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Статті в журналах з теми "Local solidification conditions":
1
Sobolev, S. L. "Rapid solidification under local nonequilibrium conditions." Physical Review E 55, no. 6 (June 1, 1997): 6845–54. http://dx.doi.org/10.1103/physreve.55.6845.
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Sobolev, S. L. "Driving force for binary alloy solidification under far from local equilibrium conditions." Acta Materialia 93 (July 2015): 256–63. http://dx.doi.org/10.1016/j.actamat.2015.04.028.
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Domeij, Björn, and Attila Diószegi. "Solidification Chronology of the Metal Matrix and a Study of Conditions for Micropore Formation in Cast Irons Using EPMA and FTA." Materials Science Forum 925 (June 2018): 436–43. http://dx.doi.org/10.4028/www.scientific.net/msf.925.436.
Анотація:
Microsegregation is intimately coupled with solidification, the development of microstructure, and involved in the formation of various casting defects. This paper demonstrates how the local composition of the metal matrix of graphitic cast irons, measured using quantitative electron microprobe analysis, can be used to determine its solidification chronology. The method is applied in combination with Fourier thermal analysis to investigate the formation of micropores in cast irons with varying proportions of compacted and spheroidal graphite produced by remelting. The results indicate that micropores formed at mass fractions of solid between 0.77 and 0.91, which corresponded to a stage of solidification when the temperature decline of the castings was large and increasing. In 4 out of the 5 castings, pores appear to have formed soon after the rate of solidification and heat dissipation had reached their maximum and were decreasing. While the freezing point depression due to build-up of microsegregation and the transition from compacted to spheroidal type growth of the eutectic both influencing solidification kinetics and the temperature evolution of the casting, the results did not indicate a clear relation to the observed late deceleration of solidification.
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Sobolev, Sergey L., Mikhail G. Tokmachev, and Yuri R. Kolobov. "Rapid Multicomponent Alloy Solidification with Allowance for the Local Nonequilibrium and Cross-Diffusion Effects." Materials 16, no. 4 (February 15, 2023): 1622. http://dx.doi.org/10.3390/ma16041622.
Анотація:
Motivated by the fast development of various additive manufacturing technologies, we consider a mathematical model of re-solidification of multicomponent metal alloys, which takes place after ultrashort (femtosecond) pulse laser melting of a metal surface. The re-solidification occurs under highly nonequilibrium conditions when solutes diffusion in the bulk liquid cannot be described by the classical diffusion equation of parabolic type (Fick law) but is governed by diffusion equation of hyperbolic type. In addition, the model takes into account diffusive interaction between different solutes (nonzero off-diagonal terms of the diffusion matrix). Numerical simulations demonstrate that there are three main re-solidification regimes, namely, purely diffusion-controlled with solute partition at the interface, partly diffusion-controlled with weak partition, and purely diffusionless and partitionless. The type of the regime governs the final composition of the re-solidified material, and, hence, may serve as one of the main tools to design materials with desirable properties. This implies that the model is expected to be useful in evaluating the most effective re-solidification regime to guide the optimization of additive manufacturing processing parameters and alloys design.
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Plotkowski, A., K. Fezi, and M. J. M. Krane. "Estimation of transient heat transfer and fluid flow for alloy solidification in a rectangular cavity with an isothermal sidewall." Journal of Fluid Mechanics 779 (August 14, 2015): 53–86. http://dx.doi.org/10.1017/jfm.2015.424.
Анотація:
Transient scaling and integral analyses were performed to predict trends in alloy solidification in a rectangular cavity cooled by an isothermal sidewall. The natural convection fluid flow was approximated by a scaling analysis for a laminar boundary layer at the solidification front, and was coupled to scaling and integral analyses of the energy equation to predict the solidification behaviour of the system. These analyses predicted several relevant aspects of the solidification process, including the time required to extinguish the initial superheat and the maximum local solidification time as a function of the system parameters and material properties. These results were verified by comparison to numerical simulations for an Al–4.5 wt% Cu alloy for various initial and boundary conditions and cavity aspect ratios. The analysis was compared to previous attempts to analyse similar fluid flow and solidification processes, and the limitations of the assumptions used for this analysis were discussed.
