Hydrogen content influence on tribological properties of nc-WC/a-C:H coatings

• Presence of H2 or CH4 in working atmosphere leads to hydrogenation of a-C matrix.
• Hybridization of carbon atoms depends on the hydrogenation degree of a-C matrix.
• Higher hydrogenation effect can be achieved by introducing methane.
• High hydrogenation degree improves tribological properties of nc-WC/a-C:H coatings.
• High hydrogenation degree improves the quality of adhesion of nc-WC/a-C:H coatings.

Hydrogen content has high influence on low-friction properties of an amorphous carbon coating a-C with or without transition metal additions. In the paper the nanocrystalline nc-WC/a-C:H coatings deposited by means of magnetron sputtering were investigated. Hydrogen content up to 37% was obtained by the use of different flows of pure hydrogen or methane mixed with pure argon. The coatings were investigated by means of SEM, EDS, and SAED HR TEM in order to obtain thickness, sufrace morphology, chemical composition as well as nanostructure. Moreover, these were investigated: type of bonds between carbon atoms by means of Raman Shift Spectroscopy and hydrogen content by means of SIMS and inert gas fusion crucible method. Tribological properties were elaborated by means of ‘pin-on-disc’ method. It was stated that coefficient of friction, microstructure and type of bonds between carbon atoms are highly dependent from the hydrogen content. It is the main parameter for achieving of low friction coefficient (below 0.1) as well as very low wear rate (in a range of 10−17 m3·N−1·m−1. Obtained results confirmed that proposed nc-WC/a-C:H coatings can be used for improving tribological properties of hard steels and hardened titanium alloys.

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