Showing papers on "Directional solidification published in 2009"
TL;DR: In this paper, the microstructural evolution of an Al-10 wt.% Cu alloy was investigated during solidification at constant cooling rate by in situ synchrotron X-ray microtomography with a resolution of 2.8 μm.
171 citations
TL;DR: In this article, a processing route for freeze-casting of particle suspensions is presented, where the microstructure development during the solidification process can be controlled precisely, and a procedure is shown to control the freezing process using the double-side cooling method.
Abstract: A processing route for freeze-casting of particle suspensions is presented, where the microstructure development during the solidification process can be controlled precisely. For this purpose, the single-side cooling and double-side cooling methods are compared. A procedure will be shown to control the freezing process using the double-side cooling method. Our approach was to determine the freezing conditions in order to forecast the freezing velocity and to carry out an advanced directional solidification setup for the experimental realization. Using this setup and the theoretical knowledge, the microstructure development can be controlled during the whole freezing process over a length of several centimeters.
149 citations
TL;DR: In this article, the behavior of colloidal suspensions of alumina partic les during directional solidification by freezing was investigated by in situ high-resolution X-ray radiography and tomography, which provided both qualitative and quantitative information about the propagation kinetic of the solid/liquid interface, the particle redistribution between the crystals and a particle-enriched phase, and the three-dimensional organization of the ice crystals.
Abstract: This paper investigates by in situ high-resolution X-ray radiography and tomography the behavior of colloidal suspensions of alumina partic les during directional solidification by freezing. The combination of these techniques provided both qualitative and quantitative information about the propagation kinetic of the solid/liquid interface, the particle redistribution between the crystals and a particle-enriched phase, and the three-dimensional organization of the ice crystals. In this first part of two companion papers, the precursor phenomena leading to directional crystallization during the first instants of solidification are studied. Mullins–Sekerka instabilities are not necessary to explain the dynamic evolution of the interface pattern. Particle redistribution during these first instants is dependent on the type of crystals growing into the suspension. The insights gained into the mechanisms of solidification of colloidal suspensions may be valuable for the materials processing routes derived for this type of directional solidification (freeze-casting), and of general interest for those interested in the interactions between solidification fronts and inert particles.
135 citations
TL;DR: By incorporating functional materials inside the polymer network, functional toroidal particles can be tailor-made for specific applications such as magnetic actuation.
Abstract: Microdoughnuts: Polymer toroidal particles such as the one shown in the left picture have been prepared by a capillary microfluidic technique. Droplets of polymer solution undergo non-uniform solidification to form the anisotropic polymer particles. By incorporating functional materials inside the polymer network, functional toroidal particles (center and right images) can be tailor-made for specific applications such as magnetic actuation.
83 citations
TL;DR: In this article, a combined theoretical/experimental approach was used to quantitatively determine the solidification parameters: tip growth rate and cooling rate of three hypoeutectic Al-Fe alloys, which were directionally solidified under unsteady state heat flow conditions.
81 citations
TL;DR: In this paper, the authors conducted directional solidification experiments on Cu-Sn peritectic alloys at very low velocity in a high-thermal-gradient Bridgman furnace.
81 citations
TL;DR: In this article, the effect of TEMC on the macroscopic interface shape and the cellular morphology under axial magnetic convection has been investigated and it has been proved experimentally that the convection will reduce the cellular spacing and cause a cellular-dendritic transition.
80 citations
TL;DR: In this paper, the authors investigated the self-organization between the solidification pattern and the convection pattern in a directional solidification environment and showed that the interaction between spacing selection and convection leads to a new type of scaling that explains results from phase field simulations and solidification experiments under enhanced gravity.
75 citations
TL;DR: In this paper, a phase-field model coupled to CALPHAD thermodynamic and kinetic databases is presented for the prediction of microstructure evolution during directional solidification of nickel-based superalloys.
71 citations
TL;DR: In this article, the formation of a fine equiaxed structure is favored by both the addition of grain refining AlTi5B1-particles and electromagnetic stirring as well, whereas adding grain refiners into the melt appears to be more efficient for achieving a reduction of the mean grain size.
67 citations
TL;DR: In this article, a graphite crucible with cooling spots was used to generate radial thermal gradients of the silicon melt for nucleation during directional solidification, and the effect of cooling spots on the grown ingot was studied by minority charge carrier lifetime mapping and electron back scattered diffraction of the grown crystals.
