Cleavages along {110} in bcc iron emit dislocations from the curved crack fronts

Body-centered-cubic (bcc) transition metals, such as α -Fe and W, cleave along the 100 plane, even though the surface energy is the lowest along the 110 plane. To unravel the mechanism of this odd response, large-scale atomistic simulations of curved cleavage cracks of α -Fe were conducted in association with stress intensity factor analyses of straight crack fronts using an interatomic potential created by an artificial neural network technique. The study provides novel findings: Dislocations are emitted from the crack fronts along the 110 cleavage plane, and this phenomenon explains why the 100 plane can be the cleavage plane. However, the simple straight crack-front analyses did not yield the same conclusion. It is suggested that atomistic modeling, at sufficiently large scales to capture the inherent complexities of materials using highly accurate potentials, is necessary to correctly predict the mechanical strength. The method adopted in this study is generally applicable to the cleavage problem of bcc transition metals and alloys.