Deposition of Thick a-C:H:Si Coatings for Tribological Applications

摘要

DLC films show many superior properties such as low coefficients of friction, high hardnesses and chemical inertness. These properties make them very attractive for a multitude of industrial applications. However, in many cases insufficient adhesion of the DLC films limits the range of application. One reason of poor adhesion is ascribed to the generation of strong residual compressive stress during growth. Si incorporation in the DLC films reduces stress and a metallic interlayer or a gradient multilayer improves the adhesion of DLC coatings. However, it is rarely reported that DLC films with thicknesses of more than 10 μm are deposited on geometrical complex parts, which show adhesive properties sufficient for an industrial use. The purpose of this study was to develop and analyse a technology which can synthesize DLC films thicker than 50 μm. a-C:H:Si coatings were deposited in an industrial DC-PACVD-system in a pressure range and parameter range normally used for plasma nitriding. HMDSO was used as Si-precursor in mixtures with Ar, H_2 and C_2H_2 as process gases. The hardnesses were evaluated by a nanoindenter and the adhesions by means of a scratch tester. The friction tests were performed using a pin-on-disc tribometer. With increasing a-C:H:Si thickness the load carrying capacity was significantly improved. The coatings get self sustaining, reaching scratch-result up to 73N on low alloyed steel. Tribological properties were obtained resulting in a friction coefficient down to 0.02 against steel.