| 1. |
- Nyberg, Harald, et al.
(författare)
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Tribochemical formation of sulphide tribofilms from a Ti-C-S coating sliding against different counter surfaces
- 2014
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Ingår i: Tribology letters. - : Springer Science+Business Media B.V.. - 1023-8883 .- 1573-2711. ; 56:3, s. 563-572
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Tidskriftsartikel (refereegranskat)abstract
- Tribochemically active Ti-C-S coatings are nanocomposite coatings containing a S-doped titanium carbide, from which S can be released in a tribological contact. This work studies tribochemical reactions between a Ti-C-S coating and various counter surface materials, and their effect on the tribological performance. Tribological tests were performed in a ball-on-disc set-up, using balls of five different materials as sliding partners for the coating: 100Cr6 steel, pure W, WC, 316-L steel and Al2O3. For W balls, a WS2 tribofilm was formed, leading to low friction (down to A mu = 0.06). Furthermore, increasing normal load on the W balls was found to lead to a strong decrease in A mu and earlier formation of the low-friction WS2 tribofilm. Similar WS2 and MoS2 tribofilms were, however, not formed from WC- and Mo-containing 316-L balls. The performance when using WC and Al2O3 balls was significantly worse than for the two steel balls. It is suggested that this is due to sulphide formation from Fe, analogous to formation of anti-seizure tribofilms from S-containing extreme pressure additives and steel surfaces. The tribochemical activity of Ti-C-S coatings, with the possibility of S release, is thus beneficial not only for pure W counter surfaces, but also for Fe-based sliding partners.
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| 2. |
- Sundberg, Jill, 1986-, et al.
(författare)
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Influence of composition, structure and testing atmosphere on the tribological performance of W-S-N coatings
- 2014
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 258, s. 86-94
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Tidskriftsartikel (refereegranskat)abstract
- W-S-N coatings deposited by reactive magnetron sputtering offer the possibility of ultra-low friction in unlubricated sliding. In this work, W-S-N coatings of different composition and structure have been deposited, characterised and evaluated with respect to the tribological performance and tribofilm formation. The composition was varied by changing the flow of N-2 into the deposition chamber, leading to N contents ranging from 0 to 47 at.%. W-S-N coatings deposited without substrate heating are amorphous, while substrate heating results in coatings containing nanocystalline tungsten sulphide (WSx) for low N contents, and nanocrystalline tungsten nitride (WyN) at a high N content. The coatings were tribologically tested against steel balls in four different atmospheres dry N-2, dry air, humid N-2 and humid air to study the effects of atmospheric O-2 and H2O both separately and simultaneously. In dry N-2, all coatings exhibited an excellent performance with very low friction (mu approximate to 0.02) and wear. Notably, this included the N-richest and hardest coating, containing nanocrystalline WyN and only 13 at.% of S. The friction and wear increased on changing the atmosphere, in the order of dry air-humid N-2-humid air. In these three non-inert atmospheres, the friction and wear also increased with increasing N content of the coating. It is thus concluded that the presence of O-2, the presence of H2O, and a high N content (i.e., low Wand S contents) are three factors increasing the risk of high friction and wear, especially when occurring together. Raman spectroscopy mapping of the contact surfaces on the coatings and the balls showed that low friction and wear is connected to the presence of WS2 tribofilms in the contact, and that the three previously mentioned factors affect the formation and function of this tribofilm.
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| 3. |
- Sundberg, Jill, 1986-, et al.
