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Lecture

WEB Equilibrium and kinetic shapes of grains in polycrystals

Thursday (24.09.2020)
15:40 - 15:55 F: Functional Materials, Surfaces, and Devices 2
Part of:


We present a suite of measurements and combined analyses of grain growth of large, oriented single crystals into polycrystals. The growth distance, its standard deviation and the microstructure evolution along the single crystal-matrix interface are used to characterize the migration behavior as a function of temperature, time, and interface orientation. The relative grain boundary mobility was determined between 1250 °C and 1600 °C for the four most important orientations {100}, {110}, {111} and {310}. Under fast growth conditions the morphology of the single crystals shows macroscopic stepping with parts of the interface rotating to low mobility orientations.

The conclusions are that (1) the kinetic crystal shape is extremely anisotropic and displays significant transitions as a function of temperature that do not mirror changes in equilibrium crystal shape, (2) the kinetic shapes observed in the microstructures are dominated by the growing side of the interface (single crystal) and not by the dissolving side (polycrystalline matrix), and (3) faster growing orientations break up into macroscopic facets composed of slower growing orientations. The implications for grain growth underscore the applicability of crystal growth models to grain growth in polycrystals. In particular, in strontium titanate, the anisotropy of the grain boundary mobility as represented in the kinetic crystal shape is expected to be reduced from five macroscopic parameters to two (interface normal) allowing for incorporation of growth rate anisotropy in simulations of microstructure evolution at the earliest stages of grain growth, i.e. at the highest driving forces.

Speaker:
Dr. Wolfgang Rheinheimer
Technische Universität Darmstadt
Additional Authors:
  • Prof. John Blendell
    Purdue University
  • Prof. Carol Handwerker
    Purdue University