Enhanced corrosion resistance and bonding strength of Mg substituted β-tricalcium phosphate/Mg(OH)₂ composite coating on magnesium alloys via one-step hydrothermal method.

Abstract

To overcome the defect of high degradation rate of magnesium (Mg), bioactive coatings with compact structure, sufficient bonding strength and enhanced corrosion resistance are essential for Mg-based biodegradable implants. In this study, a dense Mg-substituted β-tricalcium phosphate and magnesium hydroxide (β-TCMP/Mg(OH)₂) composite coating was prepared on AZ31 alloy via one-step hydrothermal method. The influences of hydrothermal temperature on its composition, microstructure of the surface and interface, bonding strength and corrosion behavior were evaluated. The results showed that the compact composite coating synthesized at 140 °C not only possessed a crack-free bilayered structure with an adequate bonding strength (more than 20.88 ± 1.60 MPa), but also got an extreme high impedance (1197.003 ± 152.817 kΩ cm²) so that significantly enhanced the corrosion resistance and inhibited the formation of pitting corrosion. Furthermore, the in vitro immersion test suggested that the composite coating slower the initial degradation rate of Mg alloys and enhanced its surface bioactivity to some extent.