Stacking fault stabilization and strengthening mechanisms in CoCrNi alloys

Abstract

Stacking faults (SFs) are a kind of key defects governing the strength and ductility of multi-principal element alloys, but their stability and size-dependent effects remain unclear. Using molecular dynamics simulations, we revealed contrasting behaviors in Ni and CoCrNi. In Ni, the high stacking fault energy causes rapid annihilation of SFs, eliminating their strengthening contribution. In CoCrNi, the ultralow stacking fault energy stabilizes SFs, which persist as barriers to dislocation glide, leading to Hall–Petch-like strengthening. Crucially, a strong coupling between grain size (d) and SF spacing (λ) emerges: at d = 15 nm, grain refinement dominates and moderate SFs induce softening, whereas at d = 10 and d = 20 nm, dense SF networks markedly enhance the strength. These results reveal the atomic-scale mechanisms of SF-mediated strengthening and highlight the need for joint design of grain size and stacking fault distribution to the design of high-performance structural alloys.