Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Triboactive Component Coatings: Tribological Testing and Microanalysis of Low-Friction Tribofilms
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Ångströms Tribomaterialgrupp)
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Coatings are often used on critical components in machines and engines to reduce wear and to provide low friction in order to reduce energy losses and the environmental impact.

A triboactive coating not only provides this desired performance, it also actively maintains the low friction by a structural or chemical change in a very thin top layer of these already micrometer thin coatings. This so-called tribofilm is often 5-50 nm thick and can be formed either from the coating itself or by a reaction with the counter surface or the surrounding atmosphere, i.e. gas, fuel, oil, etc. The tribofilm will maintain the wanted performance for as long as the system is not chemically disturbed.

This thesis provides a detailed overview of the functionality of triboactive low-friction coatings, in many different systems. The majority of the tribofilms discussed, formed in very different environments, are built up by tungsten disulfide (WS2), which is a material similar to graphite, with a lamellar structure where strongly bonded atomic planes may slip over each other almost without resistance. The major difference is that WS2 is an intrinsically triboactive material, while graphite is not. However, graphite and other carbon-based materials can be made triboactive in certain atmospheres or by addition of other elements, such as hydrogen.

The remarkable affinity and driving force to form such WS2 low-friction tribofilms, regardless of the initial states of the sulfur and tungsten, and even when the forming elements are present only at ppm levels, is a recurrent observation in the thesis.

Addition of an alloying element to sputtered coatings of WS2 can improve its mechanical and frictional properties significantly. Several promising attempts have been made to find good candidates, out of which a few important ones are investigated in this thesis. Their achievable potential in friction reductions is demonstrated.

By reducing friction, energy losses can be avoided, which also results in lower particle and exhaust emissions, which directly reduces the environmental impact. Triboactive coatings are shown to be a promising route to significantly improve tribological applications and allow more environmental friendly and energy efficient vehicles.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. , 98 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1011
Keyword [en]
tribofilms, low-friction coatings, tungsten disulfide, TEM
National Category
Materials Engineering Nano Technology
Research subject
Materials Science
Identifiers
URN: urn:nbn:se:uu:diva-191223ISBN: 978-91-554-8576-4 (print)OAI: oai:DiVA.org:uu-191223DiVA: diva2:585099
Public defence
2013-02-22, Siegbahnsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research
Available from: 2013-02-01 Created: 2013-01-09 Last updated: 2013-02-11Bibliographically approved
List of papers
1. Frictional behavior of self-adaptive nanostructural Mo-Se-C coatings in different sliding conditions
Open this publication in new window or tab >>Frictional behavior of self-adaptive nanostructural Mo-Se-C coatings in different sliding conditions
2013 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 303, no 1-2, 286-296 p.Article in journal (Refereed) Published
Abstract [en]

Sliding properties of Mo-Se-C coatings with two different carbon content deposited by magnetron sputtering were investigated in different sliding environments (argon, nitrogen, dry and humid air). Both coatings had a structure that was identified as randomly oriented structures of MoSe2 embedded into amorphous carbon matrix. The worn surfaces, i.e. the wear tracks and the wear scars of the balls, were analyzed by optical microscopy, Raman spectroscopy and scanning electron microscopy. The material transferred to the ball steel surfaces was almost exclusively MoSe2, whereas the wear tracks on the coatings were more complex, with areas rich in MoSe2 and areas similar to that of as-deposited coatings. The friction was lowest in argon (0.012 at a load of 10 N) and highest in humid air, but still remarkably low; as best 0.05 at 10 N load; however, the exceptionally low wear rate was almost identical. Thus, we focused our detailed analysis on these two examples to understand the mechanisms responsible for the difference between the friction coefficients. SEM, EDX, XPS, Raman and TEM with EELS and EDX were applied to investigate the composition and structure of localized spots of interest on the tested surfaces. In both cases, we observed well-ordered MoSe2 tribofilms with negligible amount of oxides. Carbon was not present in the sliding interfaces, although large amount of carbon was found outside the contacts on both surfaces. Based on our investigations, we suggest the increase in friction of Mg-Se-C in humid air is primarily due to the increase in shear strength of the MoSe2 structure by the presence of water molecules in the sliding interface

National Category
Materials Engineering Nano Technology Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-191179 (URN)10.1016/j.wear.2013.03.032 (DOI)000322422500033 ()
Funder
Swedish Foundation for Strategic Research Swedish Research Council
Available from: 2013-01-09 Created: 2013-01-09 Last updated: 2018-01-11Bibliographically approved
2. Ultra-low friction of W-S-N solid lubricant coating
Open this publication in new window or tab >>Ultra-low friction of W-S-N solid lubricant coating
2013 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 232, 541-548 p.Article in journal (Refereed) Published
Abstract [en]

