Abstract: Refractory high-entropy alloys have great potential to be utilized as high-temperature materials, and the repeatability and reproducibility of their mechanical properties are critical for practical applications. In this work, nevertheless, we found that the mechanical properties of the TiZrHfNb HEA greatly varied with the content of impurities in the samples even using high-purity raw materials. Specifically, the oxygen impurity is mainly responsible for the increment of the yield stress due to the strong interstitial hardening effect, whilst the ductility deterioration closely associates with the content of metalloid elements B, C, and Si. Our analysis reveals that the metalloid elements not only tend to segregate at grain boundaries but also enhance the aggregation of Zr and Ti. Such co-segregation induced the formation of strong (Zr, Ti)-metalloid bonds, resulting in grain boundary embrittlement and brittle fracture. Our current work demonstrates that the impurity contents in refractory HEAs need to be strictly controlled during production in order to improve their stability of mechanical performance.

Key words: High-entropy alloy, Impurities, Grain boundary embrittlement, Co-segregation effect