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Tribochemically Active Ti–C–S Nanocomposite Coatings
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Oorganisk kemi.
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Hungarian Acad Sci, Inst Solid State Phys & Opt, Wigner Res Ctr, H-1525 Budapest, Hungary.
Visa övriga samt affilieringar
2013 (Engelska)Ingår i: Materials Research Letters, ISSN 2166-3831, Vol. 1, nr 3, s. 148-155Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

We demonstrate a new concept of self-adaptive materials, where sulphur is incorporated into TiC/a-C coatings and may be released in, for example, a tribological contact. By reactive sputtering with H2S, sulphur goes into the carbide to form a TiC x S y phase in an amorphous carbon matrix. The addition of sulphur lowers the friction against steel. Significantly lower friction is obtained against a tungsten counter-surface, as WS2 is generated in the contact. Annealing experiments and formation energy calculations confirm that sulphur can be released from TiC x S y . Ti–C–S coatings are thus chemically active in tribological contacts, creating possibilities of new low-friction systems.

Ort, förlag, år, upplaga, sidor
Taylor & Francis, 2013. Vol. 1, nr 3, s. 148-155
Nationell ämneskategori
Oorganisk kemi Tribologi (ytteknik omfattande friktion, nötning och smörjning)
Forskningsämne
Oorganisk kemi; Teknisk fysik med inriktning mot materialvetenskap; Teknisk fysik med inriktning mot elektronik
Identifikatorer
URN: urn:nbn:se:uu:diva-202064DOI: 10.1080/21663831.2013.802262ISI: 000209767500005OAI: oai:DiVA.org:uu-202064DiVA, id: diva2:630790
Forskningsfinansiär
Stiftelsen för strategisk forskning (SSF)VetenskapsrådetKnut och Alice Wallenbergs StiftelseEU, Europeiska forskningsrådet, 247062 - ASDTillgänglig från: 2013-06-19 Skapad: 2013-06-19 Senast uppdaterad: 2018-01-11Bibliografiskt granskad
Ingår i avhandling
1. Sputtering and Characterization of Complex Multi-element Coatings
Öppna denna publikation i ny flik eller fönster >>Sputtering and Characterization of Complex Multi-element Coatings
2014 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

The thin film technology is of great importance in modern society and is a key technology in wide spread applications from electronics and solar cells to hard protective coatings on cutting tools and diffusion barriers in food packaging. This thesis deals with various aspects of thin film processing and the aim of the work is twofold; firstly, to obtain a fundamental understanding of the sputter deposition and the reactive sputter deposition processes, and secondly, to evaluate sputter deposition of specific material systems with low friction properties and to improve their performance.From studies of the reactive sputtering process, two new methods of eliminating the problematic and undesirable hysteresis effect were found. In the first method it was demonstrated that an increased process pressure caused a reduction and, in some cases, even elimination of the hysteresis. In the second method it was shown that sufficiently high oxide content in the target will eliminate the hysteresis.

Further studies of non-reactive magnetron sputtering of multi-element targets at different pressures resulted in huge pressure dependent compositional gradients over the chamber due to different gas phase scattering of the elements. This has been qualitatively known for a long time but the results presented here now enable a quantitative estimation of such effects. For example, by taking gas phase scattering into consideration during sputtering from a WS2 target it was possible to deposit WSx films with a sulphur content going from sub-stoichiometric to over-stoichiometric composition depending on the substrate position relative the target.

By alloying tungsten disulphide (WS2) with carbon and titanium (W-S-C-Ti) its hardness was significantly increased due to the formation of a new titanium carbide phase (TiCxSy). The best sample increased its hardness to 18 GPa (compared to 4 GPa for the corresponding W-S-C coating) while still maintaining a low friction (µ=0.02) due to the formation of easily sheared WS2 planes in the wear track. 

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis, 2014. s. 74
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1162
Nyckelord
thin film, coating, magnetron sputtering, modelling, tribofilm, tungsten disulphide
Nationell ämneskategori
Annan fysik
Identifikatorer
urn:nbn:se:uu:diva-229207 (URN)978-91-554-8997-7 (ISBN)
Disputation
2014-09-26, Polhemsalen, Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:00 (Engelska)
Opponent
Handledare
Forskningsfinansiär
Stiftelsen för strategisk forskning (SSF), 30003
Tillgänglig från: 2014-09-02 Skapad: 2014-08-05 Senast uppdaterad: 2014-09-08
2. Triboactive Low-Friction Coatings Based on Sulfides and Carbides
Öppna denna publikation i ny flik eller fönster >>Triboactive Low-Friction Coatings Based on Sulfides and Carbides
2014 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

For sustainable development, it is highly important to limit the loss of energy and materials in machines used for transportation, manufacturing, and other purposes. Large improvements can be achieved by reducing friction and wear in machine elements, for example by the application of coatings. This work is focused on triboactive coatings, for which the outermost layer changes in tribological contacts to form so-called tribofilms. The coatings are deposited by magnetron sputtering (a physical vapor deposition method) and thoroughly chemically and structurally characterized, often theoretically modelled, and tribologically evaluated, to study the connection between the composition, structure and tribological performance of the coatings.

