Influence of the deposition temperature on mechanical and tribological properties of a-C:H:Si coatings on nitrided and postoxidized steel deposited by DC-PACVD

Amorphous carbon-silicon coatings (a-C:H:Si) combine a series of interesting properties, such as a low friction coefficient, high hardness and wear resistance. a-C:H:Si films on nitrided steel, especially on construction and on heat treatable steels provide a substantial potential for new applications e.g. such as machine parts. Nitriding can be done with or without white layer. By a postoxidation of the nitrided surface additional corrosion resistance can be achieved. In the present study a-C:H:Si films were deposited by means of DC-PACVD using HMDSO and TMS as precursors with deposition temperatures ranging between 190 and 550 °C. Prior a-C:H:Si deposition different plasma nitriding processes have been performed and some of the samples were also postoxidized. The results show an increase of the surface energy at higher deposition temperature. Mechanical properties were studied by a Fischerscope tester whereas the phase composition was determined using XRD. The temperature has a great impact on the hardness. Also at higher deposition temperature X-ray analysis indicates no crystalline structure of the carbon films. For postoxidized steel substrates an undesirable degradation process of the oxide phase can be observed with increasing temperature. The investigation of the adhesion of the deposited coatings was evaluated by means of a scratch test method and a Rockwell C hardness tester. In addition the tribological properties of the obtained films were assessed with a ball-on-disc test at different humidity conditions.