A compression test for adhesion evaluation of diamond coatings

Abstract

A key requirement of an effective coating is its adequate adhesion to the substrate. Thus, reliable test methods to evaluate coating adhesion and to characterize the deposition parameters affecting it are necessary for the systematic development of such coatings. The conventional technique for measuring diamond coating adhesion, the scratch test, is unreliable because of wear of the stylus and influences of the substrate. Thus, a noncontact technique (compression test) of evaluating the adhesion of diamond coatings on brittle substrates was modelled and developed. This method utilizes the differences in Young's modulus between the coating and the substrate via application of an external load in order to generate interfacial stresses and debond the coating. An innovative three-dimensional numerical model, based on combining the variational and boundary integral approaches, was utilized to link the indirect (i.e. load) to the direct (i.e. debond shear stress or elastic energy of delamination) characteristics of adhesion. Factors affecting the adhesion strength of the diamond coatings are discussed in relation to the process parameters. This test offers an excellent alternative to conventional techniques for measuring the adhesion strength of diamond coatings on brittle substrates.