Effect of Ca/P ratio on the structural and corrosion properties of biomimetic CaP coatings on ZK60 magnesium alloy

- Ca-P coating was successfully coated by a simple hydrothermal deposition method.
- With increasing Ca/P ratio, the obtained Ca-P coatings show a phase transformation from whitlokite to monetite.
- The Magnesium alloy with Ca-P coating deposited at Ca/P ratio of 1.67 has the best corrosion resistance.

Magnesium and its alloys have attracted much attention as metallic biodegradable implants for their excellent biocompatibility and mechanical properties. However, magnesium has a poor corrosion resistance, causing its rapid degrading in vivo via an electrochemical reaction, which has become a major obstacle to their applications in implants. In this work, CaP coating was successfully coated on the ZK60 magnesium alloys by a simple hydrothermal deposition method. The mechanisms of the hydrothermal reactions of CaP coatings on Mg substrate are described in details. The effect of Ca/P ratio in the hydrothermal solution on the phase composition, microstructure and biodegradation properties of CaP coatings on ZK60 alloys was investigated by varying the Ca/P ratio from 0.83 to 4.18. The morphology of the CaP coating changed significantly with the Ca/P ratio. Biodegradation behavior of the CaP coating magnesium was characterized by anodic polarization and immersion tests in a simulated body fluid. It is revealed that the corrosion resistance of ZK60 magnesium alloy was greatly improved with the biomimetic CaP coatings, and the ZK60 alloy with CaP coating deposited at Ca/P ratio of 1.67 has the best corrosion resistance, which indicates that the CaP coatings are promising for improving the biodegradation properties of Mg-based orthopedic implants and devices.