Introduction and Objectives: The widespread application of NiTi alloys in biomedical implants is constrained by the release of nickel ions, which may provoke allergic responses and carcinogenic risks. Employing biocompatible hydroxyapatite composite coatings offers a promising approach to suppress nickel ion leaching and improve the electrochemical performance of NiTi alloys. This study focuses on assessing how varying the concentration of a secondary phase within the composite affects the coating’s composition, microstructure, and the overall electrochemical behavior of the substrate.
Materials and Methods: Hydroxyapatite–tantalum oxide composite coatings were produced on NiTi substrates via the electrophoretic deposition method. Tantalum oxide was introduced into the hydroxyapatite nanoparticle suspension at concentrations of 10, 15, and 20 wt.%. All coated samples were sintered at 800 °C for one hour under vacuum conditions.
Results: Experimental findings, based on nickel ion release measurements, potentiodynamic polarization, and electrochemical impedance spectroscopy, clearly demonstrate that increasing the content of the secondary phase within the composite significantly enhances the corrosion resistance of the underlying NiTi substrate. The positive effect of the secondary phase on the adhesion strength of hydroxyapatite coating to NiTi was assessed using a tensile test.
Conclusion: Engineering composite coatings with dense structural characteristics, designed to restrict the ingress of environmental corrosive species and to block nickel ion diffusion, presents a robust strategy for the safe and durable utilization of NiTi alloys in biomedical applications.