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@PHDTHESIS{Niu:760678,
      author       = {Niu, Shuai},
      othercontributors = {Senk, Dieter Georg and Bührig-Polaczek, Andreas and Tacke,
                          Karl-Hermann},
      title        = {{E}ffect of mechanical vibration on ingot solidification},
      school       = {Rheinisch-Westfälische Technische Hochschule Aachen},
      type         = {Dissertation},
      address      = {Aachen},
      reportid     = {RWTH-2019-04332},
      pages        = {1 Online-Ressource (X, 201 Seiten) : Illustrationen},
      year         = {2019},
      note         = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
                      University; Dissertation, Rheinisch-Westfälische Technische
                      Hochschule Aachen, 2019},
      abstract     = {Grain refinement is a critical method to improve the
                      mechanical and anti-fatigue properties of castings.
                      Increasing the fraction of equiaxed grains can remarkably
                      improve the ingot quality regarding solidification
                      structure, particularly the center line segregation. The
                      effect of low-frequency mechanical vibration (MV) on the
                      solidification structure was investigated and evaluated by
                      experimental methods using water model as well as hot ingot
                      casting model and numerical modelling by using Finite
                      Difference and Cellular Automaton methods. Experimental
                      results of the water model are presented for the
                      solidification of a $30\%$ NH4Cl-H2O solution inside a
                      rectangular cavity cooled by a mixture of alcohol and dry
                      ice blocks from the two narrow side walls. The temperature
                      profile of the solution and various solidification phenomena
                      such as columnar and equiaxed growth, CET (Columnar to
                      Equiaxed Transition), sedimentation of the equiaxed grains
                      were time-dependently recorded and analyzed. Furthermore,
                      two series of ingot casting experimental hot models have
                      been performed for ingots with the weight of 10 kg and 100
                      kg. The effect of mechanical vibration on solidifying steel
                      melt was revealed from the aspects of thermal effect,
                      as-cast structure and the degree of segregation. The heat
                      transfer behavior was analyzed based on the time-dependently
                      recorded temperature history of the melt during
                      solidification. The as-cast structure was revealed by hot
                      etching and sulfur prints. The segregation profile of the
                      ingots was discussed and quantified by sulfur print and
                      Electron Probe Micro Analysis (EPMA) in macro and micro
                      scale. In summary, the results show that higher heat
                      transfer efficiency, higher proportion of equiaxed grains,
                      less degree of macro-segregation as well as homogeneous
                      micro-structures can be obtained when mechanical vibration
                      has been applied during solidification. Numerical simulation
                      of the solidification structure evolution has been performed
                      to generalize the experimental results and to predict the
                      structures based on mathematical abstraction model. The
                      model consists of two schemes: The Finite Difference Method
                      (FDM) for simulation of the macroscopic heat transport of
                      the unsteady 2D temperature field in solidifying steel and
                      the Cellular Automaton (CA) method for simulating the
                      evolution of as-cast structures assuming nucleus densities.
                      The simulation results were validated by the hot model
                      experiments regarding the grain morphology. The results of
                      numerical modelling show obvious correlation to the
                      experimental results and could be used for understanding the
                      solidification structure evolution under various
                      conditions.},
      cin          = {522310 / 520000 / 526110},
      ddc          = {620},
      cid          = {$I:(DE-82)522310_20140620$ / $I:(DE-82)520000_20140620$ /
                      $I:(DE-82)526110_20140620$},
      typ          = {PUB:(DE-HGF)11},
      doi          = {10.18154/RWTH-2019-04332},
      url          = {https://publications.rwth-aachen.de/record/760678},
}