Synergistic Effects of Sr-CaP and ZrO2 Coatings on the Corrosion Behavior of Magnesium Alloy for Implant Applications

The development of biodegradable composite materials is crucial for advancing temporary medical implants. Ultrafine-grained (UFG) magnesium alloys, despite their excellent mechanical properties and biocompatibility, suffer from rapid corrosion in physiological environments. To improve this issue, we applied surface plasma modifications by first depositing strontium-doped calcium phosphate (Sr-CaP) coatings using Micro-arc oxidation method to improve osteointegration and provide initial corrosion protection followed by a zirconium dioxide (ZrO₂) top layer deposited using an RF magnetron sputtering, which further enhanced the corrosion resistance and mechanical stability of the system. The dual-layered Sr-CaP/ZrO₂ system showed a significant improvement in corrosion resistance, with a reduction in corrosion current density by several orders of magnitude and polarization resistance reaching up to 2.3 × 10⁷ Ohm cm². Optimized deposition parameters ensured the formation of a uniform ZrO₂ coating with a poorly crystalline monoclinic phase and high residual stresses, contributing to the enhanced protective properties, however still providing biodegradation possibility. This multilayered coating system provides a promising surface modification strategy for controlling the degradation rate of UFG magnesium alloys, making them suitable for use in temporary biomedical implants such as orthopedic devices.