Fretting wear of TiN PVD coating under variable relative humidity conditions – development of a “composite” wear law

摘要

Fretting is defined as a small oscillatory displacement between two contacting bodies. Theudinterface is damaged by debris generation and its ejection from the contact area. Theudapplication of hard coatings is an established solution to protect against fretting wear. For thisudstudy the TiN hard coating manufactured by a PVD method has been selected, and testedudagainst a polycrystalline alumina smooth ball. A fretting test programme has been carried outudat a frequency of 5 Hz, 100 N normal load, 100 μm displacement amplitude and at five valuesudof relative humidity: 10, 30, 50, 70 and 90% at a temperature of 296 K. The intensity of theudwear process is shown to be significantly dependent on the environmental conditions. Auddissipated energy approach has been employed in this study to quantify wear rates of the hardudcoating. The approach predicts wear kinetics under constant medium relative humidity in audstable manner. It has been shown that an increase of relative humidity promotes the formationudof hydrate structures at the interface and modifies the third body rheology. This phenomenonudhas been characterised by the evolution of wear kinetics associated with a significant variationudof the corresponding energy wear coefficient. Hence, a ‘composite’ wear law, integrating theudenergy wear coefficient as a function of relative humidity, is introduced. It permits audprediction of wear under variable relative humidity conditions from 10 to 90% within a singleudfretting test. The stability of this approach is demonstrated by comparing various variableudrelative humidity sequences.