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Surface analysis of laser cladded Stellite exposed to self-mated high load dry sliding
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Materials Science. (The Tribomaterials Group)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Materials Science. (The Tribomaterials Group)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Materials Science. (The Tribomaterials Group)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Materials Science. (The Tribomaterials Group)
2006 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 261, no 1, 96-100 p.Article in journal, Meeting abstract (Refereed) Published
Abstract [en]

Materials from the Stellite family of Co-based alloys are commonly used as low friction, galling resistant materials in high load dry sliding contact applications.

In the present investigation, the surface region of a Co-based material (Stellite 21) exposed to self-mated high load dry sliding at room temperature has been analysed in detail.

During sliding, an approximately 30 nm thick Co-enriched tribofilm is created. It exhibits low friction properties and a high galling resistance. The transformation from an face-centred-cubic structure to easily sheared hexagonal-closed-packed basal planes in the tribofilm combined with the high load carrying capacity of the underlying deformation hardened zone is suggested to explain the excellent low friction properties and galling resistance of this material.

Place, publisher, year, edition, pages
2006. Vol. 261, no 1, 96-100 p.
National Category
Natural Sciences Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-93841DOI: 10.1016/j.wear.2005.09.027OAI: oai:DiVA.org:uu-93841DiVA: diva2:167452
Conference
11th Nordic Symposium on Tribology, NORDTRIB, 1-5 June, 2004, Norway
Available from: 2005-11-25 Created: 2005-11-25 Last updated: 2017-12-14Bibliographically approved
In thesis
1. On the Mechanisms behind the Tribological Performance of Stellites
Open this publication in new window or tab >>On the Mechanisms behind the Tribological Performance of Stellites
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis reveals the tribological mechanisms behind the intrinsic low friction potential of the Co-based family of alloys called Stellites. Although being an established and important group of materials, a satisfactory explanation to why they exhibit low-friction properties under severe sliding conditions has not previously been found in the literature.

The main part of this thesis is dedicated to the clarification of the tribological performance of Stellites in highly loaded sliding contact. The results should assist the development of Co-free alternatives, suitable for replacing Stellites in nuclear applications. Owing to their beneficial properties they are today the most commonly used material in the sealing surfaces on gate valves in the primary circuits of boiling water reactors (BWR). The underlying reason for the replacement in the nuclear applications is an undesired contribution to the background radiation level, originating from the Co in the Stellite surfaces.

The Stellites mainly consist of Cr-rich carbides in a solid solution dominated by Co. The commonly used Stellite 6 and Stellite 21 were chosen as primary test materials and applied by laser cladding, providing a metallically bonded clad layer with a fine dendritic microstructure.

By combining information from a series of dedicated tribological tests and modern high-resolution analysis instruments (e.g. SEM, XRD and TEM) available at the Ångström Laboratory at Uppsala University, the following conclusions can be made regarding the tribological performance of Stellites under high load sliding.

Mechanisms. The (tested) Stellites form a thick deformation hardened layer, topped with a superficial easily sheared layer of hcp basal planes aligned parallel to the worn surface. The easy-shear layer is continually regenerated, replacing worn off material.

Technical benefits. The Stellites offer low-friction properties thanks to their easily sheared surface layers. The risk of severe galling is also avoided by restricting shear and adhesive transfer to very thin superficial layers. In closed sliding contacts, self-generated protective layers formed by re-deposition of wear fragments are also offered.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2005. 51 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 129
Keyword
Materials science, Stellite, Co-based, phase transformation, fcc, hcp, texture, alignment, low-friction, laser cladding, Materialvetenskap
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-6201 (URN)91-554-6420-3 (ISBN)
Public defence
2005-12-16, Siegbahnsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Polacksbacken, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2005-11-25 Created: 2005-11-25 Last updated: 2009-04-29Bibliographically approved
2. Solving Problems in Surface Engineering and Tribology by Means of Analytical Electron Microscopy
Open this publication in new window or tab >>Solving Problems in Surface Engineering and Tribology by Means of Analytical Electron Microscopy
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

It is well known that thin coatings can provide increased lifetime and reduced energy consumption for tools and components. During use, e.g. in sliding contact, mechanical and chemical reactions often lead to the formation of new surface layers, tribofilms, possessing different properties compared to the original surface, hence affecting the overall performance. In this work, analytical electron microscopy was applied to investigate the structure and composition of tribofilms.

Concerning coatings, deposition parameter dependencies, stability and tribology were investigated. The carbon content of hydrogen-free TiCx coatings was shown to significantly influence the morphology. Low carbon content resulted in columnar grains with a strong texture while high carbon content led to the formation of randomly ordered TiCx crystals. The application of positive bias to the substrate as opposed to the normally used negative bias gave a fibrous structure of sputtered TiB2 and low residual stress with maintained hardness. Further, oxidation stability was examined on a (Ta,Al)C:C coating where oxidation led to partial oxidation and formation of AlTaO4 with an 8 nm interface.

A focused ion beam instrument was used to extract samples from certain areas of worn specimens. Tribological contact was observed to result in phase changes and intermixing of materials present in the contact. Sliding contact involving a Co-alloy led to a phase change from fcc to hcp. A 30 nm Co-rich tribofilm was observed with basal planes parallel to the surface. Fully formulated oil was found to inflict considerable wear to a metal doped carbon film through chemical reaction with the metal dopant. WC/Co cemented carbide used for rock drilling exhibited intermixing of rock and Co binder phase after field tests. Chemical vapour deposited diamond worn in nitrogen and argon showed formation of wear debris with amorphous structure containing nitrogen and graphitic like structure, respectively.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2005. 80 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 12
Keyword
Materials science, Tribology, Electron Microscopy, Surface Engineering, Structure and Composition, Materialvetenskap
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-4785 (URN)91-554-6148-4 (ISBN)
Public defence
2005-03-11, Siegbahnsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2005-02-18 Created: 2005-02-18 Last updated: 2013-05-15Bibliographically approved

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Jacobson, StaffanHogmark, Sture

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