Adhesion strength of sol–gel derived fluoridated hydroxyapatite coatings

Dense and uniform fluoridated hydroxyapatite (FHA) coatings have been deposited on Ti6Al4V substrates by sol–gel dip coating method. X-ray photoelectron spectroscopy and X-ray diffraction analysis results show homogeneous FHA coatings with Ca / P molar ratio between 1.63 and 1.70. A scanning scratch tester is used to evaluate the adhesion between the FHA coating and the substrate. The load at which complete removal of the coating occurs is taken as an indication of the adhesion strength. With increase of fluorine concentration and firing temperature, adhesion strength increases; and at the same time, the coating-substrate interfacial failure mode changes from brittle to ductile. Based on the cross-sectional analysis, a mechanism is proposed for the increased adhesion.