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Gotterbarm, Martin R., Alexander M. Rausch, and Carolin Körner. "Fabrication of Single Crystals through a µ-Helix Grain Selection Process during Electron Beam Metal Additive Manufacturing." Metals 10, no. 3 (February 28, 2020): 313. http://dx.doi.org/10.3390/met10030313.
Анотація:
Selective Electron Beam Melting (SEBM) is a powder bed-based additive manufacturing process for metals. As the electron beam can be moved inertia-free by electromagnetic lenses, the solidification conditions can be deliberately adjusted within the process. This enables control over the local solidification conditions. SEBM typically leads to columnar grain structures. Based on numerical simulation, we demonstrated how technical single crystals develop in IN718 by forcing the temperature gradient along a µ-Helix. The slope of the µ-Helix, i.e., the deviation of the thermal gradient from the build direction, determined the effectiveness of grain selection right up to single crystals.
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Merchant, G. J., and S. H. Davis. "Kinetic Effects in Directional Solidification." Applied Mechanics Reviews 43, no. 5S (May 1, 1990): S76—S78. http://dx.doi.org/10.1115/1.3120855.
Анотація:
Mullins and Sekerka showed for fixed temperature gradient that the planar interface is linearly stable for all pulling speeds V above some critical value, the absolute stability limit. Near this limit, where solidification rates are rapid, the assumption of local equilibrium at the interface may be violated. We incorporate nonequilibrium effects into a linear stability analysis of the planar front by allowing the segregation coefficient and interface temperature to depend on V in a thermodynamically-consistent way. In addition to the steady cellular mode, we find a new branch of long-wavelength time-periodic states. Under certain conditions there exists a stability window separating the steady and oscillatory branches.
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Zimmermann, Gerhard, Viktor T. Vitusevych, and Laszlo Sturz. "Microstructure Formation in AlSi6Cu4 Alloy with Forced Melt Flow Induced by a Rotating Magnetic Field." Materials Science Forum 649 (May 2010): 249–54. http://dx.doi.org/10.4028/www.scientific.net/msf.649.249.
Анотація:
The objective of this paper is the experimental investigation of the microstructure in Al-6wt%Si-4wt%Cu alloy, directionally solidified without and with forced melt flow, induced by a rotating magnetic field. The flow leads to reduced primary dendrite spacing and to strong radial segregation of silicon and copper. As a consequence the local solidification conditions change, resulting in different types of Al2Cu phase formation. This outcome is explained by ThermoCalc calculations predicting the corresponding solidification behavior.
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Heckmann, C. J., W. Stets, and G. Wolf. "Plate Fracture of Nodular Cast Iron." Key Engineering Materials 457 (December 2010): 367–73. http://dx.doi.org/10.4028/www.scientific.net/kem.457.367.
Анотація:
Plate fracture is a defective fracture structure in nodular cast iron that can be found especially in the transition area of feeder, feeder neck and the cast part itself. It occurs rather spontaneously due to the fact that the exact reason for it is still unknown. The microstructure of the casting in the area of plate fracture comprises aligned graphite nodules in combination with a pronounced dendritic microstructure as characteristical features. A series of casting trials was performed in which plate like samples were produced. It could be shown by means of metallographic investigation of these samples in combination with the simulation of the solidification that specific local conditions during the solidification are the metallurgical reasons for the appearance of plate fracture. These specific conditions were the local temperature gradient and the velocity of the liquid/solid interface.
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Huo, Miao, Chuyue Chen, Hangyue Jian, Wenchao Yang, and Lin Liu. "The Stray Grains from Fragments in the Rejoined Platforms of Ni-Based Single-Crystal Superalloy." Metals 13, no. 8 (August 15, 2023): 1470. http://dx.doi.org/10.3390/met13081470.
