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Microstructure evolution of Ti-based and Cr cathodes during arc discharging and its impact on coating growth
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis explores the microstructure evolution of cathodes with various material compositions and grain sizes during cathodic arc evaporation processes as well as the impact on the arc movement, and the microstructure and properties of the deposited nitride coatings. The studied cathode material systems include conventionally metal forged Ti and Ti -Si cathodes, novel Ti3SiC2 MAX-phase cathodes, and dedicatedly designed powder-metallurgical Ti-Si and Cr cathodes with different grain size. The microstructure and chemical composition of the virgin and arced cathodes together with the microstructure and mechanical properties of the deposited coatings were analyzed with various characterization techniques, including x-ray diffractometry, x-ray photoelectron spectroscopy, elastic recoil detection analysis, scanning electron microscopy, focused ion beam sample preparation technique, transmission electron microscopy, energy dispersive x-ray, electron energy loss spectroscopy, and nanoindentation.

In general, a converted layer forms on the cathode surfaces during cathodic arc evaporation. The thickness, the microstructure and the chemical composition of such layer are dependent on the composition and the grain size of the virgin cathodes, the nitrogen pressure, and the cathode fabrication methods.

For Ti based materials, the converted layer is 5-12 μm thick and consists of nanosized nitrided grains caused by the high reactivity of Ti to the ambient nitrogen gas. In comparison, the Cr cathode is covered with a 10-15 μm converted layer with micrometer/sub-micrometer sized grains. Only very limited amounts of nitrogen are detected within the layer due to the low reactivity of Cr to nitrogen.

For Ti-Si cathodes, the existence of multiple phases of Ti and Ti5Si3 with different work function renders preferential arc erosion on the Ti5Si3 phase during discharging. The preferential erosion generates higher roughness of the Ti-Si cathode surface compared with Ti. By increasing the grain size of the virgin Ti-Si cathodes from ~8 μm to ~620 μm, the average roughness  increases from 1.94±0.13 μm to 91±14 μm due to the amplified impact of preferential erosion of the enlarged Ti5Si3 grains. The variation of the preferential erosion affects the arc movement, the deposition rate, and the macroparticle distribution of the deposited Ti-Si-N coatings.

A novel Ti3SiC2 MAX phase is used as cathode material for the growth of Ti-Si-C-N coating. During arcing, the cathode surface forms a converted layer with two sublayers, consisting of a several-micrometer region with a molten and resolidified microstructure followed by a region with a decomposed microstructure. The microstructure and hardness of the deposited Ti -Si-C-N coatings is highly dependent on the wide range of coating compositions attained. In the coatings with abundance of N, the combined presence of Si and C strongly disturbs cubic phase growth and compromises their mechanical strength. At a nitrogen pressure of 0.25-0.5 Pa, 45-50 GPa superhard (Ti,Si)(C,N) coatings with a nanocrystalline feathered structure were obtained.

By increasing the grain size of the elemental Cr cathodes from ~10 μm and ~300 μm, the grain structure of the converted layer on the cathode surface varies from equiaxed grains to laminated grains after evaporating in a nitrogen atmosphere. When evaporated with a stationary fixture, the worn Cr cathode surface contains an organized pattern of deep ditches in the surface. The formation of such patterns is enhanced by increasing the cathode grain size. The fixture movement, which is either stationary or single rotating, affects the phase composition, the droplet density and the microstructure of the deposited Cr-N coatings, which consequently determines the mechanical properties of the coatings.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. , 55 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1537
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-96790ISBN: 978-91-7519-539-1 (print)OAI: oai:DiVA.org:liu-96790DiVA: diva2:643350
Public defence
2013-09-20, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2013-08-27 Created: 2013-08-27 Last updated: 2016-08-31Bibliographically approved
List of papers
1. Characterization of worn Ti-Si cathodes used for reactive cathodic arc evaporation
Open this publication in new window or tab >>Characterization of worn Ti-Si cathodes used for reactive cathodic arc evaporation
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2010 (English)In: JOURNAL OF VACUUM SCIENCE and TECHNOLOGY A, ISSN 0734-2101, Vol. 28, no 2, 347-353 p.Article in journal (Refereed) Published
Abstract [en]

