Fabrication of Copper Microparticles by Copper Deposition and Dissolution in Copper Sulfate Bath for Micropored PVD Hard Coating

In an earlier study, PVD hard coatings with micropores formed by polymer microparticles were confirmed to have superior tribological properties. However, the polymer microparticles that were used were too expensive to put the process to practical use. Therefore, in this work, fabrication of copper microparticles on Ni-plated SKD11 substrate by copper deposition and dissolution in acid copper sulfate bath was investigated for use instead of polymer microparticles. The number of copper microparticles by nucleation on the Ni plated substrate by square-wave current for 1 s occurred only at the current density of a wave higher than 0.1 A/dm2. Their number increased with current density from ca. 105/mm2 to more than 108/mm2. However, by continuing electrolysis at lower current density of ca. −0.05 A/dm2 after the square-wave current pulse, only copper microparticles, as many as 104/mm2, grew exclusively. The number of them were constant independent of the initial current density. Furthermore, by application of anodic current, non-growth microparticles dissolved to disappear and the growing particles became globular. Using the Ni-plated SKD11 substrate on which Cu microparticles were formed using this method, a CrN hard coating with micropores was achieved by cathodic vacuum arc ion plating.