Structure, mechanical properties and tribology of W–N and W–O coatings

The tribological properties of nitrides and oxides of transition metal thin films deposited by reactive magnetron sputtering have been thoroughly studied for three decades. Nevertheless, there are still several gaps in knowledge. The majority of studies are focused on a limited number of metals, namely Ti, Al and Cr, while other potentially attractive compounds are aside the main attention. Even in case of TiN, probably the most studied hard thin film, the frictional and wear behaviour brings many controversies. Despite significant progress of analytical and computational methods, the analysis of the wear behaviour is still a great challenge.We are presenting here a summary of our recent work on tungsten nitride (nitrogen content 0–58 at.%) and tungsten oxide (oxygen content 0–75 at.%) coatings deposited by reactive magnetron sputtering. Our aim has been the analysis of the connection of fundamental properties of these films, such as chemical composition, structure, hardness, Young’s modulus and residual stress, with their tribological properties – friction coefficient and wear rate. We have been focused mainly on the description of the dominant wear mechanisms influencing the tribological properties. The tribological tests have been carried out both at room and elevated temperature; the temperature was increased in steps until immediate coatings failure.The tungsten nitride coatings with the “worst” parameters generally considered as vital for high wear resistance, such as hardness, were considered to have the best tribological performance.