Enhancement of the thermal stability of sputtered diamond-like carbon thin films for automotive applications

Oliver Jantschner

Research output: ThesisDoctoral Thesis

Abstract

Nowadays, the application of thin films for engine and drivetrain components in automotive industry can be seen as state-of-the-art. In particular, diamond-like carbon (DLC) coatings have been established to be potential candidates to enhance lifetime of the parts as well as to minimize surface degradation. In case of lubrication deficiency during operation, increased friction and consequently high temperatures and wear can be significantly reduced by so called solid lubricants (like graphite). The advanced design of engine and powertrain parts to maximize energy efficiency lead to an enormous increase of temperatures, pressures and speeds. Thus, the enhancement of the thermal and mechanical stability of DLC-coatings, applied for these purposes, is of high importance. Within this work, non-hydrogenated DLC-coatings were deposited by magnetron sputtering. The thermal and mechanical stability of the coatings was enhanced by addition of small contents of Cr (0-10at%) and Si (0-5at%), respectively. The individual influences of these doping elements, especially at elevated temperatures, were investigated in detail followed by the optimization of the doping element concentrations. The applied investigations can be divided into mechanical-tribological (nanoindentation and tribology) and structural (X-ray photoelectron spectroscopy, Raman spectroscopy and electron energy-loss spectroscopy) methods. In addition, structure as well as mechanical properties were modeled by implementation of ab-initio methods and compared to the results obtained from experiments. Si as a tetravalent element strengthens the carbon matrix by formation of sp3 carbide bonds to carbon. No proof of Cr carbide formation was found within the carbon matrix, leading to decreased mechanical properties like hardness and Young’s modulus. Tribological tests in air demonstrated an enormous increase of temperature- and oxidation resistance up to 450°C due to the incorporation of Si, combined with minimization of friction and wear due to the formation of Si-O-C surface-near bonds. The absence of hydrogen within the coatings leads to optimum tribological behavior in oxidizing atmosphere, while in dry inert environments (like N2 and Ar), friction and wear increase compared to hydrogen containing candidates. In addition, within this work, the overall coating system was optimized by systematic variation of the adhesion layer, the gradient layer and the chemical composition of the DLC top layer, respectively, to meet the demanding requirements, leading to increased life time of the part as well to decreased fuel consumption of the vehicles.
Translated title of the contributionErhöhung der thermischen Stabilität von gesputterten diamantartigen Kohlenstoffschichten für Automobil-Anwendungen
Original languageEnglish
QualificationDr.mont.
Supervisors/Advisors
  • Schneider, Jochen M., Assessor B (external), External person
  • Mitterer, Christian, Assessor A (internal)
Publication statusPublished - 2014

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