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The Effect of Cathodic Arc Guiding Magnetic Field on the Growth of (Ti0.36Al0.64)N Coatings
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. Department of Materials Science and Engineering, D3.3 Saarland University, Saarbrücken, Germany.
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. Seco Tools AB, SE-737 82 Fagersta, Sweden.ORCID iD: 0000-0003-4577-0976
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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. Vol. 9, no 10, article id 660
Keywords [en]
physical vapor deposition, magnetic field, optical emission spectroscopy, coatings, grain size
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:liu:diva-162141DOI: 10.3390/coatings9100660ISI: 000498263900068OAI: oai:DiVA.org:liu-162141DiVA, id: diva2:1371592
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
In thesis
1. Cathodic arc deposition process
Open this publication in new window or tab >>Cathodic arc deposition process
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:nbn:se:liu:diva-162140 (URN)9789179299668 (ISBN)
Public defence
2019-12-11, Planck, Fysikhuset, Campus Valla, Linköping, 09:15 (English)
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Available from: 2019-11-21 Created: 2019-11-21 Last updated: 2019-12-04Bibliographically approved

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Broering Chaar, Ana BeatrizSyed, Muhammad BilalHsu, Tun-WeiJohansson-Jöesaar, MatsOdén, Magnus

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