High-entropy and medium-entropy alloys are attracting keen attention as new classes of alloys in materials science. These alloys exhibit an excellent balance of strength and toughness, in addition to high corrosion resistance. The electrodeposition of such alloys has remained difficult because the overpotentials for electrodeposition vary depending on the elements which constitute the target multicomponent alloy. Furthermore, anomalous codeposition is sometimes unavoidable when the alloy includes iron group elements; in such a case, the control of composition in electrodeposition becomes nearly impossible. We have reported that these bottlenecks are overcome using water-in-oil emulsions as electrodeposition baths, where water droplets encapsulate metal ions to control the alloy composition by tuning the metal ion concentrations within the droplet. This method, by contrast, exhibited a low deposition rate because of the discontinuous supply of droplets to the electrode surface. This paper presents several strategies to increase the deposition rate: The findings clarified that increasing the metal ion concentrations within water droplets is effective, but a threshold concentration exists. The addition of multi-walled carbon nanotubes further promoted electrodeposition because they function as nucleation sites.
Improving the corrosion resistance of industrial chromium plating films necessitates stabilization of the chromium passive film and processes such as closing surface cracks. For this study, as a step toward finding a technique to improve the corrosion resistance of chromium plating, we investigated monitoring the immersion potential in hydrochloric acid solution as a method to evaluate the breakdown of the passive film of chrome plating films. The active dissolution time（tEF）of chromium plating films depends on the hydrochloric acid concentration and the measurement temperature. They likely behaved in a first-order chemical reaction manner. This method allowed the polishing and heat treatment of the chromium plating films to affect the stability of the passive films to be assessed. This simple and quick method is useful to evaluate the improvement of the corrosion resistance of industrial chromium plating products.