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Influence of Ti-Si cathode grain size on the cathodic arc process and resulting Ti-Si-N coatings
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology. Seco Tools, Fagersta, Sweden.
PLANSEE Composite Materials GmbH.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
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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. Vol. 235, no 25, 637-647 p.
Keyword [en]
cathodic arc evaporation; powder metallurgy; work function; cathode surface evolution; deposition rate
National Category
Materials Engineering
URN: urn:nbn:se:liu:diva-96402DOI: 10.1016/j.surfcoat.2013.08.042ISI: 000329596100081OAI: diva2:641634
Available from: 2013-08-19 Created: 2013-08-19 Last updated: 2016-08-31Bibliographically approved
In thesis
1. Microstructure evolution of Ti-based and Cr cathodes during arc discharging and its impact on coating growth
Open this publication in new window or tab >>Microstructure evolution of Ti-based and Cr cathodes during arc discharging and its impact on coating growth
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.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1537
National Category
Natural Sciences
urn:nbn:se:liu:diva-96790 (URN)978-91-7519-539-1 (print) (ISBN)
Public defence
2013-09-20, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Available from: 2013-08-27 Created: 2013-08-27 Last updated: 2016-08-31Bibliographically approved

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