W-S-N films were deposited by reactive magnetron sputtering from WS2 target in Ar/N-2 atmosphere. Besides the standard evaluation of composition, structure, morphology, hardness and cohesion/adhesion, the core objective of this paper was to analyze coating tribological behavior. The chemical composition was 34 at.%N, 12 at%O, 29 at.%W and 25 at.%S, and the as-deposited films were completely amorphous. The film thickness was 23 pm, including the approximately 300-nm thick adhesion improving titanium interlayer. The friction coefficient was lower than 0.003 when sliding in dry nitrogen. The coating showed remarkable wear resistance surviving more than 2 million laps on pin-on-dics. The excellent friction properties were attributed to the formation of a thin tungsten disulfide tribofilm on the top of the wear track of the coating and on the counterpart surface. Moreover, the coating showed ability to replenish damaged areas with solid lubricant. We demonstrated that a structural transformation of the coating from an amorphous-like to a gradient quasi-ordered structure and an ordered transfer layer formation improved mechanical properties and radically decreased friction and wear.

National Category
Materials Engineering Nano Technology Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Engineering Science with specialization in Materials Science; Engineering Science with specialization in Tribo Materials
Identifiers
urn:nbn:se:uu:diva-191207 (URN)10.1016/j.surfcoat.2013.06.026 (DOI)000327691300072 ()
Funder
Swedish Foundation for Strategic Research Swedish Research Council
Available from: 2013-01-09 Created: 2013-01-09 Last updated: 2018-01-11Bibliographically approved
3. Complex frictional analysis of self-lubricant W-S-C/Cr coating
Open this publication in new window or tab >>Complex frictional analysis of self-lubricant W-S-C/Cr coating
Show others...
2012 (English)In: Faraday discussions (Online), ISSN 1359-6640, E-ISSN 1364-5498, Vol. 156, 383-401 p.Article in journal (Refereed) Published
Abstract [en]

Transition metal dichalcogenides belong to one of the most developed classes of materials for solid lubrication. However, one of the main drawbacks of most of the self-lubricating coatings is their low load-bearing capacity, particularly in terrestrial atmospheres. In our previous work, alloying thin films based on tungsten disulfide with non-metallic interstitial elements, such as carbon or nitrogen, has been studied in order to improve tribological performance in different environments. Excellent results were reached with the deposited coatings hardness, in some cases, more than one order of magnitude higher than single W-S films. In this work, W-S-C films were deposited with increasing Cr contents by co-sputtering chromium and composite WS2-C and targets. Two films were prepared with approx. 7 and 13 at.% of Cr. Alloying with chromium led to dense films with amorphous microstructure; the hardness and adhesion was improved. Sliding tests were carried out in dry and humid air using a pin-on-disc tribometer with 100Cr6 steel balls as a counterpart. To analyse the sliding process, the surfaces in the contact were investigated by X-ray photoelectron spectroscopy (bonding), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. Surface and sub-surface structural modification of the coating and composition of the transferred tribolayer are discussed in detail. High friction in humid air was attributed to the absence of a well-ordered WS2 sliding interface. On the other hand, the existence of such an interface explained the very low friction observed in dry air.

National Category
Engineering and Technology Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-178152 (URN)10.1039/c2fd00003b (DOI)000305892200025 ()
Available from: 2012-07-30 Created: 2012-07-30 Last updated: 2018-01-12Bibliographically approved
4. Extreme friction reductions during inital running-in of W-S-C-Ti low-friction coatings
Open this publication in new window or tab >>Extreme friction reductions during inital running-in of W-S-C-Ti low-friction coatings
Show others...
2013 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 302, no 1-2 SI, 987-997 p.Article in journal (Refereed) Published
Abstract [en]

The disulphides of tungsten and molybdenum are known for their low friction properties when used as solid lubricants. Due to their low hardness, their load bearing capacity when used as thin films is poor. When carbon is added to a WS2 coating, both of these shortcomings are improved, and a structure consisting of nanocrystals of WS2, and possibly tungsten carbide, in a matrix of amorphous carbon is formed. In this study, an attempt is made for further increasing the hardness of such coatings, by addition of Ti, a strong carbide former. A number of W–S–C(–Ti) coatings were deposited using magnetron co-sputtering, and characterised with regard to chemical composition, structure and tribological properties. It was seen that addition of Ti significantly increased the hardness of the coatings, while maintaining their excellent low friction properties in dry atmosphere. However, the coatings with Ti showed extremely high initial friction, a feature not seen for the coatings without Ti. The mechanisms behind this running-in behaviour were investigated by studying surfaces at early stages of wear. It was observed that tribofilms formed during sliding for the coatings containing Ti consisted mainly of TiO2, with platelets of WS2 appearing in the contact only after prolonged sliding. For the pure W–S–C coatings, WS2 was observed in the sliding interface almost instantly at the onset of sliding.

