Characterization of fatigue and adhesion properties of a-C:H/CrN coatings on bearing rings by impact tests

The impact test is used for the quantitative assessment of various properties of thin hard coatings, deposited on machine elements, tools etc. This test is mainly applied on coated specimens with simple geometries such as of cutting inserts and coated plates. In the described investigations, perpendicular and inclined impact tests were conducted directly on PVD coated bearing rings. The tests were performed with the aid of appropriate fixtures on the internal cylindrical surface of the outer bearing ring, as well as on the external one of the inner ring. Through a developed FEM simulation of the contact between the indenter ball and the cylindrical ring surfaces during the perpendicular and the inclined impact test, the film fatigue endurance stress was determined and the coating's adhesion was quantified. The mechanical properties of the applied thin films and substrates, used in the FEM calculations, were detected by nanoindentations and appropriate results evaluation. The obtained film fatigue endurance stress of the investigated coating can be considered as adequate however the coating adhesion is assessed as poor.