(författare)
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Quaternary W-S-C-Ti films for tribological applications
- 2011
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Konferensbidrag (refereegranskat)abstract
- IntroductionTransition metal dichalcogenides such as WS2 are well-known for their layered structure and solid lubricant properties. The addition of another element, such as carbon, can improve the mechanical properties of the material, such as the hardness, while still maintaining the solid lubrication.1,2 Different theories regarding the friction mechanisms in W-S-C have been proposed: the low friction could be solely due to the WS2 phase2 or both the WS2 and the carbon phase could be responsible.1 Despite the hardness increase compared to pure WS2, W-S-C films still exhibit a quite low hardness. One route to increasing the hardness is to add a fourth element, which is a strong carbide-former (e. g. titanium), to form a hard carbide phase. In this work, W-S-C-Ti films have been deposited by magnetron sputtering and characterized with a variety of techniques. The mechanical and tribological properties have been studied and related to the composition.Experimental ProceduresThe films were deposited by non-reactive DC magnetron sputtering using two targets: graphitic carbon and WS2, with a ring-shaped titanium component mounted on the latter. The titanium content was varied by the size of the metal component, while the carbon content was varied by the carbon target power. Four series of films were deposited at room temperature and at 300°C.The micro- and nanostructure of the films was investigated by SEM and TEM, and XRD was used to study the presence of crystalline phases. The composition was determined by EDS, and the chemical bonding was studied by XPS and Raman spectroscopy. Nanoindentation was used to probe the mechanical properties of the different films, and ball-on-disc tests were performed in order to evaluate the tribological properties.Results and DiscussionPrevious studies on W-S-C suggest that the material consists of WS2 nanocrystallites embedded in an amorphous matrix. Also in this study, the only phase detected with XRD is WS2, with the typical WS2 peaks becoming broader with the addition of carbon indicating a decrease in crystallinity. TEM shows WS2 nanocrystallites embedded in an amorphous matrix. However, our results indicate that the composition of the matrix is more complex than what has previously been suggested. Chemical information from XPS suggests that the matrix is not based on carbon alone, but that it also includes a carbidic component. Furthermore, the S/W ratio in the samples is approximately constant but significantly lower than 2; such substochiometry in WS2 films is well known and we will discuss possible mechanisms for this behaviour.By adding titanium to W-S-C, the chemical bonding in the material is changed. XPS indicates the presence of Ti-C bonds even when no crystalline TiC grains are observed by XRD. For high titanium and carbon contents, a crystalline phase with the sodium chloride structure is observed, which has a cell parameter significantly larger than TiC. Furthermore, the added titanium changes the mechanical properties of the films, and an increase in hardness up to 100% from 6 GPa to 12 GPa can be observed. The effect of titanium addition, however, is dependent on the film composition and the deposition temperature.Tribological testing show friction coefficients down to approximately 0.02 in ball-on-disc tests using a steel ball in dry atmosphere for W-S-C films. The effect of titanium addition varies with the composition; high titanium contents combined with suitable carbon levels yields films that exhibit low and stable friction coefficients well under 0.02 under the aforementioned conditions. Thus, it is possible to tune the mechanical properties of W-S-C films, while still obtaining low friction, by the addition of titanium.References[1] A.A. Voevodin, J.S. Zabinski, Thin Solid Films 370, 223-231 (2000)[2] T. Polcar, M. Evaristo, A. Cavaleiro, Plasma Process. Polym. 6, 417-424 (2009)
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| 4. |
- Sundberg, Jill, 1986-, et al.
(författare)
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Sulfur-doping of nc-TiC/a-C films by reactive sputtering
- 2012
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Ingår i: Thirteenth International Conference on Plasma Surface Engineering, Garmisch-Partenkirchen, Germany, 10-14 September 2012.
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Konferensbidrag (refereegranskat)abstract
- Nanocomposite thin films with carbide grains in a matrix of amorphous carbon have been found interesting for various mechanical and electrical applications. An important advantage of these materials is the possibility to tune the properties by varying the composition and the microstructure. A well-known example is the nc-TiC/a-C system, which is interesting for its tribological as well as its electrical and chemically protective properties. One way to modify the material is doping with a third element. Usually, another metal or a p-element such as oxygen or nitrogen is considered. In this work, however, Ti-C films have been doped with sulfur. The doping was performed by introduction of increasing amounts of H2S to the chamber during DC magnetron sputtering from elemental Ti and C targets.An increased flow of H2S during deposition leads to an increase in the S content of the films, as well as a slight decrease in the C:Ti ratio. Pure TiC/a-C films were proved by GI-XRD and XPS to contain crystalline TiC with the NaCl structure in a matrix of amorphous carbon. The introduction of S leads to a significant and gradual increase of the cell parameter of the carbide phase – from 4.3 Å up to more than 4.8 Å for coatings with approximately 20 at-% of S. This clearly indicates that the S atoms enter the carbide phase, forming a previously unknown Ti-C-S solid solution. The addition of S also affects the mechanical properties, such as the hardness which was seen to decrease from 8 GPa for pure TiC in an amorphous carbon matrix, to 5 GPa when doped with sulfur.Thus, the introduction of S is shown to have effects on the chemistry as well as the properties of nc-TiC/a-C thin films. In the current work, the effect of S doping on the structure, chemical bonding and mechanical properties as well as tribological performance will be presented.
