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Cathodic arc deposition process
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis aims to expand the knowledge of fundamental mechanisms that govern the cathodic arc process. The first part of this thesis explores and explains the correlations between a rather unexplored process parameter (i.e. cathode microstructure) and the microstructure of the coatings. The second part of the thesis focuses on discovering and explaining the correlations between process parameters (i.e. arc guiding magnetic field and nitrogen pressure), plasma properties (i.e. plasma density, electron temperature, ion saturation density etc.), and the microstructure of the coatings.

Two aspects of the cathode microstructure are explored. The first is the cathode grain size and the second is the disparity among parent phases of the cathode in terms of work function (W.F.) and cohesive energy (C.E.).

Two material systems are selected to investigate the effects of the cathode grain size on the microstructure of the coatings. In this research evolution of the microstructure of the cathode surface under the influence of arc has also been studied. The results show that for CrN coatings a decrease in average grain size of Cr cathode is beneficial in terms of reduction in macroparticle density of Cr-N coatings. In the case of powder metallurgically prepared Ti-50 at.% Al cathodes, a decrease in grain size from 1800 μm to 100 μm promotes the intermixing of Ti and Al grains at the cathode surface which resulted in lower macroparticle density of TiAlN coatings, a Ti/Al ratio closer to cathode composition, and improved hardness. However, further reduction in grain size from 100 μm to 10 μm, upon arcing favors a self-sustaining reaction between Ti and Al grains whose end product is the γ phase. This self-sustaining reaction and arc-created holelike features on the cathode surface render the coatings rich in Al and high in macroparticle density which results in reduced hardness.

The research in the effects of disparity among the parent phases in terms of W.F. and C.E. of the constituents of Ti-50 at.% Al cathodes on the microstructural evolution of the converted layer and the coating's microstructure shows that the phase which has lower W.F. and C.E. suffers higher erosion. It is also shown that irrespective of the cathode type, the arc guiding magnetic field and the surface geometry of the cathode are two significant factors in controlling the microstructure of TiAlN coatings.

The research in finding correlations between the arc guiding magnetic field, plasma density and the microstructure of the coatings show that for a particular arc source assembly the plasma density can be altered by just changing the strength of an electromagnet. A weaker electromagnet strength results in higher plasma density of Ti-67 at.% Al cathode which promotes the growth of dual phase TiAlN coatings, while a stronger magnetic field reduces the plasma density and promotes the growth of single phase TiAIN coatings and a reduction in deposition rate.

The research in establishing the correlations between N2 pressure, plasma properties and coatings microstructure reveals that for plasma generated from Ti-50 at.% Al cathode the average charge state of Ti shows a stark increase with an increase in N2 pressure from 0 Pa to 0.07 Pa, and upon further increase in N2 pressure the average charge state gradually decreases. Moreover, the ionization of nitrogen takes place at the expense of Al2+. It has also been observed that the electron density increases with increasing the N2 pressure while the effective electron temperature decreases. Furthermore, the energetic ion flux to the coating's growth front decreases as the N2 pressure is increased which leads to the alteration of growth texture from 220 to 111.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2019. , p. 58
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 2029
National Category
Nano Technology Manufacturing, Surface and Joining Technology
Identifiers
URN: urn:nbn:se:liu:diva-162140ISBN: 9789179299668 (print)OAI: oai:DiVA.org:liu-162140DiVA, id: diva2:1371812
Public defence
2019-12-11, Planck, Fysikhuset, Campus Valla, Linköping, 09:15 (English)
Opponent
Supervisors
Available from: 2019-11-21 Created: 2019-11-21 Last updated: 2019-12-04Bibliographically approved
List of papers
1. 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, p. 021515-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.

Keywords
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: 2019-11-21Bibliographically approved
2. Morphology and microstructure evolution of Ti-50 at.% Al cathodes during cathodic arc deposition of Ti-Al-N coatings
Open this publication in new window or tab >>Morphology and microstructure evolution of Ti-50 at.% Al cathodes during cathodic arc deposition of Ti-Al-N coatings
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2017 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 121, no 24, article id 245309 (2017)Article in journal (Refereed) Published
Abstract [en]

Today's research on the cathodic arc deposition technique and coatings therefrom primarily focuses on the effects of, e.g., nitrogen partial pressure, growth temperature, and substrate bias. Detailed studies on the morphology and structure of the starting material—the cathode—during film growth and its influence on coating properties at different process conditions are rare. This work aims to study the evolution of the converted layer, its morphology, and microstructure, as a function of the cathode material grain size during deposition of Ti-Al-N coatings. The coatings were reactively grown in pure N2discharges from powder metallurgically manufactured Ti-50 at.% Al cathodes with grain size distribution averages close to 1800, 100, 50, and 10 μm, respectively, and characterized with respect to microstructure, composition, and mechanical properties. The results indicate that for the cathode of 1800 μm grain size the disparity in the work function among parent phases plays a dominant role in the pronounced erosion of Al, which yields the coatings rich in macro-particles and of high Al content. We further observed that a reduction in the grain size of Ti-50 at.% Al cathodes to 10 μm provides favorable conditions for self-sustaining reactions between Ti and Al phases upon arcing to form γ phase. The combination of self-sustaining reaction and the arc process not only result in the formation of hole-like and sub-hole features on the converted layer but also generate coatings of high Al content and laden with macro-particles.

