Properties of duplex coatings prepared by plasma nitriding and PVD Ti–C:H deposition on X20Cr13 ferritic stainless steel

Abstract

Duplex-coating procedures consisting of plasma nitriding and Me–C:H hard coating lead to an improved performance of the devices because the Me–C:H coating is supported by the nitrided phase and, therefore, the `eggshell-effect' is avoided. Furthermore, this support leads to a higher load-bearing capacity of the thin film. Two standard procedures (classical high-pressure plasma nitriding and unbalanced magnetron sputtering of Ti–C:H) were performed subsequently to prepare the duplex coatings on X20Cr13 ferritic stainless steel. The corrosion resistance of the steel could be improved by nitriding at 450°C compared to the untreated ferritic substrate. The roughness is determined by the nitriding step. The weakest point of the coating is the transition zone between the nitrided and the untreated substrate and not the interface between the Ti–C:H coating and the nitrided substrate as shown by the Rockwell and scratch tests. The adhesion of the duplex structure (plasma nitriding and Ti–C:H coating) on X20Cr13 (230 HV0.1) is superiour to the adhesion of Ti–C:H on hardened 100Cr6 ball-bearing steel (62 HRC≈820 HV0.1, not nitrided).