| Abstract Scope |
Magnesium alloys are promising biodegradable implant materials but suffer from rapid corrosion and uncontrolled hydrogen evolution in physiological environments, necessitating effective surface modification strategies. Plasma electrolytic oxidation (PEO) coatings were developed on an ultra-high-purity Mg–0.45 wt.% Ca alloy using two phosphate-based electrolytes. Their structure and composition were analyzed using advanced electron microscopy and atom probe tomography (APT). Both coatings exhibit a tri-layered architecture: a dense crystalline MgO inner barrier, a porous intermediate MgO/amorphous phosphorus-rich layer, and an outer amorphous phosphorus-rich layer influenced by electrolyte composition. APT reveals nanoscale porosity, Na segregation, and hydrogen-enriched corrosion products. Early in vitro tests in Hank’s solution show uniform dissolution for the ammonia-based system, while the Na-containing system exhibits cracking and delamination due to defect-assisted degradation. These findings demonstrate how electrolyte chemistry governs coating structure, defect distribution, and corrosion behavior, providing guidance for optimizing PEO coatings to improve implant durability. |