Microstructure and Mechanical Properties of Hydrogenated Ti-0.3Mo-0.8Ni Alloy Gas Tungsten Arc Welding Joints

Microstructure, tensile property, microhardness and fracture behavior of the hydrogenated Ti-0.3Mo-0.8Ni alloy gas tungsten arc welding (GTAW) joints were investigated. The results show that the microstructure of the hydrogenated 0.21 wt.% H weld zone were composed of alternating lamellar alpha/needle-like transformed beta and the hydride. Transformed beta was secondary decomposed into the short rod-shaped secondary alpha and lamellar residual beta. The “Pinning” effect of the hydride and more difficult dislocations cross slip directly led to the increased ultimate tensile and yield strength. Average hardness of weld zone, heat affected zone and base metal for the hydrogenated specimens were 196, 177 and 169 HV respectively. Hardness of the former was greater than that of the latter two, hydrogen-induced hardness of the welded joint was significantly increased. Fracture mode of the hydrogenated welded joints changed from the single ductile fracture to mainly brittle fracture with a few dimples fracture. Main cracks that propagated alternately to the original beta grain boundary resulted in local fracture of the microstructure, the interconnected local fractures finally led to the overall fracture of the hydrogenated welded joint.