Анотація:
Nickel-based single crystal superalloy is the most important material for blade preparation. However, some solidification defects inevitably occur during the process of preparing single-crystal blades through directional solidification. In this study, in order to study the origin of misorientation defects during solidification, a model with rejoined platforms was designed according to the geometry of single-crystal guide vanes. Electron Back-Scattering Diffraction (EBSD) was used to quantify the orientation deviation of the dendrites and identify the solidification defects in the rejoined platforms. The results showed that stray grain defects appeared in the platforms and their misorientation changed gradually, not abruptly. Combined with the simulation results, it was proposed that the stray grains formed as the result of the dendrites fragment, which was induced by solute enrichment in the mushy zone during solidification. Meanwhile, it was accompanied by a obvious dendritic deformation, which was caused by solidification shrinkage stress. This suggested that the fragmentation was induced by multiple factors, among which, the concave interface shape provided favorable conditions for solute enrichment, and the dynamic variability in the local thermal gradient and fluctuations of the solidification rate might play catalytic roles.
Дисертації з теми "Local solidification conditions":
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Banos, Julien. "Modélisation du procédé de refusion à l’arc sous vide : Échanges thermiques et défauts de solidification." Electronic Thesis or Diss., Université de Lorraine, 2023. http://www.theses.fr/2023LORR0117.
Анотація:
Le procédé de refusion à l'arc sous vide (Vacuum Arc Remelting ou VAR en anglais) est employé dans la production d'alliages métalliques à haute valeur ajoutée tels que les alliages de titane ou superalliages base nickel à destination de l'industrie aéronautique. La maîtrise des conditions de solidification constitue un enjeu industriel important pour obtenir des lingots d'une homogénéité chimique adéquate et dépourvus de défauts de solidification. Les travaux présentés dans ce document visent à améliorer la description des échanges thermiques dans un modèle du procédé VAR (SOLAR) et proposer une nouvelle approche pour la prédiction des défauts de solidification de type canaux ségrégés. Dans un premier temps, la description dans le modèle des échanges thermiques entre l'électrode, le lingot, la lingotière et le circuit de refroidissement a été améliorée. Les modifications ont fait l'objet de validation par comparaison des résultats numériques avec des mesures sur des refusions industrielles réelles. Un dispositif expérimental original de mesure de température à la paroi extérieure de la lingotière adapté aux refusions industrielles a été conçu et utilisé lors d'une campagne expérimentale sur site industriel lors de la refusion d'un alliage de titane. Les mesures obtenues ont été confrontées aux résultats numériques de SOLAR. Ces deux activités ont abouti à une première implémentation du phénomène de side-arcing dans le modèle. En parallèle, une approche numérique multi-échelle a été développée pour prédire la formation de canaux ségrégés en fonction des conditions locales de solidification. Une première étude sur un alliage Sn-Pb a été réalisée et un critère mathématique de prédiction a été calculé à partir des résultats. Cette première étude montre un impact du gradient thermique sur la formation de canaux ségrégés bien plus faible que celui généralement considéré dans la littératureThe Vacuum Arc Remelting (VAR) process is used in the production of high-added value metals such as titanium alloys or nickel-based superalloys for the aerospace industry. The control of solidification conditions is an important industrial issue in order to process ingots of adequate chemical homogeneity and free of solidification defects. The work presented in this manuscript aims at improving the description of heat exchanges in a VAR process model (SOLAR) and at proposing a new approach for the prediction of segregated channels type solidification defects. First, the description of the heat exchanges in the model between the electrode, the ingot, the mould and the cooling circuit has been improved. These modifications were validated by comparing the numerical results with measurements from real industrial melts. An original experimental apparatus for measuring the external mould temperature adapted to industrial melts was designed. This apparatus was used during an experimental campaign on an industrial site during the remelting of a titanium alloy. The measurements obtained were compared with the numerical results from SOLAR. These two activities led to a first implementation of the side-arcing phenomenon in the model. In parallel, a multi-scale numerical approach was developed to predict the formation of segregated channels as a function of local solidification conditions. A first study on a Sn-Pb alloy was carried out and a mathematical criterion was calculated from the results. This first study shows a much lower impact of the thermal gradient on the formation of segregated channels than that generally considered in the literature
Тези доповідей конференцій з теми "Local solidification conditions":
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Hope, Adam T., Hai-Lin Chen, João Pedro Oliveira, and Carolin Fink. "Solidification and Homogenization Modeling of High Entropy Alloys." In HT 2017. ASM International, 2017. http://dx.doi.org/10.31399/asm.cp.ht2017p0302.
