Mitigating grain-boundary decohesion during liquid-metal embrittlement in advanced high-strength steels

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Modern high-strength steels are a critical material class for infrastructure and the automotive sector. The ongoing development towards 3rd generation high-strength steels comes along with a decades-old problem: once galvanized (Zn coated) to passivate the steel, significant property deterioration can emerge if joined with methods that melt the Zn. Indeed, the co-existence of a liquid metal in contact with a solid substrate, here Zn and a steel, leads to embrittlement via grain-boundary phenomena and is referred to as liquid-metal embrittlement (LME). Being a pressing problem for industry, fundamental approaches are needed to understand and mitigate LME for modern steels. Based on our earlier work discovering nano-scale grain-boundary weakening intermetallic phase formation much prior to LME microcracking, and identifying a segregation transition as its cause, we set here out to conduct thermodynamically-informed mitigation of LME by suppressing the driving segregation transition. In combination with atomistic simulations and advanced transmission electron microscopy, galvanized Fe binary or ternary model alloys will be investigated, to i) systematically demonstrate how the segregation transition can be suppressed, to ii) identify initial grain-boundary phases prior to grain-boundary cracking, and to iii) quantify how specific alloying elements weaken grain-boundaries in the steel. If successful, this research project will provide a fundamental mitigation strategy for LME in advanced high-strength steels.