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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.