L12 nanoparticle-strengthened CoNi-based superalloy with ultrahigh yield stress developed using CALPHAD method

In this study, a Co-30Ni-10Ti-2Ta-3Al (30Ni3Al) alloy with high γ′ phase dissolution temperature (1215 °C), excellent mechanical properties, and low density (8.46g/cm3) was developed based on the thermodynamic database of Co-based high-temperature alloys established by our group. Compositional design and microstructure control were achieved through the utilization of thermodynamic phase diagrams and phase fractions. It is found that the addition of 2at.% Ta significantly improves the γ′ phase fraction and solvus while maintaining a suitable working window. However, a rafting trend of γ′ phase was observed as heat treatment for a long time at 750℃. By introducing 3at.% Al and 30at.% Ni into the optimized Co-10Ti-2Ta master alloy, the rafting of the γ′ phase was effectively suppressed. Benefiting from the fine, stable, high volume fraction γ′/γ microstructure, the 30Ni3Al alloy demonstrates compressive yield strengths of approximately 1487±7MPa and 1319±13MPa at room temperature and 600 ℃, respectively. The superb mechanical property at high temperatures can be attributed to the work-hardening effect resulting from the interactions of superattice stacking faults in γ′ phase.