TL;DR: Al-Cu-Ag alloy was prepared in a graphite cru- cible under a vacuum atmosphere as discussed by the authors, and the samples were direc- tionally solidified upwards under an argon atmosphere with different temperature gradients (G = 3.99-8.79 K/mm), at a constant growth rate (V = 8.30 µm/s), and with differ- ent growth rates.
Abstract: Al-Cu-Ag alloy was prepared in a graphite cru- cible under a vacuum atmosphere. The samples were direc- tionally solidified upwards under an argon atmosphere with different temperature gradients (G = 3.99-8.79 K/mm), at a constant growth rate (V = 8.30 µm/s), and with differ- ent growth rates (V = 1.83-498.25 µm/s), at a constant gradient (G = 8.79 K/mm) by using the Bridgman type directional solidification apparatus. The microstructure of Al-12.80-at.%-Cu-18.10-at.%-Ag alloy seems to be two fi- brous and one lamellar structure. The interlamellar spacings (λ) were measured from trans- verse sections of the samples. The dependence of interlamel- lar spacings (λ) on the temperature gradient (G) and the growth rate (V ) were determined by using linear regression analysis. According to these results it has been found that the value of λ decreases with the increase of values of G and V. The values of λ 2 V were also determined by using the measured values of λ and V. The experimental results were compared with two-phase growth from binary and ternary eutectic liquid.
TL;DR: In this paper, the authors present the numerical simulation of heat transfer and solidification process in an industrial silicon directional solidification system and the energy efficiency in the production system is analyzed.
TL;DR: In this article, the authors investigated the local solidification conditions and mechanisms associated with the flake-to-fiber growth mode transition in Al-Si eutectic alloys using Bridgman type gradient-zone directional solidification.
Abstract: The local solidification conditions and mechanisms associated with the flake-to-fiber growth mode transition in Al–Si eutectic alloys are investigated here using Bridgman-type gradient-zone directional solidification. Resulting microstructures are examined through quantitative image analysis of two-dimensional sections and observation of deep-etched sections, showing three-dimensional microstructural features. Several microstructural parameters were investigated in an attempt to quantify this transition, and it was found that the particle aspect ratio is effective in objectively identifying the onset and completion velocity of the flake-to-fiber transition, whereas traditional spacing parameters are not effective indicators of the transition. For a thermal gradient of 7–14 K/mm, the transition was found to occur in two stages, appearing over velocity regimes from 0.10 to 0.50 mm/s and from 0.50 to 0.95 mm/s. The initial stage is dominated by in-plane plate breakup and rod formation within the plane of the plate, whereas the second stage is characterized by the onset of out-of-plane silicon rod growth, leading to the formation of an irregular fibrous structure. The boundary between the two stages is marked by widespread fibrous growth and the disappearance of the remnant flake structure, indicating a transition in the structural feature that governs the relevant diffusion length, from inter-flake spacing to inter-rod spacing.
TL;DR: In this paper, a deterministic mathematical model for steady-state unidirectional solidification is proposed to predict the columnar-to-equiaxed transition, which is an extension to the classic model proposed by Hunt.
TL;DR: In this article, upward directional unsteady-state solidification experiments were performed with both a hypomonotectic Al-2.0 Wt% Bi alloy and a 3.2 Wt Wt Bi alloy.
TL;DR: In this article, the authors present results from directional solidification experiments with Al-8 wt.% Bi alloys and show that droplets with large radii were frequently pushed and small droplets were engulfed.
27 Mar 2009
TL;DR: In this paper, the authors evaluated the effect of leg lengths (1 mm, 500 μm, and 250 μm) on the stress level imposed by a given temperature difference that could cause their fracture and found that boundary conditions and the mechanical strength of the soldering alloys are significant factors influencing the stress distribution in the TE alloy elements.
