Quantification of fretting damage

The fretting behaviour of high speed steel SC 6-5-2 uncoated and coated with a TiN coating against an alumina ball was studied based on a fretting map approach. Cracking and material loss were observed depending an the contact loading. To quantify the damage, a methodology is proposed based on an elastic Hertzian-Mindlin contact description. The sliding regimes are clearly defined, applying some fretting sliding criteria. First appearing under partial slip conditions, the crack nucleation conditions were precisely identified for different number of cycles and normal forces. Comparison with various fatigue approaches indicates that, if the local friction coefficient as well as the local aspect of contact stressing are considered, the maximum principal and the equivalent Von Mises stresses permit a rather good quantification of cracking. Wear and debris formation mainly observed under gross slip conditions lead to a wear volume which is shown to present a linear evolution with the cumulated dissipated energy. This interfacial work approach is completed by a local description. Axial and lateral sliding axis linear energies are deduced allowing a rapid identification of the wear behaviour through different energy wear factors. Experimental comparison of the TiN coating with the steel substrate contact shows that, as long as the coating is present in the contact, the important compressive residual stresses prevent cracking whereas the energy wear analysis indicates a wear resistance of the coating up to 10 times superior to the studied steel.