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

Abstract

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 (8.46 g/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 2 at.% 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°C. By introducing 3 at.% Al and 30 at.% 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±7 MPa and 1319±13 MPa at room temperature and 600°C, 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.