Changes in the Coating Composition Due to APS Process Conditions for Al 2 O 3 -Cr 2 O 3 -TiO 2 Ternary Powder Blends
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Changes in the Coating Composition Due to APS Process Conditions for Al2O3-Cr2O3-TiO2 Ternary Powder Blends Maximilian Grimm1 • Susan Conze2 • Lutz-Michael Berger2 Gerd Paczkowski1 • Rico Drehmann1 • Thomas Lampke1
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Submitted: 2 September 2020 / in revised form: 28 October 2020 / Accepted: 16 November 2020 The Author(s) 2020
Abstract Thermally sprayed coatings from the single oxides and binary compositions of the Al2O3-Cr2O3-TiO2 system show multifunctional properties. Ternary compositions are promising for further improvement in their performance. The stability of the composition during coating formation is an important issue for blended feedstock powders in order to obtain the desired properties. This work focuses on the compositional changes of a ternary blend of Al2O3, Cr2O3 and TiOx powders of equal content by mass in a conventional atmospheric plasma spraying (APS) process using an Ar/H2 plasma gas mixture. By increasing the argon flow rate at constant hydrogen flow rate, the total plasma gas flow rate and the Ar/H2 ratio were varied. For the highest argon flow rate, this resulted in an average particle velocity of 140% and an average particle temperature of 90% of the initial values, respectively. Coating composition and microstructure were studied by optical microscopy, SEM, including EDS analyses, and XRD. In addition, the coating hardness and electrical impedance were also measured. Differences in the ‘‘difficulty of melting factor’’ (DMF) and the thermal diffusivity This article is an invited paper selected from abstracts submitted for the 2020 International Thermal Spray Conference, ITSC2020, that was to be held from June 10–12, 2020, in Vienna, Austria. The conference was cancelled due to the coronavirus (COVID-19) pandemic. The paper has been expanded from the planned presentation. & Maximilian Grimm [email protected] 1
Materials and Surface Engineering Group, Institute of Materials Science and Engineering, Chemnitz University of Technology, 09107 Chemnitz, Germany
2
Fraunhofer IKTS, Fraunhofer Institute for Ceramic Technologies and Systems, 01277 Dresden, Germany
of the three oxides appear to be responsible for the dramatic change of the coating composition with an increasing argon flow rate. For the highest argon flow rate applied, besides TiO2, the coating contains only 8 wt.% Al2O3, while the Cr2O3 content remained almost constant. At the same time, the change of the Ar/H2 ratio resulted in the formation of stoichiometric TiO2 in the coating by oxidation of TiOx in the feedstock powder. Moreover, a small content of titanium was found in the Cr2O3 splats, showing that there are only limited interactions between the large oxide powder particles. Thus, the study has shown that stability of the chemical composition during spraying of ternary powder blends is strongly influenced by the process conditions. Keywords ceramic coating microstructure plasma spraying spaying process analysis ternary composition
Introduction Coatings sprayed from the single ox
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