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Tribofilm formation from TiC and nanocomposite TiAlC coatings, studied with Focused Ion Beam and Transmission Electron Microscopy
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry. (Oorganisk kemi)
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry. (Oorganisk kemi)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
2009 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 266, no 9-10, 988-994 p.Article in journal (Refereed) Published
Abstract [en]

This work demonstrate how two different carbide coatings respond very differently to tribological stress and their very different ability to provide low friction tribofilms in dry sliding against steel. Both coatings, TiC and TiAlC, were deposited by DC-magnetron sputtering, but while the TiC is a thermodynamically stable coating, the TiAlC is made metastable with the addition of Al, and therefore releases carbon upon tribological testing. Thus, the TiAlC coating is shown to be self-lubricating on the atomic scale which makes very low friction   achievable. The primary interest in this study is the differences in the tribofilms formed on the steel balls that have been sliding against  the two coatings. Cross-section samples for transmission electron  microscopy were extracted from the ball tribofilms using a focused ion beam instrument. X-ray photoelectron spectroscopy and Raman analysis were employed to provide information on the chemical and structural  characteristics of the tribofilms. It was shown that tribofilms on steel balls largely inherit the structure and composition that evolve   in the coating wear tracks, that the tribofilm microstructure greatly affects the friction level. It was also shown that tribofilm delamination, occurring with tribofilm growth, was initiated in weak ribbon like regions inside the tribofilm.

Place, publisher, year, edition, pages
2009. Vol. 266, no 9-10, 988-994 p.
Keyword [en]
Material transfer, Tribofilm, Carbon, Graphitisation, Low friction
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-96728DOI: 10.1016/j.wear.2009.02.002ISI: 000265816800012OAI: oai:DiVA.org:uu-96728DiVA: diva2:171400
Available from: 2008-02-14 Created: 2008-02-14 Last updated: 2016-04-14
In thesis
1. Self Lubrication on the Atomic Scale: Design, Synthesis and Evaluation of Coatings
Open this publication in new window or tab >>Self Lubrication on the Atomic Scale: Design, Synthesis and Evaluation of Coatings
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis a new design concept of tribologically active coatings aimed for low friction applications, have been explored. Materials modeled by ab initio DFT calculations were realized through deposition of carbide and nanocomposite coatings by DC-magnetron sputtering.

The design concept employs destabilization of a carbide material by alloying with a weak carbide-forming element, which refines the structure into a nanocomposite. The destabilization creates a driving force for superficial ejection of carbon in a tribological contact, forming a lubricious graphitic carbon layer. The otherwise hard material limits the real contact area and the transformed layer accounts for low shear resistance. Hence, the ideal situation for low friction is provided by formation of an easily sheared thin surface layer on a hard material.

TiAlC was chosen as a model system for the theoretical modeling as well as for the depositions. The elemental composition, microstructure and mechanical properties of the coatings were characterized to relate the inherent properties to the experimentally achieved tribological response.

As predicted by theory, TiAlC coatings were shown to provide self-lubrication on the atomic scale by giving low friction through a tribologically induced surface restructuring.

It was shown possible to reduce the friction coefficient from 0.35 for TiC to 0.05 by addition of Al.

Alloying with Al also proved to be a potent method in tailoring residual stresses from high and often detrimental levels to acceptable levels, with no significant reduction in either hardness or Young’s modulus.

The effect of adding Al into TiC on the oxidation resistance was also explored. The critical temperature for onset of oxidation proved to increase with the Al-content from about 350°C for TiC to about 450°C for TiAlC with about 7 at% Al. A further increase in Al content did not change the onset temperature further but reduced the oxidation rate.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. 59 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 391
Keyword
Materials science, Tribology, low friction, PVD, sputtering, nanocomposite, Materialvetenskap
Identifiers
urn:nbn:se:uu:diva-8443 (URN)978-91-554-7088-3 (ISBN)
Public defence
2008-03-07, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, 75121 Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2008-02-14 Created: 2008-02-14 Last updated: 2010-03-03Bibliographically approved

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Jansson, UlfWiklund, Urban

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