Friction of thin coatings on three length scales under reciprocating sliding: Fid-Bau Portal

Friction of thin coatings on three length scales under reciprocating sliding

Drees, Dirk / Celis, Jean-Pierre / Achanta, Satish

Friction at different length scales has been a matter of investigation in the field of tribology. Since friction is omnipresent in every situation ranging from nanoscale to macroscale, its dependence on many operational parameters makes it difficult to analyse. Present work is an attempt to explain and analyse friction at different length scales, i.e., different magnitudes of load, pressure and sliding length. Reciprocating sliding tests were conducted on coatings like DLC, TiN with silicon nitride counterbody with varying diameters, depending on the equipment and pressure-displacement range. The experiments were performed with identical contact parameters (contact pressure, speed, environment, etc.) so as to make a comparative study of the results. All the pressure calculations were done using the Hertzian contact model (ball on flat) and experiments were carried out over the widest possible range of parameters, using three reciprocating sliding test equipment: atomic force microscope, a new mesorange tribometer and the MTM macro reciprocating tester. Experimental results show that tribological phenomena occurring at macro- and mesorange loads are identical until a threshold load value. Then, the mechanisms change on further reduction of load. Despite of this, the coefficient of friction in macro- and mesoranges is still comparable. But in the case of nanorange tests, the friction is entirely different from larger scales. The reasons for such an observation as a function of length scales are discussed.