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Phase-Field Modeling of Microstructural Pattern Formation during Ice Templating and Alloy Solidification.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Phase-Field Modeling of Microstructural Pattern Formation during Ice Templating and Alloy Solidification./
作者:	Ji, Kaihua.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2021,
面頁冊數:	246 p.
附註:	Source: Dissertations Abstracts International, Volume: 83-05, Section: B.
Contained By:	Dissertations Abstracts International83-05B.
標題:	Condensed matter physics. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28860919
ISBN:	9798496529419

Phase-Field Modeling of Microstructural Pattern Formation during Ice Templating and Alloy Solidification.
Ji, Kaihua.

Phase-Field Modeling of Microstructural Pattern Formation during Ice Templating and Alloy Solidification. - Ann Arbor : ProQuest Dissertations & Theses, 2021 - 246 p.

Source: Dissertations Abstracts International, Volume: 83-05, Section: B.

Thesis (Ph.D.)--Northeastern University, 2021.

This item must not be sold to any third party vendors.

The pattern formation of complex microstructures during solidification processes, such as cellular and dendritic structures, governs the mechanical properties of final solidified materials. Over the past several decades, many experimental, analytical, and computational studies have focused on the microstructure selection during directional solidification of metallic alloys and their transparent analogs, which share atomically rough solid-liquid interface and usually exhibit a weak interfacial anisotropy. Although a number of questions remain open, such as how alloy microstructures formed in directional solidification would evolve under various growth conditions, previous studies have led to significant progress in our understanding of the pattern formation in those non-faceted systems. In comparison, our understanding of pattern formation during directional solidification of faceted crystals is largely limited, where the solid-liquid interface is atomically smooth in the faceted growth directions and usually exhibits a strong interfacial anisotropy. A fundamental understanding of how microstructures would form and evolve in the faceted system is highly desired. It can contribute to the development of ice templating (also known as freeze casting), a novel manufacturing method that utilizes the highly anisotropic growth behaviors of ice crystals to template polymers, ceramics, and metals with hierarchical architectures.In this dissertation, we primarily use the phase-field (PF) method to investigate the microstructural pattern formation during the solidification processes in both faceted and non-faceted systems. This dissertation consists of three major projects: the first project is the PF study of the faceted ice-crystal growth during unidirectional freezing of binary aqueous mixtures in a temperature gradient, and the main goal of this project is to elucidate the fundamental mechanisms of hierarchical pattern formation in ice templating that are still not well understood; the second and the third projects are PF and analytical studies of microstructural pattern formation during directional solidification of binary alloys, where the former focuses on the cellular structure, and the latter focuses on the dendritic structure.In the first project, we model and explain the microstructural pattern formation during ice templating by developing a novel PF model that can accurately simulate the growth of a highly anisotropic ice-water interface. Using quantitative PF simulations, we report a broken parity symmetry of faceted crystal growth fronts, which provides a theoretical basis for the hierarchical pattern formation during ice templating. When the ⟨11¯20⟩ preferred growth direction of the ice crystal is aligned with the temperature gradient, spontaneous symmetry breaking leads to two partially faceted structures of ice lamellae that are mirror images of each other and drifting with kinetics-controlled velocities in two ⟨0001⟩ directions. When a misorientation is present, the parity-breaking bifurcation becomes asymmetric and leads to two branches of solutions that compete with each other, in which only one branch is dynamically selected. Then, by comparing three-dimensional (3D) PF simulations to experimental observations, we explain the formation mechanisms of characteristic structures of ice-templated materials, including the lamellar structure and pore morphology at top levels, and the substructures, such as ridges and jellyfish-like polymer caps, formed on only one side of the ice lamellae.In the second project, we investigate the microstructural evolution of cellular arrays during directional solidification of a dilute binary alloy using PF and analytical methods. Alloy microstructures formed by directional solidification are often polycrystalline, made up of several large grains of different crystallographic orientations with respect to the temperature gradient. While strongly misoriented grains are generally eliminated at the early stage of growth, grains with misorientations less than about 15° can persist to late stages and form sub-boundaries (SBs), which can influence microstructure selection by mechanisms that are still not well understood. In order to simulate the effects of SBs on microstructure evolution at experimentally relevant time and length scales, we develop a massively parallel implementation of quantitative PF simulations. Then, we compare PF results to the experiments carried out in the DEvice for the study of Critical LIquids and Crystallization (DECLIC) experimental set-up aboard the International Space Station (ISS) where a transparent succinonitrile (SCN)-camphor alloy contained within a 3D crucible is solidified under purely diffusive growth regime. The in situ observations exhibit both convergent and divergent SBs, where two grains drift laterally to converge on and diverge from each other, respectively. 3D PF simulations reproduce those observations and shed light on the effects of SBs on the dynamical microstructure evolution. We further develop a two-dimensional (2D) theoretical model to explain the primary spacing evolution near a divergent SB, which yields good agreement with PF simulations in a thin-sample geometry. In addition to the SB, we also investigate how other factors, including the radial temperature gradient and misorientation, can have separate or combined effects on the microstructure evolution.In the third project, we develop 2D and 3D isotropic finite-difference approximations for PF simulations of alloy solidification that typically form well-developed microstructures consisting of spatially extended dendritic grains of different growth orientations. While the commonly used finite-difference implementations can resolve the dendrite tip operating state of misoriented grains at relatively small growth velocities, we find that they yield poor convergence of both the tip operating state and growth direction of the dendrite in a higher velocity regime, where the spurious lattice anisotropy brought by the spatial discretization becomes significant. To circumvent this problem, we use known methods in both real and Fourier space to derive finite-difference approximations of leading differential terms in PF models that are isotropic at order h2 of the lattice spacing h. We find the finite-difference implementation with isotropic discretizations of leading differential terms can significantly reduce the spurious lattice anisotropy effects and improve the convergence of PF results. Then, we apply this isotropic finite-difference implementation to PF simulations of grain competition in the well-developed dendritic regime relevant for the casting of concentrated alloys. We show that a characteristic length scale, the measured distance between the most advanced tips of the well-orientated and misoriented grains in PF simulations, agrees well with an analytical prediction from the solvability theory.

