Liquid metal embrittlement transport mechanism in the Fe/Zn system: Stress-assisted diffusion

Grain boundaries in polycrystalline materials are a critical feature for structural applications but also create the risk of intergranular embrittlement phenomena, such as liquid metal embrittlement (LME). In LME, an aggressive liquid metal attacks the grain boundary network of a solid metal leading to fracture. Thus far, experimental work and fundamental theories on LME in the Fe/Zn system have provided contradicting results on the embrittler transport mechanism to the grain boundaries. In this study, the LME transport mechanism was determined to be stress-assisted diffusion by both experimental and numerical methods. For the first time, LME formation was incrementally observed which revealed the LME transport mechanism and the role of stress in LME onset. Stress created an additional diffusion flux that enhanced the embrittler penetration. This study provides new insight into the significance of thermomechanical state for the onset of LME and provides evidence for LME as a diffusion-based phenomenon.