Effect of Zr content on microstructure and mechanical properties of MoNbTaTiZr_x refractory high-entropy alloy

Abstract

The purpose of this paper is to explore how Zr content affects the crystal structure, micro-morphology, and mechanical properties of (MoNbTaTi) 100-xZrx alloys (x = 5,15,25). The results reveal that with the varying Zr contents, the alloy changes from a single-phase solid solution structure of Zr5 to a solid solution structure of Zr15 and Zr25 with a double BCC phase. Higher Zr levels lead to more pronounced elemental segregation, particularly, which makes Zr element enriched in the interdendritic region, and with the increase of segregation degree, the second phase separates between dendrites. In other words, Zr and Ti elements are densely distributed in the BCC2 phase. With the formation of the BCC2 phase, the mechanical properties of the alloy also changed obviously. Notably, as the Zr content rises, the alloy’s hardness and strength improve, while its ductility initially decreases before subsequently increasing. The Zr15 alloy was in a transition period of a two-phase structure, and the two-phase structure was not stable at this time, which led to a decrease in the plasticity of the alloy. The yield strength of Zr25 alloy is 1595 Mpa, the Vickers hardness is 542 HV, and the compressive fracture strain is 29%, showing the best comprehensive properties.