Annealing-induced extra-strengthening and ductility via grain boundary engineering in a pre-impact FCC high entropy alloy

Pre-deformation combined with heat treatment is a common method for producing advanced metallic materials. Typically, conventional annealing restores some plasticity but sacrifices strength in most metals. Herein, we report an unexpected phenomenon where annealing of a pre-impact-deformed Al_0.1CoCrFeNi high entropy alloy (HEA) simultaneously induces significant strengthening and substantial recovery of plasticity. Uniaxial tensile tests show that yield strength rises from ∼1.1 GPa for the pre-impact specimen to ∼1.3 GPa after annealing, with elongation restored to over 20 %. Microscopy reveals subgrain formation and microstructural evolution within grains and at grain boundaries (GBs) during annealing at a critical temperature. More importantly, the newly formed grain boundaries (GBs) display exceptional stability. After 20 h of annealing at 550℃, minimal grain growth occurs, while the yield strength stays near 1.3 GPa and work hardening capability is enhanced. This outstanding GB stability offers a unique avenue for tailoring mechanical properties via GB engineering. Furthermore, molecular dynamics simulations were employed to provide atomic-scale insight into the grain boundary evolution and dislocation interactions during annealing. Our findings on enhancing the mechanical performance of HEA may offer an effective approach for developing advanced structural materials with practical applications.