Influence of nitrided and nitrocarburised layers on the functional properties of nitrogen-doped soft carbon-based coatings deposited on 316L steel under DC glow-discharge conditions

Abstract

Improvement of the tribological properties of steels can be achieved by increasing the hardness of the surface and by reducing roughness and the coefficient of friction. The formation of composite layers on steel, consisting of a hard nitrided or nitrocarburised diffusion layer and an external carbon coating with a low coefficient of friction, seems to be a prospective solution with significant potential. The paper presents an innovative method of producing carbon-based coatings on diffusion layers by means of a low-temperature process utilizing a single device for glow-discharge treatment. 316L austenitic stainless steel, one of the most popular and most readily available single-phase steels, was used in the tests. The layers have been formed in successive processes of nitriding or nitrocarburising in low-temperature plasma followed by deposition of a nitrogen-doped carbon coating under DC glow-discharge conditions. An evaluation was made of the impact of the nitrided and nitrocarburized layers on the properties and morphology of the carbon coatings formed, by comparing them to a coating produced on unpretreated steel substrates. A study of the surface topography, roughness, nanohardness, coefficient of friction, wear, adhesion and corrosion resistance shows a significant importance of the substrate type the coatings are formed on.