Microstructure and mechanical properties of TiNbV0.5Ta0.5Cr (x=0, 0.1, 0.2, 0.5) refractory high-entropy alloys

The TiNbV0.5Ta0.5Crx (x = 0, 0.1, 0.2, 0.5) refractory high-entropy alloys (RHEAs) with an excellent combination of ductility and strength were designed and prepared for high-temperature applications. The yield strength, ultimate tensile strength, and elongation of the TiNbV0.5Ta0.5Cr0.1 alloy were 878 MPa, 928 MPa, and 21.6% respectively. Important issues of microstructure evolution, precipitation process, and their impact on mechanical properties were concerned. Then, the effect of Cr content on the mechanical properties of TiNbV0.5Ta0.5Crx alloys was evaluated through a quantitative analysis of the strengthening mechanism, which elucidated the trade-off relationship between solid solution strengthening and precipitation strengthening in RHEA. The microstructure evolution of the TiNbV0.5Ta0.5Crx alloys involved the formation and interconversion of titanium allotropes (α-Ti and β-Ti) and the precipitation of the Laves phase. Significant embrittlement was induced by the preferential precipitation of α-Ti on the grain boundary. The TiNbV0.5Ta0.5Crx alloys exhibited an incubation period for Laves phase precipitation, which was related to the Cr content in the alloy. The Laves phase preferentially nucleated next to α-Ti due to the redistribution of elements during the α-Ti precipitation process. The precipitation of the Laves phase played an important role in enhancing the strength of the TiNbV0.5Ta0.5Crx alloys.