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Influences of Surface Finishes on Properties of Biological Zinc Phosphate Conversion Coating on Titanium

Chemically formed phosphate conversion coatings (PCC) usually have good adhesion strength due to in situ growth and have great potential for biomedical applications. However, the fabrication of PCC on titanium (Ti) metals has seldom been studied because inherent chemical inertia and oxide layer block the dissolving process. Previously, the authors successfully fabricate intact PCC on pure Ti by a novel hydrothermal phosphorization method, and the coating shows good adhesion. However, metallographically polished specimens are used only in order to eliminate the influences of surface topography. In this study, the feasibility of such method to be performed on sandpaper polished and acid‐etched pure Ti are studied. Results show that rough surface benefit the nucleation of PCC and refine the crystal size, whereas, a smooth surface allow sufficient growth of crystal grain resulting in a thicker coating with stronger adhesive strength. In spite of rough surface, PCC formation on acid‐etched Ti is depressed due to the existence of titanium hydride. All the coatings obviously improve corrosion resistance of Ti substrate. The cytotoxicity test suggests that the PCCs present no adverse effects on L‐929 cells and has a cytotoxicity ranking of 0–I grade. The study shows that the hydrothermal zinc phosphorization has a potential to be extensively used for Ti‐based implants with different surface finishes.