Heterogeneous structure with high-fraction coherent L1₂ precipitates enables good strength-ductility synergy in a high-entropy superalloy over a wide temperature range

This study designed and developed a potential Ni₄₃Co₂₈Cr_7.9Al₁₀Fe₅Ti₂Ta₂Mo₁Nb₁B_0.1 (at.%) high-entropy superalloy. A heterogeneous, partially recrystallized microstructure is achieved via thermomechanical processing. Primary blocky and secondary spherical L1₂ precipitates form in high density in both the recrystallized and non-recrystallized regions. These L1₂ precipitates reach a volume fraction of up to ∼67% and are identified as the multi-component (Ni,Co)₃(Al,Ti,Ta,Nb) phase. At room temperature, the alloy exhibits a high yield strength of ∼1003 MPa, an ultimate tensile strength of ∼1533 MPa, and a good ductility of ∼17.0 %. The yield strength continuously decreases with increasing temperature from room temperature to 900 °C, and its mechanical properties are superior to those of most conventional superalloys and high-entropy alloys. Strengthening is primarily attributed to two mechanisms: precipitation strengthening and dislocation strengthening. The dominant deformation mechanisms involve dislocation slip and the formation of stacking faults. Furthermore, the observations of the side-surface morphologies reveal a dual role for the NR regions. At room temperature, the high dislocation density within these regions enhances strength, whereas at elevated temperatures, they help to maintain ductility. This unique dual functionality, coupled with the absence of grain boundaries in the NR regions, facilitates plastic deformation and mitigates intermediate-temperature embrittlement. In summary, the design strategy of heterogeneous-structured superalloy with high-fraction L1₂ precipitates provides valuable insight for developing novel high-entropy superalloys with superior properties.