Tribological ta-C Coatings

ta‑C carbon coatings are characterized by extremely high hardness and thus exceptional wear resistance, combined with universally low friction. The coating is deposited at temperatures below 100°C, which means that temperature-sensitive steels, aluminum, and even plastics such as polyamide can be coated with ta-C.

The chemically inert carbon coatings reduce the tendency of counter materials to adhere, thus allowing lubricant-free use with low friction coefficients of around 0.1. In combination with certain lubricants, ultra-low friction < 0.01 can even be achieved. ta‑C is temperature-stable up to 400°C.

Customized ta‑C coatings on components of bearings, guide rails, and piston-cylinder pairs reduce friction and provide long-lasting wear protection. With hardnesses of up to 70 GPa (equivalent to 7000 HV), surfaces remain almost wear-free even in the presence of extremely abrasive microparticles. The ta‑C coatings also bridge insufficient lubrication conditions and even temporary lubricant losses.

Friction reduction and wear protection in a gear transmission can be achieved with a thick ta‑C coating without further modification of the tooth geometry. ta‑C coatings are also ideal for wear protection in media-lubricated systems.

Suitable adhesion layer technologies and a special coating architecture enable the deposition of ta‑C on gears with thicknesses of 10 µm and more. It is possible to use so-called run-in layers, which are applied to the wear-resistant ta‑C base layer. This reduces the load during initial contact and ensures gentle running-in of the sliding surfaces.

The long-term process stability of laser arc technology combined with a concept of residual stress management enables the deposition of ultra-thick ta‑C layers. These can be used for extremely high wear requirements, e.g., for plain bearings or for applications with high particle erosion.

The layer has a homogeneous structure and exhibits virtually no hardness gradient, as demonstrated by nanohardness measurements on the cross-section. The internal stress of the layer is relatively moderate at approx. 1.6 GPa (compressive stress). The layer can be applied to a wide variety of substrate materials, even plastics.

Thanks to the low deposition temperature, ta‑C can be deposited on plastics with high adhesion. The super-hard ta‑C coating protects against abrasive stress in gearboxes with plastic gears, for example.

Special adhesion layer concepts have been developed for coating plastics. Special hardness-graded running-in layers prevent overload during initial tribological contact with sensitive counter materials and ensure smooth running-in.

Due to the atomistic surface structure of ta‑C coatings, these form extremely slippery surfaces when used with certain lubricants. It is therefore possible to achieve superlubrication with ta‑C coatings, e.g., in plain bearings with ta‑C-coated bearing discs.

Fraunhofer IWS is a global leader in the development of superlubricated tribological systems based on ta‑C-coated sliding components and conducts extensive tribology research in this field.