ISBN: 9798496529419Subjects--Topical Terms:

3173567
Condensed matter physics.
Subjects--Index Terms:

Alloy solidification

Phase-Field Modeling of Microstructural Pattern Formation during Ice Templating and Alloy Solidification.
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100 1 $a Ji, Kaihua. $3 3685629
245 1 0 $a Phase-Field Modeling of Microstructural Pattern Formation during Ice Templating and Alloy Solidification.
260 1 $a Ann Arbor : $b ProQuest Dissertations & Theses, $c 2021
300 $a 246 p.
500 $a Source: Dissertations Abstracts International, Volume: 83-05, Section: B.
500 $a Advisor: Karma, Alain.
502 $a Thesis (Ph.D.)--Northeastern University, 2021.
506 $a This item must not be sold to any third party vendors.
520 $a The pattern formation of complex microstructures during solidification processes, such as cellular and dendritic structures, governs the mechanical properties of final solidified materials. Over the past several decades, many experimental, analytical, and computational studies have focused on the microstructure selection during directional solidification of metallic alloys and their transparent analogs, which share atomically rough solid-liquid interface and usually exhibit a weak interfacial anisotropy. Although a number of questions remain open, such as how alloy microstructures formed in directional solidification would evolve under various growth conditions, previous studies have led to significant progress in our understanding of the pattern formation in those non-faceted systems. In comparison, our understanding of pattern formation during directional solidification of faceted crystals is largely limited, where the solid-liquid interface is atomically smooth in the faceted growth directions and usually exhibits a strong interfacial anisotropy. A fundamental understanding of how microstructures would form and evolve in the faceted system is highly desired. It can contribute to the development of ice templating (also known as freeze casting), a novel manufacturing method that utilizes the highly anisotropic growth behaviors of ice crystals to template polymers, ceramics, and metals with hierarchical architectures.In this dissertation, we primarily use the phase-field (PF) method to investigate the microstructural pattern formation during the solidification processes in both faceted and non-faceted systems. This dissertation consists of three major projects: the first project is the PF study of the faceted ice-crystal growth during unidirectional freezing of binary aqueous mixtures in a temperature gradient, and the main goal of this project is to elucidate the fundamental mechanisms of hierarchical pattern formation in ice templating that are still not well understood; the second and the third projects are PF and analytical studies of microstructural pattern formation during directional solidification of binary alloys, where the former focuses on the cellular structure, and the latter focuses on the dendritic structure.In the first project, we model and explain the microstructural pattern formation during ice templating by developing a novel PF model that can accurately simulate the growth of a highly anisotropic ice-water interface. Using quantitative PF simulations, we report a broken parity symmetry of faceted crystal growth fronts, which provides a theoretical basis for the hierarchical pattern formation during ice templating. When the ⟨11¯20⟩ preferred growth direction of the ice crystal is aligned with the temperature gradient, spontaneous symmetry breaking leads to two partially faceted structures of ice lamellae that are mirror images of each other and drifting with kinetics-controlled velocities in two ⟨0001⟩ directions. When a misorientation is present, the parity-breaking bifurcation becomes asymmetric and leads to two branches of solutions that compete with each other, in which only one branch is dynamically selected. Then, by comparing three-dimensional (3D) PF simulations to experimental observations, we explain the formation mechanisms of characteristic