High-temperature structural and mechanical stability of refractory high-entropy alloy Nb40Ti25Al15V10Ta5Hf3W2

Abstract

Refractory high-entropy alloys (RHEAs) with superior mechanical properties have been considered as a potential next-generation candidate for high-temperature structural materials. However, the structural stability of RHEAs at high temperatures is still noncommittal so far. Especially, the Al containing RHEAs with coherent BCC/B2 microstructure usually form intermetallic phases following short/long term aging at elevated temperatures, which deteriorate the mechanical performance. In this work, we systematically determine the microstructural evolution, including intergranular precipitates, BCC/B2 morphology, and corresponding mechanical properties changes of the Nb40Ti25Al15V10Ta5Hf3W2 RHEA from 923 K to 1123 K. The density of antiphase domain boundaries (APBs) in the RHEA after aging at 923 K is significantly higher than at 1023 K and 1123 K. Only a low volume fraction of tetragonal (Nb, Hf)2Al phase precipitates along grain boundaries after aging at 1123 K. However, the microhardness and yield strengths of the RHEA after aging at 923 K - 1123 K are close to those of the as-cast RHEA, which proves that the APBs and low-density (Nb, Hf)2Al precipitates have a negligible effect on the mechanical performance of the RHEA. Therefore, the Nb40Ti25Al15V10Ta5Hf3W2 RHEA exhibits superior structural stability from 923 K to 1123 K, which also imparts the mechanical stability. This work guides towards tailoring the composition and microstructure of RHEAs for even better high-temperature mechanical performance.