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MM: Fachverband Metall- und Materialphysik
MM 16: Microstructure and Phase Transformations I
MM 16.2: Talk
Monday, March 26, 2012, 16:00–16:15, H 1029
Crystallization behavior of an amorphous matrix with embedded heterogeneously distributed preexisting crystals: Geometric crystallization simulations and the Johnson-Mehl-Avrami analysis — •Martin Peterlechner1, Thomas Waitz2, and Gerhard Wilde1 — 1Institute of Materials Physics, Westfälische Wilhelms-University, Münster, Germany — 2Physics of Nanostructured Materials, Faculty of Physics, University of Vienna, Vienna, Austria
Nanocrystalline materials can be processed via crystallization of an intermediate amorphous phase. Controlling the grain size and thus the functional properties requires thorough knowledge of the kinetics of the crystallization processes. Probably the most widely applied kinetic model for crystallization reactions by nucleation and growth is the Johnson-Mehl-Avrami (JMA) model. The JMA model is analytical but based on rather strict assumptions such as a homogeneous distribution of nuclei with zero initial volume. To account for preformed heterogeneously distributed crystals that can strongly impact the crystallization behavior the present work focuses on simulations. A two-dimensional geometric model was used to systematically analyze the spatial distribution and initial volume fraction of preexisting crystals on the crystallization behavior. Using a constant nucleation and growth rate, it can be shown that with heterogeneously distributed preexisting crystals a bimodal structure after crystallization develops. The influence on the amount of heterogeneity and the number of preexisting crystals on the kinetic analysis using JMA is discussed.