Excellent room-temperature tensile ductility in as-cast Ti37V15Nb22Hf23W3 refractory high entropy alloys

An as-cast Ti37V15Nb22Hf23W3 refractory high entropy alloy (RHEA) with outstanding tensile properties designed by the natural mixing method and solid solution strengthening theoretical model is reported. The current as-cast RHEA presents a random solid solution with a body-centered cubic (BCC) crystal structure and inherits the natural-mixing characteristics. Interestingly, When compared to the W-free Ti38V15Nb23Hf24 RHEA, minor addition of 3 at. % W atoms increases the yield strength by 26.6% to 980(-19)(+17) MPa while preserving 19.8(-0.5)(+0.5) % tensile ductility at room temperature. Toward a better understanding of high yield strength, a solid solution model is proposed to explain strong strengthening, and the experimental value is in good agreement with the theoretical one, indicating the significant solid solution strengthening effect in strengthening the RHEAs. The widespread planar dislocation glide favors the production of complicated dislocation structures (e.g., jogs, dipoles, and loops) as well as dense dislocation networks, which can further obstruct dislocation motion meanwhile effectively relieving stress concentration. The dislocation tangles, loops, dipoles, and jogs together with their interactions postpone the local deformation, results in the excellent ductility.