Correlating tensile fracture behavior with thermodynamic stability in Fe-P metallic glass

Despite extensive studies of metallic glasses (MGs), the coupling between thermodynamic evolution, atomic-scale structural rearrangement, and fracture behavior during tensile deformation remains poorly understood, particularly in Fe-P MGs. In this work, molecular dynamics (MD) simulations were performed to investigate the tensile deformation and fracture behavior of Fe-P MGs with different compositions. The results reveal a pronounced non-monotonic compositional dependence of fracture behavior: the toughness decreases with increasing Fe concentration from 14% to 36% and subsequently increases with further Fe enrichment. During the late stage of fracture, atoms bridging the crack surfaces undergo rapid collective clockwise or counterclockwise rotations, accompanied by local structural rearrangement and stress redistribution. Thermodynamic analysis based on an effective Gibbs free-energy framework shows that the free-energy evolution is dominated by mechanically induced enthalpy accumulation under the present low-temperature conditions, while the radial distribution function (RDF)-derived two-body excess entropy provides a structural descriptor of configurational rearrangement. The change of maximum effective free-energy increase, △G_eff, exhibits a non-monotonic dependence on Fe concentration, increasing from 2.578 eV/atom at Fe₁₄P₈₆ to 5.144 eV/atom at Fe₇₃P₂₇ and then decreasing to 4.28 eV/atom at Fe₈₄P₁₆. Meanwhile, the entropy change exhibits a strongly nonlinear compositional dependence, with relatively large values at Fe₁₄P₈₆ and Fe₈₄P₁₆ and smaller values at intermediate compositions. These results demonstrate that the tensile fracture behavior of Fe-P MGs is governed by the coupled evolution of mechanically accumulated energy and atomic-scale structural rearrangement, providing a thermodynamic-structural perspective on composition-dependent fracture behavior in metallic glasses.