Microstructures and mechanical properties of Al-Ti-Zr-Nb-Ta-Mo-V refractory high-entropy alloys with coherent B2 nanoprecipitation

In this work, the microstructural evolution and mechanical properties of new body-centered cubic (BCC)-based Al-Ti-Zr-Nb-Ta-Mo-V refractory high-entropy alloys (RHEAs) with coherent B2 precipitation are investigated. These designed alloy ingots were solid-solutionized at 1573 K for 2 h and then aged at 873 K for 24 h, in which each treatment was followed by water quenching. It was found that there exists phase separation of BCC matrix, Ti/Zr-rich BCC1 and Nb/Ta-rich BCC2 in these alloys. Moreover, ultra-fine spherical B2 nanoparticles with a size of 3~5 nm were dispersed in BCC2 matrix. These B2 nanoparticles could be coarsened up to 25~50 nm after aging and the particle morphology also changes to a cuboidal shape due to a moderate lattice misfit (ε = 0.7~2.0%). Also, Zr₅ Al₃ phase could coexist with the B2 phase, where the difference between them is that the Ti element is enriched in B2 phase, rather than in Zr₅ Al₃. Among them, the solutionized Al₂ Ti₅ Zr₄ Nb_2.5 Ta_2.5 RHEAs exhibit good compressive mechanical property with a high yield strength of 1240 MPa and a large plasticity, which is mainly attributed to the coherent precipitation in the BCC matrix.