Role of Random and Coincidence Site Lattice Grain Boundaries in Liquid Metal Embrittlement of Iron (FCC)-Zn Couple

Liquid metal embrittlement (LME) has frequently been reported in various systems: Cu-Bi, Ni-Bi, Al-Ga, and Fe-Zn for more than 60 years. Although advances have been made in understanding the phenomenon, the role of grain boundary (GB) type and characteristics in LME has remained unclear. The present work shows that liquid metal penetration only occurs in random GBs, where its propagation path is a function of misorientation angle (θ) and stress component perpendicular to GB plane. In contrast, low-Σ coincidence site lattice (CSL) boundaries: Σ3 (θ = 60 deg) and Σ5 to 9 (~ θ = 40 deg) resist LME, even at the maximum stress component. Triple junctions of CSL and random GB block liquid metal penetration by modifying of the random GB misorientation angle. These findings provide insights to employ grain boundary engineering techniques to increase population of CSLs over random GBs and, hence, mitigate LME.