Hard coatings durability under fretting wear

摘要

Fretting wear, defined as a small displacement amplitude oscillatory motion between two solids in contact, is usually induced by vibrations. In the case of surface coatings application it is crucial to establish when the substrate is reached to prevent from catastrophic consequences. Moreover, a reliable selection of surface treatment is of great interest for industrial applications. In this work fretting tests were carried out on different PVD hard coatings (TiN, TiC, TiCN, VC, TiC/VC, (TiC/VC)_(x2)) under wide range of normal loadings and displacement amplitudes. A ball-against-flat specimen arrangement has been analyzed under gross slip fretting regime. The coatings durability criterion based on local dissipated energy has been developed and related to the friction process. The wear depth extension is referred to the cumulated density of friction work dissipated during the test. An averaged cumulated density of dissipated friction energy is successively introduced to rationalize the coating lifetime. The critical dissipated energy density related to the coatings durability has been determined for each analyzed coating and the critical number of fretting cycles has been established. Taking into account this critical value an Energy Density-Coating Endurance chart has been proposed where the coating duration is predicted as a function of the pressure, the displacement amplitude and the friction coefficient. Nevertheless, some divergence has been observed between the predicted and detected surface coating endurance. This has been explained by a coating spalling phenomenon observed below a critical residual coating thickness. Introducing an effective wear coating parameter the coating endurance is better quantified and finally an effective energy density threshold, associated to a friction energy capacity approach, is introduced to rationalize the coating endurance prediction. The investigated hard coatings are compared independently of the loading conditions and its thickness. Finally the global procedure to establish the coatings durability has been presented.