Multi-phase FCC-based composite eutectic high entropy alloy with multi-scale microstructure

Multi-phase multi-scale composite eutectic alloys containing micrometer-scale dendrites and nano structures provide an opportunity for the development of ultrahigh strength materials. Eutectic high entropy alloys (EHEAs) facilitate the design of eutectic alloys with such structures in the as-cast state due to the hysteretic diffusion effect characteristic of high entropy alloys. Nevertheless, the prevailing design approach for eutectic high-entropy alloys predominantly emphasizes biphase eutectics, with limited attention directed towards methods for designing multiphase eutectic structures. In this work, we propose a pseudo-ternary based idea to design and prepare multiphase multiscale FCC-based triple-phase eutectic high-entropy alloys, i.e., CoCrFeNi–NiAl-X. Using this strategy, a series of triple-phase EHEAs consisting of face-centered cubic (FCC), ordered body-centered cubic (B2), and Laves phase with topologically-close-packed structure (TCP) were successfully prepared by arc melting, like CoCrFeNi–NiAl–Nb. The four designed FCC-based multi-phase multi-scale EHEAs can be categorized into two main groups: 1) primary phase FCC and biphase or triple-phase eutectic; and 2) primary phase FCC, biphase eutectic and triple-phase eutectic. The designed FCC-based multi-phase multi-scale EHEAs exhibit promising mechanical properties. The design idea is not only applicable to the current work, but also provides a new strategy for the later design of other multi-phase multi-scale composite EHEAs, like CoCrFeNi–NiAl–Ta.