Dresden 2020 – scientific programme
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MM: Fachverband Metall- und Materialphysik
MM 30: Poster Session II
MM 30.5: Poster
Tuesday, March 17, 2020, 18:15–20:00, P4
Fractal abnormal grain growth in nanocrystalline Pd(Au): a result of abnormal growth triggered by pinning centers? — •Raphael Zeller1, Tobias Okker1, Karina De La Torre1, Christian Braun2, Mingyan Wang1, Rainer Birringer2, and Carl E. Krill III1 — 1Institute of Functional Nanosystems, Ulm University, Germany — 2Experimental Physics, Saarland University, Germany
Although physical models have succeeded in explaining the migration of grain boundaries in polycrystals having micrometer-sized grains, our understanding of grain growth in nanocrystalline materials is still rudimentary. For example, in nanocrystalline Pd–10 at% Au produced by inert gas condensation, microstructural coarsening is found to be doubly abnormal, with a subpopulation of rapidly growing grains sending forth “tentacles” into the surrounding matrix, encircling nearby grains and then consuming them; moreover, the perimeters of the resulting grains resemble those of fractal objects. Computer simulations have ruled out two possible mechanisms for this fractal abnormal grain growth (AGG): coalescence via grain rotation and boundary migration according to highly anisotropic (reduced) mobilities. In Monte Carlo simulations reported by Holm et al., pinning particles were observed to trigger explosive AGG. Since our nanocrystalline Pd–10 at% Au samples contain a small volume fraction of pores that could act as pinning centers, we performed phase field simulations to determine the pinning force per pore and to search for a connection between boundary fractality and the size and spatial distribution of pinning centers.