L1₂-Strengthened Co-Rich Alloys for High-Temperature Structural Applications : A Critical Review

Tremendous efforts have been made to accelerate the design of advanced high-temperature structural materials, leading to the development of high-performance Ni-based superalloys with both superior thermal stability and creep resistance. However, further gains in the temperature capabilities are difficult to achieve due to the narrow gap between the γ′-solvus temperature and their melting temperatures within Ni-based superalloys. Given the 50–150 °C advantages in the melting points of Co-rich alloys than those of the Ni-based superalloys, as well as the discovery of L1₂ precipitates in the ternary Co–Al–W alloys, the L1₂-strengthened Co-rich alloys are immediately recognized as the promising candidates to be developed as next-generation high-temperature structural materials. Follow-up studies indicate that they also preserve a mild segregation tendency during solidification and superior particle coarsening resistance as compared with Ni-based superalloys. Promising research directions in the field of Co-rich high-temperature alloys are also discussed herein, including thermodynamic-guided alloy design, grain boundary characteristics, and their correlations with mechanical properties, as well as unique deformation mechanisms and particle shearing configurations.