Effect of sub-solvus treatment on discontinuous precipitation behavior and mechanical properties of AlCrFeNiV multi-principal element alloy

Abstract

The discontinuous precipitation (DP) behavior of AlCrFeNiV multi-principal element alloys (MPEAs) based on initial face-centered-cubic (FCC) single-phase structure is investigated in this work. The investigation focuses on the impact of a novel sub-solvus (SS) treatment, which accelerates the DP transformation kinetics by refining the microstructure, as compared to the conventional total-solution (TS) treatment. This acceleration is attributed to an increase in nucleation sites or localized changes in chemical composition. The presence of NiAl phases with a B2 structure, which precipitate along prior grain boundaries, is believed to play a dominant role in grain refinement. Additionally, highly dispersed L12 nano-precipitates are observed within the FCC matrix in both TS- and SS-treated samples. Building upon the strengthening effect of L12 nanoprecipitates, further optimization strategies are explored through variations in isothermal aging treatments. This leads to the preparation of DP structures with various degrees and morphologies, consisting of BCC phases and a coherent FCC/L12 microstructure. The additional HDI hardening stemming from the resulting DP/non-DP heterogeneous structure and the spheroidization of the ultrafine DP lamellar structure allowed the alloy to exhibit excellent mechanical properties, the latter of which yielded an interesting combination of strength (1907 MPa tensile strength, 1694 MPa yield strength) and ductility (10.1% elongation). These findings highlight the effect of the prior grain refinement on the DP transition kinetics, BCC lamellae stability, and the overall mechanical performance of AlCrFeNiV multi-principal element alloys (MPEAs).