OPTIMIZATION OF THE SURFACE MECHANICAL STRENGTH OF AISI 316L PHYSICALLY VAPOR-DEPOSITED NITROGEN-DOPED COATINGS ON AISI 316L SUBSTRATES

High load Vickers indentation, scratch testing under constant and progressive loading as well as pin-on-disc wear testing were used to assess the overall strength of coated specimens. In scratch testing, the major damage mechanism was found to be brittle, by thickness cracking of the coating with growth defects the dominant crack initiators. No adhesive failure was observed within the load range considered (0-200 N, empty set 1.58 mm WC ball as pin). Under high load, WC ball-on-disc wear testing with significant plastic deformation, analogous brittle cracking mechanisms were observed. The coating process parameters optimized simultaneously with respect to scratch and wear resistance were the percentage of reactive nitrogen in the plasma, related to the level of nitrogen-doping and hardness of the coating, and the substrate bias voltage. During wear testing, an adhesive transfer layer built up on the WC ball during the run-in phase was found to have a detrimental influence on the long-term wear rate.