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Nanoparticle assisted tribofilm formation and material transfer studied with SEM and TEM
Stockholm University, Faculty of Science, Department of Physics. (Instrumenation Physics)
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The discovery and subsequent synthesis of metal containing fullerenes- IFS (Inorganic Fullerene-like Structures) by R. Tenne et al. has generated considerable scientific interest with great potential impact in many industrial application areas such as lubrication. The lubrication mechanism (tribofilm formation) via exfoliation and deposition of the atomic layers from this cage-like IF-particles was revealed and demonstrated first by this research group. The incorporation of the nanoparticles into lubricants (oils, greases) is however not straightforward.

When two surfaces are sliding against each other and a lubricant is used, a thin layer (tribofilm) is formed on the contact area. The friction reducing effects of the nanoparticles can be altered or hindered by certain additives that are used in lubricative oils. The effects of such additives on the tribological behavior of the nanoparticles are investigated by analyzing the tribofilms formed on the worn surfaces using energy-dispersive X-ray spectroscopy in a scanning electron microscope. Another challenge of nanoparticles in lubricants is the penetration of the nanoparticles into the contact zone. A possible solution of this problem is briefly discussed.

A modified burnishing technique can be used to coat sliding metallic surfaces with a friction reducing tribofilm. The morphology and composition of these tribofilms was investigated with analytical electron microscopy techniques.

In the second part of the thesis electron microscopy was used to investigate the material transfer. Titanium is an elements with high adhesive ability to the counter surface, it displays poor tribological properties in sliding metallic contacts. This can lead to material transfer and consequently severe surface damage. The cold formation and machining of titanium, thus can lead rapid tool wear and poor surface finish. Electron microscopy techniques were used to study the mechanism of titanium transfer to different counter surfaces.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2015. , 140 p.
Keyword [en]
WS2 inorganic fullerene-like nanoparticles, lubrication, tribofilm, SEM, TEM, EELS, EDS, coating, surface analysis, friction, wear, titanium, material transfer
National Category
Physical Sciences
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-114745ISBN: 978-91-7649-116-4 (print)OAI: oai:DiVA.org:su-114745DiVA: diva2:793956
Public defence
2015-04-24, sal FD5, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2015-04-01 Created: 2015-03-09 Last updated: 2015-04-09Bibliographically approved
List of papers
1. Correlation Studies of WS2 Fullerene-Like Nanoparticles Enhanced Tribofilms: A Scanning Electron Microscopy Analysis
Open this publication in new window or tab >>Correlation Studies of WS2 Fullerene-Like Nanoparticles Enhanced Tribofilms: A Scanning Electron Microscopy Analysis
2013 (English)In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 51, no 3, 461-468 p.Article in journal (Refereed) Published
Abstract [en]

The beneficiary effects of tungsten disulphide (WS2) inorganic fullerene-like nanoparticles (IFLNPs) in the lubrication industry were shown in recent years. However, their successful incorporation into lubricants (oils, greases) is not straightforward. In practice, the lubricant contains several components for different purposes, e.g. reducing the oxidization of the oil (antioxidant), minimizing the wear rate (anti-wear additive), dispersants, etc. These additives can contain chemically active compounds, which under the lubrication process (where locally extreme conditions can develop: high pressure and flash temperatures) can change the chemistry in the contact zone and block the beneficial effects of the inorganic nanoparticles. In this investigation, poly-alpha-olefin (PAO) is being used as base oil in which the WS2 nanoparticles and different additives are mixed. A ball-on-disc sliding test revealed that certain additives inhibit the nanoparticles to reduce friction (less than 5 % decrease in friction coefficient), while in other cases, the friction reduction was above 50 %. The comparison is being made between PAO + additive and PAO + additive + IFLNPs. Scanning electron microscope and energy dispersive X-ray spectroscopy were used to investigate the elemental composition of the tribofilms formed on the wear marks. Further analysis was made in order to reveal correlations between elemental compositions of the tribofilms and external parameters such as the friction coefficient and wear rate. For instance, a strong correlation between tungsten content of the tribofilm and the friction coefficient was found.

