Recent Developments in the Design of Next Generation γ′-Strengthened Cobalt–Nickel Superalloys

A new γ′-strengthened Co–Ni-base superalloy was developed using a combination of computational thermodynamics and lab-scale experimental heats. Multiple 18 and 180 kg ingots were melted under vacuum and forged to study the composition–process–property relationship. Several heat treatments were developed to evaluate the balance between strength and creep resistance. In the fine-grain condition, the superalloy exhibits a yield strength of almost 1300 MPa at room temperature, 1071 MPa at 704 °C, and 766 MPa at 816 °C. In the coarse-grain condition, the creep resistance is superior to that of Waspaloy and comparable to that of alloy 720. Sulfidation and cyclic oxidation tests show better resistance to environmental damage than Waspaloy and alloy 720 due to the formation of a protective alumina layer. We also show that this superalloy can be atomized and processed via powder metallurgy. Potential applications include disks and casings in land-based and jet engine turbines, fasteners, bolts, and studs in automotive exhaust systems and exhaust valves in internal combustion engines.