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Friction and Wear Mechanisms of Ceramic Surfaces: With Applications to Micro Motors and Hip Joint Replacements
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences. (Tillämpad materialvetenkap)
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Surfaces exposed to wear always transform and typically a layer of new structure and composition is formed. This layer, often called tribofilm, changes the friction and wear properties. Tribofilms formed on ceramic surfaces may consist of products from chemical reactions between the materials in contact and the environment or consist of compacted wear debris.

In this thesis, focus has been to understand the friction and wear mechanisms of ceramic surfaces, as well as acquiring knowledge about the properties of the new surfaces created during wear. Ultimately, this understanding can be used to develop ceramic systems offering high or low friction, while the material loss in both cases should be minimised. Such ceramics could improve numerous tribological systems and applications, out of which ultrasonic motors, low-friction ceramic coatings and hip joint replacements have been treated in this thesis. Friction and wear tests, and subsequently various surface analyses have been essential for the knowledge about the friction, wear and tribofilm formation.

 For ultrasonic motors of the studied type, the highest driving force is achieved when the friction is high between the alumina components in the friction drive system. The highest friction was here accomplished with a thick tribofilm on the surfaces. The formation of such tribofilms was favoured by dry conditions, and using an initially rough surface, which increased the initial generation of wear debris.

In a detailed investigation of the importance of microtopography on tribofilm formation and friction behaviour, a low-friction, PVD coating of TaC/a-C was studied. This coating showed a very low, stable friction. High sensitivity to the microtopography was demonstrated, smooth coating exhibited a faster build-up of a dense tribofilm of fine ground material on the counter steel surface and subsequently a faster running in and friction decrease. 

The life span for total hip joint replacements can be prolonged by minimising the wear particles that cause inflammation and subsequent implant loosening. In this work coatings of amorphous/nanocrystalline silicon nitride have shown low wear rate, and hence produce a minimum of wear particles. Furthermore, these particles that are expected to resorb in vivo. This system therefore has potential to reduce problems with inflammation and osteolysis connected to wear particles.    

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2011. , 65 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 841
Keyword [en]
Tribology, Friction, Wear, Ceramic, Tribofilm, Alumina, Silicon nitride, Ultrasonic Motors, Hip Joint Replacement, PVD coating
National Category
Materials Engineering
Research subject
Engineering Science with specialization in Materials Science
Identifiers
URN: urn:nbn:se:uu:diva-156801ISBN: 978-91-554-8123-0 (print)OAI: oai:DiVA.org:uu-156801DiVA: diva2:433714
Public defence
2011-09-23, Häggsalen, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2011-09-02 Created: 2011-08-09 Last updated: 2011-11-03Bibliographically approved
List of papers
1. On the role of tribofilm formation on the alumina drive components of an ultrasonic motor
Open this publication in new window or tab >>On the role of tribofilm formation on the alumina drive components of an ultrasonic motor
2009 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 267, no 5-8, 1295-1300 p.Article in journal (Refereed) Published
Abstract [en]

Ultrasonic motors typically have a friction drive system to transfer the movement. The miniaturized motor type investigated here has a friction drive system consisting of two drive pads that transfer the high frequency oscillating movement of two piezoelectric elements to a linear drive rail. The pads and rail consist of alumina.

Fiction tests were carried out to investigate how the coefficient of friction between the drive pads and the drive rail depends on the number of strokes of the rail. It was found to initially increase with the number of strokes and then stabilize.

Scanning electron microscopy studies of the friction drive surfaces show how a tribofilm forms and develops with the number of strokes. Interestingly, the smooth tribofilm surface gives a higher coefficient of friction than the original rougher surface. To further investigate the nature of the tribofilm. cross section samples were produced with a focused ion beam instrument. The tribofilms show different characters and appear to form gradually by agglomeration and sintering of wear debris. Transmission electron microscopy showed the tribofilm to be amorphous and partly nano-crystal line. This high resolution investigation also clearly demonstrated that the tribofilm bonds very well to the underlying alumina grains.

