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Dependence of the Stabilization of α-Alumina on the Spray Process

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A phase change from α-alumina (corundum) in the feedstock powder to predominantly other alumina phases, such as γ-alumina in the coating normally takes place, as a result of the spray process. It is expected that the prevention of this phase transformation will significantly improve the mechanical, electrical, and other properties of thermally sprayed alumina coatings. The results regarding the possibility of stabilization of α-alumina through addition of chromia published in the literature are ambiguous. In this work, stabilization using different spray processes (water-stabilized plasma (WSP), gas-stabilized plasma (APS), and high-velocity oxy-fuel spray (HVOF)) was studied. Mechanical mixtures of alumina and chromia were used, as were prealloyed powders consisting of solid solutions. The investigations focused on mechanical mixtures with both APS and WSP and on prealloyed powders with WSP. The coatings were studied by x-ray diffraction, including Rietveld analysis, and analysis of the lattice parameters. Microstructures were investigated by optical microscopy using metallographic cross-sections. It was shown that in the case of the mechanically mixed powders, the stabilization predominantly depends on the applied spray process. The stabilization of the α phase by use of the WSP process starting from mechanical mixtures was confirmed. It appears that stabilization exhibits a complex dependence on the spray process, the process parameters (in particular the thermal history), the nature of the powder (mechanically mixed or prealloyed), and the chromia content.

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Acknowledgments

The work of the Czech authors was supported by the Czech research foundation (GACR, project number 106/05/0483). The authors would like to thank Ms. B. Wolf (Fh-IWS) for metallographic preparation of the coatings.

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Authors and Affiliations

  1. Fraunhofer Institute for Material and Beam Technology, Winterbergstrasse 28, 01277, Dresden, Germany

    Carl Christoph Stahr, Sabine Saaro & Lutz-Michael Berger

  2. Institute of Plasma Physics, Academy of Science, Za Slovankou 3, P.O. Box 17, 182 21, Prague 8, Czech Republic

    Jiri Dubský & Karel Neufuss

  3. Fraunhofer Institute for Ceramic Technologies and Systems, Winterbergstrasse 28, 01277, Dresden, Germany

    Mathias Herrmann

Authors
  1. Carl Christoph Stahr
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  2. Sabine Saaro
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  3. Lutz-Michael Berger
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  4. Jiri Dubský
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  5. Karel Neufuss
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  6. Mathias Herrmann
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Corresponding author

Correspondence to Carl Christoph Stahr.

Additional information

This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.

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Stahr, C., Saaro, S., Berger, LM. et al. Dependence of the Stabilization of α-Alumina on the Spray Process. J Therm Spray Tech 16, 822–830 (2007). https://doi.org/10.1007/s11666-007-9107-7

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  • DOI: https://doi.org/10.1007/s11666-007-9107-7

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