Tungsten disulfide, WS2, is a layered material with the possibility of ultra-low friction. This work presents a number of nanocomposite or amorphous coatings based on WS2, which combine the low friction with improved mechanical properties. Addition of N can give amorphous coatings consisting of a network of W, S and N with N2 molecules in nanometer-sized pockets, or lead to the formation of a metastable cubic tungsten nitride. Co-deposition with C can also give amorphous coatings, or nanocomposites with WSx grains in an amorphous C-based matrix. Further increase in coating hardness is achieved by adding both C and Ti, forming titanium carbide. All the WS2-based materials can provide very low friction (down to µ<0.02) by the formation of WS2 tribofilms, but the performance is dependent on the atmosphere as O2 and H2O can be detrimental to the tribofilm functionality.

Another possibility is to form low-friction tribofilms by tribochemical reactions between the two surfaces in contact. Addition of S to TiC/a-C nanocomposite coatings leads to the formation of a metastable S-doped carbide phase, TiCxSy, from which S can be released. This enables the formation of low-friction WS2 tribofilms when a Ti-C-S coating is run against a W counter-surface. Reduced friction, at a moderate level, also occurs for steel counter-surfaces, likely due to formation of beneficial iron sulfide tribofilms.

The studied coatings, whether based on WS2 or TiC, are thus triboactive, with the ability to form low-friction tribofilms in a sliding contact.

 

 

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis, 2014. s. 86
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1183
Nyckelord
coatings, thin films, tribology, tungsten disulfide, transition metal dichalcogenide, nanocomposite, TiC/a-C, tribofilms, PVD, XPS, HAXPES, XRD, SEM, TEM, Raman spectroscopy, nanoindentation
Nationell ämneskategori
Oorganisk kemi
Forskningsämne
Kemi med inriktning mot oorganisk kemi
Identifikatorer
urn:nbn:se:uu:diva-230989 (URN)978-91-554-9041-6 (ISBN)
Disputation
2014-10-31, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2014-10-09 Skapad: 2014-09-02 Senast uppdaterad: 2015-01-23Bibliografiskt granskad
3. Formation and Function of Low-Friction Tribofilms
Öppna denna publikation i ny flik eller fönster >>Formation and Function of Low-Friction Tribofilms
2014 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

The use of low-friction coatings on machine elements is steadily increasing, and they are expected to play an important role in the reduction of fuel consumption of future motorized vehicles. Many low-friction coatings function by transformation of the outermost coating layer into tribofilms, which then cover the coating surface and its counter surface. It is within these tribofilms that sliding takes place, and their properties largely determine the performance. The role of the coating is then not to provide low friction, but to supply support and constituents for the tribofilm.

In this thesis, the formation of such tribofilms has been studied for a number of different low-friction coatings. The sensitivity of the tribofilm formation towards changes in the tribological system, such as increased surface roughness, varied surrounding atmosphere and reduced availability of the tribofilm constituents has been given special attention.

For TaC/aC coatings, the formation of a functioning tribofilm was found to be a multi-step process, where wear fragments are formed, agglomerated, compacted and eventually stabilized into a dense film of fine grains. This formation is delayed by a moderate roughening of the coated surface.

Coatings based on tungsten disulphide (WS2) are often able to provide exceptionally low friction, but their use is restricted by their poor mechanical properties and sensitivity to humidity. Large improvements in the mechanical properties can be achieved by addition of for example carbon, but the achievable hardness is still limited. When titanium was added to W-S-C coatings, a carbidic hard phase was formed, causing drastically increased hardness, with retained low friction. Titanium oxides in the tribofilms however caused the friction to be high initially and unstable in the long term. In a study of W-S-N coatings, the effects of humidity and oxygen were studied separately, and it was found that the detrimental role of oxygen is larger than often assumed.

Low friction tribofilms may form by rearrangement of coating material, but also by tribochemical reactions between constituents of the coating and its counter surface. This was observed for Ti-C-S coatings, which formed WS2 tribofilms when sliding against tungsten counter surfaces, leading to dramatic friction reductions.

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis, 2014. s. 76
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1187
Nyckelord
tribology, tribofilm, PVD, coating, low-friction, tungsten disulphide, transition metal dichalcogenide, tribochemistry
Nationell ämneskategori
Tribologi (ytteknik omfattande friktion, nötning och smörjning)
Forskningsämne
Teknisk fysik med inriktning mot tribomaterial
Identifikatorer
urn:nbn:se:uu:diva-233712 (URN)978-91-554-9065-2 (ISBN)
Disputation
2014-11-28, Polhemsalen, Lägerhyddsvägen 1, Uppsala, 10:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2014-11-05 Skapad: 2014-10-08 Senast uppdaterad: 2018-01-11

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Sundberg, JillNyberg, HaraldSärhammar, ErikKádas, KrisztinaEriksson, OlleNyberg, TomasJacobson, StaffanJansson, Ulf

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