INTRODUCTION: In cross-country skiing, reducing the friction coefficient between the skis and snow is essential for sportive performance [1]. Fluorinated waxes, i.e. containing perfluoroalkyl (PFA) are known for their hydrophobic properties and were remarkably efficient in wet snow conditions. However, the International Ski and Snowboard Federation (FIS) has banned fluorinated wax since winter 2023/2024 -for health and environmental reasons [2]. Since then, no alternative with equivalent performance has been found. This project aims to develop hard and hydrophobic coatings based on titanium nitride (TiN), aluminum nitride (AlN) and alumina (Al2O3) materials deposited on ski bases and UHMW polyethylene. METHODS: The thin films were deposited using magnetron sputtering, a vacuum technique consist of creating a vapor from a target of the desired material that is then condensed onto the substrate, the ski bases. The vapor is created by a plasma from which ions bombard the target and eject atoms from it. The surface (contact angle, roughness, chemical composition), mechanical and thermal properties of the coatings were investigated. The friction coefficient of the coated samples was evaluated on snow with a linear tribometer (speed: 0.1 m/s, contact pressure: 50 kPa) in a cold-room at 0°C. Snow with different liquid water content were used for the tests. RESULTS/DISCUSSION: The deposition on the ski base is possible at ambient temperature with adhesive and dense coatings. The coating thickness was evaluated by electronic microscopy between 50 and 200 nm depending on process parameters. Chemical analysis with XPS indicates the nitride films contain a relative high amount of carbon and oxygen. Only a few coatings, selected for their hydrophobicity and structural properties, were investigated in gliding tests. AlN and Al2O3-based coatings presented very high friction coefficient (0.2-0.3). TiN-based coating had the lower friction coefficient with a value of 0.11 on very wet snow, whereas a ski waxed with PFA friction coefficient was measured at 0.072. No correlation was found between the friction coefficient and neither the wettability nor the roughness. Other properties might have a major impact. Indeed, TiN is known for better mechanical properties [3] and lower thermal conductivity [4] which will be further investigated. CONCLUSION: The deposition of sputtered coatings was realized with success and may be a promising technique for preparing competition skis. The versatility of this technique allows the use of several different materials from pure metals, to alloys and ceramics. For winter sport application, titanium nitride seems to be the most promising. Next, the project will focus next on TiN coatings with different properties and on multilayers based on TiN, known to improve mechanical and thermal properties [5].
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