Grain-boundary migration induced abnormally increased flow stress under large strain in a high-temperature compressed Ti-22Al-25Nb alloy

摘要

The flow stress of Ti-22Al-25Nb alloy abnormally increased during uniaxial compression at large strains in the B2 phase field. This phenomenon is dependent on the influence of oriented grain boundary (GB) migration on GB sliding. In the early stages of deformation, straight and smooth GBs gradually evolved facilitating GB sliding, and the (00 1)/(1 1 1) double fiber texture has formed. There is a stored energy difference between (001) and (111) grains due to their different Taylor factors. Under low strain rates, the energy difference between the two fibers will drive GB to migrate, making the GBs zigzag and impeding GB sliding. Thus, greater stress is required to achieve further deformation, namely, the flow stress increased. The dislocation density in the shear band near the GB rapidly increased. Although the current alloy has a high stacking fault energy (SFE), the high dislocation density is sufficient to cause discontinuous dynamic recrystallization (DDRX).