Coating shows unexpected potential to improve reliability in wind power

Researchers from Argonne's SLIDE initiative developed a 'diamond-like' coating that could prove benefitial when used to coat equipment for wind turbines, like the bearing in this photo. L-R Levent Eryilmaz, Giovanni Ramirez, Ali Erdemir and Aaron Greco
A group of researchers from the US Department of Energy's (DOE) Argonne National Laboratory and the University of Akron discovered that a particular form of carbon coating not necessarily designed for wind turbines may indeed prove beneficial to the wind industry.

Due to the strenuous environment inherent in wind turbine drivetrains, key components such as actuators, bearings and gears are prone to failure, meaning turbines require regular maintenance that drives up the price of wind energy. Prolonging the life of these components could greatly reduce the cost of wind power, 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, even worse, the drivetrain fails.

Argonne's Tribology and Thermal-Mechanics Section’s Surface and Lubrication Interaction, Discovery and Engineering (SLIDE) initiative investigates how lubricants and materials interact and develops novel lubrication and coating concepts that reduce friction, and therefore micropitting, prolonging component life across a range of energy technologies. The SLIDE researchers applied this ‘diamond-like’ coating to wind turbine components.

"We felt that if it was working under other sliding conditions, it might work in wind turbine drivetrains as well," said SLIDE's Ali Erdemir. "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, named N3FC, has proven its worth through more than 100million 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 millions of dollars worth of savings in terms of maintenance and prevention of failure in wind turbines nationwide.

But first, Erdemir added, they need to learn exactly why it works: "We don't yet understand the exact mechanism. 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 now plans to work with companies to see how N3FC performs in the field. 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.

Author
Tom Austin-Morgan

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