Mechanically propelled ion exchange regulates metal/bioceramic interface characteristics to improve the corrosion resistance of Mg composite for orthopedic applications

The orthopedic application of Mg alloys suffers from excessive degradation. In this study, hydroxyapatite (HAP) nanoparticles are doped with MgO by high-energy ball milling, and then the obtained powders are compounded with WE43 powders and prepared into implants by laser powder bed fusion. During milling process, Mg2+ ions on MgO exchange some Ca2+ in HAP by mechanical collision and friction, which forms covalent bonds on the MgO/HAP interface. Subsequently, TEM observation showed that MgO on HAP forms semi-coherent interfaces with α-Mg, contributing to good bonding on the Mg/MgO interface. In this manner, strong bonding interfaces between ceramic particles and α-Mg were established, thereby preventing the agglomeration of nanoparticles. The well-dispersed ceramic particles provided more nucleation sites for apatite deposition, which benefits the formation of the passivation layer and thereby improves corrosion resistance. As a consequence, the composite exhibited a low corrosion density (20.1 ± 1.3 μA/cm2), high corrosion resistance (752.8 ± 19.7 Ω cm2), and low carrier concentration (1.28 ± 0.01 cm−3), indicating the formation of a more protective passivation layer. These findings suggested that the mHAP incorporated Mg composite may be a potential candidate for orthopedic implant.