The Origins of Spinodal Decomposition and Ductile-to-Brittle Transition in Fe–P Metallic Glass: MD Simulations, DFT Calculations and CALYPSO Searches

The existence of the spinodal decomposition phenomenon in the Fe-P metallic glasses (MGs) has long been debated, and the fundamental physical mechanism underlying the ductile-to-brittle transition, which is closely related to the chemical composition of Fe-P MGs, has remained unresolved. In this study, we employ molecular dynamics (MD) simulations based on empirical potentials, ab initio molecular dynamics (AIMD) based on density functional theory (DFT), and the CALYPSO structure search software, which utilizes a particle swarm optimization algorithm, to systematically investigate the rapid solidification, tensile fracture behavior, and geometric configurations of ground-state atomic clusters in Fe-P MGs with six different chemical compositions (Fe₈₄P₁₆, Fe₇₃P₂₇, Fe₆₄P₃₆, Fe₅₀P₅₀, Fe₃₆P₆₄, Fe₁₄P₈₆). Our results demonstrate that spinodal decomposition is an intrinsic atomic structural feature of the Fe-P MGs, rather than an artifact of empirical potential functions. This unique atomic structure arises from the strong electronic interactions between Fe atoms, which are governed by a mix of metallic and ionic bonding. Additionally, microcracks are found to preferentially propagate along P-enriched regions, owing to the high energy, reduced structural stability, and extremely weak electronic interactions between P atoms within these clusters. These factors collectively promote crack initiation and growth, fundamentally contributing to the ductile-to-brittle transition in Fe-P MGs. This work establishes a robust theoretical framework for understanding the intrinsic mechanical behavior of Fe-P MGs and provides valuable guidance for future research.