A new systematic method of characterization for the strength of thin films on substrates -: evaluation of mechanical properties by means of 'film projection'

The strength of a thin film deposited on a substrate should be recognized as the strength of a materials system which is made of a film, a substrate and an interface. The macroscopic fracture of this system should be controlled by the strength of the film and the interface, as well as the residual stress and elastic properties in/of the film. We have developed a systematic method of measurement for all these properties by means of a specimen with 'film projection'. By applying external load to the film projecting a little out of the edge of the substrate, cracks can be introduced exclusively in the film or along the interface. The strength of film and interface is independently evaluated in terms of toughness on the basis of crack extension resistance. Deformation of the film projection gives its Young's modulus, and the buckling behavior is used to estimate the residual stress. As an application example of the method, those properties mentioned above were evaluated for the case of a diamond film deposited on a cobalt-cemented tungsten carbide cutting tool. (C) 2002 Elsevier Science B.V. All rights reserved.