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A Theoretical Perspective on the Chemical Bonding and Structure of Transition Metal Carbides and Multilayers
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The present thesis deals with a theoretical description of issues regarding chemical bonding, structure and stability of transition metal carbides and multilayered structures.

First principles density functional theory has been used extensively to investigate the properties of alloyed solutions of transition metal carbides. Joint theoretical and experimental investigations have shown that there is a driving force for carbon to be released from these ternary carbide systems as a response to the alloying. This release of carbon was shown to yield favorable lubricating properties in the case of alloyed solutions of Ti-Al-C, that were not present in the case of pure TiC, a property that can be used to design new materials that combine high hardness with favorable tribological properties.

From calculations of the activation energy of C diffusion in the vicinity of substitutional transition metal impurities (M) in TiC, it is found that the mobility of C atoms is increased due to the presence of the impurities. The lowering of the activation energy barriers suggests that the mobility of C in alloyed solutions of Ti-M-C is increased and will be more pronounced at lower temperature than for C diffusion in TiC.

The magnetic properties of alloyed solutions of Ti-Fe-C has been investigated using both theory and experiment. Theoretical calculations reveal that the magnetic moment and the critical temperature increase when increasing the Fe content as well as when lowering the C content in the system. Furthermore, the magnetic exchange parameters between Fe atoms were found to clearly reflect changes in the chemical bonding when varying the C content. Experimentally the magnetic properties were found to be rather substantial. Furthermore, the magnetic properties changes upon annealing due to the formation of Fe-rich and Fe-poor regions in the system. After long enough annealing times precipitates of α-Fe are formed which is consistent with theoretical predictions.

The interaction between TiC(111) surfaces and C in the form of graphite has also been investigated. For these systems it was found that graphite was rather strongly bonded to the carbide surface and that the atomic as well as electronic structure at the interface depend on the termination of the carbide surface. This research was motivated by the recent interest in graphene, but also to investigate how carbide grains interacts with C when dispersed in a carbon matrix.

A model for the calculation of structural parameters in multilayer structures has been presented and evaluated. The model is based on classical elasticity theory and uses the elastic constants of the materials constituting the multilayer as the only input.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2010. , p. 61
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 749
Keywords [en]
Electronic structure, transition metal carbides, density functional theory, disorder, multilayers, chemical bonding, materials science
National Category
Condensed Matter Physics
Research subject
Materials Science
Identifiers
URN: urn:nbn:se:uu:diva-123485ISBN: 978-91-554-7827-8 (print)OAI: oai:DiVA.org:uu-123485DiVA, id: diva2:314586
Public defence
2010-06-11, Häggsalen, Ångström Laboratory, Lägerhyddsvägen 1, Polacksbacken, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2010-05-21 Created: 2010-04-27 Last updated: 2010-05-21Bibliographically approved
List of papers
1.
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2. A first principles study of the stability and mobility of defects in titanium carbide
Open this publication in new window or tab >>A first principles study of the stability and mobility of defects in titanium carbide
(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Research subject
Materials Science
Identifiers
urn:nbn:se:uu:diva-123481 (URN)
Available from: 2010-04-27 Created: 2010-04-27 Last updated: 2017-01-25
3. Surface and interface properties of graphene on titanium carbide: A first principles study
Open this publication in new window or tab >>Surface and interface properties of graphene on titanium carbide: A first principles study
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(English)Manuscript (preprint) (Other (popular science, discussion, etc.))
National Category
Condensed Matter Physics
Research subject
Materials Science
Identifiers
urn:nbn:se:uu:diva-123482 (URN)
Available from: 2010-04-27 Created: 2010-04-27 Last updated: 2017-01-25
4. Design of the Lattice Parameter of Embedded Nanoparticles
Open this publication in new window or tab >>Design of the Lattice Parameter of Embedded Nanoparticles
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2010 (English)In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 496, no 1-3, p. 95-99Article in journal (Refereed) Published
Abstract [en]

It is found that the bonding of nanoparticles in nancomposites can be influenced by interactions with a surrounding matrix phase. A model involving charge transfer between phases is presented, and supported by DFT-simulations. The model explains observations in nanocomposite nc-TiCx/a-C of additional interface states and lattice expansion of TiCx. It is suggested that this approach can be extended to other types of nanocomposites, and that it opens for new possibilities in materials design.