structures of ice-templated materials, including the lamellar structure and pore morphology at top levels, and the substructures, such as ridges and jellyfish-like polymer caps, formed on only one side of the ice lamellae.In the second project, we investigate the microstructural evolution of cellular arrays during directional solidification of a dilute binary alloy using PF and analytical methods. Alloy microstructures formed by directional solidification are often polycrystalline, made up of several large grains of different crystallographic orientations with respect to the temperature gradient. While strongly misoriented grains are generally eliminated at the early stage of growth, grains with misorientations less than about 15° can persist to late stages and form sub-boundaries (SBs), which can influence microstructure selection by mechanisms that are still not well understood. In order to simulate the effects of SBs on microstructure evolution at experimentally relevant time and length scales, we develop a massively parallel implementation of quantitative PF simulations. Then, we compare PF results to the experiments carried out in the DEvice for the study of Critical LIquids and Crystallization (DECLIC) experimental set-up aboard the International Space Station (ISS) where a transparent succinonitrile (SCN)-camphor alloy contained within a 3D crucible is solidified under purely diffusive growth regime. The in situ observations exhibit both convergent and divergent SBs, where two grains drift laterally to converge on and diverge from each other, respectively. 3D PF simulations reproduce those observations and shed light on the effects of SBs on the dynamical microstructure evolution. We further develop a two-dimensional (2D) theoretical model to explain the primary spacing evolution near a divergent SB, which yields good agreement with PF simulations in a thin-sample geometry. In addition to the SB, we also investigate how other factors, including the radial temperature gradient and misorientation, can have separate or combined effects on the microstructure evolution.In the third project, we develop 2D and 3D isotropic finite-difference approximations for PF simulations of alloy solidification that typically form well-developed microstructures consisting of spatially extended dendritic grains of different growth orientations. While the commonly used finite-difference implementations can resolve the dendrite tip operating state of misoriented grains at relatively small growth velocities, we find that they yield poor convergence of both the tip operating state and growth direction of the dendrite in a higher velocity regime, where the spurious lattice anisotropy brought by the spatial discretization becomes significant. To circumvent this problem, we use known methods in both real and Fourier space to derive finite-difference approximations of leading differential terms in PF models that are isotropic at order h2 of the lattice spacing h. We find the finite-difference implementation with isotropic discretizations of leading differential terms can significantly reduce the spurious lattice anisotropy effects and improve the convergence of PF results. Then, we apply this isotropic finite-difference implementation to PF simulations of grain competition in the well-developed dendritic regime relevant for the casting of concentrated alloys. We show that a characteristic length scale, the measured distance between the most advanced tips of the well-orientated and misoriented grains in PF simulations, agrees well with an analytical prediction from the solvability theory.
590 $a School code: 0160.
650 4 $a Condensed matter physics. $3 3173567
650 4 $a Physics. $3 516296
653 $a Alloy solidification
653 $a Ice templating
653 $a Pattern formation
653 $a Phase-field modeling
690 $a 0611
690 $a 0605
710 2 $a Northeastern University. $b Physics. $3 1025764
773 0 $t Dissertations Abstracts International $g 83-05B.
790 $a 0160
791 $a Ph.D.
792 $a 2021
793 $a English
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28860919