Unique precipitations in a novel refractory Nb-Mo-Ti-Co high-entropy superalloy

Herein, a novel refractory Nb₃₀Mo₃₀Ti₂₀Co₂₀ (at. %) high-entropy superalloy (RHESA) is introduced. Annealing at 1200 °C led to the precipitation of a semi-coherent individual (Co, Ti)-rich B2, (Ti, O)-rich fcc (Ti-rich oxides), and hierarchical B2 + fcc nanoparticles in the (Nb, Mo)-rich RHESA bcc phase. B2 + fcc dispersoids were dominant, and they nucleated heterogeneously because of the coherency ensured by the Baker–Nutting orientation relationship. The emergence of multi-type nanoprecipitates doubled the room-temperature compressive ductility without sacrificing strength. Our study can solve a chief problem of current RHESAs—the low stability of B2 dispersoids at T > 700 °C.

Multi-type B2, fcc, and B2 + fcc nanoprecipitates balancing mechanical properties of the refractory Nb₃₀Mo₃₀Ti₂₀Co₂₀ high-entropy superalloy (RHESA) endow new prospects for application of RHESAs at T ≥ 1200 °C.