From single crystals to multi-principal element alloys: A mini-review of fracture behaviours in FCC metals via molecular dynamics simulations

This paper summarises recent advances in studying the fracture behaviour of face-centred cubic (FCC) metals through molecular dynamics (MD) simulations. The review follows a progression from single crystals to bicrystals, polycrystals, and finally to multi-principal element alloys (MPEAs), with particular emphasis on the role of microstructural features including grain boundaries (GBs), twin boundaries, and chemical complexity. In single crystals, orientation-dependent crack propagation is governed by anisotropic fracture mechanics, where the competition between cleavage, and dislocation emission determines brittle–ductile transitions. Bicrystal studies reveal that grain boundary geometries such as the inclination and misorientation angles influence the crack propagation modes, with crack tip blunting, transgranular cracking, and intergranular sliding emerging as dominant patterns. Polycrystalline investigations demonstrate that grain size critically affects fracture behaviour through either Hall–Petch strengthening or inverse Hall–Petch softening mechanisms, while grain boundary-mediated plasticity becomes increasingly important at ultra-fine grain sizes. In MPEAs, low stacking fault energy (SFE) and chemical short-range order introduce additional complexity, enabling transformation-induced plasticity (TRIP), and twin-mediated toughening mechanisms that can overcome the traditional strength–ductility tradeoff. This mini-review highlights the unique capabilities of MD simulations in uncovering atomistic mechanisms governing the fracture behaviours of FCC metals. The emerging trends and future directions are also discussed, including machine learning-accelerated atomistic simulations.