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TRIGUS – Tribologically induced changes of boundary surfaces and bulk structures in dry lubricated systems under defined atmospheres

Subject Area Coating and Surface Technology
Synthesis and Properties of Functional Materials
Term from 2019 to 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 415726702
 
Final Report Year 2025

Final Report Abstract

In the TRIGUS project, structural changes caused by friction in two dry friction model systems, hydrogen-free amorphous carbon (ta-C) and molybdenum disulfide (MoS₂), were investigated as a function of atmosphere, counter body, and foreign atoms. More than 150 friction experiments were conducted under controlled atmospheric conditions. The initial layers, friction tracks, and counter body imprints were characterized laterally and in-depth using ion beam microanalysis, Raman spectroscopy, scanning electron microscopy, and, in some cases, crosssectional transmission electron microscopy. The advancement of triboscopic methods and new approaches enabled a quantitative evaluation of the temporal and lateral tribological behavior. Ion beam microanalysis, which to our knowledge was used for the first time to analyze dry friction systems, provided detailed information on element transfer, distribution and concentration in the friction track and on the counter body, which could be correlated with the friction mechanism. By implanting Si and Ta in ta-C and co-deposition of C and Si, the environmental dependence of the friction coefficient of ta-C could be significantly reduced. The ta-C:Ta layer also had an almost unchanged high hardness and a similarly high modulus of elasticity as ta-C, which was attributed to structural peculiarities of this system. In the frictional contact of ta-C with 4 metallic and 2 ceramic counter bodies, the ta C/brass pairing was characterized by a shortterm friction coefficient of 0.05 ≤ µ ≤ 0.13 both under ambient conditions and in pre-vacuum and high vacuum. For the MoS₂/100Cr6 steel friction system, the atmosphere-dependent friction coefficient was correlated with structural changes in the friction layer and counterbody surface. Contrary to current knowledge, no oxidation of the MoS₂ layer was found after friction experiments in dry air. However, a heterogeneous element and structural distribution, including oxygen, was observed on the counterbody. This was attributed to a series of complex intermediate compounds with the general composition FenMoxOySz. The proposed friction mechanism involved the transfer of MoS₂ onto the counterbody, where it underwent incomplete oxidation under friction pressure and possible interaction with the counterbody material. Furthermore, the interaction between ta-C and MoS₂ layers was studied using microstructured substrates, demonstrating increased mechanical durability in both air and vacuum conditions. The results clarify and expand the understanding of friction mechanisms and will allow improved tribological properties to be achieved in the future through suitable adaptation of surfaces in aerospace, medical technology and vacuum technology.

Link to the final report

https://nbn-resolving.org/urn:nbn:de:bsz:d120-qucosa2-994165

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