The microstructural evolution of Ti1-xSix cathode surfaces (x=0, 0.1, 0.2) used in reactive cathodic arc evaporation has been investigated by analytical electron microscopy and x-ray diffractometry. The results show that the reactive arc operated in N-2 atmosphere induces a 2-12 mu m thick N-containing converted layer consisting of nanosized grains in the two-phase Ti and Ti5Si3 cathode surface. The formation mechanism of this layer is proposed to be surface nitriding and redeposition of macroparticles formed during the deposition process. The surface roughness of the worn Ti1-xSix cathodes increases with increasing Si content, up to 20 at. %, due to preferential erosion of Ti5Si3.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-54604 (URN)10.1116/1.3330767 (DOI)000275515000029 ()
Note
Original Publication: Jianqiang Zhu, Anders Eriksson, Naureen Ghafoor, M P Johansson, J Sjolen, Lars Hultman, Johanna Rosén and Magnus Odén, Characterization of worn Ti-Si cathodes used for reactive cathodic arc evaporation, 2010, JOURNAL OF VACUUM SCIENCE and TECHNOLOGY A, (28), 2, 347-353. http://dx.doi.org/10.1116/1.3330767 Copyright: American Vacuum Society http://www.avs.org/ Available from: 2010-03-26 Created: 2010-03-26 Last updated: 2016-08-31
2. Influence of Ti-Si cathode grain size on the cathodic arc process and resulting Ti-Si-N coatings
Open this publication in new window or tab >>Influence of Ti-Si cathode grain size on the cathodic arc process and resulting Ti-Si-N coatings
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2013 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 235, no 25, 637-647 p.Article in journal (Refereed) Published
Abstract [en]

The influence of the Ti-Si cathode grain size on cathodic arc processes and resulting Ti-Si-N coating synthesis has been studied. 63 mm Ti-Si cathodes containing 20-25 at % Si with four dedicated grain size of ~8 µm, ~20 µm, ~110 µm, and ~600 µm were fabricated via spark plasma sintering or hot isostatic pressing. They were evaporated in 2 Pa nitrogen atmosphere in an industrial-scale arc deposition system and the Ti-Si-N coatings were grown at 50 A, 70 A, and 90 A arc current. The composition and microstructure of the virgin and worn cathode surfaces as well as the resulting coatings were characterized using optical and electron microscopy, x-ray diffraction, elastic recoil detection analysis, x-ray photoelectron spectroscopy, and nanoindentation. The results show that the existence of multiple phases with different work function values directly influences the cathode spot ignition behavior and also the arc movement and appearance. Specifically, there is a preferential erosion of the Ti5Si3-phase grains. By increasing the grain size of the virgin cathode, the preferential erosion is enhanced, such that the cathode surface morphology roughens substantially after 600 Ah arc discharging. The deposition rate of the Ti-Si-N coating is increased with decreasing grain size of the evaporated Ti-Si cathodes. The composition, droplet density, and droplet shape of the coatings are influenced by the arc movement, which is also shown to depend on the cathode grain size.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
cathodic arc evaporation; powder metallurgy; work function; cathode surface evolution; deposition rate
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-96402 (URN)10.1016/j.surfcoat.2013.08.042 (DOI)000329596100081 ()
Available from: 2013-08-19 Created: 2013-08-19 Last updated: 2017-12-06Bibliographically approved
3. Microstructure evolution of Ti3SiC2 compound cathodes during reactive cathodic arc evaporation
Open this publication in new window or tab >>Microstructure evolution of Ti3SiC2 compound cathodes during reactive cathodic arc evaporation
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2011 (English)In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 29, no 3, 031601- p.Article in journal (Refereed) Published
Abstract [en]

The microstructure evolution and compositional variation of Ti3SiC2 cathode surfaces during reactive cathodic arc evaporation are presented for different process conditions. The results show that phase decomposition takes place in the near-surface region, resulting in a 5-50 mu m thick converted layer that is affected by the presence of nitrogen in the deposition chamber. This layer consists of two different sublayers, i.e., 1-20 mu m thick top layer with a melted and resolidified microstructure, followed by a 4-30 mu m thick transition layer with a decomposed microstructure. The converted layer contains a polycrystalline TiCx phase and trace quantities of Si-rich domains with Ti5Si3(C) at their interface. The arc discharge causes Si redistribution in the two regions of the layer, whose Si/(Ti+Si) ratio is higher in the top region and lower in the transition region compared to the virgin material.

