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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
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. Linköping University. (Nanostructured Materials)
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. SECO Tools AB, Fagersta, Sweden.ORCID iD: 0000-0003-4577-0976
PLANSEE Composite Materials GmbH, Lechbruck am See, Germany.
PLANSEE Composite Materials GmbH, Lechbruck am See, Germany.
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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. Vol. 357, p. 393-401
Keywords [en]
Cathodic arc, TiAlN, Work function, Reactive hot isostatic pressing, Coatings
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:liu:diva-152247DOI: 10.1016/j.surfcoat.2018.10.027ISI: 000455691100060Scopus ID: 2-s2.0-85054904870OAI: oai:DiVA.org:liu-152247DiVA, id: diva2:1258079
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
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)
Opponent
Supervisors
Available from: 2019-11-21 Created: 2019-11-21 Last updated: 2019-12-04Bibliographically approved

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The full text will be freely available from 2020-10-15 12:50
Available from 2020-10-15 12:50

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Syed, BilalJöessar, Mats J.Odén, Magnus

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