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Friction and wear studies of some PEEK materials
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Tribomaterials)ORCID iD: 0000-0001-5928-0834
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
2015 (English)In: Tribologia - Finnish Journal of Tribology, ISSN 0780-2285, Vol. 33, no 2, 20-28 p.Article in journal, Editorial material (Refereed) Published
Abstract [en]

The friction and wear behavior of several types of PEEK polymers and composites were studied. The influence of carbon fiber, lubricant and thermally conductive fillers were evaluated, as well as the effects of contact load and temperature. The tests were done using a reciprocating ball-on-disc set-up. The materials were tested under the load of 5 N and 15 N, at room temperature, 80 °C, 120 °C and 150 °C. The difference between the materials was substantial, with a friction coefficient varying between 0.03 and 0.3 for the different materials at 120 °C. PEEK with carbon fiber filler showed an improvement in both friction and wear compared to unfilled PEEK. When adding lubricant, PTFE, to the composite the friction and wear were improved even more. PEEK with thermally conductive filler on the other hand had both highest friction and wear. Increasing the temperature slightly decreased both friction and wear for most of the PEEK materials. At 150 °C, only the composite with PTFE lubricant had a low friction and wear.

Place, publisher, year, edition, pages
2015. Vol. 33, no 2, 20-28 p.
Keyword [en]
PEEK, carbon fiber, friction, wear
National Category
Textile, Rubber and Polymeric Materials
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
URN: urn:nbn:se:uu:diva-267460OAI: oai:DiVA.org:uu-267460DiVA: diva2:876166
Available from: 2015-12-02 Created: 2015-11-23 Last updated: 2017-11-08
In thesis
1. Tribology of polymer composites for elevated temperature applications
Open this publication in new window or tab >>Tribology of polymer composites for elevated temperature applications
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Polymers as construction material are common in the industry. Although more recently the use of polymer composites in more demanding applications has increased, requiring more of them mechanically, tribologically and thermally. To enhance the properties various fillers are used, from common glass fibers to more advanced nanoparticles. For this study three types of base polymers have been studied: poly-amide (PA), poly-phenylene-sulphide (PPS) and poly-ether-ether-ketone (PEEK). They have been filled with glass fibers, carbon fibers, poly-tetra-fluoro-ethylene (PTFE), graphite and thermally conductive modifier in various combinations. Fibers are used to increase the mechanical properties, PTFE and graphite are added as lubricating additives to reduce the friction, and the thermally conductive modifier to increase the thermal conductivity. Five general groups of polymer composites were studied.

  • Pure PEEK
  • PPS, PA and PEEK filled with fibers
  • PPS, PA and PEEK filled with fibers and lubricating additives
  • PA filled with lubricating additives
  • PEEK filled with fibers and additives for lubrication and thermal conductivity

The polymer composites have been tribologically tested in a reciprocating sliding test set-up. Friction, wear and surface damage have been studied. Three types of counter surfaces have been used: ball bearing steel balls, stainless steel cylinders and anodized aluminum cylinders. Load, surface temperature of the polymer composites and number of cycles were varied to study any changes in friction and wear. The wear marks on the polymer composites were studied using an SEM. Cross sections of some tested samples were prepared to study any subsurface damage.

From the tests the polymer composites showed similarities in friction. Lubricating additives gave lower friction, often around 0.05-0.15, while pure and only reinforced gave higher, often around 0.4-0.5. The wear was also less for polymer composites with lubricating additives. There was no clear influence of temperature but for most tests an increase in temperature gave lower friction. The only influence of load was that higher load gave wider wear tracks. Since no cross sections were prepared to compare subsurface damage due to different loads there might be a possibility that there were some differences below the surface as well. Otherwise cross sections showed that polymer composites with only fibers had cracks and cracked fibers below the surface due to the high stresses the polymer composite had been subjected to. With lubricating additives there was no large subsurface damage and it seems as if the lubricating additives formed a protective tribofilm in the wear track, giving both lower friction and wear. The presence of such a tribofilm was confirmed by XPS analysis that showed a surface layer containing F from PTFE.

The conclusions are that the tribological properties of a polymer composite are strongly dependent on its fillers. Lubricating additives form a tribofilm that lowers friction and wear. Elevated temperatures might drastically change the tribological behavior of a polymer composite why it is important to do tests at higher temperatures. Cross sections can give information about subsurface damage and might help to understand the wear mechanisms and deformation of polymer composites better. More microscopy and mechanism studies are required in order to further understand the tribological behavior of polymer composites.

Place, publisher, year, edition, pages
Uppsala: Uppsala University, 2017. 33 p.
Keyword
tribology, polymer composite, friction, wear
National Category
Materials Engineering
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
urn:nbn:se:uu:diva-332985 (URN)
Presentation
2017-02-02, 13:15 (English)
Opponent
Supervisors
Available from: 2017-11-08 Created: 2017-11-08 Last updated: 2017-11-08Bibliographically approved

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Lind, JonnaKassman Rudolphi, Åsa

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