Characterization, mechanical properties, corrosion behavior and bone-like apatite formation ability of fluorine substituted hydroxyapatite coating

Abstract

Hydroxyapatite (HA) is a non-bioceramic commonly used in human implants in the form of coatings, which are limited in their application by mechanical and wear resistance properties, as well as biodegradability. In this study, fluorine substituted hydroxyapatite (FHA) coatings were prepared on Ti-6Al-4V surfaces by plasma spraying method using a mixture of calcium fluoride and hydroxyapatite powders. The prepared coatings were characterized by X-ray diffraction and fourier transform infrared (FTIR) spectroscopy at different levels of calcium fluoride (3 wt%, 6 wt%, 9 wt%, and 12 wt%). The biocompatibility of the coatings was evaluated by in vitro mineralization experiments. Experimental results showed that at 9 wt% of calcium fluoride, the prepared FHA coatings had better mechanical properties, with improved bond strength (28.2 MPa). The X-ray diffraction patterns of the coatings reflect the fluorine substitution during the spraying process and the 9FHA has the highest crystallinity according to the XRD analysis, which is closely related to the biological activity of the coating. In addition, Potentiodynamic polarisation showed that the sample coated with the 9FHA coating had the highest Ecorr and lowest Icorr, indicating the best corrosion resistance. The FHA coating exhibits faster apatite deposition in simulated body fluid, and the efficiency of apatite deposition increases with the increase of CaF₂.

Keywords: Corrosion resistance; FHA coating; Phase constitution; Plasma spray.