Good strength-ductility synergy achieved in a Fe62Ni16Co9Mn9Ti3Si1 Fe-high-entropy alloy with heterogeneous structures

Abstract

Developing metal structural materials with a good combination of strength-ductility is of great significance for the rapid development of the aerospace industry and the energy industry. High-entropy alloys (HEAs) have attracted widespread attention due to their excellent mechanical properties, especially the excellent ductility and toughness of face-centered cubic (FCC) high-entropy alloys. However, similar to traditional alloys, there is a trade-off between strength and ductility in HEAs. In this paper, we report the successful preparation of Fe-HEA (Fe62Ni16Co9Mn9Ti3Si1 (atomic percentage, %)) with high strength-ductility synergy at room temperature by cryo-rolling and annealing at 600 °C for 10 minutes (CR600), which increases the yield strength by 59% compared to room temperature rolling (RR600), while the uniform elongation decreases by only 20%. The ultra-high yield strength and the not significant reduction in uniform elongation are mainly attributed to the formation of high-density dislocations, dual-phase bimodal ultra-fine grain heterostructures, (NiMn)3-xTix and (Fe, Ni)2SiTi composite nanoprecipitates, precipitation-induced chemical composition heterogeneity, and BCC→HCP phase transformation during tensile deformation during CR and subsequent annealing at a reduced temperature (600 °C). In addition, by increasing the annealing temperature of the alloy after CR to 800 °C, its uniform elongation can be increased to 53%, which is mainly due to the excellent strain hardening ability induced by changes in heterogeneous structures, nanoprecipitates, and martensitic phase transformation. Compared with other similar alloys, our CR alloy exhibits higher strength-ductility synergy. The results of this study provide a new perspective for developing HEAs with higher strength-ductility synergy.