Place, publisher, year, edition, pages
Elsevier, 2013
National Category
Nano Technology Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Engineering Science with specialization in Tribo Materials; Engineering Science with specialization in Materials Science; Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-191211 (URN)10.1016/j.wear.2013.01.065 (DOI)000322682800018 ()
Conference
19th International Conference on Wear of Materials 2013; 14-18 April 2013; Portland, OR, USA
Funder
Swedish Foundation for Strategic Research
Available from: 2013-01-09 Created: 2013-01-09 Last updated: 2018-01-11Bibliographically approved
5. Nanoparticle based and sputtered WS2 low-friction coatings - Differences and similarities with respect to friction mechanisms and tribofilm formation
Open this publication in new window or tab >>Nanoparticle based and sputtered WS2 low-friction coatings - Differences and similarities with respect to friction mechanisms and tribofilm formation
2013 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 232, 616-626 p.Article in journal (Refereed) Published
Abstract [en]

MoS2 and WS2 are widely known intrinsic low-friction materials that have been extensively used and thoroughly investigated in literature. They are commonly produced in the form of sputtered coatings and show extremely low friction coefficients in non-humid environments, but rapidly degrade in humid conditions. Close nested fullerene-like nanoparticles of these materials have been proposed to have better oxidation resistance due to their closed form with the absence of dangling bonds. In the present study, an electrochemically deposited coating consisting of fullerene-like nanoparticles of WS2 embedded in a Ni-P matrix is tested under various loads and humidity conditions and compared with a sputtered WS2 coating with respect to their tribological behavior. The formation of a tribofilm on both surfaces is known to be crucial for the low-friction mechanism of WS2 and the different mechanisms behind this formation for the two types of coatings are investigated. It is shown that despite the completely different transformation processes, the resulting tribofilms are very similar. This is analyzed thoroughly using SEM, AES and TEM. The friction coefficient is known to be lower at higher normal loads for these materials and in the present study the mechanical and chemical responses of the tribofilm to higher normal loads during sliding are investigated. It was observed that the basal planes become aligned more parallel to the surface at higher loads, and that the tribofilm is less oxidized. It is suggested that these mechanisms are connected and are crucial keys to the wear life of these materials.

National Category
Materials Engineering Nano Technology Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Engineering Science with specialization in Materials Science; Engineering Science with specialization in Tribo Materials
Identifiers
urn:nbn:se:uu:diva-191210 (URN)10.1016/j.surfcoat.2013.06.045 (DOI)000327691300081 ()
Funder
Swedish Foundation for Strategic Research Swedish Research Council
Available from: 2013-01-09 Created: 2013-01-09 Last updated: 2018-01-11Bibliographically approved
6. Performance and Tribofilm Formation of a Low-Friction Coating Incorporating Inorganic Fullerene Like Nano-Particles
Open this publication in new window or tab >>Performance and Tribofilm Formation of a Low-Friction Coating Incorporating Inorganic Fullerene Like Nano-Particles
2012 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 206, no 8-9, 2325-2329 p.Article in journal (Refereed) Published
Abstract [en]

A new tribological coating with potential as a coating for components for low-friction applications is tested and compared to three, state of the art, commercial low-friction PVD coatings. The new coating is an electrodeposited coating composed by a Ni-P matrix incorporating fullerene like nanoparticles of WS2. The performance of the new coating is compared with three reference coatings in a ball-on-disc setup. The tribological tests involved ball bearing steel balls slid on coated discs, under different conditions of humidity and also with or without oil lubrication. Both mating surfaces were closely investigated in a scanning electron microscope and the low-friction tribofilms formed were further analysed. The correlations found between coefficient of friction, surface roughness of the wear scar, tribofilm formation and contact conditions are discussed. The new coating exhibits a very low coefficient of friction at low humidity, a behaviour closely resembling that of the MoS2-based commercial reference, whereas the carbon based PVD coatings tested exhibit the reversed dependence of humidity. The low-friction behaviour of the new coating is correlated to the formation of a WS2 tribofilm with a superficial alignment of the basal planes parallel to the sliding direction. When lubricated with a base oil, the beneficial tribofilm is not formed and the coefficient of friction is much higher. The results show that even though the coating is an electrodeposited coating it can compete with state of the art commercial PVD coatings.

