Nitrogen induced heterogeneous structures overcome strength-ductility trade-off in an additively manufactured high-entropy alloy

Abstract

The strength-ductility trade-off has been the long-standing barrier in the pursuit of high-performance structural materials. Here, by exploiting the merit of interstitial nitrogen, a novel additive manufacture-based approach is proposed to process the hierarchically heterogeneous structured FeCoNiCrN high-entropy alloy (HEA). Compared to the undoped alloy, the 1.8 at. % nitrogen-doped HEA shows a simultaneous increase in both strength and ductility, thereby producing exceptional combination of tensile strength (853 MPa) and elongation (34 %) that outperforms many other single phase FCC HEAs. The unusual inverse strength-ductility relationship is ascribed to the strong strengthening effect and progressive strain hardening arising from the hierarchically heterogeneous structure, the latter of which is highly beneficial to the ductility. The present approach creates heterogeneous structure avoiding surface-mechanical or thermo-mechanical treatments, and thus, enables to produce readily available components with complex geometry.