Multiple minor elements improve strength-ductility synergy of a high-entropy alloy

Abstract

The developments of multicomponent high-entropy alloys usually put emphasis upon the roles of multiple principal elements in optimizing the various properties. Instead of tuning the principal elements, here we propose to use multiple minor alloying elements to improve performance of HEAs. To this end, the microstructure and mechanical behavior of a newly developed alloy, i.e., Fe35Ni20Co20Cr20Al2.5Ti1.0Cu1.0Si0.5 (at. %), have been investigated. The alloy decorated by the multiple minor alloying elements (i.e., Al, Ti, Cu and Si) exhibits a single face-centered cubic (FCC) γ phase in fully recrystallized state. Compared with the undecorated Fe40Ni20Co20Cr20 (at. %) counterpart with similar grain size, the yield strength of the decorated alloy sample with multiple minor elements is enhanced by ∼19% at a high elongation of ∼74%. Microstructural characterizations indicate that dislocation slip prevails at the early stages of plastic deformation while mechanical twins are observed to occur at the late deformation stage. The local stress field caused by the atomic size mismatch and elastic mismatch originated from the multiple minor elements significantly impedes the movement of dislocations thus improves the strength. Such retarding effect of the multiple minor elements on mobile dislocation further hinders the generation of stacking faults on adjacent atomic planes and thereby increases the FCC-γ phase stability, which also postpones the deformation twinning upon tension. This work demonstrates the practical significance of introducing multiple minor alloying elements with their synergistic effect into HEAs, and the design strategy enlarges the space for compositional design of advanced alloys.