Electrochemical conversion of oxide spinels into high-entropy alloy

Single-phase equiatomic CoCrFeNi high-entropy alloy has been synthesised by direct electrochemical reduction from oxide precursors according to the concept of the FFC-Cambridge process. Metal oxide mixtures were heat treated in air to provide a blend of spinels, which was then employed as the cathode in the electro-deoxidation process. Melts of eutectic CaCl2-NaCl and pure CaCl2 were used as the electrolytes. Varying the experimental conditions in terms of processing temperature and time yielded CoCrFeNi alloys of diverse morphologies, ranging from fine dispersed powders to solid three-dimensional objects, as they are of relevance for additive manufacturing and near-net-shape fabrication. Notably, all solid alloy samples exhibited a higher hardness than calculated by the rule of mixture, despite the presence of significant residual porosity. The results highlight the versatility of the FFC-Cambridge process for alloy preparation and suggest the possibility of economically viable large-scale manufacture of steel-type high-entropy alloys. [Display omitted] •Low-temperature synthesis of single-phase CoCrFeNi high-entropy alloy at 923–1173 K.•Direct conversion of metal oxide mixture into CoCrFeNi alloy via electrochemical deoxidation.•Preparation of both CoCrFeNi crystalline fine powders and three-dimensional solid objects.•Control of CoCrFeNi alloy morphology via processing temperature and other process parameters.•Evaluation of effect of process parameters on microhardness of CoCrFeNi alloy.