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@PHDTHESIS{Schweda:134264,
      author       = {Schweda, Mario},
      title        = {{O}ptimierung von
                      {APS}-{Z}r{O}$_{2}$-{W}ärmedämmschichten durch {V}ariation
                      der {K}riechfestigkeit und der {G}renzflächenrauhigkeit},
      volume       = {109},
      issn         = {1866-1793},
      school       = {RWTH Aachen},
      type         = {Dr.},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2013-02511},
      isbn         = {978-3-89336-711-5},
      series       = {Schriften des Forschungszentrums Jülich : Energie $\&$
                      Umwelt / Energy $\&$ Environment},
      pages        = {168 S., Anh.},
      year         = {2010},
      note         = {RWTH Aachen, Diss., 2010},
      abstract     = {Gas turbines operate at combustion chamber temperatures up
                      to 1400°C. Therefore the blades and the combustion chamber
                      lining, which consist of Ni-superalloys for highest loads,
                      are coated with a thermal barrier coating (TBC) of zirconium
                      oxide and an underlying oxidation protection coating of
                      MCrAlY-alloys (M=Ni, Co). At high temperature the
                      MCrAlY-coating oxidizes and an Al$_{2}$O$_{3}$-scale
                      (thermally grown oxide, TGO) forms between MCrAlY-coating
                      and TBC, what constrains the oxidation of the base material.
                      At plasma sprayed TBCs, the MCrAlY-coating provides a bond
                      coat (BC) for the TBC at the same time and therefore is
                      roughened by sandblasting before the deposition of the TBC.
                      By the growth of the Al$_{2}$O$_{3}$-scale and the start up
                      and run down of the gas turbine, stresses arise in the
                      TBC,which lead to lateral crack formation in the field of
                      the TBC-BC-interface and finally to the spallation of the
                      TBC. Thereby other parts of the turbine can be damaged, what
                      causes high costs. Therefrom the aim is to delay the crack
                      growth as strong as possible or rather to maximize the
                      lifetime of the TBC. For this purpose the material
                      properties of the coating components have to be optimized.
                      In the present work, the influence of creep strength of BC
                      and TGO and the influence of TBC-BC-interface-roughness on
                      the lifetime and damage evolution of plasma sprayed
                      ZrO$_{2}$-TBCs are investigated. To determine the lifetime,
                      cylindrical specimens with plasma sprayed ZrO$_{2}$-TBC were
                      produced and thermally cycled with a minimum and maximum
                      temperature of 60°C and 1050°C and a dwell time at maximal
                      temperature of 2h. To exclude the interdiffusion and thermal
                      mismatch between BC and Nisuperalloy, a model system was
                      used: The Ni-superalloy was left and the substrate material
                      consists completely of a BC-like FeCrAlY-alloy. The model
                      system was simulated by the project partner TU Braunschweig
                      with the FE-method. The TBC-BC-interface-roughness was
                      abstracted by a 2-dimensional sine-shaped periodic roughness
                      profile. To be able to compare the simulation results with
                      real TBC-systems, a 2-dimensional periodic roughness profile
                      was produced by high speed drawing. Additionally a
                      3-dimensional stochastic roughness profile was produced by
                      sandblasting. To vary the creep strength of the substrate a
                      conventional (creep weak) and an
                      oxide-dispersion-strengthened (creep strong) FeCrAlY-alloy
                      was used. The creep strength of the Al$_{2}$O$_{3}$-scale
                      was varied by depositing a fine crystalline (creep weak)
                      Al$_{2}$O$_{3}$-scale on the FeCrAlY-substrates by PVD and a
                      coarsecrystalline (creep strong) Al$_{2}$O$_{3}$-scale by
                      pre-oxidation of the FeCrAlY-substrates at 1050°C in air.
                      The roughness depth was varied by drawing with different
                      feed rates in the case of the periodic roughness profile and
                      sandblasting with different grain sizes in the case of the
                      stochastic profile. To investigate the damage evolution,
                      infra-red-impulse-thermographypictures of the specimens were
                      made in regular cycle intervals. The thermography method was
                      optimized in such a way, that delaminations of the TBC are
                      detectable with a detection limit of 1-2 $\mu$m lift-off and
                      0.7-0.8 mm wide. The results show, that the damage evolution
                      and lifetime are significantly influenced by the creep
                      strength of the FeCrAlY-substrate, the TBC-BC-interface
                      roughness depth and the profile type. Based on the results
                      of the investigation of the damage evolution by
                      thermography, a model was created, which gives a good
                      description of the increase of total delamination area on a
                      specimen in principle. The comparison of the FEM-simulation
                      of the present TBC-model-system with the failure mode of the
                      real TBC-specimens with periodic roughness profile showed
                      agreements but also disagreements.},
      keywords     = {Dissertation (GND)},
      cin          = {IEK-2},
      cid          = {I:(DE-Juel1)IEK-2-20101013},
      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/134264},
}