Анотація:
Abstract High entropy alloys (HEA) are an exciting new class of alloys composed of several metallic elements with equiatomic or near-equiatomic composition to maximize configurational entropy, leading to desirable properties. However, during solidification, as in casting or welding processes, elements segregate, creating local regions of distinct composition. In conventional alloy systems, homogenization heat treatments are used to remove this segregation effect. This study examines the conditions of the heat treatment needed in HEA alloys. First, the solidification behavior of equiatomic alloy composition AlCoCrCuFeNi is modeled using the Scheil module within Thermo-Calc along with the TCHEA2 database. Energy dispersive spectroscopy (EDS) is performed across the dendrite arms of the as-melted HEA to compare with the Scheil calculations. The resulting dendritic and interdendritic compositions are used as inputs in Thermo- Calc to determine the stable phases as a function of temperature. Selected heat treatments are conducted on the as-melted HEA to compare with the calculation results.
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Vasileiou, A. N. "Investigating the suitability of using a single heat transfer coefficient in metal casting simulation: An inverse approach." In Material Forming. Materials Research Forum LLC, 2023. http://dx.doi.org/10.21741/9781644902479-128.
Анотація:
Abstract. In metal casting simulation the Heat Transfer Coefficient (HTC) is unknown as it depends on melt and mold materials, on the casting modulus at different regions of the casting and on local conditions at the mold-casting gap. In this paper, thermocouple measurements at three regions of a brass investment casting provided reference cooling curves. A genetic algorithm (GA) determined the optimum 3-step time-dependent HTC for the whole of the casting in a simulation program for which cooling curves are as close as possible to the reference curves. The resulting prediction of solidification times is satisfactory but prediction of qualitative characteristics such as start / end of solidification in different regions was not accurate enough.
3
Schulte-Fischedick, Jan, Rainer Tamme, and Ulf Herrmann. "CFD Analysis of the Cool Down Behaviour of Molten Salt Thermal Storage Systems." In ASME 2008 2nd International Conference on Energy Sustainability collocated with the Heat Transfer, Fluids Engineering, and 3rd Energy Nanotechnology Conferences. ASMEDC, 2008. http://dx.doi.org/10.1115/es2008-54101.
Анотація:
CFD analysis has been conducted to obtain information on heat losses, velocity and temperature distribution of large molten salt Thermal Energy Storage (TES) systems. A two-tank 880 MWh storage system was modeled according to the molten salt TES containment design proposed for the 50 MWel commercial parabolic trough solar thermal power plants in Spain. Heat losses were established using the Finite Element Method (FEM), and used to determine the boundary conditions for the subsequent two- and three-dimensional Computational Fluid Mechanics (CFD) calculations. The investigations reveal that a high heat loss flux occurs at the lower edges of the salt storage tanks (between side wall and bottom plate). Thus the maximum temperature difference can be found at this location, resulting in the onset of local solidification within 3.25 days in the case of the empty cool tank. As a consequence, the detailed design of the lower edge has a large impact on both the overall heat losses and the period until the onset of local solidification.
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Rawlings, A. L. K., A. J. Birnbaum, J. G. Michopoulos, J. C. Steuben, A. P. Iliopoulos, and H. Ryou. "Simulation Informed Effects of Solidification Rate on 316L Single Tracks Produced by Selective Laser Melting." In ASME 2020 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/detc2020-22451.
Анотація:
Abstract The formation of sub-grain cellular structures generated during the rapid solidification associated with selective laser melting (SLM) typically yields enhanced mechanical properties in terms of yield stress without considerable loss in ductility when compared with those of wrought material. The extent to which the sub-grain structure appears under standard metallographic preparation shows dependence on multiple systematic conditions. This study identifies the effects of solidification and cooling rate on the grain and sub-grain structure in stainless steel through varying the processing parameters (laser power, scan velocity and spot size) of single tracks on both as-received, small grain and annealed, giant grain substrates. The process parameters, in conjunction with the initial substrate microstructure, are key components in understanding the resulting microstructure. Process parameters, particularly scan velocity, dictate the solidification rate and primary regrowth directions while the initial microstructure and its thermomechanical history dictate the propensity for stored strain energy density. Modeling the thermal process allows for experimental analysis within the context of predicted location within processing space as it pertains to local interface velocity and temperature gradient. Furthermore, it highlights the fact that this specific material system behaves in a manner that is inconsistent with classical solidification theory.
