A novel low-density Co-Ni-Al-Nb-based multicomponent superalloy with superior medium-to-high temperature mechanical properties and oxidation resistance

Chromium (Cr) is widely used in superalloys to improve oxidation resistance and creep strength. Still, excessive additions can promote the formation of detrimental topologically close-packed (TCP) phases, compromising microstructural stability. Therefore, controlling the Cr content to achieve excellent overall performance is a critical aspect in the design of superalloys. By employing the CALPHAD approach and the Co-based superalloy thermodynamic database developed by our research team, in conjunction with investigations into the γ/γ′ microstructure, phase transformation temperatures, and lattice misfit, this study optimized a Co-40Ni-14.5Al-4Nb alloy. Based on this alloy, the Cr content was systematically incorporated and controlled through CALPHAD calculations combined with experimental characterization. This led to the development of an optimized Co-40Ni-14.5Al-4Nb-12Cr alloy, featuring a high γ′ solvus temperature (1172 °C), a well-aligned γ/γ′ microstructure, and a reduced lattice misfit. Moreover, this alloy exhibited a compressive yield strength of 745 MPa at 800 °C, a low density of 7.73 g/cm³ , and excellent specific yield strength. Notably, the alloy maintained a high compressive yield strength with minimal variation over the 500–800 °C temperature range, owing to the interaction between lattice misfit and dislocation behavior. After 200 h of oxidtion, a protective oxide layer composed of Al₂O₃, Nb₂O₅, and (Al,Cr)₂O₃ formed, markedly enhancing oxidation resistance. These findings highlight the effectiveness of Cr content optimization in achieving a balanced enhancement of mechanical and oxidation performance, offering valuable insights for next-generation superalloy design. • A novel low-density Co-based superalloy with a high γ′ solvus was successfully developed. • CALPHAD-guided design enabled a γ/γ′ structure with optimized Nb and Cr content. • Nearly constant yield strength from 500–800 °C ensures superior high-temperature performance. • Cr addition reduces γ/γ′ lattice misfit and enhances interfacial coherency. • A protective multilayer oxide scale provides excellent oxidation resistance at 1000 °C.