The topics of friction, lubrication and wear are becoming increasingly important against the background of environmental and climate protection, energy efficiency and electric mobility. The research focus of the department of surface technology is therefore the development of tribological functional coatings. On the one hand, this includes novel friction-reducing hard material coatings to increase energy efficiency and the service life of transmission components, especially for rolling bearings and gears. On the other hand, tribological functional coatings are also used for coating high-performance cutting and forming tools. For cutting tools, the development goals are dry machining, hard machining, tools for workpiece materials that are difficult to machine, and increasing the cutting path and metal removal rate. For forming tools, the focus is on dry machining, increasing tool life and workpiece quality.
Increasing the energy efficiency and service life of gear components
Increasing the energy efficiency and service life of transmission components by means of friction- and wear-minimizing surfaces is an important future topic for climate protection. This applies both to the area of primary energy generation and to the areas of industry, trade and mobility. The great importance of tribology for climate protection is highlighted in the current study "Tribology in Germany: Cross-sectional technology for reducing CO2 emissions and conserving resources" by the Gesellschaft für Tribologie e.V. (2019) is impressively presented.
For example, this study shows that a compact and therefore lightweight design of electric motors requires high speeds in the range of 10,000 to 30,000 rpm. This results in numerous tribological challenges for the reduction gears required. In addition to minimizing friction and wear and the use of new low-viscosity lubricants, tribo-acoustic emissions in particular play a major role in such gears.
This is because these emissions are often in a frequency range that is uncomfortable for humans and are easier to hear due to the significantly lower overall noise emissions of electric vehicles compared to combustion engines. In the future, therefore, friction, lubricant film formation, wear as well as the acoustic emissions of high-speed transmission components must be controlled by various measures such as friction-reducing hard material coatings or by targeted microstructuring of the surfaces of the machine elements used.
In the field of hard material coating for high-performance cutting tools, the topics of dry machining, machining of difficult-to-machine workpiece materials such as titanium or cobalt-chrome alloys from the medical sector, but also increasing the cutting path and the metal removal rate are of great importance. For the coating of forming tools (cold massive forming) the topics of dry machining and increasing tool life are in the focus. If cooling lubricants are completely dispensed with, subsequent cleaning processes are not required. Thus, new tool coatings, which allow dry machining with the same tool life and workpiece quality, contribute directly to environmental protection and resource efficiency.
In the surface technology department, the application of tribological hard material coating systems is mainly carried out using the PVD magnetron sputter process. Magnetron sputtering is an industrially used physical vapor deposition process (PVD: Physical Vapour Deposition). In cooperation with project partners, hard material coatings deposited by the PVD-Arc process are also being investigated. In general, the environmental compatibility of physical vapour deposition processes is relatively good despite the complex vacuum system technology required, since both arc evaporation in the PVD-Arc process and cathode sputtering in magnetron sputtering of the mostly metallic target materials produce no or only slightly environmentally harmful waste products.
PDV processes enable the deposition of a very wide range of metallic and non-metallic coating materials. Reactive PVD processes can also be used to incorporate light elements such as nitrogen, carbon, oxygen, but also boron or hydrogen into the layers, so that in combination with metallic target materials such as titanium, chromium, vanadium, molybdenum, zirconium, tungsten, aluminium etc., the corresponding nitrides, carbides, oxides or borides can also be deposited. In this way, an almost unlimited number of different hard materials can be deposited using PVD processes. This includes in particular also purely covalently bonded hard materials such as diamond or diamond-like amorphous carbon layers.
In the field of friction-reducing coatings for rolling bearing rings and gears, the Surface Technology Department works on the further development of hydrogen-containing amorphous carbon coatings (a-C:H) as well as on the development of novel self-lubricating hard material coating systems based on various PVD solid lubricant coatings in combination with transition metal nitride coatings (TiAlN, CrAlN, ...). Besides layer composition and layer build-up, the tribology can also be influenced by setting defined surface topographies in the micrometer range. The microstructuring of the layers or substrates before coating is carried out in close cooperation with the Laboratory for Micromachining as well as with partner institutes in the field of laser processing.
The trend towards the increasing integration of further functions such as corrosion protection, electrical, optical, acoustic or antimicrobial properties in functionalized surfaces of tools and machine elements also continuously leads to new research topics. Further research areas of the department of surface technology are new metallic alloys produced by PVD processes, corrosion research and sol-gel coating processes.