Tribological analysis of thin films by pin-on-disc: Evaluation of friction and wear measurement uncertainty

Pin-on-disc is widely used to evaluate tribological properties of thin films. However, the results are often present without standard uncertainties; moreover, in many cases the standard uncertainty is replaced by standard deviation, which is a strong underestimation of real uncertainty. In this study we have followed ISO and NIST guidelines to investigate the possible sources of uncertainties related to friction and wear rate measurement and to apply them on two selected coating systems - TiN and DLC. We show that influence of operator is a significant contribution to the uncertainty of the wear rate, particularly in the case of very low wear of DLC coatings. We discuss why variance should be used instead statistic deviation and suggest a method to calculate uncertainties in case of small number of measurements. The paper could be used as a guide to evaluate friction and wear data of thin films and coatings using the pin-on-disc technique.