Unveiling the superior mechanical performance of heterogeneous medium entropy alloy across a broad temperature regime

To overcome the bottlenecks of the mechanical properties of conventional alloys in extreme environments, the present study developed a CoCrNi-based medium-entropy alloy (MEA) with a layered distribution of Al and Ti elements. Here, a CoCrNi MEA strengthened by nano-L1₂ precipitates with heterogeneous size and distribution is fabricated via laser directed energy deposition additive manufacturing, followed by heat treatment, which possesses remarkable combinations of mechanical properties across a broad range of temperatures from 77 to 1073 K. The current heterogeneous CoCrNi-based MEA exhibits excellent tensile strengths of 1.4, 1.1, and 925 MPa at 77, 298, and 873 K, respectively, while delivering an outstanding fracture elongation of ∼40%. The correlation between the deformation microstructure of heterogeneous MEA and its excellent performance across a broad temperature regime is systematically investigated. The deformation behavior of the heterogeneous MEA shows a significant temperature dependence, and its superior elongation originates from the synergistic effect of multiple deformation mechanisms. Compared to cryogenic temperatures, strain tends to concentrate at grain boundaries during tensile deformation at elevated temperatures. More importantly, the heterogeneous MEA undergoes a distinct ductile to brittle transition at 1073 K due to oxygen-induced dynamic embrittlement. This study provides theoretical support and technical guidance for the design and preparation of medium/high-entropy alloys applicable to extreme environments.