National Category
Inorganic Chemistry
Research subject
Materials Science; Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-123483 (URN)10.1016/j.cplett.2010.07.013 (DOI)000281296900019 ()
Note
Uppdaterad från Manuskript till Artikel 20101203Available from: 2010-04-27 Created: 2010-04-27 Last updated: 2017-12-12Bibliographically approved
5. Design of carbide-based nanocomposite thin films by selective alloying
Open this publication in new window or tab >>Design of carbide-based nanocomposite thin films by selective alloying
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2011 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 206, no 4, p. 583-590Article in journal (Refereed) Published
Abstract [en]

This paper reviews a series of studies on alloying of sputtered TiC coatings with weak carbide-forming metals, Me, such as Al, Fe, Ni, Pt and Cu. Metastable solid solutions with Me on the Ti sites are easily obtained by magnetron sputtering at low temperatures (< 300 °C). First principles density functional theory (DFT) calculations of such carbides show that a driving force exists to remove carbon from the structure as an alternative and kinetically more favourable route compared to Me precipitation. This leads to a situation where additional control of the phase composition is given by annealing: both direct influence during film growth, as well as through subsequent annealing. Thus, alloying of the nanocomposite with weak carbide-forming metals can be used to tune many mechanical, electric and magnetic properties of a carbide-based nanocomposite film.

Keywords
Nanocomposite, Metastable phases, Alloying, Microstructure, Carbide
National Category
Inorganic Chemistry Engineering and Technology
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-123484 (URN)10.1016/j.surfcoat.2010.06.017 (DOI)000297086700002 ()
Available from: 2010-04-27 Created: 2010-04-27 Last updated: 2017-12-12Bibliographically approved
6. Wear-resistant magnetic thin film material based on a Ti1−xFexC1−y nanocomposite alloy
Open this publication in new window or tab >>Wear-resistant magnetic thin film material based on a Ti1−xFexC1−y nanocomposite alloy
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2010 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 81, no 1, p. 014405-Article in journal (Refereed) Published
Abstract [en]

In this study we report on the film growth and characterization of thin films deposited on amorphous quartz. The experimental studies have been complemented by first-principles density-functional theory metastable Ti-Fe-C film changes. With increasing annealing time, there is a depletion of iron close to the surface of the film, while regions enriched in iron are simultaneously formed deeper into the film. Both the magnetic ordering temperature and the saturation magnetization changes significantly upon annealing. The DFT calculations show that the critical temperature and the magnetic moment both increase with increasing Fe and C-vacancy concentration. The formation of the metastable iron-rich Ti-Fe-C compound is reflected in the strong increase in the magnetic ordering temperature. Eventually, after enough annealing time nanocrystalline -Fe starts to precipitate, the amount and size of which can be controlled by the annealing procedure; after 20 min of annealing, the experimental results indicate a nanocrystalline iron-film embedded in a wear-resistant TiC compound. This conclusion is further supported by transmission electron microscopy studies on epitaxial Ti-Fe-C films deposited on single-crystalline MgO substrates where, upon annealing, an iron film embedded in TiC is formed. Our results suggest that annealing of metastable Ti-Fe-C films can be used as an efficient way of creating a wear-resistant magnetic thin film material. approximately 50-nm-thick Ti-Fe-CDFT calculations. Upon annealing of as-prepared films, the composition of the10 min, nanocrystalline -Fe starts to precipitate, the amount and size of which can be controlled by the annealing procedure; after 20 min of annealing, the experimental results indicate a nanocrystalline iron-film embedded in a wear-resistant TiC compound. This conclusion is further supported by transmission electron microscopy studies on epitaxial Ti-Fe-C films deposited on single-crystalline MgO substrates where, upon annealing, an iron film embedded in TiC is formed. Our results suggest that annealing of metastable Ti-Fe-C films can be used as an efficient way of creating a wear-resistant magnetic thin film material.

Place, publisher, year, edition, pages
The American Physical Society, 2010
National Category
Inorganic Chemistry Engineering and Technology
Research subject
Inorganic Chemistry; Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-119941 (URN)10.1103/PhysRevB.81.014405 (DOI)000274001800047 ()
Available from: 2010-03-03 Created: 2010-03-03 Last updated: 2017-12-12Bibliographically approved
7. Design of Nanocomposite Low-Friction Coatings
Open this publication in new window or tab >>Design of Nanocomposite Low-Friction Coatings
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2007 (English)In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 17, no 10, p. 1611-1616Article 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.

Keywords
Coatings, Nanocomposites, Thin films
National Category
Engineering and Technology Natural Sciences
Identifiers
urn:nbn:se:uu:diva-96306 (URN)10.1002/adfm.200600724 (DOI)000248062100003 ()
Available from: 2007-10-19 Created: 2007-10-19 Last updated: 2017-12-14Bibliographically approved
8. Elasticity model for the calculation of lattice parameters in multilayer structures
Open this publication in new window or tab >>Elasticity model for the calculation of lattice parameters in multilayer structures
(English)Manuscript (Other academic)
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-96007 (URN)
Available from: 2007-05-15 Created: 2007-05-15 Last updated: 2012-04-01Bibliographically approved

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