Abstract: Our research group developed over the past years a method to produce n- and p-type bismuth telluride alloys by mechanical alloying and powder extrusion. The resulting extruded rods possess a particular crystalline texture, which is advantageous for module fabrication processes but may have an impact on the stress distribution in modules under operating conditions. The reported mechanical strength of the extruded polycrystalline thermoelectric (TE) materials is larger than those of materials produced by directional solidification, allowing the fabrication of thinner TE modules in order to increase power densities. The stress arising from the resulting higher thermal gradients in thinner legs can eventually become greater than the TE material strength, which would limit further module thickness reduction. We present results of numerical simulations of TE modules behavior undertaken to evaluate the effect of leg lengths (1 mm, 500 μm, and 250 μm) on the stress level imposed by a given temperature difference that could cause their fracture. Different boundary conditions were imposed on the outer ceramic surfaces delimiting the module (e.g., both free or one anchored on a flat rigid surface). The boundary conditions and the mechanical strength of the soldering alloys are significant factors influencing the stress distribution in the TE alloy elements. We have also examined the effect of the crystalline texture of the extruded TE materials on the distribution and levels of stress, and found it to be marginal.
TL;DR: In this paper, a mathematical model and its analytical solution describing directional solidification of a ternary (three-component) system cooled from below is presented, where the phase transition temperatures in two mushy layers represent arbitrary functions of the compositions.
Patent•
15 Jun 2009
TL;DR: In this article, a system and methods for producing monocrystalline materials such as silicon, the monocrystine materials being usable in semiconductor and photovoltaic applications, are provided.
Abstract: Systems and methods are provided for producing monocrystalline materials such as silicon, the monocrystalline materials being usable in semiconductor and photovoltaic applications. A crucible (50) is received in a furnace (10) for growing a monocrystalline ingot, the crucible (50) initially containing a single seed crystal (20) and feedstock material (90), where the seed crystal (20) is at least partially melted, and the feedstock material (90) is completely melted in the crucible (50), which is followed by a growth and solidification process. Growth of monocrystalline materials such as silicon ingots is achieved by directional solidification, in which heat extraction during growth phases is achieved using insulation (14) that is movable relative to a crucible (50) containing feedstock (90). A heat exchanger (200) also is provided to control heat extraction from the crucible (50) during the growth and solidification process to achieve monocrystalline growth.
TL;DR: In this paper, the microstructure of Sn-1.2-wt.% Cu alloy was determined by using the Jackson-Hunt eutectic theory and the rod spacings were measured from both transverse and longitudinal sections of the samples.
TL;DR: In this article, a 3D cellular automaton-finite element (CAFE) model was used to predict the axial texture evolution of a single-crystal (SX) casting.
Abstract: The solidification grain structure and texture evolutions during single crystal (SX) casting of the advanced Ni-base superalloy CMSX-4 have been investigated. In order to understand the development of the solidification grain structure, SX casting experiments were carried out with a specially designed grain selector in a Bridgman directional solidification (DS) furnace. In addition to casting trials, the SX casting process was simulated by a 3-D cellular automaton-finite element (CAFE) model. The predicted solidification grain structure and the texture evolutions were validated by comparison with the microstructural observation and the electron back scattered diffraction (EBSD) results. It was shown that the overall grain structure, crystallographic texture evolution, and the location where the final selection of the single crystal occurs can be predicted well by the present CAFE model. The axial texture evolution of the single crystal was found to be significantly influenced by the grain density at the chill surface. The CAFE predictions also revealed that the geometry of the grain selector plays a significant role in the final selection of the single crystal.
TL;DR: In this article, a directional unsteady-state solidification experiment was carried out with a monotectic Al-3.2%Bi alloy and the thermal parameters such as growth rates and thermal gradients rates were experimentally determined by cooling curves recorded along the casting length.
Book•
01 Jan 2009
TL;DR: In this article, Czochralski crystalline growth for photovoltaic applications is discussed, as well as the mechanism of Dendrite crystal growth and the development of new Crystalline Si ribbon materials.
Abstract: Feedstock.- Czochralski Silicon Crystal Growth for Photovoltaic Applications.- Floating Zone Crystal Growth.- Crystallization of Silicon by a Directional Solidification Method.- Mechanism of Dendrite Crystal Growth.- Fundamental Understanding of Subgrain Boundaries.- New Crystalline Si Ribbon Materials for Photovoltaics.- Crystal Growth of Spherical Si.- Liquid Phase Epitaxy.- Vapor Phase Epitaxy.- Thin-Film Poly-Si Formed by Flash Lamp Annealing.- Polycrystalline Silicon Thin-Films Formed by the Aluminum-Induced Layer Exchange (ALILE) Process.- Thermochemical and Kinetic Databases for the Solar Cell Silicon Materials.
