deformation activation energy was calculated to be 831 kJ•mol^-1. The globularization of O-phase lamellae is hard to occur at low temperatures or at high strain rates due to slow diffusion rate or insufficient diffusion time. The main globularization mechanism is the kink and shear of the O-phase lamellae, which is confirmed to be a dynamic recrystallization behavior. The dynamic globularization kinetics was also studied, which is sensitive to deformation conditions including deformation temperatures and strain rates and follows an Avrami type sigmoid equation.