Achieving excellent elevated-temperature mechanical properties in dual-phase high-entropy alloys via nanoscale co-precipitation and heterostructure engineering

Abstract

Eutectic high-entropy alloys (EHEAs) have favorable mechanical properties at room temperature but limited strength at elevated temperatures. Here we report a novel approach to remarkably enhance both room- and elevated-temperature mechanical properties of EHEAs via nanoscale co-precipitation and heterostructure engineering. We found that the addition of Nb to an Al–Co–Cr–Fe–Ni EHEA not only triggers the precipitation of L12 nanoprecipitates in the FCC phase but also induces the co-precipitation of α' and Laves nanoprecipitates in the B2 phase, resulting in the formation of a hierarchical heterostructure. The precipitation strengthening from the L12, α', and Laves nanoprecipitates and the hetero-deformation induced strengthening elevate the yield strength to 1076 MPa at room temperature and 905 MPa at 700 °C while maintaining a high ductility of 10%–50% in this temperature range. First-principles calculations were used to evaluate the intrinsic energetics of the multicomponent FCC and B2 phases, and the results reveal that both phases can accommodate plastic deformation via a dislocation slip mechanism. The dislocation interactions in the two phases and the hetero-deformation induced strengthening contribute to the large strain hardening of the alloy at room temperature. At 700 °C, the increased atomic mobility facilitates the movement of dislocations in the deformable B2 and FCC phases, and the deformation also induces grain boundary sliding and dynamic recrystallization, which together substantially enhance the alloy ductility at elevated temperatures. The strategy of nanoscale co-precipitation and heterostructure engineering can be applied to other materials for achieving excellent mechanical properties.