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Title: Microstructure selection in thin-sample directional solidification of an Al-Cu alloy: In situ X-ray imaging and phase-field simulations

We study microstructure selection during during directional solidification of a thin metallic sample. We combine in situ X-ray radiography of a dilute Al-Cu alloy solidification experiments with three-dimensional phase-field simulations. Here we explore a range of temperature gradient G and growth velocity V and build a microstructure selection map for this alloy. We investigate the selection of the primary dendritic spacing Λ and tip radius ρ. While ρ shows a good agreement between experimental measurements and dendrite growth theory, with ρ~V $-$1/2, Λ is observed to increase with V (∂Λ/∂V > 0), in apparent disagreement with classical scaling laws for primary dendritic spacing, which predict that ∂Λ/∂V<0. We show through simulations that this trend inversion for Λ(V) is due to liquid convection in our experiments, despite the thin sample configuration. We use a classical diffusion boundary-layer approximation to semi-quantitatively incorporate the effect of liquid convection into phase-field simulations. This approximation is implemented by assuming complete solute mixing outside a purely diffusive zone of constant thickness that surrounds the solid-liquid interface. This simple method enables us to quantitatively match experimental measurements of the planar morphological instability threshold and primary spacings over an order of magnitude in V. Lastly, we explain themore » observed inversion of ∂Λ/∂V by a combination of slow transient dynamics of microstructural homogenization and the influence of the sample thickness.« less
Authors:
; ORCiD logo ; ; ; ; ; ;
Publication Date:
Report Number(s):
LA-UR-16-22554
Journal ID: ISSN 1359-6454; TRN: US1700525
Grant/Contract Number:
AC52-06NA25396; FG02-07ER46400; AC02-06CH11357
Type:
Accepted Manuscript
Journal Name:
Acta Materialia
Additional Journal Information:
Journal Volume: 129; Journal Issue: C; Journal ID: ISSN 1359-6454
Publisher:
Elsevier
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE Office of Science (SC). Basic Energy Sciences (BES) (SC-22); USDOE
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; Directional solidification, Microstructure selection, X-ray radiography, Phase-field modeling
OSTI Identifier:
1345148
Alternate Identifier(s):
OSTI ID: 1397797

Clarke, A. J., Tourret, D., Song, Y., Imhoff, S. D., Gibbs, P. J., Gibbs, J. W., Fezzaa, K., and Karma, A.. Microstructure selection in thin-sample directional solidification of an Al-Cu alloy: In situ X-ray imaging and phase-field simulations. United States: N. p., Web. doi:10.1016/j.actamat.2017.02.047.
Clarke, A. J., Tourret, D., Song, Y., Imhoff, S. D., Gibbs, P. J., Gibbs, J. W., Fezzaa, K., & Karma, A.. Microstructure selection in thin-sample directional solidification of an Al-Cu alloy: In situ X-ray imaging and phase-field simulations. United States. doi:10.1016/j.actamat.2017.02.047.
Clarke, A. J., Tourret, D., Song, Y., Imhoff, S. D., Gibbs, P. J., Gibbs, J. W., Fezzaa, K., and Karma, A.. 2017. "Microstructure selection in thin-sample directional solidification of an Al-Cu alloy: In situ X-ray imaging and phase-field simulations". United States. doi:10.1016/j.actamat.2017.02.047. https://www.osti.gov/servlets/purl/1345148.
@article{osti_1345148,
title = {Microstructure selection in thin-sample directional solidification of an Al-Cu alloy: In situ X-ray imaging and phase-field simulations},
author = {Clarke, A. J. and Tourret, D. and Song, Y. and Imhoff, S. D. and Gibbs, P. J. and Gibbs, J. W. and Fezzaa, K. and Karma, A.},
abstractNote = {We study microstructure selection during during directional solidification of a thin metallic sample. We combine in situ X-ray radiography of a dilute Al-Cu alloy solidification experiments with three-dimensional phase-field simulations. Here we explore a range of temperature gradient G and growth velocity V and build a microstructure selection map for this alloy. We investigate the selection of the primary dendritic spacing Λ and tip radius ρ. While ρ shows a good agreement between experimental measurements and dendrite growth theory, with ρ~V$-$1/2, Λ is observed to increase with V (∂Λ/∂V > 0), in apparent disagreement with classical scaling laws for primary dendritic spacing, which predict that ∂Λ/∂V<0. We show through simulations that this trend inversion for Λ(V) is due to liquid convection in our experiments, despite the thin sample configuration. We use a classical diffusion boundary-layer approximation to semi-quantitatively incorporate the effect of liquid convection into phase-field simulations. This approximation is implemented by assuming complete solute mixing outside a purely diffusive zone of constant thickness that surrounds the solid-liquid interface. This simple method enables us to quantitatively match experimental measurements of the planar morphological instability threshold and primary spacings over an order of magnitude in V. Lastly, we explain the observed inversion of ∂Λ/∂V by a combination of slow transient dynamics of microstructural homogenization and the influence of the sample thickness.},
doi = {10.1016/j.actamat.2017.02.047},
journal = {Acta Materialia},
number = C,
volume = 129,
place = {United States},
year = {2017},
month = {5}
}