Carbon coating saves fuel

Dr. Volker Weihnacht, Prof. Andreas Leson and Dr. Hans-Joachim Scheibe (left to right) claim to have successfully developed a laser arc method of depositing friction-reducing, wear-resistant coatings on components.
Researchers from Fraunhofer have developed a laser arc method with which layers of carbon almost as hard as diamond can be applied on an industrial scale at high coating rates and with high thicknesses. The researchers claim fuel consumption can be reduced by applying carbon coatings to engine components such as piston rings and pins.

"Systematic application of our new method could save more than 100 billion litres of fuel each year over the next ten years," said Professor Andreas Leson from the Fraunhofer Institute for Material and Beam Technology IWS in Dresden.

Carbon-based coatings are already used in volume production. But the team of IWS researchers led by Prof Leson, Dr Hans-Joachim Scheibe and Dr Volker Weihnacht say they have succeeded in producing hydrogen-free ta-C coatings on an industrial scale at a consistent level of quality. These tetrahedral amorphous carbon coatings are significantly harder and thus more resistant to wear than conventional diamond-like coatings.

In a similar style to film projectors, the laser arc method generates an arc between an anode and a cathode (the carbon) in a vacuum. The arc is initiated by a laser pulse on the carbon target. This produces a plasma consisting of carbon ions, which is deposited as a coating on the workpiece in the vacuum. To run this process on an industrial scale, a pulsed laser is vertically scanned across a rotating graphite cylinder as a means of controlling the arc. The cylinder is converted evenly into plasma due to the scanning motion and rotation. To ensure a consistently smooth coating, a magnetic field guides the plasma and filters out any particles of dirt.

The laser arc method can be used to deposit thick ta-C coatings of up to 20µm at high coating rates. "High coating thicknesses are crucial for certain applications – especially in the auto industry, where components are exposed to enormous loads over long periods of time," Dr Weihnacht added.

Tom Austin-Morgan

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