Hydride Precipitation in the Hydrogenated 0.12 wt.%H Weld Zone of Ti-0.3Mo-0.8Ni Alloy Argon-Arc-Welded Joints

To reveal the influence of hydrogen on the characteristics of defect-free titanium alloy welded joints, the effects of hydrogen addition on the precipitation behavior in the hydrogenated 0.12 wt.%H weld zone of Ti-0.3Mo-0.8Ni alloy argon-arc-welded joints have been investigated. The results showed that lamellar δ-hydride (face-centered cubic) could only precipitate from α-lamellae, but not from the transformed β-phase due to the high hydrogen solubility in β-phase. Formation of δ-hydride was the result of the α_H-phase separation reaction: α_H → α (H-lean region) + δ (H-rich region). The formation mechanism of the relatively massive δ-hydride in the α_H-matrix was mainly based on the combined effects of harsh stress field states and stringent hydrogen content requirements. A sharp drop in elongation and a slight increase in weld zone hardness of the hydrogenated welded joint were associated with δ-hydride precipitation.