Microstructural, mechanical, and wear behavior of hydroxyapatite-based composite coatings on magnesium alloy

Biodegradable magnesium alloys are promising materials for temporary orthopedic implants, but their clinical performance is often compromised by poor tribological behavior. During implant insertion and post-operative micromotion, friction and fretting wear can generate debris and accelerate local material degradation, leading to premature mechanical failure. In this study, hydroxyapatite (HAp) and a ternary HAp–Al ₂ O ₃ –TiO ₂ composite coating were deposited on Mg–1 wt% Ca alloy via electrophoretic deposition (EPD) and systematically compared to elucidate microstructure–mechanical–tribological relationships. SEM revealed a porous morphology for HAp, whereas the composite coating exhibited a denser and more uniform structure; EDS and XRD confirmed successful incorporation of Al ₂ O ₃ and TiO ₂ into the HAp matrix. The composite coating significantly improved hardness, Young's modulus, and adhesion strength (0.39 GPa, 10.07 GPa, and 9.49 MPa) compared with HAp alone (0.23 GPa, 7.48 GPa, and 7.48 MPa). Under identical fretting conditions, the composite achieved a lower specific wear rate (1.52 × 10 ⁻³ mm ³ /N·m) than HAp (1.74 × 10 ⁻³ mm ³ /N·m). The novelty of this work lies in demonstrating a tribology-driven composite coating strategy for magnesium-based implants, moving beyond corrosion-focused surface modifications and directly addressing wear-related degradation relevant to in vivo mechanical loading.