Crack propagation in BCC Fe and the influence of Zn: An atomistic exploration

The intricate mechanism underlying brittle fractures in steel materials, particularly Zn-induced liquid metal embrittlement in BCC Fe, remains poorly understood. Accordingly, systematic investigations on crack propagation in BCC Fe, leveraging the anisotropic linear elastic fracture mechanics and a state-of-the-art Fe-Zn binary machine learning moment tensor potential, were performed in this work. Both theoretical analyses and atomic simulations reveal that the ( 001 ) [ 110 ] crack is intrinsically brittle, whereas the ( 110 ) [ 1 1 ¯ 0 ] crack can be blunted due to the emission of 〈 111 〉 dislocations, exhibiting a certain degree of toughness. At elevated temperatures, the reduced unstable stacking fault energy promotes dislocation emission . Zn doping facilitates the ( 001 ) [ 110 ] crack to propagate at lowered loads and enhances the dislocation emission of the ( 110 ) [ 1 1 ¯ 0 ] crack. Notably, our atomic simulations reveal a novel mechanism of Zn-induced liquid metal embrittlement : while Zn enhances dislocation emission at the crack tip, it fails to effectively blunt the crack. Instead, Zn infiltrates the crack surface via the steps caused by dislocation emission, ultimately driving brittle crack propagation .