Hydrogen diffusion behavior within microstructures near crack tip: A crystal plasticity study

The hydrogen diffusion and damage characteristics within the microstructure at the crack tip are direct factors determining hydrogen embrittlement (HE) phenomena, yet research in this area from a mesoscale perspective is still insufficient. This study employs a non-local crystal plasticity constitutive model coupled with a hydrogen diffusion model that considers grain boundary (GB) characteristics and incorporates fracture initiation parameter accounting for the HELP + HEDE mechanisms. The research investigates hydrogen diffusion behavior at the crack tip in pure nickel and provide a detailed exploration of the mechanism underlying hydrogen-assisted crack propagation. The results indicate that the non-local model exhibits advantages in simulating the hydrogen diffusion process. Hydrogen induces intragranular cracks to propagate along slip planes with a high dislocation density. High-energy GBs and triple junctions are more susceptible to hydrogen accumulation, and under the influence of the HEDE mechanisms, they represent the primary sites for crack initiation. The entire fracture process involves the continuous coalescence of primary cracks with secondary cracks. Moreover, the HE resistance is better in equiaxed microstructures compared to rolled microstructures, particularly when the crack plane is parallel to the TD direction.