A simple technique for measuring the adhesion of brittle films to ductile substrates with application to diamond-coated titanium

We have developed a new technique for measuring the adhesion of brittle films to ductile substrates. In this technique, a wedge indenter is driven through the brittle coating and into the underlying substrate. Plastic deformation of the substrate causes the coating to delaminate from the substrate. The width of the delaminated area can be directly related to the interface toughness. We present a simple analysis of this technique and apply it to diamond-coated titanium. The toughness of the diamond-titanium interface as measured with this wedge delamination technique is approximately 51 +/- 11 J/m(2). XPS measurements reveal that a reaction layer of titanium carbide forms between the diamond coating and the titanium substrate. Delamination of the coating occurs by crack propagation in this reaction layer and in the diamond film itself. These observations agree well with nanoindentation measurements performed in the delaminated area of the substrate.