A novel L12-strengthened multicomponent Co-rich high-entropy alloy with both high γ′-solvus temperature and superior high-temperature strength

A L1₂-strengthened multicomponent Co-rich high-entropy alloy with superior microstructural stability was developed in this study. High-density cuboidal γ′ particles were found to embed in the matrix for the alloy subjected to isothermal aging at temperatures ranging from 800 to 1100 °C without the formation of brittle intermetallic phases neither at grain boundaries nor grain interior after long-term thermal exposure. Atom probe analyses indicated that Ta and Nb elements preferentially partitioned to the γ′ intermetallic phase, which is found to be substantially important for stabilizing the L1₂ ordered crystalline structure. More importantly, the present alloy exhibited a good combination of both high γ′-solvus temperature (1125°C) and low mass density (8.28 g cm⁻³), together with superb high-temperature tensile strength (755 MPa at 800 °C and 664 MPa at 900 °C). The present findings offer an essential paradigm for designing advanced L1₂-strengthened high-temperature alloys with broader temperature capabilities based on Co.