Abstract
Many heavy duty components or particularly exposed surfaces in automotive applications are coated with diamond-like carbon (DLC). In this paper, two DLC coatings with different top layer chemistries were tested in various fuels to investigate how the chemistry impacts the tribological properties. A multilayer DLC coating with a softer tungsten doped top layer was compared to a DLC coating designed for automotive applications. The coatings were tested in different fuels under boundary lubrication conditions. The top layer containing tungsten was shown to enable the formation of WS2 in the contact when sliding in diesel and FAME. The process involves extraction of sulphur from the fuel and chemical reaction with W and transfer to the counter surface. Results are shown from SEM, Raman, XPS and TEM. The presence of WS2 was shown to coincide with a reduction of the counter surface wear as well as the friction.
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