Growth competition during columnar solidification of seaweed microstructures
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THE EUROPEAN PHYSICAL JOURNAL E
Regular Article
Growth competition during columnar solidification of seaweed microstructures Insights from 3-D phase-field simulations Kumar Ankit1,a and Martin E. Glicksman2 1
2
School for Engineering of Matter, Transport and Energy, Arizona State University, 551 E. Tyler Mall, Tempe, AZ 85287, USA Florida Institute of Technology, Allen S. Henry Chair and University Professor, 150 W. University Blvd., Melbourne, FL 32955, USA Received 2 June 2019 and Received in final form 3 January 2020 Published online: 25 February 2020 c EDP Sciences / Societ` a Italiana di Fisica / Springer-Verlag GmbH Germany, part of Springer Nature, 2020 Abstract. The mechanisms by which interfacial instabilities instigate the growth of solidification patterns is a topic of longstanding interest. In columnar solidification of metallic melts, where the solid-liquid interfacial energy is anisotropic, evolving dendritic patterns compete depending on their relative misorientation. By contrast, organic “plastic crystals”, such as alloys based on succinonitrile, where the anisotropy in their solid-liquid interfacial energy is extremely weak, solidify forming seaweed patterns that typically exhibit little, if any, growth competition. We explore in this study mechanisms by which columnar solidification microstructures of binary alloys with low crystalline anisotropy compete. We adopt toward this end a validated Navier-Stokes multiphase-field approach to characterize the influence of grain misorientation, seed morphology, and melt advection on the growth competition. Simulated seaweed patterns indicate profound influences of all three factors, although characteristic solidification morphologies are observed to evolve depending on the melt flow intensity.
1 Introduction Theoretical criteria for the linear instability of a planar interface were first derived by Mullins and Sekerka [1], who proposed that the stability of monocrystalline solid/liquid interfaces during solidification is governed by the interfacial wavelength of the perturbation and the extent of constitutional supercooling. However, when a polycrystal is in contact with its melt, the solidification front is replete with grain boundary grooves (GBGs) that can initiate instabilities due to redistribution of solute near the solid-liquid interface. Several experimental studies [2–7] on directional solidification of weakly anisotropic organic crystals, such as succinonitrile (SCN) and its derivative alloys reported morphological instability at GBGs, characterized by amplification of adjacent humps projecting into the melt. If the melt is supercooled, humps adjacent to GBGs amplify and often compete to outgrow each other. In the presence of anisotropy of the solid-liquid interfacial energy, amplifying humps evolve into dendrites and the ensuing growth Contribution to the Topical Issue “Branching Dynamics at the Mesoscopic Scale”, edited by Yongsheng Han, Hui Xing, Dongke Sun. a e-mail: [email protected]
competition is governed by the relative misorientation of grai
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