Heterogeneous structure and dual precipitates induced excellent strength-ductility combination in CoCrNiTi0.1 medium entropy alloy

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Developing advanced structural materials with high strength and excellent ductility is crucial for meeting aerospace and military requirements. High/medium entropy alloys (H/MEAs) have garnered significant attention due to their superior mechanical properties. In this study, through severe deformation followed by heat treatment at temperatures in the range of 700–900 °C, we successfully obtained a fully recrystallized structure with double precipitates in non-equiatomic CoCrNiTi0.1. Tensile tests at room temperature revealed that the alloy annealed at 700 ° C for 1 h exhibited exceptional mechanical properties, with a yield strength of 1575 MPa, tensile strength of 1735 MPa, and ductility of 15 %. The ultrahigh yield strength is primarily attributed to the synergistic strengthening mechanisms including precipitation strengthening, grain-boundary strengthening, and HDI strengthening. The FCC/L12 interface facilitated dislocation transfer during deformation, reducing stress concentration and promoting uniform deformation. Additionally, deformation mechanisms such as stacking faults and trace twinning contributed to the alloy's excellent ductility, ensuring substantial work-hardening capability and achieving a remarkable strength-ductility combination. These findings not only offer an effective strategy for enhancing the mechanical performance of non-equiatomic MEAs but also deepen our understanding of synergistic strengthening and deformation mechanisms in alloys.