The Effect of Roughness on Nanoindentation Results

Instrumented Indentation Technique (IIT) or nanoindentation is widely used to measure mechanical properties on nano to macro scales. Due to the simple testing procedure and the continuously increasing sensor sensitivity there exists practically no limitation on application scale and specimen size. One of the most important sources of error in IIT test is the inevitable roughness of the tested surface. The nanoindentation test is more sensitive for the roughness of the sample as the conventional hardness test because of its shallower penetration in the sample, especially in the case of thin films' characterization, when the indentation depth is limited by the film thickness. The question, what an effect the roughness on the value of hardness has, was not studied in detail yet. In this study we applied specially roughened samples in tests, carried out with different indenter tips and by various instruments to determine experimentally the effect of roughness. Other parameters (as indenter rounding and shape, penetration depth, wavelength of the roughness) do have some effect on test results. The initial theoretical findings were confirmed by a considerable accuracy in the experiments.