Ultrastrong and ductile medium-entropy alloys via hierarchical ordering
Lei Gu, Yonghao Zhao, Yong Li, Rui Hou, Fei Liang, Ruisheng Zhang, Yinxing Wu, Yong Fan, Ningning Liang, Bing Zhou, Yang Chen, Gang Sha, Guang Chen, Yandong Wang, Xiang Chen
Abstract
Long-range ordered phases in most high-entropy and medium-entropy alloys (HEAs/MEAs) exhibit poor ductility, stemming from their brittle nature of complex crystal structure with specific bonding state. Here, we propose a design strategy to severalfold strengthen a single-phase face-centered cubic (fcc) Ni 2 CoFeV MEA by introducing trigonal κ and cubic L1 2 intermetallic phases via hierarchical ordering. The tri-phase MEA has an ultrahigh tensile strength exceeding 1.6 GPa and an outstanding ductility of 30% at room temperature, which surpasses the strength-ductility synergy of most reported HEAs/MEAs. The simultaneous activation of unusual dislocation multiple slip and stacking faults (SFs) in the κ phase, along with nano-SF networks, Lomer-Cottrell locks, and high-density dislocations in the coupled L1 2 and fcc phases, contributes to enhanced strain hardening and excellent ductility. This work offers a promising prototype to design super-strong and ductile structural materials by harnessing the hierarchical ordered phases.