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@PHDTHESIS{Ebert:133240,
      author       = {Ebert, Svenja Maria},
      title        = {{V}ersagensverhalten plasmagespritzter
                      {M}g-{A}l-{S}pinell-{S}chichten unter {T}hermozyklierung},
      volume       = {166},
      school       = {Ruhr-Universität Bochum},
      type         = {Dissertation},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2013-01778},
      isbn         = {978-3-89336-853-2},
      series       = {Schriften des Forschungszentrums Jülich : Energie $\&$
                      Umwelt / Energy $\&$ Environment},
      pages        = {X, 173 S.},
      year         = {2013},
      note         = {Dissertation, Ruhr-Universität Bochum, 2013},
      abstract     = {One possibility to increase the efficiency in gas turbines
                      is the application of abradable coatings. The housing from
                      the inside is coated with special, high temperature
                      resistant ceramics. Thermal loadings and the centrifugal
                      force causes the turbine to expand. Theblade tips drive into
                      the liners. This minimizes the clearance distance between
                      the rotating blade tips and the stationary components, which
                      leads to increases in efficiency and reductions in fuel
                      consumption. The presented work grew out of the
                      collaboration with Rolls-Royce Deutschland. The cycling
                      behaviour of a multilayer system was tested. Disc-shaped
                      Inconel738-substrates were coated with a vacuum
                      plasma-sprayed bondcoat and a doublelayer ceramic system.
                      The ceramic system was atmospheric plasma-sprayed and
                      consisted of a yttria-stabilisedzirconia (YSZ) layer and a
                      Mg-Al-spinel layer. The cycling was carried out with a gas
                      burner and thermal gradient from surface to bottom. Two
                      different failure mechanisms were observed for the
                      Mg-Al-spinel layer. On the one hand the coating spalled of
                      at the interface between YSZ and Mg-Al-spinel. On the other
                      hand only a spalling on top of the Mg-Al-spinel layer was
                      found. A dependence on the spraying parameters was observed.
                      Goal of the presented work was the clarification of these
                      failure mechanisms. First of all the microstructure after
                      spraying and cycling was analysed. For an alumina rich
                      spinel the thermal cycling and thermal energy leads to the
                      formation of three different phases in thermal equilibrium:
                      Mg-Al-spinel, $\alpha$ -Al$_{2}$O$_{3}$ und
                      CaO*6Al$_{2}$O$_{3}$ (CaO as contamination in the powder).
                      During the heating time of the cycling a dense layer at the
                      surface of the Mg-Al-spinel coating is formed. This layer
                      consists of Mg-Al-spinel and CaO*6Al$_{2}$O$_{3}$ needles.
                      Stress calculationswere carried out, which show that the
                      surface of the Mg-Al-spinel coating is under compression
                      stress during heating. Hot pressing experiments confirmed
                      the compression stress as a cause for the densification.
                      Under this dense layer cracks are formed during cycling,
                      which are the reason for the spalling. Crack formation under
                      the dense layer takes place, when the energy release rate
                      stored in the coating system reaches the critical value. The
                      transfer of the spraying in the industry required new
                      spraying parameters for coating of real engine parts. In the
                      context of this work it was found out, that a coating
                      temperature under 200°C seems to be too low for a good
                      connection between the Mg-Al-spinel splats inside the
                      coating. The coating spalls close to the interface between
                      YSZ and Mg-Al-spinel.},
      keywords     = {Dissertation (GND)},
      cin          = {IEK-1},
      cid          = {I:(DE-Juel1)IEK-1-20101013},
      pnm          = {122 - Power Plants (POF2-122)},
      pid          = {G:(DE-HGF)POF2-122},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/133240},
}