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@PHDTHESIS{Song:19785,
      author       = {Song, Peng},
      title        = {{I}nfluence of {M}aterial and {T}esting {P}arameters on the
                      {L}ifetime of {TBC} {S}ystems with {MC}r{A}l{Y} and
                      {N}i{P}t{A}l {B}ondcoats},
      volume       = {137},
      school       = {RWTH Aachen},
      type         = {Dr. (Univ.)},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {PreJuSER-19785},
      isbn         = {978-3-89336-783-2},
      series       = {Schriften des Forschungszentrums Jülich : Energie $\&$
                      Umwelt / Energy $\&$ Environment},
      pages        = {V, 126 S.},
      year         = {2011},
      note         = {Record converted from JUWEL: 18.07.2013; RWTH Aachen,
                      Diss., 2011},
      abstract     = {The oxidation behavior of the bond coat is an important
                      factor determining the lifetime of thermal barrier coatings
                      (TBC) in the advanced gas turbine components. In the present
                      work, the effect of various testing parameters, such as
                      hot/cold dwell time, heating/cooling rate, atmosphere
                      composition on the bondcoat oxidation and associated TBC
                      lifetime has been investigated. The range of coating systems
                      included Electron Beam - Physical Vapor Deposited (EB-PVD)
                      and Air Plasma Sprayed (APS) TBC´s with MCrAlY (M = Ni, Co)
                      and NiPtAl- bondcoats of various compositions. The effect of
                      the testing parameters strongly depended on the type and
                      properties of the studied system. The lifetime of EB-PVD TBC
                      systems with conventional MCrAlY and NiPtAl bondcoats
                      forming uniform, flat alumina scales was found to be limited
                      by critical scale thickness, upon which a rapid crack
                      propagation at the scale/bondcoat interface results in
                      macroscopic failure. The lifetime of such systems was found
                      to be affected by factors, which influence the scale growth
                      rate and adherence (in particular by oxygen partial pressure
                      (pO$_{2}$) and water vapor content in the test gas in the
                      case of MCrAlY), whereas the temperature cyclic frequency
                      showed no significant effect. NiPtAl bondcoats showed a
                      superior behavior than the conventional MCrAlY-bondcoats due
                      to slower scale growth rate and better scale adherence. For
                      EB-PVD TBC systems with Zr-doped MCrAlYbondcoats the
                      lifetime is mainly determined by the crack growth rate in
                      the inhomogeneous inwardly growing oxide scales, whereas the
                      lifetime is not dependent on the pO$_{2}$ but rather on the
                      cyclic frequency. For APS TBC systems the bondcoat oxidation
                      is only one of several factors determining the ceramic
                      topcoat lifetime. Therefore the oxide scale adherence is of
                      less importance for lifetime of APS TBCs as compared to
                      EBPVD TBCs. For the former systems, the cracks initiated at
                      the convex asperities of the rough oxide scale / bondcoat
                      interface need to propagate through the TBC to cause
                      macroscopic failure. The rate of crack propagation in the
                      TBC is a critical step, which depends substantially on its
                      microstructural properties. In addition to the TBC-porosity
                      the bondcoat roughness profile is shown to be an important
                      parameter, which to a large extent determines the rate of
                      crack initiation and propagation. Higher Co-content in the
                      bondcoat was found to stabilize its microstructure thereby
                      lowering the CTE-mismatch stress in the ceramic topcoat thus
                      extending the TBC-lifetime. The major drawback of high
                      Co-contents was that such bondcoats are prone to form
                      fast-growing spinel oxides. This effect, which was
                      especially pronounced on rough surfaces could be suppressed
                      by only a minor (few microns) enrichment of Al on the
                      bondcoat surface prior to TBC-deposition produced by
                      heat-treatment in high vacuum. With respect to the effects
                      of experimental parameters it was found that contrary to
                      EB-PVD TBC systems a higher cycle frequency leads to
                      shortening of the APS TBC lifetime, whereas higher water
                      vapor content had no significant influence. The results of
                      the present work indicate that the lifetime of the TBC
                      systems with MCrAlY bondcoats would be shorter than that
                      required for long-term operation (25 000 hours) at the
                      envisaged operating temperature of 1000°C. Under such
                      circumstances using NiPtAl-type of bondcoats or perhaps
                      Pt-modified MCrAlY-bondcoats would be an option to obtain
                      the necessary lifetime extension, which can even justify the
                      high cost of metallic Pt.},
      cin          = {IEK-2},
      ddc          = {500},
      cid          = {I:(DE-Juel1)IEK-2-20101013},
      pnm          = {Rationelle Energieumwandlung},
      pid          = {G:(DE-Juel1)FUEK402},
      typ          = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
      url          = {https://juser.fz-juelich.de/record/19785},
}