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An atomistic approach to the initiation mechanism of galling
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Materials Science.
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2006 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 37, no 3, 193-197 p.Article in journal (Refereed) Published
Abstract [en]

Sliding metallic contacts are accompanied by a severe wear phenomenon named galling. This is manifested in adhesion followed by a substantial increase of friction and subsequent deterioration of the contact surfaces. Experiments on titanium- and vanadium-nitride coated surfaces slid against steels indicate that VN exhibits low friction and improved galling characteristics, clearly outperforming the widely used TiN coating. Using first principles simulations, based on the exact muffin-tin orbital and pseudopotential methods, we present an insight to the atomic level processes initiating galling at Ti(V)N-Fe interfaces. It is found that the equilibrium atomic-scale contacts between nitrides and Fe are adhesive. We demonstrate that the close-packed (001) VN-Fe interface exhibits a lower atomic-level roughness and a reduced atomic-friction coefficient than that in the case of TiN. These theoretical results indicate that VN is less prone to galling compared to TiN.

Place, publisher, year, edition, pages
2006. Vol. 37, no 3, 193-197 p.
Keyword [en]
density functional calculations, adhesion, atomic friction, galling
National Category
Engineering and Technology
URN: urn:nbn:se:uu:diva-96665DOI: 10.1016/j.commatsci.2005.08.006ISI: 000239678700001OAI: oai:DiVA.org:uu-96665DiVA: diva2:171314
Available from: 2008-01-24 Created: 2008-01-24 Last updated: 2016-06-22Bibliographically approved
In thesis
1. On Adhesion and Galling in Metal Forming
Open this publication in new window or tab >>On Adhesion and Galling in Metal Forming
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Metal forming is widely used in the industry to produce cans, tubes, car chassis, rods, wires etc. Forming certain materials such as stainless steel, aluminium and titanium, is often difficult, and problems associated with transfer of work material to the tool material are frequent. Transferred material may scratch and deform the following manufactured pieces, a phenomenon named galling. Lubricants can, to some degree, solve these problems. However, many forming oils are hazardous to the environment, and therefore it is highly desirable to replace them or get rid of them.

This thesis investigates the nature of the galling phenomenon and tries to explain under which conditions such problems arise. Dry sliding tests have been performed in a dedicated load-scanner equipment. Difficult work materials have been tested against tool materials under various conditions and the samples have then been studied by advanced analytical techniques, such as ESCA and TEM, to study the detailed tribological mechanisms occurring in the contact between work and tool material.

The general assumption is that material transfer only occurs when there is metal to metal contact. In this work it has been found that, for stainless steel, the oxide plays a very important role for the sticky behaviour of stainless steel, and that metal to metal contact is not a necessary condition for galling.

Several PVD-coated tool materials have been tested and it was found that vanadium nitride coatings can be tuned regarding their chemical composition, to be more galling resistant than conventional coatings.

The surface roughness of the tool material is very strongly coupled to the tools ability to resist galling. The smoother the tool surface, the less risk of material transfer and galling.

Some work materials, like aluminium and titanium, transfer to even the smoothest tool materials. A proposed explanation for this is that their oxides are much harder than the bulk material and the tool material matrix. When deforming the work material, the oxide will fracture into small hard scales, which can indent the tool material. Indented hard scales will then contribute to material transfer of more work material to the tool.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. 52 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 388
Engineering physics, adhesion, galling, dry sliding, stainless steel, vanadium nitride, metal forming, Teknisk fysik
urn:nbn:se:uu:diva-8417 (URN)978-91-554-7072-2 (ISBN)
Public defence
2008-02-15, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:00
Available from: 2008-01-24 Created: 2008-01-24Bibliographically approved

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Vitos, LeventeLarsson, KarinJohansson, BörjeHanson, MagnusHogmark, Sture
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