Analysis of the tribological behaviour of W-Ti-N coatings

Abstract

The aim objective of this work is to provide an experimental database for the tribological characteristics, at room and warm temperature (100ºC, 150ºC and 200ºC), between the AA5754-O aluminium alloy and a steel (H13) coated with a thin film (W-Ti-N). The experimental database was built based on pin-on-disk tests, without lubricant and using a minimum amount of lubricant. In order to reproduce the different contact conditions associated to sheet metal forming process, two types of steel samples were coated: planar and spherical. The first type of samples was tested using as counter-body aluminium pins. The second type of samples was the counter-body of the tests performed with aluminium sheets. The pin-on-disk tests were performed under identical conditions for: (i) planar sample coatings, obtained with different deposition conditions, tested at room temperature with the goal of analysing the influence of the coating properties in the contact conditions; (ii) aluminium sheets, using coated balls corresponding to one of the deposition conditions (N9). A different amount of lubricant was applied for each aluminium sheet, with the main goal of analysing the influence of the lubricant amount in the contact conditions, including the temperature effect; (iii) planar sample coatings (N9) using different amounts of lubricant, in order to evaluate the influence of the lubricant amount in the contact conditions, including the temperature effect. The analysis of the minimum, maximum and average friction coefficients determined for each test, allowed to draw some global conclusions. The coated samples that present the lower range for the friction coefficient are not necessarily the ones with the lower wear volume for the pin. For the tests performed with aluminium sheets against coated and steel balls, it was observed a different evolution of the friction coefficient with time, associated to the temperature increase, as a result of the alteration of the lubricant characteristics. This effect was not observed for the tests performed with coated samples against the aluminium pins, which can be related with the different sample roughness. Globally, the average friction coefficient increases with temperature in case of the sheet planar sample, while it was not possible to determine the influence of the lubricant amount for the coated planar samples, since the average friction coefficient is similar for both samples, for each temperature. This work also constitutes an important database for allowing the improving of the experimental procedure, results analysis and test planning in future works. In this context, some recommendations were listed for future reference.