Affiliation: | a Materials Center Leoben, Franz-Josef-Straße 13, A-8700, Leoben, Austria b Department for Physical Metallurgy and Materials Testing, University of Leoben, Franz-Josef-Straße 18, A-8700, Leoben, Austria c Department for General and Analytical Chemistry, University of Leoben, Franz-Josef-Straße 18, A-8700, Leoben, Austria d Department for Mineralogy and Petrology, University of Leoben, Peter-Tunner-Straße 5, A-8700, Leoben, Austria e Institute of General Physics, Vienna University of Technology, Wiedner Haupstraße 8-10, A-1040, Wien, Austria |
Abstract: | Recently, several new solid lubricants and modern lubrication concepts have been developed to achieve lower friction and wear and thus longer lifetime in severe tribological applications. The aim of this study is to characterize tribo-layers formed during ball-on-disc testing on low-friction, Cl-containing TiN coatings deposited by plasma assisted chemical vapor deposition and to clarify their formation mechanism. Characterization of the transfer layers was done by optical microscopy, optical profilometry, Raman spectroscopy, Auger electron spectroscopy and X-ray photoelectron spectroscopy. Differential scanning calorimetry was used to provide information on the chlorine-influenced chemical reactions of the coatings in ambient air. Iron oxide layers of a thickness in the nm-range have been found on low-chlorine containing TiN coatings (<3 at.% Cl) showing friction coefficients of approximately 0.8, whereas on TiN coatings with higher chlorine contents (>3 at.% Cl) rutile layers were preferably formed, resulting in friction coefficients below 0.2. This self-lubrication mechanism can be explained by the in-situ formation of easy-shearable titanium oxides in the contact zone in the presence of humidity and oxygen. |