In Situ SEM Observations of the Liquid Metal Embrittlement of α-Brasses in Contact with the Liquid Ga-In Eutectic at Room Temperature

Liquid metal embrittlement (LME) occurs when a normally ductile alloy undergoes brittle fracture in contact with a liquid metal. The mechanisms behind LME remain unclear, and most of the models rely on post mortem analyses. In this work, we overcome this limitation by performing in situ scanning electron microscopy (SEM) notched micro-bending tests on α-brasses exposed to the gallium–indium eutectic (EGaIn) at room temperature, enabling real-time correlation between load–displacement curves and crack evolution during LME. In the Cu-30%Zn alloy, LME was observed only after prior plastic deformation and ductile crack growth, confirming that liquid metal did not influence early plasticity. A two-step experiment further showed that a pre-existing crack in contact with EGaIn, under continued loading, was sufficient to trigger brittle fracture. The Cu-20%Zn alloy displayed alternating ductile and brittle events, with brittle cracks propagating horizontally before arresting in undeformed zones, leading to stepped load–displacement curves. By contrast, pure Cu and Cu-15%Zn showed only ductile fracture despite continuous contact with EGaIn. These results demonstrate that LME in the Cu-Zn/EGaIn system acts during crack propagation rather than initiation. The present in situ SEM methodology provides direct evidence of fracture mechanisms and a framework for future experimental modeling comparisons.