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 gamma ' phase dissolution temperature (1215 degrees 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 gamma ' phase fraction and solvus while maintaining a suitable working window. However, a rafting trend of gamma ' phase was observed as heat treatment for a long time at 750 degrees C. By introducing 3 at.% Al and 30 at.% Ni into the optimized Co-10Ti-2Ta master alloy, the rafting of the gamma ' phase was effectively suppressed. Benefiting from the fine, stable, high volume fraction gamma '/gamma microstructure, the 30Ni3Al alloy demonstrates compressive yield strengths of approximately 1487 +/- 7 MPa and 1319 +/- 13 MPa at room temperature and 600 degrees 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 gamma ' phase.