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@INPROCEEDINGS{Terberger:154267,
      author       = {Terberger, Philipp and Sebold, Doris and Quadakkers, Willem
                      J. and Vassen, Robert},
      title        = {{I}nterdiffusion between vacuum plasma-sprayed protective
                      bond coats and γ`-strengthened {C}obalt-base superalloys
                      during thermal treatment},
      reportid     = {FZJ-2014-03641},
      year         = {2014},
      abstract     = {γ`-strengthened Ni-base superalloys are commonly used for
                      high-temperature, high-load applications in gas turbine
                      blades. The recent discovery of a γ/γ` microstructure in
                      the ternary Co-Al-W alloy system [1] led to intensive
                      research in the design of γ`-strengthened Co-base
                      superalloys. They promise higher operating temperatures
                      compared to Ni-base superalloys. [2] As a new candidate for
                      a turbine blade construction material, Co-base superalloys
                      have to be compatible with state of the art protective bond
                      coats. Vacuum plasma-sprayed (VPS) MCrAlY bond coats
                      (M=Co,Ni) are commonly used for this application in
                      gas-fired industrial turbines.In the present investigation
                      the interaction of VPS bond coats with γ`-strengthened
                      Co-base superalloys during isothermal heat treatment is
                      studied. Hence, the focus is on the interdiffusion processes
                      and the resulting phase changes at the interface between
                      coating and base material. Interdiffusion can lead to
                      depletion or enrichment of certain elements that induce
                      phase changes and thus influence properties of the bond coat
                      and the superalloy substrate. Knowledge about these
                      processes will help to anticipate detrimental effects that
                      can arise during service of the new superalloys.Co-9Al-9W
                      (in $at\%)$ single crystal samples were coated with either a
                      Ni-base or Co-base MCrAlY bond coat using vacuum
                      plasma-spraying. They were heat treated in vacuum at 1080
                      °C and subsequently thermally treated in air at 900 °C for
                      up to 500 hours. Phases formed in the interdiffusion zone
                      were identified and analysed using SEM and EDX, complemented
                      by thermodynamic simulations. It was observed that the γ`
                      phase quickly dissolves due to the enrichment of Cr and the
                      depletion of Al. The interdiffusion zone shows a large
                      amount of W-rich precipitates, mainly consisting of Co7W6
                      and Co23Cr15W15. At the interface of γ/γ` microstructure
                      and interdiffusion zone, thin needle-like precipitates were
                      found that may be Co3W and that serve as nucleation sites
                      for the above mentioned W-rich phases. In direct comparison
                      the Co-base bond coat shows better compatibility with the
                      substrate than the Ni-base bond coat, because it exhibits
                      fewer and smaller W-rich precipitates and thinner
                      interdiffusion zones. This may be due to the higher Co
                      content, the lower Cr activity, and the higher W-solubility
                      of the Co-base bond coat.},
      month         = {Jun},
      date          = {2014-06-22},
      organization  = {Thermal Barrier Coatings IV, Kloster
                       Irsee, Irsee (Germany), 22 Jun 2014 -
                       27 Jun 2014},
      subtyp        = {Other},
      cin          = {IEK-1 / IEK-2},
      cid          = {I:(DE-Juel1)IEK-1-20101013 / I:(DE-Juel1)IEK-2-20101013},
      pnm          = {122 - Power Plants (POF2-122) / HITEC - Helmholtz
                      Interdisciplinary Doctoral Training in Energy and Climate
                      Research (HITEC) (HITEC-20170406)},
      pid          = {G:(DE-HGF)POF2-122 / G:(DE-Juel1)HITEC-20170406},
      typ          = {PUB:(DE-HGF)24},
      url          = {https://juser.fz-juelich.de/record/154267},
}