| The critical loads in scratch test are used for the comparison of adhesion in film/substrate systems. But the critical loads are strongly affected by various parameters such as scratching speed, indenter tip radius and film thickness. Therefore, to assess the reliable interfacial adhesion strength, the stress generated by sliding circular indenter was analyzed by considering the static indentation stress, frictional stress and residual stress. Static indentation stress consists of the elastic stress and blister stress generated by plastic deformation of substrate. On the basis of the stress analysis, the elastic deformation energy of film was evaluated under the condition of strain matching criterion at the interface. When the elastic deformation energy stored in film reaches the critical value, this energy will be released by delamination and spallation of film. Thus the interfacial adhesion strength in terms of work of adhesion can be evaluated by extracting the surface energy generated by spallation from the elastic deformation energy. The work of adhesions of PECVO-prepared DLC film on WC-Co substrate were evaluated. In spite of the distinctly different critical loads measured with the change of scratching speed and film thickness, the comparatively constant work of adhesions were obtained. |
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