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Insights into wear and deformation of alternative binder hardmetals
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Tribomaterial)
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Description
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 [en]
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: urn:nbn:se:uu:diva-395619ISBN: 978-91-513-0789-3 (print)OAI: oai:DiVA.org:uu-395619DiVA, id: diva2:1362889
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
List of papers
1. Life time of cemented carbide inserts with Ni-Fe binder in steel turning
Open this publication in new window or tab >>Life time of cemented carbide inserts with Ni-Fe binder in steel turning
2017 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 376, p. 1822-1829Article in journal (Refereed) Published
Abstract [en]

Health concerns associated with cobalt powder are a strong motivator for conducting research on alternative binders for cemented carbides. It has previously been shown possible to make cemented carbides with alternative binders, which offer good hardness and toughness. However, it is not fully known if these cemented carbides can be successfully used as metal cutting tools. In this study we have tested turning inserts from cemented carbide with a nickel-iron binder and compared these with cobalt based reference inserts in dry face turning of steel in a pairwise comparison. To facilitate relevant comparisons, both the alternative binder and the reference cemented carbide are gradient sintered and coated in the same way as commercial turning grades. It is found that the life time in this dry face turning test is only approximately 15% shorter with the nickel-iron binder than with the cobalt reference, which motivates further studies with this alternative binder. Flaking of the coating and thus less coating adhesion was identified as one reason for the shorter life time.

Keywords
Cutting tools, Cemented carbide, Alternative binder, Face turning
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-329133 (URN)10.1016/j.wear.2017.02.018 (DOI)000403902000097 ()
Funder
VINNOVA
Available from: 2017-10-10 Created: 2017-10-10 Last updated: 2019-10-22Bibliographically approved
2. Towards understanding plastic deformation in hardmetal turning inserts with different binders
Open this publication in new window or tab >>Towards understanding plastic deformation in hardmetal turning inserts with different binders
(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
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:nbn:se:uu:diva-395617 (URN)
Available from: 2019-10-22 Created: 2019-10-22 Last updated: 2019-10-22
3. Orientation of binder phase lamellae formed through grain boundary sliding in hardmetal turning inserts
Open this publication in new window or tab >>Orientation of binder phase lamellae formed through grain boundary sliding in hardmetal turning inserts
(English)Manuscript (preprint) (Other academic)
Keywords
hardmetal; cemented carbide; grain boundary sliding; alternative binders
National Category
Engineering and Technology Materials Engineering
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
urn:nbn:se:uu:diva-395616 (URN)
Available from: 2019-10-22 Created: 2019-10-22 Last updated: 2019-10-22
4. Deformation induced martensite in a Fe-Ni-Co binder phase of a hardmetal
Open this publication in new window or tab >>Deformation induced martensite in a Fe-Ni-Co binder phase of a hardmetal
2019 (English)In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 155, article id 109783Article in journal (Refereed) Published
Abstract [en]

This paper investigates deformation induced martensite in a hardmetal binder phase with target composition 50 wt% iron, 25 wt% nickel and 25 wt% cobalt. A fully austenitic ion polished cross-section surface was scratched with a diamond indenter and investigated with X-ray and electron diffraction. It was found that the top 100 nm of the scratched surface contained a mixture of austenite and a second phase identified as BCC/BCT martensite. The martensite grain size varied between a few 10 nm and a over 1 mu m in dimensions.

Keywords
Hardmetal, Deformation, Diffraction, Electron microscopy, Martensite
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:uu:diva-394261 (URN)10.1016/j.matchar.2019.06.025 (DOI)000483411900015 ()
Funder
Vinnova, Co-2014-01916
Available from: 2019-10-11 Created: 2019-10-11 Last updated: 2019-10-22Bibliographically approved
5. Abrasive wear of hardmetals with a binder phase forming deformation induced martensite
Open this publication in new window or tab >>Abrasive wear of hardmetals with a binder phase forming deformation induced martensite
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Hardmetals with alternative binder phases with compositions tailored for specific applications may be used to achieve improved performance of tools. In this paper an iron based binder phase that has previously been found to undergo a phase transformation from austenite to martensite as a response to plastic deformation is tested in three different tests: Micro scratch tests, micro abrasion and rock turning. All three tests show characteristic wear of the tungsten carbide and removal of binder phase from the surface.

Keywords
hardmetal, alternative binders, cemented carbides, rock drilling, microscale abrasion, micro scratch testing
National Category
Engineering and Technology Materials Engineering
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
urn:nbn:se:uu:diva-395618 (URN)
Available from: 2019-10-22 Created: 2019-10-22 Last updated: 2019-11-06

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