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Design of Nanocomposite Low-Friction Coatings
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
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.
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2007 (English)In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 17, no 10, 1611-1616 p.Article in journal (Refereed) Published
Abstract [en]

Friction and wear between moving surfaces is unavoidable and is an important reason for failure of mechanical components. A wear-resistant and low-friction coating can prolong the lifetime of an engineered component. Here we demonstrate a new concept for the design of low-friction nanocomposite carbide coatings with an intrinsic driving force to form amorphous carbon (C-C bonds). Ti-Al-C has been chosen as a model system, but the idea is general and should be applicable to a wide class of materials. The ability to intrinsically form amorphous carbon is achieved by a substitutional solid solution of the weak-carbide-forming metal (Al) into the thermodynamically stable monocarbide (TiC). This creates, in a controllable manner, a driving force for phase separation of carbide particles embedded in a matrix of amorphous carbon. In a tribological contact the amorphous carbon can be further graphitized and thereby lower the friction coefficient. Consequently, the model system has a self-lubricating mechanism but at the same time a tunable share of the two phases, which gives excellent possibilities to design wear resistance and toughness. In this paper we show that the friction coefficient can be lowered by more than 50 % for Al-containing TiC coatings without severe loss in mechanical characteristics.

Place, publisher, year, edition, pages
2007. Vol. 17, no 10, 1611-1616 p.
Keyword [en]
Coatings, Nanocomposites, Thin films
National Category
Engineering and Technology Natural Sciences
Identifiers
URN: urn:nbn:se:uu:diva-96306DOI: 10.1002/adfm.200600724ISI: 000248062100003OAI: oai:DiVA.org:uu-96306DiVA: diva2:170837
Available from: 2007-10-19 Created: 2007-10-19 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Synthesis and Characterization of Ternary Carbide Thin Films
Open this publication in new window or tab >>Synthesis and Characterization of Ternary Carbide Thin Films
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis reports on synthesis, microstructure and properties of binary and ternary carbide thin films deposited by dc magnetron sputtering. These materials are interesting since they exhibit a wide range of useful properties, such as high hardness, resistance to wear and oxidation, and high electrical conductivity. Here, an early transition metal (M) and carbon (C) have been used as the basis, often with the addition of a second M-element or an A-group element (A). In these systems nanocomposites, metastable solid solutions, multilayers, or Mn+1AXn-phases have been deposited. The Mn+1AXn-phases are a group of nanolaminated compounds with a unique mixture of metallic and ceramic properties. In general X is carbon or nitrogen, although here only carbon has been used.

Epitaxial MAX-phase thin films of Ti2AlC, Ti3AlC2 and V2GeC have been deposited for the first time. They have been studied with emphasis on phase stability, phase composition and nucleation characteristics to gain deeper insights into their growth. The microstructure of the films was characterized by electron microscopy and X-ray diffraction. In addition, bond strength characteristics have been studied by soft X-ray spectroscopy and complementary calculations within DFT. Their mechanical and electrical properties have been studied, and the results are discussed on the basis of their electronic structure. Furthermore, by interleaving the Ti3SiC2 MAX-phase with TiC0.67 a multilayer structure has been formed, for which a new intrusion-type deformation behaviour has been described.

A new concept in the design of nanocomposite films has been developed, whereby a solid solution of a weak carbide-forming element in the carbide structure creates a driving force for surface segregation of C. This concept has been verified both theoretically and experimentally for the Ti-Al-C and Ti-Fe-C systems. It has been shown by pin-on-disc measurements that this surface segregation leads to graphitization and consequently a very low friction coefficient for these films. Finally, it has been demonstrated that low-friction films with tunable magnetic properties can be achieved in the Ti-Fe-C system.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 62 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 353
Keyword
Chemistry, Thin film, dc magnetron sputtering, tribology, carbide, PVD, MAX-phase, DFT, solid solution, Kemi
Identifiers
urn:nbn:se:uu:diva-8265 (URN)978-91-554-6991-7 (ISBN)
Public defence
2007-11-09, Häggsalen, Ångström Laboratory, Lägerhyddsvägen 1, 751 21, Uppsala, 10:15
Opponent
Supervisors
Available from: 2007-10-19 Created: 2007-10-19 Last updated: 2010-09-13Bibliographically approved
2. 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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Lewin, ErikSanyal, BiplabWiklund, UrbanEriksson, Olle

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