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Lubricants 2016, 4(2), 19; doi:10.3390/lubricants4020019

Microstructural and Chemical Characterization of the Tribolayer Formation in Highly Loaded Cylindrical Roller Thrust Bearings

1
Department of Material Science and Engineering, Saarland University, Saarbrücken 66123, Germany
2
Department of Physics, Pontifical Catholic University of Chile, Santiago de Chile 7820436, Chile
3
Institute for Machine Elements and Machine Design, RWTH Aachen, 52062 Aachen, Germany
*
Author to whom correspondence should be addressed.
Academic Editors: Werner Oesterle and Ga Zhang
Received: 24 March 2016 / Revised: 13 May 2016 / Accepted: 18 May 2016 / Published: 8 June 2016
(This article belongs to the Special Issue Tribofilms and Solid Lubrication)
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Abstract

Zinc dithiophosphates (ZDDP) have been widely applied in automobile industry for over 70 years as a lubricant additive for wear protection. Tribolayers have been described as blue- and brown-colored layers on surfaces observed by microscopical observation or even bare eye presumably as a consequence of layer thickness or chemical composition. However, the reaction pathways of ZDDP tribolayers are still not yet fully understood. In the present study, the difference between the blue- and brown-colored tribolayers has been revealed by high resolution methods in cylindrical roller thrust bearings at relatively high contact pressures of around 1.92 GPa. After running a FE8 standard bearing test with a normal load of 80 kN and a temperature of 60 °C, said tribolayers could be identified on the bearing surfaces. By using Raman spectroscopy, it could be shown that the blue-colored layers are enriched by FeS and ZnS whereas the brown-colored layers show a significant amount of Fe3O4. This is an interesting finding as it clearly shows a correlation between the color appearance of the films and the chemical composition besides potential film thickness variations. Finally, transmission electron microscopy verified the amorphous nature of the formed tribolayer which is in a good agreement with literature. View Full-Text
Keywords: Lubrication; additives; ZDDP; tribolayer; bearings; microstructure Lubrication; additives; ZDDP; tribolayer; bearings; microstructure
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Gachot, C.; Hsu, C.; Suárez, S.; Grützmacher, P.; Rosenkranz, A.; Stratmann, A.; Jacobs, G. Microstructural and Chemical Characterization of the Tribolayer Formation in Highly Loaded Cylindrical Roller Thrust Bearings. Lubricants 2016, 4, 19.

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