Effect of hydrogen on hot deformation behavior and microstructure evolution of Ti65 alloy

Abstract

Thermohydrogen processing (THP) is a potential method for enhancing the formability of titanium alloys. However, there has been no report on the deformation behavior and microstructure evolution of hydrogenated Ti65 alloys, which are new high-temperature titanium alloys used above 600 °C. In this study, we conducted a series of isothermal hot compression tests in the α+β and β phase field of Ti65 alloy specimens with varying hydrogen content to investigate the effect of hydrogen on high-temperature flow behavior and microstructure evolution. The results showed that after hydrogenation, the number of α phases in Ti65 alloy significantly decreased. δ hydride precipitates were observed in the specimen with 0.43 wt% hydrogen, resulting in an apparent refinement of its microstructure. Adding 0.25 wt% hydrogen reduced the deformation temperature by about 60 °C and increased deformation strain rate by nearly two orders of magnitude for Ti65 alloy. This improvement can be attributed to how hydrogen promotes dislocation movement, dynamic recrystallization (DRX), and dynamic recovery (DRV) during deformation. Similarly, as strain increases, the instability region on the hot processing map gradually decreases or even disappears due to broadening effects from added hydrogen; thus expanding its hot processing window further. This research deepens our understanding regarding deformation behavior while providing theoretical guidance for THP applications using Ti65 alloy.