Keyword
WS2 inorganic fullerene-like nanoparticles, Lubrication, Tribofilm, SEM, EDS
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-94184 (URN)10.1007/s11249-013-0184-0 (DOI)000323332800016 ()
Note

AuthorCount:3;

Available from: 2013-10-01 Created: 2013-09-30 Last updated: 2017-12-06Bibliographically approved
2. Morphology and composition of tribofilms deposited using tribochemical burnishing technique
Open this publication in new window or tab >>Morphology and composition of tribofilms deposited using tribochemical burnishing technique
2014 (English)In: Tribology - Materials, Surfaces & Interfaces, ISSN 1751-5831, E-ISSN 1751-584X, Vol. 8, no 1, 14-20 p.Article in journal (Refereed) Published
Abstract [en]

Using a modified burnishing technique, low friction tribofilms can be formed on steel and cast iron surfaces in a controlled manner, before the part is mounted in e.g. an engine. The influence on the underlying substrate as well as the morphology and composition of the tribofilm has been thoroughly investigated in this paper. The coating process was found to smoothen rough plateaus, but not affecting deeper scratches and grooves, e.g. a honing pattern. The influence on the substrate was limited and no significant stresses were introduced in the surface. The tribofilm was mostly amorphous and typically 50–80 nm thick, composed of Fe, O and W, with minor additions of C and S.

Place, publisher, year, edition, pages
Maney Publishing, 2014
Keyword
Tribofilm, Coating, Surface analysis, Friction, Wear
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-114741 (URN)10.1179/1751584X14Y.0000000069 (DOI)
Available from: 2015-03-09 Created: 2015-03-09 Last updated: 2017-12-04Bibliographically approved
3. Transfer of titanium in sliding contacts-New discoveries and insights revealed by in situ studies in the SEM
Open this publication in new window or tab >>Transfer of titanium in sliding contacts-New discoveries and insights revealed by in situ studies in the SEM
2014 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 315, no 1-2, 87-94 p.Article in journal (Refereed) Published
Abstract [en]

Titanium and its alloys generally display poor tribological properties in sliding contacts due to their high chemical activity and strong adhesion to the counter surface. The strong adhesion causes a high tendency to transfer and ultimately galling or build-up edge formation, resulting in severe surface damage. As a result, forming and machining of titanium and its alloys are generally associated with significant problems such as high friction, rapid tool wear and poor surface finish of the formed/machined surface. In the present study, in situ tests in a scanning electron microscope have been performed to increase the understanding of the mechanisms controlling the initial transfer of titanium (Grade 2) in sliding contact with tool surfaces. Tool materials included cover cold work tool steel, cemented carbide, CVD deposited Al2O3 and PVD deposited DLC. In these tests, a relatively sharp tip, representing the titanium work material, slides against a flat surface, representing the tool. The contact conditions result in plastic deformation of the work material against the tool surface, thereby simulating forming or machining. The limited and well-defined contact, along with the possibility to study the sliding in the SEM, makes it possible to correlate local surface variations to transfer of work material and frictional response. Post-test characterization of the contact surfaces was performed by high-resolution SEM, TEM, EDS and EELS. The initial friction was low and stable against all tested materials, but then gradually escalated against all surfaces except the DLC. The friction escalation was associated to increasing levels of transfer, while the DLC stayed virtually free from transfer. From these very initial sliding tests DLC is a promising tool coating in forming and machining of titanium.

Keyword
Surface topography, Coatings, Titanium, Material transfer, Galling, Friction
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-106316 (URN)10.1016/j.wear.2014.04.006 (DOI)000337877700012 ()
Note

AuthorCount:4;

Available from: 2014-08-06 Created: 2014-08-04 Last updated: 2017-12-05Bibliographically approved

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