Electrodeposited NiFeCo-(Mo,W) high-entropy alloys with nanocrystalline and amorphous structures

High-entropy alloy (HEA) design is an emerging methodology that stabilizes nanocrystalline materials, which themselves are highly sought after due to their high strength and hardness resulting from grain boundary hardening. In the past decade, studies have examined the synthesis and performance of such materials made primarily from vapour- and solid-state processing methods, which offer little flexibility in scalability. By contrast, electrodeposition is a relatively low-cost, highly scalable fabrication route for nanocrystalline materials that can be applied to almost any substrate shape or material, which also has industrial-scale infrastructure already in place. Here, we report the first comprehensive study on the synthesis and characterization of electrodeposited HEAs made from aqueous electrolytes, building on the groundwork of past work on electrodeposited medium-entropy alloys. High-quality alloys of NiFeCo-W, NiFeCo-Mo, and NiFeCo-MoW were deposited onto Cu substrates at thicknesses in the range 31–44 µm. W-containing alloys took on banded structures with underlaying growth-oriented features that are postulated to be nanoglass domains. NiFeCo-Mo exhibited the highest hardness-to-density ratio among these alloys, owing to its laminated nanocrystalline-amorphous structure. We also revealed an inverse Hall-Petch relationship in NiFeCo-W, as well as a linear dependence of hardness on Ni content in the alloys. Our study continues to build a framework for electrodeposition of HEAs, paving the way for developing new high-strength, thermally stable, and scalable nanostructured materials.