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Yang, Zhuo, Brandon Lane, Yan Lu, Ho Yeung, Jaehyuk Kim, Yande Ndiaye, and Sundar Krishnamurty. "Using Coaxial Melt Pool Monitoring Images to Estimate Cooling Rate for Powder Bed Fusion Additive Manufacturing." In ASME 2022 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/detc2022-89934.
Анотація:
Abstract Cooling rate is a decisive index to characterize melt pool solidification and determine local microstructure formation in metal powder bed fusion processes. Traditional methods to estimate the cooling rate include in-situ temperature measurement and thermal simulation. However, these methods may not be accurate or efficient enough under complex conditions in real-time. This paper proposes a method to approximate the melt pool cooling rate using temperature profile acquired via thermally-calibrated melt pool camera, and based on continuous pixel tracking result. The proposed method can estimate the temperature and associated cooling rate for every pixel immediately, which is potentially applicable for real-time process monitoring. This paper focuses on investigating image data processing, method development, and cooling condition analysis. This work presents the preliminary result of the cooling rate estimation under different conditions such as position, layer number, and overhanging.
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Wang, G. X., Chengcai Yao, and B. T. F. Chung. "On Physical Mechanisms of Mushy Zone Formation in Solidification of Pure Semitransparent Materials." In ASME 1999 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/imece1999-1039.
Анотація:
Abstract Two different models, the isothermal mushy zone model and the non-equilibrium planar interface model, are employed to solve the solidification problem of a one-dimensional semitransparent slab subject to radiative and convective cooling at the surface. The mushy zone model is based on the assumption of local equilibrium and predicts the formation of a mushy zone as soon as the temperature of the slab surface reaches the equilibrium melting temperature. The non-equilibrium planar interface model, on the other hand, assumes a stable planar solid/liquid interface during solidification. It allows the existence of melt undercooling at the interface and in the bulk melt. The stability of the planar interface is then examined approximately using the linear stability criterion derived for an opaque material. It is found that a planar interface would be stable even if a large undercooling is generated in the bulk melt in front of the interface. If the rate of external heat transfer is small, however, the planar interface will break down and develop into thermal cells or dendrites. In addition, a transition from a mushy zone to a planar interface is also observed. Based on these results, the thermodynamics and kinetics of crystalline nucleation and growth are examined to illustrate the physical mechanisms of mushy zone formation during solidification of a semi transparent material. It is suggested that the isothermal mushy model and the planar interface model are valid only under corresponding processing conditions, and more research is needed to provide a complete description of the process.
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Wan, Y. P., X. Y. Jiang, H. Zhang, S. Sampath, V. Prasad, and J. R. Fincke. "Modeling of Oxidation of Plasma-Sprayed Molybdenum Coatings." In ITSC 2000, edited by Christopher C. Berndt. ASM International, 2000. http://dx.doi.org/10.31399/asm.cp.itsc2000p0135.
Анотація:
Abstract A model for oxidation of molybdenum particles during plasma spray deposition is developed. The diffusion of metal an-ions or oxygen cat-ions through a thin oxidized film, chemical reactions on the surface, and diffusion of oxidant in gas phase are considered as possible rate-controlling mechanisms with controlling parameters as the temperature of the particle surface, and local oxygen concentration and flow field surrounding the particle. The deposition of molten particle and its rapid solidification and deformation is treated using a Madejski-type model, in which the mechanical energy conservation equation is solved to determine the splat deformation and one-dimensional heat conduction equation with phase change is solved to predict the solidification and temperature evolution. Calculations are performed for a single molybdenum particle sprayed under the Sulzer Metco-9MB spraying conditions. Results show that the mechanism that controls the oxidation of this droplet is the diffusion of metal/oxygen ions through a very thin oxide film. A higher substrate temperature results in a larger rate of oxidation at the splat surface, and hence, a larger oxygen content in the coating layer. Compared to the oxidation of droplet during m-flight, the oxidation during deposition is not weak and can become dominant at high substrate temperatures.