TL;DR: In this article, the relationship between the solidification processing parameters and microindentation hardness and cellular spacing was investigated by linear regression analysis, and the results obtained in this work have been compared with the previous similar experimental results obtained for binary alloys.
TL;DR: In this article, the formation and evolution of the CET are influenced by the processing parameters and the natural convection in refined Al-3.5 wt.% Ni alloys and Al-7.0 wt% Si alloys.
TL;DR: In this article, a DS of magnesium alloys AZ31 and AM50 was carried out to investigate microstructures and microsegregation under controlled solidification conditions, which revealed the opposite segregation behavior of manganese compared to both aluminum and zinc and provided an impartial basis for the advanced weighted-interval ranking sort sorting scheme of electron probe microanalysis (EPMA) data.
Abstract: Directional solidification (DS) of magnesium alloys AZ31 and AM50 was carried out to investigate microstructures and microsegregation under controlled solidification conditions. The methodology used is based on a customized DS technique elaborated on in Part I of this work. Dendritic microstructures observed in longitudinal sections of the quenched mushy zone, X-ray maps of fully directionally solidified cross sections, and quantitative solute profiles reveal the impact of cooling rate and alloy type. The solute-solvent correlation discloses the opposite segregation behavior of manganese compared to both aluminum and zinc and provides an impartial basis for the advanced weighted-interval ranking sort (WIRS) sorting scheme of electron probe microanalysis (EPMA) data. Precipitates Al8Mn5 and γ-Mg17Al12, predicted by thermodynamic calculations, are identified in the microstructure. The effect of back-diffusion during solidification, most pronounced for the component zinc, was clearly observed for both alloys in comparison with dedicated Scheil-total calculations.
TL;DR: In this article, a coupled cellular automaton (CA)-finite element (FE) model was developed to calculate dendrite growth during the solidification of hexagonal metals, and the model solved the conservation equations of mass, energy and solutes in order to calculate the temperature field, solute concentration and the dendritic growth morphology.
Abstract: A coupled cellular automaton (CA)–finite element (FE) model was developed to calculate dendrite growth during the solidification of hexagonal metals. The model solved the conservation equations of mass, energy and solutes in order to calculate the temperature field, solute concentration and the dendritic growth morphology. Validation of the model was performed by comparing the simulation results with experimental and computational data from previously published works, showing qualitatively good agreement in the dendritic morphology. Application to magnesium alloy AZ91 (approximated with the binary Mg–8.9 wt%Al) illustrates the difficulty of modeling dendrite growth in hexagonal systems, observed as deviations in the growth direction caused by mesh-induced anisotropy. The model was applied to the simulation of small specimens with equiaxed grain growth and columnar grain growth in directional solidification. The influences of cooling rate, mesh size and kinetic parameters such as surface tension and anisotropy coefficient on the grain morphology were also discussed.
TL;DR: In this paper, the microstructure evolution of near rapidly directionally solidified AISI 304 stainless steel was investigated and the formation mechanism of the coupled microstructures was analyzed based on the nucleation and constitutional undercooling criterion that the δ ferrite phase and austenite phase formed alternately before the steady state growth of each phase is reached due to larger under cooling.
Abstract: The microstructure evolution of near rapidly directionally solidified AISI 304 stainless steel was investigated in the present paper. It is found that the microstructure consists of δ ferrite dendrites with developed sidebranches and interdendritic austenite (γ) under the temperature gradient (G) of 20 K mm–1 and growth rate (V) of 1·0 mm s–1. Coupled growth microstructures of thin lamellar ferrite and austenite begin to form at a higher growth rate of 2·0 mm s–1. The formation mechanism of the coupled microstructures is analysed based on the nucleation and constitutional undercooling criterion that the δ ferrite phase and austenite phase form alternately before the steady state growth of each phase is reached due to larger undercooling. With further increase of the growth rate up to 3·0 mm s–1, the morphology of the δ ferrite transforms from lathy to cellular.
TL;DR: In this paper, the formation and evolution details of a blocky microstructure in AISI 304 stainless steel are studied by quenching method during directional solidification, and the formation of the blocky ferrite indicates that reverse solid-state transformation from austenite to ferrite takes place.