The present work investigated the formation of coherent body-centered-cubic (BCC)/B2 microstructure in Al–Ti–Zr–Nb–Ta–Cr/Mo refractory high-entropy alloy system, in which three alloys with the composition of Al₂Ti₆Zr₂Nb₃Ta₂(Cr/Mo)₁ were designed. These as-cast alloy ingots were homogenized at 1573 K for 2 h and then aged at different temperatures for 24 h. It is found that the BCC/B2 coherent microstructure with cuboidal BCC nanoprecipitates into the B2 matrix would be formed in 873 K-aged Al₂Ti₆Zr₂Nb₃Ta₂Cr_0.5Mo_0.5 alloy with half Cr and half Mo, which is ascribed to a moderate lattice misfit (ε = 0.94%) between BCC and B2 phases. It is due to the special coherent microstructure that results in a prominent mechanical property with the highest compressive yield strength (σ_YS = 1314 MPa) and good plasticity among these alloys, while coarse Cr₂Ti and Zr₅Al₃ particles are existed in 873 K-aged alloy with Cr₁. After 1073 K aging, all these alloys with Cr₁, Cr_0.5Mo_0.5 and Mo₁ consist of BCC, B2 and Zr₅Al₃, in which BCC/B2 coherent microstructure is destabilized. The strengthening mechanism of BCC/B2 coherent microstructure in 873 K-aged alloy with Cr_0.5Mo_0.5 was also discussed.

Graphical abstract