Significantly ameliorating room-temperature brittleness of refractory high-entropy alloys via in situ heterogeneous structure

Although refractory high-entropy alloys (RHEAs) possess excellent softening resistance and thermal stability at high temperatures, their practical application is often limited due to room temperature (RT) brittleness. In this work, we successfully achieved RT plasticization in a brittle (TaMoTi)92Al8 RHEA via in situ forming heterogeneous structure (HS) with the doping of Zr. Different from the mainstream design concept of “soft solid solution matrices with hard intermetallic phases” proposed in the literature, the newly developed TaMoZrTiAl RHEA is featured by a hard disordered BCC phase embedded into a soft intermetallic B2 matrix. Such an HS leads to the remarkable strength–plasticity synergy in this alloy at RT, showing a large plasticity of > 20%, associated with a high strength of > 2380 MPa. It was found that solid solution strengthening and heterodeformation-induced strengthening caused by dislocation pile-ups at phase boundaries are responsible for the enhancement in the yield strength, while deformation-induced strain partition and the frequent operation of dislocation cross-slip substantially improve the work hardening capacity of alloy, thus enabling the high strength and good RT plasticity. In short, the current work not only reveals the micromechanisms of the influence of heterogeneous dual-phase structure on the RT mechanical behaviour in RHEAs but also provides a useful strategy for plasticizing brittle RHEAs.