Fatigue crack growth behavior and fracture model of the hydrogenated Ti-0.3Mo-0.8Ni alloy gas tungsten arc welded joints

Fatigue crack growth behavior of the hydrogenated Ti-0.3Mo-0.8Ni alloy gas tungsten arc welded (GTAW) joints was investigated. Fracture model of hydrogen-induced GTAW joint was revealed in details. The results show that as hydrogen level increased, crack growth rate in Paris and instability growth zones increased, the more the hydride, the more crack growth channels, the faster crack growth rate, and brittle fracture was intensified. There was the mutation of dislocation density on both sides of the hydride, and dislocation tangles and dislocation lines were concentrated in the vicinity of the hydride. Dislocation weakening caused by solute hydrogen and internal stress generated by hydrogen-rich clusters respectively promoted crack initiation. Evolution of hydride morphology and distribution caused by the interaction between the hydride and persistent slip bands (PSB) significantly reduced crack initiation resistance. Hydride inside the PSB as a hardening phase accelerated to separate from the matrix or itself fracture, which further promoted crack initiation. Cracks in Paris zone rapidly propagated along grain boundary of coarse size “cluster”, alpha / beta phase boundary and the hydride, or cut through alternating lamellar alpha and fine needle beta grains and the hydride.