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

Abstract

The hot deformation behavior of Ti22Al25Nb1.0B 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 microstructural evolution with different lnZ 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 lnZ 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 lnZ values. At high lnZ values obtained in the B2 phase region, the dislocation pile-up and dynamic recovery (DRV) can be found in the high lnZ values rather than cracking or localized plastic flow due to low activation energy. The full dynamic recrystallization (DRX) occurs in the lnZ values at 29.7–25.09. With decreasing the value of lnZ to 24, the size of recrystallization grain becomes larger. The optimum hot working conditions are obtained at lnZ values at 45.34–25.09.