DLC film coating on plasma-carburized austenitic stainless steel

Low temperature plasma carburizing to austenitic stainless steels is attracted special attention because it can harden the surfaces without degradation of its corrosion resistance. The carburized layer shows very high saturation of carbon and it is called as S phase layer. However, this layer leads to give relatively high friction coefficients to the steels. In this study, diamond-like carbon (DLC) film coating was applied to improve the friction property of the S phase layer. AISI 304 austenitic stainless steel was pre-treated by peening and plasma carburized at low temperature. The carburized specimen with no DLC film shows a high friction coefficient of about 0.55. And the DLC coated specimen not carburized preliminarily shows it to be about 0.20 only at the beginning of the friction test, and to increase gradually to about 0.43. In contrast, the friction coefficient of the specimen, carburized initially and then coated with DLC, shows a low and stable value to be about 0.20. Accordingly, it has been concluded that the duplex treatment of carburizing and DLC film coating is effective to improve the friction property of S phase layer. Furthermore, using the peening process, the DLC film could be coated directly on the carburized substrate without pre-depositing a usual interlayer.