Cr addition-mediated simultaneous achievement of excellent strength and plasticity in non-equiatomic Nb-Ti-Zr-Ta-base refractory high-entropy alloys

Structural materials with broad application prospects often feature comprehensive strength and plasticity synergy. However, there seems to be an inevitable trade-off between material strength and plasticity associated with post-processing technologies. In this work, an as-cast non-equiatomic NbTiZrTa0.25-based refractory high-entropy alloy (RHEA) with excellent specific strength and plasticity synergy was developed via Cr alloying modification. The yield strength of NbTiZrTa0.25Cr0.2 reached 1054 MPa, with a density of only 7.2981 g/cm3 and plasticity above 60 %. Increasing the amount of Cr in the base alloy did not diminish the plasticity until the single BCC phase was transformed to the BCC + Laves phases at a Cr content up to 0.4, whereas a monotonous improvement in strength was observed. The strength improvement was predominantly related to the solid solution strengthening and consecutive fine-grain strengthening. Embrittlement was attributed to the appearance of the brittle Laves phase. The NbTiZrTa0.25Cr0.2 RHEA with an outstanding specific strength and plasticity is a promising material for use in harsh environments and as a model material to develop new high-temperature alloys.