Achieving superior strain hardening in a bimodal L1₂-strengthened CoNiAlNbMoTa multi-principal element alloy

Achieving substantial strain hardening in gigapascal-yield-strength face-centered cubic (FCC) alloys is highly challenge. Herein we developed a CoNiAlNbMoTa multi-principal element alloy (MPEA) with bimodal coherent L1₂ nanoprecipitates and Mo-tuned stacking-fault-energy (SFE). This alloy exhibits a excellent yield strength (YS) of 1055 MPa, 19.71% uniform elongation, and an ultra-high ultimate-tensile-strength (UTS) of 2034 MPa, yielding a rare UTS/YS ratio of ∼1.93 for precipitation-strengthened systems. The matrix SFE, calculated via a classical thermodynamic model, is 34.99 mJ/m² (low-to-medium range), providing a theoretical basis for activating of stacking-fault-mediated deformation mechanisms. The superior performance originated from a synergistic mechanism: bimodal precipitates provide initial strengthening and induce heterogeneous deformation, while tailored SFE enables sequential multi-stage hardening via planar slip, twinning, and microbanding.