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Kocherlakota, Pavan, and Jerome Savarimuthu. "Effect of Welding Conditions on TIG Welded AISI 304 Stainless Steels Using FEM and Experimental Methods." In ASME 2008 Pressure Vessels and Piping Conference. ASMEDC, 2008. http://dx.doi.org/10.1115/pvp2008-61047.
Анотація:
Classical approaches to the modeling of welding, whilst accurate, are not readily usable in the industry. The time and cost associated with running such models appear to be the main reasons contributing to the situation. The use of computer simulative techniques has the potential to significantly reduce the cost of welded fabrications by allowing for predictions to be made long before a single weld bead is put down on the workshop floor. In this paper, a computational procedure is presented to analyze temperature fields during TIG welding process using a non linear transient thermal analysis in ANSYS [1]. Various phenomena associated with welding like temperature dependent material properties, effects of latent heat of fusion are accounted for in the model. The heat loss through radiation and effect of shielding gas are neglected here. This work has considered only a 2D analysis considering axis symmetric model. The analysis was done on AISI 304 stainless steels. The effect of welding conditions on the weld microstructure is studied over a range of heat input values and welding speed and the columnar to equiaxed transition (CET) is investigated. The influence of the welding conditions is related to changes in temperature gradient G, and local solidification velocity R, at the solid-liquid interface along the weld pool edge. It was observed that increase in the welding speed increases the equiaxed fraction. The effect of alloy composition on CET was neglected during this study. The results of finite element analysis were compared with experimental results and were found in good agreement. Based on these studies, a simplified modelling procedure of reasonable accuracy was proposed.
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Kavicka, Frantisek, Karel Stransky, Bohumil Sekanina, Jana Dobrovska, and Josef Stetina. "Cooling of a Massive Casting of Ductile Cast-Iron and Its Numerical Optimization." In ASME 2009 Pressure Vessels and Piping Conference. ASMEDC, 2009. http://dx.doi.org/10.1115/pvp2009-77914.
Анотація:
The numerical models of the temperature field of solidifying castings often observe two main goals: directed solidification and optimization of the technology. These goals can be achieved only if the deciding factors which either characterize the process or accompany it are analysed and their influence controlled. An original application of ANSYS, based on the numerical finite-element method, is applied. The numerical model simulated the forming of the temperature field of a two-ton 500×500×1000 mm casting from ductile cast-iron during the application of various methods of its cooling using steel chills. This model managed to optimize more than one method of cooling but, in addition to that, provided results for the successive model of structural and chemical heterogeneity, and so it also contributes to influencing the pouring structure. The file containing the acquired results from both models, as well as from their organic unification, brings new and, simultaneously, remarkable findings of causal relationships between the structural and chemical heterogeneity and the local solidification time in any point of the casting. This has established a tool for the optimization of the structure with an even distribution of the spheroids of graphite in such a way so as to minimize the occurrence of degenerated shapes of graphite, which is one of the conditions for achieving good mechanical properties of castings of ductile cast-iron.
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Wang, C., D. Sun, H. Zhang, L. Zheng, and B. Yang. "Continuous Silicon Wafer Manufacturing by EFG Method." In ASME 2003 Heat Transfer Summer Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/ht2003-47007.
Анотація:
A comprehensive two-dimensional numerical model, which accounts for heat/mass transfer, solidification, and electromagnetic field, has been developed to simulate the silicon tube growth by the Edge-defined film-fed (EFG) method. A multi-block grid system has been employed to yield a high accuracy in the vicinity of die tip with relatively low CPU time, and the solution procedure is satisfied the flux conservation at the block interface. Selected results of magnetic and temperature fields have been presented for the silicon tube growth system of 30cm in diameter and 0.3mm in thickness. Two local models have also been developed to study the effect of the size of window opening and tube thickness on the maximum growth rate using the inner and outer heater temperature profiles as boundary conditions.