Influence of current density on the microstructural, mechanical, and electrochemical properties of hydroxyapatite coatings fabricated by micro-arc oxidation

Hydroxyapatite (HA) coatings were fabricated on Ti6Al4V alloy by micro-arc oxidation (MAO) to enhance implant performance. The influence of current density on the structural, mechanical, and electrochemical properties of the coatings was systematically investigated. Surface morphology, topography, phase constituents, and elemental composition were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDS), while corrosion behavior was evaluated using electrochemical impedance spectroscopy (EIS) in simulated body fluid (SBF). Mechanical properties were determined by nanoindentation testing. Quantitative microstructural analysis revealed that increasing the current density from 100 to 300 mA/cm 2 resulted in a significant coarsening of the surface structure, with the average pore size increasing from 1.92 μm to 5.40 μm, surface roughness ( ) rising from 0.11 μm to 0.31 μm, and the total surface porosity rising from 9.45 % to 17.25 %. Additionally, the Ca/P ratio slightly increased (1.61–1.72), reaching values close to the stoichiometric ratio of hydroxyapatite (1.67), with XRD confirming the in-situ synthesis of crystalline HA. Coatings formed at lower current density exhibited superior corrosion resistance, with the highest polarization resistance of 58.46 kΩ·cm 2 . Conversely, coatings produced at higher current densities demonstrated improved mechanical performance, with hardness increasing from 1.12 to 1.56 GPa and elastic modulus from 51 to 73 GPa. These findings confirm that current density is a decisive factor in controlling the balance between corrosion protection and mechanical durability of MAO-derived HA coatings, providing valuable guidance for optimizing bioactive coatings for orthopedic and dental implants. • HA coatings on Ti6Al4V were produced by MAO for implant applications. • Current density, controlled coating porosity, thickness, and microstructure. • Ca/P ratios near stoichiometric HA ensured good bioactivity for implants. • Corrosion resistance was highest at low current density in SBF solution. • Higher current density improved hardness, enhancing implant durability.