Tribology Innovation Center Dresden (TICD)

In times of global efforts to reduce climate-damaging CO₂ emissions, the issue of friction often plays an underestimated role. After all, up to 20 percent of the primary energy used in a wide variety of vehicles, machines and systems is unnecessarily lost due to friction. In addition, there is the problem of tribological wear of tools and components, which limits the service life of systems in many applications or causes downtimes and maintenance times and results in high resource consumption.

In the Tribology Innovation Center Dresden (TICD) Fraunhofer IWS together with the TU Dresden researches tribological basic phenomena as well as suitable tribological measures, especially through coatings or other surface modifications. The goal is a significant reduction of friction and wear, whereby the solutions found should be as universally applicable as possible. Attention is paid to ensuring that the technologies developed are suitable for series production and can be used directly in the production of components and tools. 

The focus is on the so-called ta-C layer (tetrahedral amorphous carbon), the hardest variant from the group of diamond-like carbon (DLC) layers. Structurally and chemically, it combines extremely high hardness with very low friction under almost all conditions. This combination predestines the ta-C coating for numerous applications of components and tools in a wide range of industries.

The Laser-Arc process for ta-C coating developed at Fraunhofer IWS is now industrially established and is used in the series production of ta-C coatings. A fundamental problem is the particle-induced roughness of the coatings. Currently, work is being done on a new generation of plasma filters to deposit almost defect-free ta-C coatings.

Several projects are dedicated to supra-low friction with ta-C layers. For this purpose, solutions are being developed that transfer the phenomenon of supra-friction, which has so far only been observed in the tribometer, to mechanical engineering applications (CHEPHREN, SUPRASLIDE).

Coating systems based on ta-C with various dopants (ta-C:X) are also being produced for critical ambient conditions (dry to vacuum). Here, a combination of ta-C with the solid lubricant MoS₂ is proving particularly promising. Suitable hybrid coating systems are being developed in the LUBRICOAT project.

The laser as a tool is capable of shaping the topography of component surfaces with micrometer precision. By means of laser structuring, two- and three-dimensional micro- and nanostructures can be applied and thus the tribological behavior of sliding surfaces can be changed in a targeted manner. This is done either by influencing the wetting and viscosity-related lubricant film structure, the reservoir effect of micro-lubricant film pockets, hydrodynamics or oil conduction structures.

The structuring process can be adapted to the material and surface to be processed by selecting the right wavelength and pulse duration. With the direct-writing process, flexible, freely designed surface structures can be generated. By superimposing several partial beams from a laser source and the resulting periodic interference pattern in the superposition volume, direct laser interference patterning (DLIP) allows the generation of up to one million structures per laser pulse. As a result, it is possible to apply large-area laser-structured surfaces to tribological parts and components, such as bearing washers and piston rings, in a very short time and thus to use the process economically in series production.

In addition to the focus on application-specific coating development and friction minimization, the TICD also conducts extensive research into the fundamentals of tribological characterization. Great importance is attached to reproducing real loads by means of suitable geometries and test parameters. Testing can also be carried out in different atmospheres, including ultra-high vacuum. 

Tribological analysis is accompanied by comprehensive coating and surface analysis. All common methods of basic coating and surface analysis are available at the TICD – from basic mechanical characterization to topography/roughness analysis and adhesion tests, as well as electron microscopy, Raman spectroscopy and X-ray reflectometry for chemical and structural analyses.

A second focus is research on new methods of tribological characterization, tribometry. Current topics are the investigation of the lubrication condition by means of high-resolution measurement of the complex electrical resistance, visualization of time- and spatially-resolved information (triboscopy) and metrological recording of suprashming in geometry similar to the component and close to the application. 

Ultra-low friction allows friction losses in internal combustion engines to be cut in half compared to current state-of the art. The friction coefficient is between 0.01 and 0.05, which is roughly equivalent to the friction of very smooth steel sliding on ice.

Experts, on the other hand, only speak of superlubricity when the friction coefficient falls below 0.01. To illustrate this, one can imagine a five-ton elephant standing on a plate. If this plate is super-lubricated, a person could push the elephant effortlessly.