Effect of multiple hydrogen embrittlement mechanisms on crack propagation behavior of FCC metals: Competition vs. synergy

Abstract

Premature failure due to hydrogen has been widely observed in different metallic materials. How does hydrogen affect the competition between brittle cleavage and ductile fracture is an important scientific question to be addressed. The key to solve this problem is to quantitatively depict the interactions between hydrogen and various defects in metals. In the present work, four atomically-informed mesoscale models which depict quantitatively four widely used hydrogen embrittlement (HE) mechanisms are established by DFT or MD simulations, and then integrated into the XFEM-based DDD framework. By this multi-scale framework, hydrogen-induced intergranular fracture in FCC Al and Ni is investigated, with typical twin boundary (TB) and high angle grain boundary (HAGB) considered for comparison. Computational results show that the dominant HE mechanism in different metals depends on the GB type when multiple HE mechanisms coexist and interact with each other. Compared with the HAGB, the TB has better resistance to hydrogen embrittlemen. The adsorption-induced dislocation emission (AIDE) mechanism dominates the crack propagation along the TB in Al and Ni, while the hydrogen-enhanced decohesion (HEDE) mechanism dominates the crack propagation along the HAGB in Al and Ni. Compared with the HEDE and AIDE mechanisms, the other two mechanisms, i.e., the elastic shielding (ES) and the hydrogen-enhanced strain-induced vacancy (HESIV), have much weaker effect on the hydrogen-induced intergranular fracture, unless the hydrogen concentration is unusually high. These results are helpful for us to understand the complex physical mechanisms behind the hydrogen embrittlement phenomenon.