Coating engine components with hard carbon reduces friction to almost zero – a development that could save billions of liters of fuel worldwide every year. Now researchers have developed a new laser method to apply the coating on the production line. Scientists already know how to coat components with diamond-like carbon to minimize friction. But now researchers of the Fraunhofer Institute for Material and Beam Technology IWS in Dresden 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. By applying carbon coatings to engine components such as piston rings and pins, fuel consumption can be reduced.
Carbon-based coatings are already used in volume production. But now the team of IWS researchers led by Prof. Leson, Dr. Hans-Joachim Scheibe and Dr. Volker Weihnacht has 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. “Unfortunately, you can’t just scrape off diamond dust and press it onto the component. So we had to look for a different method,” says Dr. Scheibe, who has spent over 30 years investigating carbon’s friction-reducing properties.
A pulsed laser controls the light arc
In a similar style to old-fashioned 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 thanks 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 very thick ta-C coatings of up to 20 micrometers 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,” says Dr. Weihnacht.
The automotive and motorcycle manufacturer BMW is working intensively on the industrial-scale implementation of ta-C engine components in its various vehicle models with the aim of reducing their fuel consumption.
Dr. Volker Weihnacht, Prof. Andreas Leson and Dr. Hans-Joachim Scheibe (left to right) successfully developed a laser arc method of depositing friction-reducing, wear-resistant coatings on components. © Dirk Mahler/Fraunhofer
NASA is working plasma spray coating for high temperature resistant coatings
Harder and a team of materials researchers and engineers at NASA Glenn are currently developing the next generation of coatings to allow for operation of turbine engine components up to 2700°F and beyond.
The applications of this game-changing technology are far reaching according to Harder. “Using this high temperature process, we can potentially create coatings rapidly with varied architecture and composition for fuel cells, batteries and sensors, as well as a host of other technologies including space applications,” he says.
NASA Glenn is maturing and developing this technology while making direct contributions to NASA’s aeronautic mission.
SOURCES – Fraunhofer-Gesellschaf, NASA, Youtube