Enhanced corrosion properties of biological NiTi alloy by hydroxyapatite and bioglass based biocomposite coatings

Enhanced corrosion resistance is always an obligatory property in biomedical applications. For this purpose, the surfaces of NiTi alloy were duplex coated both by Hydroxyapatite (HA)/Silver (Ag) and BioGlass (BG)/Silver (Ag) using the sol-gel method. The surface morphologies, and corrosion behaviours of the coatings were examined via SEM, EDS, XRD, and mechanically, by means of hardness as well as adhesion and corrosion tests. SEM analyses showed that the homogenous and crack-free structures were obtained in the biocomposite coatings. Spherical-like structures in the coatings were observed and pitting type of corrosion was formed in the biocomposite coated NiTi surfaces. After the corrosion tests, enhanced corrosion resistance was observed in both HA- and BG- based coatings. However, HA-based HA/Ag coatings on NiTi alloys were obtained to have higher adhesion strength as well as higher corrosion resistance compared to the BG-based biocomposite coatings. The findings in the present study can help the design of future implants with higher corrosion resistance.