Serrated grain boundary modulation inhibits nano cracks propagation in pure magnesium: A phase field crystal and quasi in-situ EBSD study

Modulating serrated grain boundaries (SGB) has the potential to enhance fracture properties in materials. This work investigates the crack behavior at SGB during loading through high-resolution transmission electron microscopy, quasi in-situ electron backscatter diffraction and phase field crystal simulations. Experimental results demonstrate that nano-crack initiation and propagation at SGBs driven by basal or prismatic <a> slip at varying angles between grains. Additionally, large shear strains are observed in the SGB bending regions, and portions of these regions that align with the loading direction impede crack propagation. Previous studies have suggested that a loading direction perpendicular to the grain boundary (GB) promotes intergranular fracture. However, our research demonstrates that the influence of the angle between GB and the loading direction on crack propagation is localized, with previous conclusions valid only within a strain range of 10-27%. Beyond this critical strain, cracks predominantly transgranular propagate in a brittle manner, with a weaker effect in the loading direction. Furthermore, when the angle between SGB and the loading direction is less than 65°, the proportion of the SGB parallel to the loading direction increases, thereby inhibiting intergranular fracture. Additionally, SGB curvature significantly impacts crack extension, with an optimal curvature of approximately 0.151 1/nm for double-serrated grain boundaries that effectively suppresses nano-crack propagation. The hindering effect of Lommer–Cottrell locks at the SGB bends on crack propagation is quantified by the geometric compatibility factor. This work may provide insights into enhancing material fracture strength through the control of SGB.