A coupled diffusional-mechanical model accounting for hydrogen enhancements of strain-induced dislocations and vacancies

Informed by the current understanding of hydrogen-dislocations/vacancies interactions, a coupled diffusionalmechanical model accounting for hydrogen-enhanced strain-induced dislocations and vacancies is developed. This model is applied to capture hydrogen diffusion and trapping in the uniaxially tensioned column and type-I loaded crack specimens of nickel alloy, with special attentions paid to the influence of hydrogen-vacancies interaction on them, which is seldom discussed in previous studies. The results show that the hydrogenenhanced hardening rate and the hydrogen-promoted vacancy enrichment for the nickel alloys observed in experiments can be addressed well by the present model. The strain-induced vacancies rather than dislocations dominate the hydrogen trapping behavior, due to their higher hydrogen binding energies for the nickel alloy. The hydrogen-saturated state of vacancies can heavily impact hydrogen diffusion/trapping, which could be characterized by the effective trap concentration. The supersaturated vacancies caused by hydrogen-enhanced straininduced vacancies can promote void growth through vacancy condensation, thus accelerating plastic localization or interface rupture. For the type-I loaded blunt crack specimen, the hydrogen-enhanced dislocation multiplication contributes to intergranular cracking in the pressure valley, while hydrogen-enhanced vacancy generation facilitates void growth in the plastic zone, both of which can exacerbate plastic localization ahead of crack tip. A quantitative model for plasticity localization that accounts for the influences of hydrogen-induced IG cracking and void growth would be helpful in physically based modeling of hydrogen embrittlement.

Automated summary

Informed by the current understanding of hydrogen-dislocations/vacancies interactions, a coupled diffusional-mechanical model is developed to capture hydrogen diffusion and trapping in nickel alloy. The model shows good agreement with experimental results and highlights the dominance of strain-induced vacancies in hydrogen trapping behavior. The impact of hydrogen-saturated vacancies on hydrogen diffusion and trapping is characterized by the effective trap concentration. The model also provides insights into the influence of hydrogen on plastic localization and interface rupture, which is important for modeling hydrogen embrittlement.