A simple technique for measuring the adhesion of brittle films to ductile substrates with application to diamond-coated
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A simple technique for measuring the adhesion of brittle films to ductile substrates with application to diamond-coated titanium Joost J. Vlassak Department of Materials Science and Engineering, Stanford University, Stanford, California 94305
M. D. Drory Crystallume, Santa Clara, California 95054
W. D. Nix Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (Received 18 November 1996; accepted 6 March 1997)
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 6 11 Jym2 . 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.
I. INTRODUCTION
The reliability of many thin-film coatings in engineering applications depends critically on the adhesion of the coating to its substrate. If adhesion is poor, the coating may fail even if the coating itself satisfies the design criteria. Despite this fact, relatively few measurement techniques are available to quantify the energy required to separate a coating from the substrate, particularly for brittle substrates. Here we introduce a new technique for measuring the adhesion of strongly adhering brittle films to ductile substrates and we use it to measure the adhesion of diamond to titanium. By far the most popular technique is the scratch test, in which a stylus is drawn over the coating with an ever increasing load until the coating spalls. This technique allows one to compare the adhesion of various coatings qualitatively, but does not provide an absolute measure for the critical crack extension force for the substrate-coating interface. More quantitative techniques have also been developed such as the blister test,1–3 the residual stress driven delamination test,4 and the edge delamination test.5,6 These techniques usually require complicated sample preparation and are often limited to coatings with poor adhesion. Delamination of ductile coatings on brittle substrates has been studied successfully by means of micro1900
http://journals.cambridge.org
J. Mater. Res., Vol. 12, No. 7, Jul 1997
Downloaded: 11 Mar 2015
indentation.7–9 In this technique, the coating is deformed by means of a microindenter, avoiding penetration of the substrate. The residual st
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