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@PHDTHESIS{LopezBarrilao:828724,
      author       = {Lopez Barrilao, Jennifer Katharina},
      title        = {{M}icrostructure {E}volution of {L}aves {P}hase
                      {S}trengthened {F}erritic {S}teels for {H}igh {T}emperature
                      {A}pplications},
      volume       = {375},
      school       = {RWTH Aachen},
      type         = {Dr.},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2017-02590},
      isbn         = {978-3-95806-231-3},
      series       = {Schriften des Forschungszentrums Jülich Reihe Energie $\&$
                      Umwelt / Energy $\&$ Environment},
      pages        = {XVI, 134 S.},
      year         = {2017},
      note         = {RWTH Aachen, Diss., 2016},
      abstract     = {The present investigation focuses on a new concept of high
                      strength, high chromium (18 - 23 $wt.\%),$ fully ferritic
                      steels on the technical basis of Crofer$^{®}$ 22 H for the
                      application in high temperature energy conversion systems.
                      Fully ferritic means, that these steels possess a ferritic
                      matrix at any temperature below the melting point, i.e. no
                      martensitic transformation occurs. During Crofer$^{®}$ 22
                      APU and Crofer$^{®}$ 22 H development, over 50 trial alloys
                      with slight changes in chemical composition were designed.
                      Both steels are used as interconnect materials for solid
                      oxide fuel cells (SOFCs) and were developed by the Institute
                      for Microstructure and Properties of Materials (IEK- 2) at
                      Forschungszentrum Jülich GmbH in cooperation with VDM
                      Metals GmbH. Such steels possess potentially sufficient
                      steam oxidation resistance up to 650 $^{\circ}$C, because of
                      their high chromium content [1]. In contrast the steam
                      oxidation resistance of state of the art 9 - 12 \%Cr
                      advanced ferritic martensitic (AFM) steels is limited to
                      temperatures of approximately 620 $^{\circ}$C. To ensure
                      sufficient steam oxidation resistance of AFM steels above
                      620 $^{\circ}$C a higher chromium content is needed [2,3].
                      However, this promotes Z-phase formation on the expense of
                      the strengthening MX (M = V, Nb; X = C, N) particles [4],
                      what causes a drop in long-term creep strength.
                      Strengthening of the new fully ferritic steels is achieved
                      by solid-solution hardening and in case of Crofer$^{®}$ 22
                      H by supplemental intermetallic (Fe,Cr,Si)2(Nb,W) Laves
                      phase particles. The 22 H trial alloys possess superior
                      creep behaviour in the temperature range from 600
                      $^{\circ}$C to 650 $^{\circ}$C [1] and therefore may
                      potentially provide a basis for tackling the future
                      requirements of power plant operation, e.g. higher
                      operational flexibility, higher conversion efficiency and
                      thus lower CO$_{2}$ emission. In order to further
                      optimisation of these fully ferritic alloys the
                      investigation was performed on three various 22 H trial
                      alloys. The investigations aimed on the identification and
                      classification of Laves phase particles as well as on the
                      influence of chemical composition on the presence of
                      different Laves phases and particle size evolution in the
                      temperature range from 600 $^{\circ}$C to 650 $^{\circ}$C
                      after different annealing time utilising electron microscopy
                      techniques. Concurrently the suitability of a commercially
                      available thermodynamic modelling tool was checked and rated
                      as doubtful for further in detail alloy development of such
                      ferritic steels. Particle evolution results explain the
                      different creep behaviour of the trial alloys and show
                      promising thermodynamic stability of particle over the whole
                      covered time range (e.g. approximately 40,000 h at 600
                      $^{\circ}$C and approximately 10,000 h at 650 $^{\circ}$C).
                      Furthermore, investigation of microstructure evolution at
                      650 $^{\circ}$C focused on sub-grain formation, the
                      formation of particle free zones and associated dislocation
                      density in these. Due to missing particle strengthening in
                      these zones and consequently a drop in creep strength, the
                      particle free zones are suspected to be a reason of
                      premature material failure.},
      cin          = {IEK-2},
      cid          = {I:(DE-Juel1)IEK-2-20101013},
      pnm          = {899 - ohne Topic (POF3-899)},
      pid          = {G:(DE-HGF)POF3-899},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/828724},
}