Wear resistance of fine-grained high nitrogen austenitic stainless steel coated with amorphous carbon films: The soft X-ray spectroscopy approach

The wear resistance dependence on grain size of a high-nitrogen-alloyed austenitic stainless steels (HN) is investigated and compared to measurements for the same samples coated with amorphous carbon (a-C : H) and nitrogenated amorphous carbon (a-C : H(N)) films, deposited by means of plasma-enhanced chemical vapour deposition. A synergic effect between the grain re. ning and the film in the case of nitride amorphous carbon overcoats is observed in terms of increased low-friction performance duration. The temperature dependence of the wear resistance of a micro crystalline HN stainless steel coated with carbon films is also investigated. An overall decrease of the films' wear resistance is found with increasing temperature. Furthermore, a higher wear resistance is found in the a-C : H coated steel with respect to the a-C : H: N material. High-lateral-resolution photoemission microscopy reveals that inhomogeneities within the film after wear testing are correlated to an increase of the number of N-sp(2) C-bonded sites. The study of energy-distribution curves and high-lateral-resolution images on the nitrogenated samples shows that a modi. cation of the surface chemistry occurs by mechanical action; in particular this implies that existing N-sp(2) C sites are beginning to cluster as temperature increases. RI Valentini, Luca/D-5238-2011; Kenny, Jose/F-9372-2010