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Lecture

3D characterization of dendritic microstructures and the evolution of crystal mosaicity in Ni-base superalloys

Thursday (27.09.2018)
12:15 - 12:30 S1/01 - A04
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The present work investigates the microstructural evolution during solidification of single crystal Ni-base superalloys of CMSX-4 type. We use a Bridgman seed technique for solidification experiments, which allows to precisely control the parameters which govern solidification [1]. A special effort was made to characterize dendritic microstructures using a new tomographic method. The as-grown single crystal (diameter: 12mm, length: 120mm) was cut into 1 mm thick sections which were subsequently characterized by optical microscopy in combination with quantitative image analysis, scanning electron microscopy (SEM), and electron back scatter diffraction (EBSD). Using precisely aligned montages of large numbers of optical micrographs, we were able to trace more than 3000 individual dendrites, to determine their growth trajectories and to evaluate local dendrite spacings. Emphasis was placed on neighbourhood relationships between individual primary dendrites. Our results show that the growth directions of dendrites deviate more and more from the original growth direction as solidification proceeds. In rare cases, sudden changes in growth directions were documented. These types of orientation defects are related to dendrite bending which is based on a slight rotation of the crystal lattice due to local stress fields. Using tomographic microstructure snapshots, we document how dendrite branching events and the interaction between slightly misaligned individual dendrites affect the formation of microstructures in different stages of the crystal growth process. We discuss our findings in the light of the present state of knowledge on dendritic solidification and crystal mosaicity.

Speaker:
Felicitas Scholz
Ruhr-Universität Bochum
Additional Authors:
  • Daniel Kotzem
    Ruhr-Universität Bochum
  • Mustafa Cevik
    Ruhr-Universität Bochum
  • Pascal Thome
    Ruhr-Universität Bochum
  • Prof. Dr. Jürgen Schreuer
    Ruhr-Universität Bochum
  • Prof. Dr. Ingo Steinbach
    Ruhr-Universität Bochum
  • Dr. Jan Frenzel
    Ruhr-Universität Bochum
  • Prof. Dr. Gunther Eggeler
    Ruhr-Universität Bochum