Solid solution softening or hardening induced by minor substitutional additions in a Hf20Nb31Ta31Ti18 refractory high entropy alloy

The effect of minor additions substitutional elements such as Al, Cu, Mn, and Fe on the room-temperature (RT) elevated-temperature hardness a single bcc phase Hf20Nb31Ta31Ti18 refractory high entropy alloy is studied here. Interestingly, 2.5 at. % nominal addition hardened base in temperature range from RT to 800 °C, while same content Mn softened 1000 °C. Regardless solid solution hardening or softening, variation with essentially showed three-stage pattern for all alloys here: temperature-dependent decrease below 300 °C/400 followed by temperature-independent plateau between 300/400 finally at temperatures higher than mechanism softening bcc-structured discussed, together their dependence.