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Towards understanding plastic deformation in hardmetal turning inserts with different binders
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
Sandvik Coromant R&D.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
(English)In: International journal of refractory metals & hard materials, ISSN 0958-0611, E-ISSN 2213-3917Article in journal (Refereed) Submitted
Abstract [en]

This works investigates the deformation of coated hardmetal turning inserts used until the end of life. Three different hardmetals with binder phases, pure cobalt, 15 wt% iron 85 wt% nickel and 85 wt% iron 15 wt% nickel are tested. It is shown that grain boundary sliding accommodated by formation of binder phase lamellaeis present in all tested inserts, given by a clear increase in number of lamellae in the microstructure of a tested cutting edge compared to a pristine cutting edge ofthe same material. The lamellae formation is discussed and can be explained by the stresses experienced by the cutting edge during turning. The importance of good coating adhesion was shown by formation of cavities in inserts that experienced akiflng of the coating.

Keywords [en]
Hardmetal, steel turning, plastic deformation, grain boundary sliding
National Category
Engineering and Technology Materials Engineering
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
URN: urn:nbn:se:uu:diva-395617OAI: oai:DiVA.org:uu-395617DiVA, id: diva2:1362887
Available from: 2019-10-22 Created: 2019-10-22 Last updated: 2019-10-22
In thesis
1. Insights into wear and deformation of alternative binder hardmetals
Open this publication in new window or tab >>Insights into wear and deformation of alternative binder hardmetals
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This work presents new insights into how hardmetals with alternative binders as well as cobalt based references react to wear and deformation. The main focus has been on hardmetals for steel turning, but also on studying certain fundamental properties of the new binder materials.

Cobalt has traditionally been the most common binder phase for tungsten carbide grains in hardmetals, but recent insights into the carcinogenicity of cobalt powder has led to a need to research alternatives. In this work hardmetals with binder phases consisting of alloys of iron and nickel or iron, nickel and cobalt have been studied.

Coated hardmetal inserts used until end of tool life in steel turning have been evaluated with respect to the plastic deformation and coating adhesion. It was found that grain boundary sliding of tungsten carbide/tungsten carbide grain boundaries is an important deformation mechanism during dry face turning, concluded based on an increased number of binder phase lamellae in tungsten carbide/tungsten carbide grain boundaries in the deformed microstructure.  The lamellae were found to have a preferred orientation, coinciding with the expected flow of material during deformation.

For turning inserts with exposed hardmetal due to flaked coating it was further observed that the microstructure contained cavities caused by the increased temperature of the hardmetal when the protective coating layers are lost. No cavities were found in samples which were still covered by coating at the end of a test. It was therefore concluded that improving the coating adhesion is an important step towards improved performance of alternative binder hardmetals.

Some of the alternative binders in this work were iron rich alloys. Alloys rich in iron can be either austenitic, martensitic or a mixture of the two and this will have a large influence on the final hardmetal properties. It is also possible to make an iron rich alloy which is austenitic at room temperature, but forms deformation induced martensite as a response to stress or strain. This work investigated deformation induced martensite formed during scratching and in abrasive wear of a binder phase alloy of iron, nickel and cobalt. Electron diffraction in both scanning electron microscopes and transmission electron microscopes showed that scratching the surface of this hardmetal resulted in a finely grained surface layer of mixed austenite and martensite. This could prove beneficial in applications.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. p. 77
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1873
Keywords
hardmetal, cemented carbide, alternative binders, steel turning, electron microscopy, electron diffraction
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
urn:nbn:se:uu:diva-395619 (URN)978-91-513-0789-3 (ISBN)
Public defence
2019-12-06, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2019-11-14 Created: 2019-10-22 Last updated: 2019-11-14

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Toller-Nordström, LisaNorgren, Susanne

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