Regensburg 2019 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 29: Microstructure and Phase Transformations
MM 29.8: Vortrag
Mittwoch, 3. April 2019, 17:00–17:15, H46
Fractal abnormal grain growth in nanocrystalline Pd90Au10: a simulation study comparing possible mechanisms — •Raphael A. Zeller1, Christian Braun2, Mingyan Wang1, Rainer Birringer2, and Carl E. Krill III1 — 1Institute of Functional Nanosystems, Ulm University, Germany — 2Experimental Physics, Saarland University, Germany
Although the phenomenon of grain growth is well understood in samples having micrometer-sized grains, our understanding of the corresponding process in nanocrystalline materials is rudimentary at best. At the nanoscale the dominant mode of coarsening appears to be abnormal in nature, with a few grains growing orders of magnitude larger than their neighbors. In samples of nanocrystalline Pd90Au10 produced by inert gas condensation, microstructural coarsening is doubly abnormal, with the rapidly growing grains observed to send forth ”tentacle“ into the matrix, quickly encircling nearby grains and then consuming them. The perimeters of the resulting grains resemble those of fractal objects. Recent experiments suggest two possible mechanisms for fractal abnormal grain growth: (1) coalescence via grain rotation or (2) migration according to highly anisotropic grain boundary (reduced) mobilities. By combining a phase field model for boundary migration with boundary-specific selection rules, we have developed a ”hybrid“ simulation algorithm for each of these scenarios. A comparison of computational results with experiment reveals that one of the proposed mechanisms does a better job than the other at capturing the main features of fractal abnormal grain growth.