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| 5. |
- Hansen, Jonny, et al.
(författare)
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Elastohydrodynamic performance of a hydrocarbon mimicking ionic liquid additive
- 2017
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Konferensbidrag (refereegranskat)abstract
- Machine elements operating under lubricated conditions will eventually fail due to high stresses and fatigue-related causes. In order to find optimum protective measures, it is important to understand how the stresses arise and what factors that influence their magnitude. With the current shift for more sever lubricating regimes, the role of tribo-improvers is becoming vital. At this point, the interplay between the chemisorption mechanism of various lubricant compounds and surface failure is not yet fully understood. To obtain a better understanding of this, a newly developed ionic structured tribo-improving additive, based on silicon, was investigated and benchmarked against conventional heavy-duty gearbox additives. A ball on disc device was operated under heavily loaded rolling/sliding conditions, at elevated temperature to simulate gear like conditions, and lubricating performance was subsequently evaluated in terms of friction and wear. Such results highlight the importance of properly designed lubricants for optimal tribo-performance under rolling-sliding conditions
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| 6. |
- Kröll, Mirco, et al.
(författare)
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Auswirkungen von vereinheitlichten Prozeduren auf tribologische Versuche
- 2021
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Ingår i: 62. Tribologie-Fachtagung der Gesellschaft für Tribologie.
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Konferensbidrag (refereegranskat)abstract
- Anerkannte Institutionen stellen ihre Kompetenzen auf dem Gebiet tribologischer Charakterisierungen Industrie und Forschung zur Verfügung (https://www.i-tribomat.eu/). Ein Aspekt hierbei ist eine tribologische Datenbank. Um die nötige Qualität der Daten sicherzustellen, sind vereinheitlichte Prozeduren erforderlich, in deren Auswirkungen dieser Vortrag einen Einblick gibt.
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| 7. |
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| 8. |
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| 9. |
- Kröll, Mirco, et al.
(författare)
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On the quality of wear volume data of laboratory model tests
- 2022
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Ingår i: 63. Tribologie-Fachtagung der Gesellschaft für Tribologie.
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Konferensbidrag (refereegranskat)abstract
- This contribution will concentrate on wear as volume loss, which is a crucial part in quantifying the performance of a tribological system. Wear is an outcome of a tribological experiment and affected by the variables of the tribological system including the samples involved. It can be detected and assessed in various ways (e.g., via changes in volume, weight, geometry, morphology, and topography). There are several methods to measure the wear volume. Some of them are standardised, others aren’t. The comparability of these methods was analysed in two Inter-Partner Round-Robin Tests (IP-RRT) using reciprocating laboratory model tests. The evaluation of wear volumes was done on two levels for each IP-RRT. The first level focused on the comparison of wear volumes caused by different tribological experiments with the same parameters conducted by various operators at the partners with several tribometers. The second level focused on the methods used to determine the wear volume of circulated samples with wear scars produced by the tribological tests in those IP-RRTs. These considerations are especially important as within the European Tribology Centre “i-TRIBOMAT” (Grant Agreement no. 814494; call: H2020-NMBP-TO-IND-2018; https://www.i-tribomat.eu/) a shared infrastructure of more than 100 tribometers is formed. Additionally, this centre incorporates the capacities of tribological characterisation of different renowned institutions. To ensure that the wear results determined by this Open Innovative Test Bed are characteristic as well as descriptive, trustworthy, comparable, and reproducible, appropriate procedures are needed. Hence, they safeguard respective quality features, such as low standard deviations. An essential part in the development of these procedures is the continuous improvement process that was set in place within the quality management system. It contains IP-RRTs that collect data, methods used, expenses and suggestions for improvements. They also validate the procedures developed. The presentation will show that harmonised procedures and Best Practices reduce influences caused, for example, by the operators, which is necessary to reach the quality demands of the European Tribology Centre.
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| 10. |
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