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

Abstract

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.

Keywords

• refractory high-entropy superalloys
• hierarchical precipitates
• b2 phase
• baker-nutting orientation relationship
• mechanical properties