The results presented in Fig. The thickness of the coating is approximately 400 nm. The first critical force value of 3.26 N corresponds to damage along the sides of the scratch path. The tip is loaded and the electrical resistance measured between the tip and the sample. For many systems, particularly metals, a sudden drop in resistance can be attributed to the breaking of the oxide film and the resultant contact between the two conductors.
Future work is hoped in adapting potentiostatic control to scratch testing.
J. B. Pethica and D. Tabor, Surf. D. F. Bahr, J. C. Nelson, N. I. Tymiak and W. W. Gerberich, J. Mater.