Preparation of a-C:H/a-C:H:Si:O and a-C:H/a-C:H:Si multilayer coatings by PACVD

Carbon based multilayer coatings were prepared by plasma assisted chemical vapor deposition (PACVD) using methane (CH4) and hexamethyldisiloxane (HMDSO) or methane and tetramethylsilane (TMS) as precursors. These coatings were deposited in a modified plasma nitriding plant operated at relatively high working pressures of 20 Pa. The multilayer design consisted of a-C:H and a-C:H:Si:O or a-C:H and a-C:H:Si single layers, respectively. The number of single layers and the material of the top layer were varied at constant total coating thicknesses. These multilayer coatings were investigated with regard to their morphology and composition as well as indentation hardness, abrasive wear, lubricant free friction and wetting behavior via contact angle measurements. The multilayer coatings exhibited lower wear rates and higher hardness values than a-C:H:Si:O or a-C:H:Si single layers and lower friction coefficients than pure a-C:H coatings under unlubricated test condition. Utilizing duplex processes, combining plasma nitriding pretreatment and a following coating deposition, the adhesion of the multilayer coatings on high speed and cold working steel substrates could be considerably improved.