Low-friction PACVD TiN coatings: influence of Cl-content and testing conditions on the tribological properties

It has been reported in our earlier paper, that TiN coatings deposited by plasma-assisted chemical vapour deposition (PACVD), showing a low chlorine content are well suited to reduce the friction coefficient against steel to low values of approximately 0.2. The aim of this study was to use the PACVD technique to deposit different TiN coatings with defined chlorine contents and to investigate the tribological properties of these coatings in the temperature range from 25 to 150 °C. Dry sliding experiments were conducted in ambient air and dry nitrogen. The coatings were worn against ball-bearing steel using a ball-on-disc configuration. An optical 3d profiler was used to investigate the geometry of the wear tracks after ball-on-disc testing. Coating characterisation was done using electron probe microanalysis (EPMA) and scanning electron microscopy (SEM). The abrasion resistance of the coatings investigated was evaluated using a small-scale abrasive wear test. Hardness measurements were performed with a nanoindenter. Low friction coefficients of approximately 0.14–0.17 have been obtained during ball-on-disc testing at room temperature in ambient air for coatings containing more than 3 at.% chlorine. The friction coefficient against ball-bearing steel increases to values of approximately 0.7–0.8 at enhanced temperatures. For testing in dry nitrogen atmosphere, the friction coefficient increases to the same range.