Keyword
Friction, Wear, Tungsten disulphide, Nanoparticles, Fullerene, Tribofilm
National Category
Materials Engineering
Research subject
Engineering Science with specialization in Tribo Materials; Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-160806 (URN)10.1016/j.surfcoat.2011.10.012 (DOI)000300458500038 ()
Available from: 2011-10-31 Created: 2011-10-31 Last updated: 2017-12-08
7. Friction and wear behaviour of low-friction coatings in conventional and alternative fuels
Open this publication in new window or tab >>Friction and wear behaviour of low-friction coatings in conventional and alternative fuels
2012 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 48, 22-28 p.Article in journal (Refereed) Published
Abstract [en]

Today low-friction PVD coatings are used regularly in combustion engines to reduce wear and energy loss due to friction. Three coatings based on transition-metal dichalcogenides and three DLC coatings were tested with respect to tribological behaviour in non-conformal sliding contact, in five conventional and alternative fuels and fuel blending components. The friction and wear proved to vary substantially between the different tested systems. The DLC coatings exhibited extremely good wear properties, but also higher friction. Contrastingly the TMD coatings showed promising friction results, but in their present forms they do not offer sufficient wear resistance in the tested severe contact situation.

National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Engineering Science with specialization in Materials Science; Engineering Science with specialization in Tribo Materials
Identifiers
urn:nbn:se:uu:diva-167604 (URN)10.1016/j.triboint.2011.06.001 (DOI)000302394700005 ()
Conference
14th Nordic Symposium on Tribology (NORDTRIB), JUN 08-11, 2010, SWEDEN
Available from: 2012-01-31 Created: 2012-01-31 Last updated: 2018-01-12Bibliographically approved
8. Formation of tribologically beneficial layer on counter surface with smart chemical design of DLC coating in fuel contact
Open this publication in new window or tab >>Formation of tribologically beneficial layer on counter surface with smart chemical design of DLC coating in fuel contact
2012 (English)In: Tribology - Materials, Surfaces & Interfaces, ISSN 1751-5831, E-ISSN 1751-584X, Vol. 6, no 3, 102-108 p.Article in journal (Refereed) Published
National Category
Materials Engineering Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Engineering Science with specialization in Tribo Materials; Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-190043 (URN)10.1179/1751584X12Y.0000000013 (DOI)
Funder
Swedish Foundation for Strategic Research Swedish Research Council
Available from: 2013-01-07 Created: 2013-01-07 Last updated: 2018-01-11Bibliographically approved
9. Performance of DLC coatings in heated commercial engine oil
Open this publication in new window or tab >>Performance of DLC coatings in heated commercial engine oil
Show others...
2013 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 304, no 1-2, 211-222 p.Article in journal (Refereed) Published
Abstract [en]

Multilayer Diamond Like Coatings (DLC) are widely used to protect highly loaded components from wear and/or to reduce the friction losses in combustion engines. The uppermost layer of the coating controls the chemical situation in the contact and is therefore a very important part of modern multilayer coatings. To examine the individual performances and assess differences and potentials of modern DLC coatings, four commercially available DLCs designed for automotive components with different doping elements together with an uncoated reference were tested in high performance engine oils heated to 90 °C at two different initial contact pressures. The coefficient of friction generally was higher in the tests with the lower initial contact pressure (approximately 20% for all combinations) and the specific wear rate was also up to 100% higher for some combinations. It was also found that a used motor oil showed up to 30% higher friction than when fresh and at the same time reduced the wear in most cases. The tungsten doped coating showed the highest wear, but also the lowest coefficient of friction. The Si doped coating showed the best wear results, most probably due to the ability to make use of the additives in the oil to form a protecting tribofilm.

National Category
Nano Technology Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-192720 (URN)10.1016/j.wear.2013.04.036 (DOI)000322611800026 ()
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research
Available from: 2013-01-25 Created: 2013-01-25 Last updated: 2018-01-11Bibliographically approved

Open Access in DiVA

fulltext(26502 kB)4568 downloads
File information
File name FULLTEXT01.pdfFile size 26502 kBChecksum SHA-512
1b6ecbc69092012ca454f9c67b6ae1145f7c71d1fe415546e5083513688a36849cd187be2ef9cebc9b24410b2a0f3649c1b66f25bda90614f52e63d0a1647f81
Type fulltextMimetype application/pdf
Buy this publication >>

Search in DiVA

By author/editor
Gustavsson, Fredrik
By organisation
Applied Materials Sciences
Materials EngineeringNano Technology

Search outside of DiVA

GoogleGoogle Scholar
Total: 4568 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 2202 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf