Corrosion behavior and mechanical performance of Mg-Hydroxyapatite nanocomposites for biodegradable implants: The role of nanoparticle concentration and dispersion

This study investigates the influence of hydroxyapatite nanoparticle (HAP np ) content (1–3 wt.%) on the microstructural, mechanical, and bio-corrosion behavior of magnesium (Mg)-based nanocomposites fabricated via powder metallurgy for biodegradable implant applications. Quantitative scanning electron microscopy analysis revealed increasing nanoparticle clustering with higher reinforcement content, as the degree of agglomeration rose from 18% in Mg-2HAP to 45.1% in Mg-3HAP. Brinell hardness improved from 46.29 ± 1.29 HB (pure Mg) to 51.83 ± 1.90 HB (Mg-3HAP), with Mg-2HAP showing the optimal balance of hardness (47.82 ± 1.73 HB) and microstructural uniformity. Electrochemical impedance spectroscopy exhibited the highest charge transfer resistance (Rct) for Mg-2HAP (283.77 Ω), indicating superior corrosion resistance. Tafel polarization further confirmed this trend, with Mg-2HAP displaying the lowest corrosion current density (263.16 ± 128.65 µA·cm −2 ) and corrosion rate (CR) (5.40 ± 2.05 mm·year −1 ), a ∼53% reduction compared to pure Mg (11.46 ± 0.55 mm·year −1 ). In contrast, Mg-3HAP composite exhibited the worst corrosion performance (Rct of 231.39 Ω; CR of 15.05 ± 2.12 mm·year −1 ), due to increased porosity and HAP np agglomeration. Energy-dispersive spectroscopy analysis confirmed enhanced bioactivity in HAP-reinforced samples, with higher Ca and P deposition than pure Mg. These results show that carefully controlling HAP np content and dispersion is essential for balancing the mechanical and degradation properties of future Mg-based implants.