Effects of hydrogen addition on the high temperature deformation behavior of TC21 titanium alloy

► Suitable hydrogen addition can improve the hot workability of TC21 alloy. ► The softening mechanisms are DRX in α + β phase field and DRV in β phase. ► Hydrogen addition decreases the β transus leading to the decrease of flow stress. ► Hydrogen has similar effects on the hot deformation behavior of α + β Ti alloys.