Place, publisher, year, edition, pages
American Vacuum Society, 2011
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-68016 (URN)10.1116/1.3569052 (DOI)000289689000021 ()
Available from: 2011-05-06 Created: 2011-05-06 Last updated: 2017-12-11
4. Ti-Si-C-N Thin Films Grown by Reactive Arc Evaporation from Ti3SiC2 Cathodes
Open this publication in new window or tab >>Ti-Si-C-N Thin Films Grown by Reactive Arc Evaporation from Ti3SiC2 Cathodes
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2011 (English)In: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 26, 874-881 p.Article in journal (Refereed) Published
Abstract [en]

Ti-Si-C-N thin films were deposited onto WC-Co substrates by industrial scale arc evaporation from Ti3SiC2 compound cathodes in N2 gas. Microstructure and hardness were found to be highly dependent on the wide range of film compositions attained, comprising up to 12 at.% Si and 16 at.% C. Nonreactive deposition yielded films consisting of understoichiometric TiCx, Ti and silicide phases with high (27 GPa) hardness. At a nitrogen pressure of 0.25-0.5 Pa, below that required for N saturation, superhard, 45-50 GPa, (Ti,Si)(C,N) films with a nanocrystalline feathered structure were formed. Films grown above 2 Pa displayed crystalline phases of more pronounced nitride character, but with C and Si segregated to grain boundaries to form weak grain boundary phases. In abundance of N, the combined presence of Si and C disturb cubic phase growth severely and compromises the mechanical strength of the films.

Place, publisher, year, edition, pages
Cambrdige University Press, 2011
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-61992 (URN)10.1557/jmr.2011.10 (DOI)
Note

Original Publication: Anders Eriksson, Jianqiang Zhu, Naureen Ghafoor, Jens Jensen, Grzegorz Greczynski, Mats Johansson, Jacob Sjölen, Magnus Odén, Lars Hultman and Johanna Rosén, Ti-Si-C-N Thin Films Grown by Reactive Arc Evaporation from Ti3SiC2 Cathodes, 2011, Journal of Materials Research, (26), 874-881. http://dx.doi.org/10.1557/jmr.2011.10 Copyright: Mrs Materials Research Society http://www.mrs.org/

Available from: 2010-11-18 Created: 2010-11-18 Last updated: 2017-12-12
5. Effects of cathode grain size and substrate fixturing on the microstructure evolution of arc evaporated Cr-cathodes and Cr-N coating synthesis
Open this publication in new window or tab >>Effects of cathode grain size and substrate fixturing on the microstructure evolution of arc evaporated Cr-cathodes and Cr-N coating synthesis
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2014 (English)In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 32, no 2, 021515- p.Article in journal (Refereed) Published
Abstract [en]

The influence of the cathode grain size and the substrate fixturing on the microstructure evolution of the Cr cathodes and the resulting Cr-N coating synthesis is studied. Hot isostatic pressed Cr cathodes with three different grain sizes were arc evaporated in a nitrogen atmosphere and Cr-N coatings were deposited on cemented carbide substrate at 2 and 4 Pa nitrogen pressure, respectively. The Cr cathodes before and after arc discharging are composed of polycrystalline α-Cr regardless of the grain size. A converted layer forms on the Cr cathode surface and its microstructure differs with the cathode grain size. A stationary substrate fixturing results in ditches covering the cathode surface while a single rotating fixturing does not. The increased grain size of the virgin Cr cathodes enhances the quantities of the ditches. The possible causes are addressed. At 2 Pa nitrogen pressure, the Cr-N coatings deposited with the single rotating fixturing comprise only cubic CrN phase while the ones deposited with the stationary fixturing contain a mixture of hexagonal Cr2N and cubic CrN phases. By the increasing grain size of the Cr cathode, the droplet density of the Cr-N coatings increase somewhat while the hardness decreases for the Cr-N coatings deposited with stationary fixturing at 2 Pa nitrogen pressure.

Keyword
Cathodic arc deposition, cathode surface evolution, substrate fixturing, wormlike ditches, grain size
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-96789 (URN)10.1116/1.4865923 (DOI)000335964200056 ()
Available from: 2013-08-27 Created: 2013-08-27 Last updated: 2017-12-06Bibliographically approved

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