Researchers from Argonne National Laboratory and the University of Akron have applied a “diamond-like” coating to wind turbine drivetrains that could prolong their life.

Due to the strenuous environment inherent in such drivetrains, key components such as actuators, bearings and gears are prone to failure, meaning turbines require regular maintenance that helps drive up the price of wind energy. Prolonging the life of these components could greatly reduce the cost of wind power, thereby making it a more attractive energy source.

These failures are often due to a phenomenon known as micropitting, in which the repeated rolling and sliding cycles in the gears and bearings of turbines lead to cracks on the surface of drivetrain components. Further contact only exacerbates the cracking once it begins, chipping away at the metal and increasing the severity of the existing cracks until costly maintenance is necessary or the drivetrain fails.

Enter Argonne's Tribology and Thermal-Mechanics Section and its Surface and Lubrication Interaction, Discovery and Engineering (SLIDE) initiative, which investigates how lubricants and materials interact and develops novel lubrication and coating concepts that reduce friction, and therefore micropitting. The team applied a coating, N3FC, whose carbon-to-carbon bonding is similar to that of diamonds, to wind turbine components, which was not the intended use.

SLIDE Initiative members (l-r) Levent Eryilmaz, Giovanni Ramirez, Ali Erdemir and Aaron Greco. Image credit: ANL."We felt that if it was working under other sliding conditions, it might work in wind turbine drivetrains as well," says SLIDE's Ali Erdemir, an Argonne Distinguished Fellow. "Initially, our expectations were low, as we thought the coating would wear out due to the high stresses inherent in wind turbines, but that didn't happen."

So far, the coating has proved its worth through more than 100 million testing cycles with no appreciable micropitting. Erdemir admits that they don't know exactly how far it could go, as it has surpassed the time limit of SLIDE's benchtop micropitting test rig. If the coating performs similarly under real-world conditions, it could mean huge savings in terms of maintenance and prevention of failure in wind turbines nationwide, Erdemir says.

But first, he adds, they need to learn exactly why it works.

"We don't yet understand the exact mechanism," says Erdemir. "The general belief is that component wear life extension requires a much harder coating, as more hardness reduces wear. But in this case, the coating has less hardness than the base steel, so conventional thought doesn't apply."

The team is now eager to work with companies to see how N3FC performs in the field. Until then, they will stay busy trying to discover the mechanism behind this surprising scientific development. "We would love to get to the bottom of this and design even better coatings," Erdemir says.

The team is also testing the coating in sealing applications for compressors. As a low-friction surface coating, it may also prove beneficial in natural gas and hydrogen environments. "It appears to have multiple capabilities in terms of performance," Erdemir says.