Deposition of amophous Si-doped carbon layers via plasma-enhanced chemical vapor deposition

Keyan Liu

Research output: Types of ThesesMaster's Thesis / Diploma Thesis

Abstract

DLC (Diamond-Like-Carbon)-coatings combine a number of interesting properties: they show high hardness and low coefficients of friction. Due to their amorphous structure they can increase corrosion resistance of steel surfaces remarkably. This work contains the deposition of amorphous Si-doped carbon layers (a-C:H:Si) on nitrided, post oxidized and polished steel substrates by means of PACVD and the characterisation of the resulting coatings. The deposition was done by using Hexamethyldisiloxan (HMDSO), hydrogen (H2), argon (Ar), methane (CH4) or acetylene (C2H2) and nitrogen (N2). The effects caused by the pre-treatment of the substrates, the loading of the reactor and the deposition parameters (substrate temperature, power density, process pressure, pulse times, gas composition) on the coating properties (microstructure, chemical composition and mechanical properties) were examined and discussed. The surface tensions of the a-C:H:Si layers lie in the range of 30 mN/m and are strongly depending on the surface roughness. Compared to untreated, nitrided or post oxidized samples the coefficient of friction could be substantially reduced (µ ≈ 0,05) by a-C:H:Si-coatings. The coefficient of friction of the a-C:H:Si layers depend strongly on the surface roughness, chemical compositions and relative air humidity. With increasing Si- or N-content the coefficients of friction of the layers increase no-ticeable. Amorphous Si-doped carbon layers coatings on all three differently pre-treated steel substrates led to significant reduction of wear. This remarkable reduc-tion of wear was observed along the wear trace on the sample and also at the anti-bodies. Adhesive strength measurements show that by plasma nitriding and forming graduated intermediate layers before the deposition critical loads up to 30N could be obtained. Salt spray tests showed that a-C:H:Si-coatings can increase the corrosion resistance of polished, nitrided and post oxidized steel surfaces substantially.
Translated title of the contributionDeposition of amophous Si-doped carbon layers via plasma-enhanced chemical vapor deposition
Original languageGerman
Publication statusPublished - 2008

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