Synthesis of ceramic surface on Zr alloy using plasma electrolytic oxidation in molten salt

Zirconium alloys are known as bioinert materials that are widely applicable in biomedical applications. However, the enhancement of Zr alloys bonding with human tissues is still the focus of the majority of research works. This issue may be achieved by the development of porous structures using various surface treatment methods. Here, a promising approach of plasma electrolytic oxidation (PEO) surface treatment in molten salt is shown. PEO is an electrochemical method to create a highly adhesive surface to bioenvironment. Processing in molten salt electrolyte diminishes impurities on the surface, which usually form in traditional PEO by decomposition of an aqueous electrolyte. ZrO₂ synthesized by PEO processing for various durations was studied in this work. Phase analysis revealed that the t-ZrO₂ to m-ZrO₂ transformation occurred over a longer process. The surface and cross-section morphologies illustrated the appearance of a two-layered oxide coating fabricated by PEO with more pronounced porosity with the duration of the treatment. The obtained surfaces exhibited high biocompatibility, as determined by the wettability test with Hank's balanced salt solution (HBSS). Additionally, the synthesized coatings exhibited fourfold enhancement in microhardness performance and corrosion resistance by one order of magnitude.