The processes of friction increase and tribofilm build-up stabilize early compared to the lifetime of the motor.

Place, publisher, year, edition, pages
Elsevier, 2009
Keyword
tribofilm, alumina, friction, ultrasonic motor
National Category
Materials Engineering
Research subject
Materials Science
Identifiers
urn:nbn:se:uu:diva-111717 (URN)10.1016/j.wear.2009.01.020 (DOI)000267580700084 ()
Available from: 2009-12-21 Created: 2009-12-21 Last updated: 2017-12-12Bibliographically approved
2. The influence of grain size and surface treatment of the tribofilm formation on alumina components
Open this publication in new window or tab >>The influence of grain size and surface treatment of the tribofilm formation on alumina components
2012 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 292, 17-24 p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Elsevier, 2012
National Category
Materials Engineering
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-156792 (URN)10.1016/j.wear.2012.06.004 (DOI)000308628400003 ()
Available from: 2011-08-09 Created: 2011-08-09 Last updated: 2017-12-08Bibliographically approved
3. Influence from humidity on the alumina friction drive system of an ultrasonic motor
Open this publication in new window or tab >>Influence from humidity on the alumina friction drive system of an ultrasonic motor
2009 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 42, no 10, 1467-1477 p.Article in journal (Refereed) Published
Abstract [en]

Miniaturized ultrasonic motors, based on piezoelectric movement, are rapidly developing and the number of commercial applications is steadily growing. The details of the friction drive system of these motors still need systematic studies to fully utilize the potential of the technique. The friction drive system transfers the high frequency oscillatory movement from the stator to a drive rail. The friction force should be maximized and stabilized to achieve the best motor performance, while maintaining a low wear rate.

The mating parts of a friction drive system typically consist of alumina which is selected due to its relatively low wear rate and relatively high coefficient of friction. With increasing relative humidity, the friction coefficients of alumina ceramics generally decrease.

This work examines how water and humidity affect a friction drive system with respect to coefficient of friction and wear of the mating surfaces. Ball-on-disc experiments were used to evaluate the tribological properties. The worn surfaces were studied by scanning electron microscopy.

The coefficient of friction was found to be relatively low but stable with water on the surface but higher and more fluctuating in dryer conditions. The character of the worn surfaces did not clearly correlate to the friction behaviour.

Place, publisher, year, edition, pages
Elsevier, 2009
Keyword
tribofilm, alumina, ultrasonic motor
National Category
Materials Engineering
Research subject
Materials Science
Identifiers
urn:nbn:se:uu:diva-111722 (URN)10.1016/j.triboint.2009.05.010 (DOI)000270126500010 ()
Available from: 2009-12-21 Created: 2009-12-21 Last updated: 2017-12-12Bibliographically approved
4. Tribofilm formation of lightly loaded self mated alumina contacts
Open this publication in new window or tab >>Tribofilm formation of lightly loaded self mated alumina contacts
2012 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 289, 39-45 p.Article in journal (Refereed) Published
Abstract [en]

A tribofilm is formed on alumina surfaces that have been slid against alumina surfaces. The tribofilm is formed by alumina wear particles that have been ground, agglomerated and tribosintered to a film. The tribofilm smoothens out the surface topography and fills up cavities. Tribofilms on alumina surfaces have been investigated with respect to surface appearance, hardness and chemical composition. Surface preparation and surrounding humidity have shown to affect the character and lateral distribution of the tribofilm. The tribofilm that was formed in humid air was softer than the tribofilm formed in dry air. XPS analysis revealed the chemical shift of the Al 2p peak did not differ between the tribofilms that was formed in different humidity, nor the unworn reference surface, finding that no hydroxide was found on the alumina surfaces. Also, no tribochemical changes could be detected by ToF-SIMS analysis.

