Abstract: Nb_0.5TiZrV_0.5 alloy is one of the lightweight refractory high-entropy alloys (RHEAs) and has a great potential to be structural materials. Here, the microstructural evolution at the grain boundaries (GBs), the tensile properties and the deformation mechanism including dislocation and kink evolution of arc-melting (Nb_0.5TiZrV_0.5)_100-xCe_x RHEAs (at.%, x = 0, 0.005, 0.01, referred to as 0Ce, 0.005Ce and 0.01Ce alloys) at room temperature (RT) were systematically investigated. Ce was found to segregate at GBs and the most pronounced grain refinement effect in the 0.005Ce sample. With the Ce content increased from 0.005 at.% to 0.01 at.%, the Ce concentration at GBs increased from 0.12 at.% to ∼1.17 at.%, subsequently, inducing compositional fluctuation and facilitating transformation of BCC band (V-rich but Zr-poor) to ω-like phase with a non-close-packed hexagonal structure (NCPHS, V- and Zr-rich but Ti-poor) at GBs. The 0.005Ce alloy exhibited the optimized ductility (ε_f∼7.15%) and maintained yield strength of approximately 964 MPa at RT. The better balance of strength-ductility in the 0.005Ce alloy was resulted from synergistic deformation of multiple grains, high fraction (55.6%) of movable edge dislocations and abundant kink bands with the most slip systems. However, deteriorating ductility (ε_f∼2.29%) of the Nb_0.5TiZrV_0.5 alloy with 0.01 at.% Ce addition was mainly attributed to precipitation of the brittle ω-like phase at GBs. These results may provide theoretical and experimental guidance for design of the advanced RHEAs with high specific strength through doping Ce or other rare-earth elements.

Key words: Refractory high entropy alloy, Cerium addition, Microstructure, Tensile behaviors, Deformation