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Assessing the hardness and residual stress at the very edge of a TiAlN coated cutting insert
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Tribomaterial)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Tribomaterial)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Tribomaterial)
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(English)In: Surface and coatings technology, ISSN 0257-8972Article in journal (Refereed) Submitted
Abstract [en]

A method for determining residual stresses through nanoindentation has been used in order to evaluate the local residual stress in a PVD Ti0.5Al0.5N coating. The influence of residual stress on the measured hardness is obtained by comparing the hardness of as deposited, residually stressed, coating and stress relieved pillars made in the very same coating. The technique offers high lateral resolution, and it can be applied on complex geometries where conventional stress measurements fall short. In this work, the method proved useful for estimating the residual stress at such a complex geometry as a sharp cutting edge. Edges with two different radii were analysed and it was concluded that the nominal residual compressive stress given to a coating can locally, on the very cutting edge, become significantly reduced by elastic relaxation .This effects the cohesion of the coating at that position which, together with the lift-off stress generated at the edge, make the coating in that region especially vulnerable to damage. The experimental results correlated very well with finite element simulations of the residual stress state around cutting edges with the same geometries.

Place, publisher, year, edition, pages
Elsevier.
Keyword [en]
Residual stress, PVD coating, Cutting edge, Nanoindentation
National Category
Materials Engineering
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
URN: urn:nbn:se:uu:diva-183161OAI: oai:DiVA.org:uu-183161DiVA: diva2:562058
Available from: 2012-10-23 Created: 2012-10-23 Last updated: 2013-01-23Bibliographically approved
In thesis
1. Tribology at the Cutting Edge: A Study of Material Transfer and Damage Mechanisms in Metal Cutting
Open this publication in new window or tab >>Tribology at the Cutting Edge: A Study of Material Transfer and Damage Mechanisms in Metal Cutting
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The vision of this thesis is to improve the metal cutting process, with emphasis on the cutting tool, to enable stable and economical industrial production while using expensive tools such as hobs. The aim is to increase the tribological understanding of the mechanisms operating at a cutting edge and of how these can be controlled using different tool parameters. Such understanding will facilitate the development and implementation of future, tribologically designed, cutting tools.

Common wear and failure mechanisms in gear hobbing have been identified and focused studies of the material transferred to the tool, in both metal cutting operations and in simplified tribological tests, have been conducted. Interactions between residual stresses in the tool coating and the shape of the cutting edge have also been studied.

It was concluded that tool failure is often initiated via small defects in the coated tool system, and it is necessary to eliminate, or minimize, these defects in order to manufacture more reliable and efficient gear cutting tools. Furthermore, the geometry of a cutting edge should be optimized with the residual stress state in the coating, in mind. The interaction between a compressive stress and the geometry of the cutting edge will affect the stress state at the cutting edge and thus affect the practical toughness and the wear resistance of the coating in that area.

An intermittent sliding contact test is presented and shown to be of high relevance for studying the interaction between the tool rake face and the chip in milling. It was also demonstrated that material transfer, that can have large effects on the cutting performance, commences already after very short contact times. The nature of the transfer may differ in different areas on the tool. It may include glassy layers, with accumulations of specific elements from the workpiece, and transfer of steel in more or less oxidized form. Both tool coating material, its surface roughness, and the relative speed between the tool surface and the chip, may influence the extent to which the different transfer will occur.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 77 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 988
Keyword
Tribology, Metal cutting, Gear hobbing, Wear, Coating, Residual stress, Material transfer, Steel
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
urn:nbn:se:uu:diva-183186 (URN)978-91-554-8514-6 (ISBN)
Public defence
2012-12-07, 2005, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (Swedish)
Supervisors
Available from: 2012-11-16 Created: 2012-10-23 Last updated: 2013-01-23Bibliographically approved

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