High temperature tribology

High-temperature tribology: friction and wear at high temperatures 

High operating temperatures are omnipresent: whether in drives, in industrial manufacturing processes such as hot forming and machining or power generation. Everywhere there is the problem that when lubrication with oil or grease is no longer sufficient, unlubricated friction contacts must function reliably for as long as possible. High temperatures often determine or limit the performance of friction-loaded systems. High temperatures are not only caused by the environment, but are also generated by frictional heat. Different classes of materials - polymers, metals, ceramics and coatings - react very differently to increased operating or frictional temperatures: while polymers and some coatings tend to decompose thermally, other materials react more strongly with the atmosphere or are plastically deformed in highly adhesive frictional contact. A particular challenge is an experimental test in which the thermal effects, including the interactions with the atmosphere, can be simulated close to the application. Only then can relevant statements on the tribological behavior of systems under elevated temperatures be obtained.

We measure friction and wear on materials and components at temperatures of up to 800 °C. We clarify the underlying damage mechanisms, describe them and derive measures to optimize tribological systems in terms of performance, reliability and service life.

R&D services for high-temperature tribology for your company

Tribological standard tests

• Vibration friction wear test (SRV) with modified high-temperature test setup for better temperature distribution
• Impact test or sliding wear test with simple contact geometry (pin/plate) for material screening of armor and high-temperature materials under atmospheric influence (ammonia, methanol, gasoline)
• Corrosion testing under hot gas or hydrothermal test conditions with different atmospheres
• Qualification of coatings for high application temperatures  

Tribological component testing

• Plain bearings: Friction and wear behavior at high operating temperatures in combustion atmospheres
• Valves: Application-related wear test for valve seat/valve seat ring
• Valve guides: Testing with engine components (valve stem / valve guide sleeve) for tribological component characterization
• Tribological qualification of ceramic or coated cutting tools

Material analysis

• Surface analyses to identify wear mechanisms using light microscopy, laser microscopy, scanning electron microscopy
• Investigation of microstructural damage as a result of tribological stress using light microscopy, scanning electron microscopy
• In situ analysis of the oxide formation of materials using temperature-dependent Raman spectroscopy and infrared spectroscopy
• Tribological characterization of different oxides with regard to their friction properties (glaze layer)

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Wear mechanisms of exhaust-loaded, non-lubricated tribological systems

Efficiency and emission requirements for combustion engines lead to higher combustion temperatures and pressures and make complex exhaust systems with multi-stage turbochargers and exhaust gas recirculation necessary. The control effort of these complex exhaust systems requires the use of different actuators, such as exhaust gas flaps or valves, VTG guide vanes, EGR flaps, brake flaps or wastegates on turbochargers. Manufacturers require new material technology solutions for the increasing tribological loads on the bearing points. An efficient and application-oriented qualification strategy was developed in this project for this purpose.

Gas engines with energy-efficient system technologies and integral robustness

Power-to-X technologies offer interesting solutions for storing electricity generated from renewable sources. Gas engines that can use renewable fuels flexibly are used for reconversion into electricity. A joint research project between industrial partners and Fraunhofer IWM aims to find solutions for increasing the load capacity, reliability and service life of components in gas engines that are subject to the highest tribological stresses in order to enable further improvements in efficiency and reduce emissions.

One of the biggest tribological challenges of gas engines are the lubrication conditions in the valve seat and guide sections. To investigate the friction behavior and wear of valve guides close to the application, a test set-up was developed to simulate engine-like conditions in terms of lubrication, temperature and lateral forces on the valves. This enables a direct comparison of lubricants, valve stems and guide sleeves at a test level close to the application and can save expensive engine test runs.

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Publications

• Zhao, B.; Khader, I.; Liu, H.; Zhou, T.; Konrath, G.; Kailer, A., Tribological characterization of an alumina-based composite in dry sliding contact against laser-heated and unheated Inconel 718, Tribology International 155 (2021) Art. 106773, 13 Seiten Link
• Zhao, B.; Khader, I.; Raga, R.; Konrath, G.; Degenhardt, U.; Kailer, A., High temperature tribological properties of silicon nitride in dry sliding contact against Inconel 718 heated by laser, Wear 434-435 (2019) 203000, 9 Seiten Link
• Khader, I.; Renz, A.; Kailer, A.; A wear model for silicon nitride in dry sliding contact against a nickel-base alloy; Wear 376-377/Part A (2017) 352-362 Link
• Renz, A.; Kürten, D.; Lehmann, O.; Wear of hardfaced valve spindles in highly loaded stationary lean-burn large bore gas engines; Wear 376-377/Part B (2017) 1652-1661 Link
• Renz, A.; Khader, I.; Kailer, A.; Tribochemical wear of cutting-tool ceramics in sliding contact against a nickel-base alloy; Journal of the European Ceramic Society 36/3 (2016) 705-717 Link
• Rapoport, L.; Moshkovich, A.; Perfilyev, V.; Lapsker, I.; Kugler, M.; Kailer, A.; Renz, A.; Hollstein, T.; High temperature friction behavior of CrVxN coatings; Surface and Coatings Technology 238 (2014) 207-215 Link
• Khader, I.; Renz, A.; Kailer, A.; Haas, D.; Thermal and corrosion properties of silicon nitride for copper die casting components; Journal of the European Ceramic Society 33/3 (2013) 593-602 Link
• Khader, I.; Hashibon, A.; Albina, J.-M.; Kailer, A.; Wear and corrosion of silicon nitride rolling tools in copper rolling; Wear 271/9-11 (2011) 2531-2541 Link
• Khader, I.; Kailer, A.; Damage mechanisms in silicon nitride wire-rolling tools: Lab-scale experiments and correlation with finite element modeling; Journal of Materials Processing Technology 210/10 (2010) 1314-1325 Link
• Kailer, A.; Mauk, P.-J.; Eckardt, C.; Berroth, K.; Kozlowski, J.; Wagemann, A.; Ceramic rolling tools for enhanced lifetime and product quality; Steel Research International 79/Special Edition; Pietrzyk, M. (Ed.) Verlag Stahleisen, Düsseldorf (2008) 401-406 Link

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