Influence of high-temperature hydrogen charging on microstructure and hot deformability of binary TiAl alloys

The high-temperature hydrogen charging was carried out to reveal the effect of hydrogen on the microstructure and hot deformability of TiAl alloys. The Ti-44Al (at.%) alloy and Ti-48Al alloy were hydrogenated at temperature range from 1373 K to 1693 K under hydrogen pressure of 0.1 MPa, and effects of hydrogen on the hot deformation behavior were tested on Gleeble-1500D at temperature of 1373-1523 K under strain rate of 0.01 s−1. Results show that hydrogen content increases with increasing of temperature and the volume fraction of α2 phase, and hydrogen absorption reaches to equilibrium within 30 min at high temperature. There is a linear relationship between lnCH and 1/T, the heat of solution of hydrogen is calculated as 86.0 kJ/mol and 76.2 kJ/mol respectively, suggesting that hydrogen absorption in TiAl alloys is an endothermic reaction. Hydrogen promotes the formation of γ phases because hydrogen promotes the transition of L(α2/γ)→γ and nucleation of γ phase. The presence of hydrogen promotes the dynamic recrystallization and dislocation movement during hot deformation, resulting in decrease of flow stress. The peak stresses of Ti-44Al alloy and Ti-48Al alloy are decreased by 29% and 38% respectively after hydrogenation, which corresponds to the decrease of deformation temperature by about 50 K.