Hot deformation behavior and microstructural evolution of Ti-22Al-25Nb-1.0B alloy prepared by elemental powder metallurgy

摘要

The hot deformation behavior of Ti-22Al-25Nb-1.0B alloy has been investigated at the temperature range of 1000-1200 °C and strain rate range of 0.001-1.0s~(-1) by hot compression tests. The micro-structural evolution with different InZ parameters was also analyzed by optical microscopy (OM) and transmission electron microscopy (TEM). Results showed that the flow stresses and microstructure evolution were sensitive to deformation parameters. The peak stress level decreased with increasing deformation temperature and decreasing strain rate. The hot deformation activation energy was calculated to be 524.02 kj/mol in the α2+B2 phase region and 378.59 kj/mol in the B2 phase region, respectively. Under conditions of high InZ values at 49.51 -47.21 in the α2+B2 phase region, cracking and localized plastic flow occurred, which should be avoided in hot working process. According to the microstructure evolution in TEM, it was found that the main soften mechanism transformed from dynamic recovery to dynamic recrystallization at low /nZ values. At high /nZ values obtained in the B2 phase region, the dislocation pile-up and dynamic recovery (DRV) can be found in the high InZ values rather than cracking or localized plastic flow due to low activation energy. The full dynamic recrystallization (DRX) occurs in the InZ values at 29.7-25.09. With decreasing the value of InZ to 24, the size of recrystallization grain becomes larger. The optimum hot working conditions are obtained at /nZ values at 45.34-25.09.