Keyword
Tribofilm, Wear, Alumina, Humidity, Nano hardness
National Category
Materials Engineering
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-156799 (URN)10.1016/j.wear.2012.03.007 (DOI)000306777000005 ()
Available from: 2011-08-11 Created: 2011-08-09 Last updated: 2017-12-08Bibliographically approved
5. On the influence from micro topography of PVD coatings on friction behaviour, material transfer and tribofilm formation
Open this publication in new window or tab >>On the influence from micro topography of PVD coatings on friction behaviour, material transfer and tribofilm formation
Show others...
2011 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 271, no 9-10, 204-2057 p.Article in journal (Refereed) Published
Abstract [en]

PVD coatings based on amorphous carbon with metal-carbides are currently gaining a high interest for use on machine elements due to their potential to give low friction and low wear of the counter surface. However, the performance varies significantly between the various types of such coatings and the causes of this are not clear. One factor is the micro topography of the coating surface. This topography may influence the friction in many ways; by changing the state of lubrication, by causing scratching of the counter surface, by modifying the topography of the counter surface the material transfer, the tribofilm formation, etc.

TaC/a-C coatings, produced by co-sputtering of carbon and tantalum in an argon atmosphere, were deposited on high speed steel substrates exposed to varying degrees of etching to produce a range of surface roughnesses. Ball-on-disc experiments were used to evaluate the tribological properties of the coatings in dry condition against a ball bearing steel ball. The surfaces were analysed using various advanced techniques, including, SEM, XPS, Raman, EDS and AFM, all both prior to and after the testing.

It was shown that the resulting surface topography of the coating is affected even by very small protrusions on the substrate. The coefficient of friction decreased during use to a stable level, due to a complex process including tribofilm build-up on the sliding ball. Surfaces with lower protrusions exhibited a faster friction decrease, i.e. a faster running in.

Place, publisher, year, edition, pages
Elsevier, 2011
Keyword
PVD coating, Wear, Tribofilm, Topography, TaC/a-C
National Category
Materials Engineering Engineering and Technology
Research subject
Engineering Science with specialization in Tribo Materials; Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-156788 (URN)10.1016/j.wear.2010.12.036 (DOI)000294590200106 ()
Available from: 2011-08-09 Created: 2011-08-09 Last updated: 2017-12-08
6. Evaluation of silicon nitride as a wear resistant and resorbable alternative for total joint replacement
Open this publication in new window or tab >>Evaluation of silicon nitride as a wear resistant and resorbable alternative for total joint replacement
Show others...
2012 (English)In: Biomatter, ISSN 2159-2527, Vol. 2, no 2, 94-102 p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Landes Bioscience, 2012
National Category
Materials Engineering
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-156793 (URN)10.4161/biom.20710 (DOI)
Available from: 2011-08-09 Created: 2011-08-09 Last updated: 2014-04-29Bibliographically approved
7. Fabrication and evaluation of SixNy coatings for total joint replacements
Open this publication in new window or tab >>Fabrication and evaluation of SixNy coatings for total joint replacements
Show others...
2012 (English)In: Journal of materials science. Materials in medicine, ISSN 0957-4530, E-ISSN 1573-4838, Vol. 23, no 8, 1879-1889 p.Article in journal (Refereed) Published
Abstract [en]

Wear particles from the bearing surfaces of joint implants are one of the main limiting factors for total implant longevity. Si3N4 is a potential wear resistant alternative for total joint replacements. In this study, SixNy-coatings were deposited on cobalt chromium-discs and Si-wafers by a physical vapour deposition process. The tribological properties, as well as surface appearance, chemical composition, phase composition, structure and hardness of these coatings were analysed. The coatings were found to be amorphous or nanocrystalline, with a hardness and coefficient of friction against Si3N4 similar to that found for bulk Si3N4. The low wear rate of the coatings indicates that they have a potential as bearing surfaces of joint replacements. The adhesion to the substrates remains to be improved.

National Category
Materials Engineering Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry; Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-156798 (URN)10.1007/s10856-012-4625-3 (DOI)000306586900005 ()
Available from: 2011-08-09 Created: 2011-08-09 Last updated: 2017-12-08Bibliographically approved

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Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
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Output format
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