Novel high-entropy alloys with high-density ε-D019 and abnormal phase transformation

Precipitation strengthening is considered to be one of the most effective ways to improve engineering structural materials. However, introducing high-density nanoprecipitates in alloys is a big challenge. In this study, novel CoFeNiVTa(Nb) high-entropy alloys (HEAs) with high-density epsilon-D0(19) nanoprecipitates featuring Widmanstatten patterns and coherent interfaces with the matrix are developed using the lattice misfit design concept. The highly ordered hexagonal epsilon-D0(19) phase is identified as (Co, Ni, Fe)(3)(V, Nb, Ta, Fe) by atomic resolution energy dispersive spectrometry and this phase is metastable and can be abnormally transformed into delta-D0(a) phase instead of eta-D0(24). The superior thermodynamic stability of the delta phase compared with the epsilon phase is confirmed by first-principle calculations. High-density epsilon-D0(19) precipitates with Widmanstatten patterns contribute to the improved strengthens and friction properties of CoFeNiVTa(Nb) HEAs. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

Precipitation strengthening is an effective method to enhance engineering structural materials, with high-density nanoprecipitates in alloys being a significant challenge. This study developed novel CoFeNiVTa(Nb) high-entropy alloys with high-density epsilon-D0(19) nanoprecipitates featuring Widmanstatten patterns. The superior thermodynamic stability of delta phase compared to epsilon phase was confirmed, contributing to improved strengthens and friction properties of the alloys.