Evaluating mechanical adhesion of sol–gel titanium dioxide coatings containing calcium phosphate for metal implant application

The adhesion of thin (<10 μm) sol–gel calcium phosphate–titanium dioxide films bonded to a titanium substrate was studied using two different tests: a rotating–bending test and a tensile bond test. The former evaluates the impact of both the coating procedure and the surface pre-treatment on the resistance to fatigue of the substrate as well as the adhesion of the coating; the latter measures the tensile adhesion strength of the coating. Both tests gave similar results. A reduction of the thickness of the coating or an increase of the roughness of the substrate improves the quality of the interface. A comparison of the adhesion of the calcium phosphate–titanium dioxide film with that of a pure calcium phosphate coating obtained by a similar route suggests the involvement of a chemical component in the binding.