Place, publisher, year, edition, pages
Melville, New York 11747-4300: American Institute of Physics (AIP), 2017
Keywords
cathodic arc, Ti-Al-N, metallurgy, work function, cohesive energy, coatings, microsturcture, Ti-50 at.% Al
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-139116 (URN)10.1063/1.4990425 (DOI)000430928300011 ()2-s2.0-85021732715 (Scopus ID)
Projects
FunMat
Funder
VINNOVA
Available from: 2017-07-02 Created: 2017-07-02 Last updated: 2019-11-21Bibliographically approved
3. Effect of work function and cohesive energy of the constituent phases of Ti-50 at.% Al cathode during arc deposition of Ti-Al-N coatings
Open this publication in new window or tab >>Effect of work function and cohesive energy of the constituent phases of Ti-50 at.% Al cathode during arc deposition of Ti-Al-N coatings
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2019 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 357, p. 393-401Article in journal (Refereed) Published
Abstract [en]

The differences in work function (W.F.) and cohesive energy (C.E.) of the phases constituting the cathode, plays an important role in the formation of the converted layer at its near-surface region during cathodic arc deposition. As a consequence, this also affects the deposition conditions for the coatings. In this study, we explore the effect of W.F. and C.E. of the constituent phases during arc evaporation by utilizing two kinds of customized Ti-50 at.% Al cathodes with different phase compositions. Our results show that during reactive arc evaporation the disparity in W.F. and C.E. among the constituent phases of Ti-50 at.% Al cathodes leads to preferential erosion of the phases with lower W.F. and C.E. The aforementioned preferential erosion begets higher surface roughness on the Ti-50 at.% Al cathode with a wider range of W.F. and C.E. disparity. It is also observed that the thermal conductivity of the Ti-50 at.% Al cathode plays a dominant role in the deposition rate of Ti-Al-N coating. This article also presents how the surface geometry of the cathode in the presence of arc guiding magnetic field significantly influences the microstructure of the deposited coatings.

Place, publisher, year, edition, pages
USA: Elsevier, 2019
Keywords
Cathodic arc, TiAlN, Work function, Reactive hot isostatic pressing, Coatings
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-152247 (URN)10.1016/j.surfcoat.2018.10.027 (DOI)000455691100060 ()2-s2.0-85054904870 (Scopus ID)
Projects
FunMat-II
Funder
VINNOVA, 2016-05156
Note

Funding agencies: VINN Excelence Excellence Center in Research and Innovation on Functional Nanoscale Materials (FunMat-II) by the Swedish Governmental Agency for Innovation Systems [2016-05156]

Available from: 2018-10-23 Created: 2018-10-23 Last updated: 2019-11-21Bibliographically approved
4. The Effect of Cathodic Arc Guiding Magnetic Field on the Growth of (Ti0.36Al0.64)N Coatings
Open this publication in new window or tab >>The Effect of Cathodic Arc Guiding Magnetic Field on the Growth of (Ti0.36Al0.64)N Coatings
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2019 (English)In: Coatings, ISSN 2079-6412, Vol. 9, no 10, article id 660Article in journal (Refereed) Published
Abstract [en]

We use a modified cathodic arc deposition technique, including an electromagnetic coil that introduces a magnetic field in the vicinity of the source, to study its influence on the growth of (Ti0.36Al0.64)N coatings. By increasing the strength of the magnetic field produced by the coil, the cathode arc spots are steered toward the edge of the cathode, and the electrons are guided to an annular anode surrounding the cathode. As a result, the plasma density between the cathode and substrate decreased, which was observed as a lateral spread of the plasma plume, and a reduction of the deposition rate. Optical emission spectroscopy shows reduced intensities of all recorded plasma species when the magnetic field is increased due to a lower number of collisions resulting in excitation. We note a charge-to-mass ratio decrease of 12% when the magnetic field is increased, which is likely caused by a reduced degree of gas phase ionization, mainly through a decrease in N2 ionization. (Ti0.36Al0.64)N coatings grown at different plasma densities show considerable variations in grain size and phase composition. Two growth modes were identified, resulting in coatings with (i) a fine-grained glassy cubic and wurtzite phase mixture when deposited with a weak magnetic field, and (ii) a coarse-grained columnar cubic phase with a strong magnetic field. The latter conditions result in lower energy flux to the coating’s growth front, which suppresses surface diffusion and favors the formation of c-(Ti,Al)N solid solutions over phase segregated c-TiN and w-AlN.

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
physical vapor deposition, magnetic field, optical emission spectroscopy, coatings, grain size
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-162141 (URN)10.3390/coatings9100660 (DOI)000498263900068 ()
Note

Funding agencies: Swedish Research CouncilSwedish Research Council [621-2012-4401]; Swedish government strategic research area grant AFM-SFO MatLiU [2009-00971]; VINNOVA FunMat-IIVinnova [2016-05156]

Available from: 2019-11-20 Created: 2019-11-20 Last updated: 2019-12-09

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