Crystal phase transformation controlling crack propagation and interaction between cracks: A molecular dynamics simulation in <i>α</i> -Fe

Crack propagation and interaction in metals are often governed by stress-driven phase transformations at the atomic scale. Here, we uncover how the body-centered cubic (bcc) to face-centered cubic (fcc) transformation in α-Fe (a prototypical bcc metal) not only delays crack growth but also dynamically mediates crack coalescence, even between misaligned cracks across a broad temperature range. Employing molecular dynamics simulations based on the embedded-atom model, we systematically investigate these phenomena across 100–700 K. Our findings reveal that elevated temperatures distinctly increase atomic mobility near crack tips, promoting structural transformations from bcc to fcc and to intermediate transitional phases. These structural transformations significantly influence local stress redistribution, retard crack growth, and enhance the material’s ductility. By systematically varying crack spacing and alignment, we provide critical insights into how crack proximity and arrangement dictate structural transformations, stress distribution, and crack coalescence behaviors. Detailed analyses of local stress fields, structural evolutions, and atomic arrangements underscore the decisive role of phase transitions and atomic rearrangements in controlling fracture mechanics. In particular, extended fcc regions and associated twin bands strongly guide crack propagation paths and facilitate crack interaction before physical coalescence. These insights enhance our fundamental understanding of fracture and crack interactions in bcc metals, providing potential strategies to improve material performance.