A COMPRESSION TEST FOR ADHESION EVALUATION OF DIAMOND COATINGS

A key requirement of an effective coating is its adequate adhesion to the substrate. Thus, reliable test methods to evaluate coating adhesio n and to characterize the deposition parameters affecting it are neces sary for the systematic development of such coatings. The conventional technique for measuring diamond coating adhesion, the scratch test, i s unreliable because of wear of the stylus and influences of the subst rate. Thus, a noncontact technique (compression test) of evaluating th e adhesion of diamond coatings on brittle substrates was modelled and developed. This method utilizes the differences in Young's modulus bet ween 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 v ariational and boundary integral approaches, was utilized to link the indirect (i.e. load) to the direct (i.e. debond shear stress or elasti c energy of delamination) characteristics of adhesion. Factors affecti ng the adhesion strength of the diamond coatings are discussed in rela tion to the process parameters. This test offers an excellent alternat ive to conventional techniques for measuring the adhesion strength of diamond coatings on brittle substrates.