Plasma deposited silicon incorporated amorphous carbon thin films for automotive applications

Abstract

Mechanical losses due to friction can account for 10-15% of the energy used in engines [Dahotre and Nayak, 2005, Taylor, 1998]. This thesis aimed to reduce those losses by addressing the friction in moving components. The aim was to achieve this goal with the utilisation and modification of Diamond-Like Carbon (DLC) coatings. DLC offers low frictional values and low wear rates, which makes it an ideal candidate for coating mechanical components. The problem with coating engine components with DLC is the instability of the coating at elevated operating temperatures. Current DLC formulations start to degrade in temperatures over ∼200◦C with a major increase in this degradation at ∼400◦C. It was found that with the addition of silicon doping, the DLC coating can be modified to be more stable and work at higher temperatures. Adding silicon to the DLC film was shown to improve the thermal stability up to 400◦C, but over this temperature the film degraded to graphite-like carbon and silicon-oxide layers as shown by XPS (X-ray Photoelectron Spectroscopy) and ToF.SIMS (Time of Flight Secondary Ion Mass Spectrometry). Adding silicon and reducing hydrogen content in the film was shown to further increase the thermal stability. This was achieved with the use of a novel gas mixture, utilising CO2 & TMS precursor gases. These films showed reduced signs of graphitisation at elevated temperatures and increased film adhesion to metallic substrate. The doped films
all showed an increase in friction over the non doped DLC film. High temperature tribology tests revealed that none of the selected films were suited for operating at 400◦C.

Date of Award	Oct 2010
Original language	English
Supervisor	Jim McLaughlin (Supervisor) & Justin Quinn (Supervisor)