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

Abstract 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 e-D019 nanoprecipitates featuring Widmanstatten patterns and coherent interfaces with the matrix are developed using the lattice misfit design concept. The highly ordered hexagonal e-D019 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 δ-D0a phase instead of η-D024. The superior thermodynamic stability of the δ phase compared with the e phase is confirmed by first-principle calculations. High-density e-D019 precipitates with Widmanstatten patterns contribute to the improved strengthens and friction properties of CoFeNiVTa(Nb) HEAs.