Atomic-scale Investigation of Liquid-Metal-Embrittlement Crack-path: Revealing Mechanism and Role of Grain Boundary Chemistry

Although a high population of grain boundaries in polycrystalline materials improves structural strength, it increases risk of grain boundary-based degradations such as liquid metal embrittlement (LME). In LME, an aggressive liquid metal attacks the grain boundary network of solid metal, leading to fracture. Thus far, LME studies have been limited to micro- and meso-scale grain boundary investigations. However, to fully understand the LME phenomenon, atomic-scale investigation of LME crack-path is required. The present atomic-scale investigation provides the first-time experimental support for the recently proposed hypothesis of embrittler-induced alteration of charge density as a viable LME mechanism. The micro-events leading to grain boundary decohesion ahead of progressing LME-crack are described. Atom probe tomography (APT) analysis and molecular dynamics (MD) simulation explain why high-misorientation-angle random grain boundaries are more sensitive to LME than special (ordered) grain boundaries.