Optimizing strength and ductility in CoCrNiAl alloys by coupling lattice distortion with stacking fault energy

Overcoming the strength–ductility trade-off in structural alloys has long relied on micro/nanoscale defect engineering. Here we present a coordinated design framework that combines lattice distortion with control of stacking fault energy (SFE) in a CoCrNiAl multi-principal element alloy (MPEA). Al, with a 14 % atomic size mismatch, is selected to induce strong lattice distortion while simultaneously lowering the SFE. First-principles calculations reveal that this dual effect arises from both increased bond length variation, which enhances solid-solution strengthening, and charge transfer with bond strengthening, which reduces the SFE. The lowered SFE activates deformation twinning and stacking fault formation, sustaining strain hardening and improving ductility. This cross-scale design offers a complementary perspective to conventional defect-based approaches for developing high-performance alloys.