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Tresa M Pollock - One of the best experts on this subject based on the ideXlab platform.
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stability of dendrite growth during directional Solidification in the presence of a non axial thermal field
Acta Materialia, 2014Co-Authors: J D Miller, Tresa M PollockAbstract:Abstract The liquid–metal-cooling (LMC) directional-Solidification process offers refinement of dendritic structure due to the increased cooling rate from enhanced heat extraction. However, under some conditions in the LMC process substantial lateral heat extraction occurs that leads to a change in dendrite morphology, resulting in grain nucleation or lateral growth – the formation of long secondary dendrite arms overgrowing favorably aligned primary dendrites. The conditions under which lateral growth occurs during Solidification of alloys CMSX-486 and Rene-N4 have been studied experimentally and via Solidification Modeling. Solidification experiments have been conducted in a LMC furnace that utilizes liquid tin as the cooling medium and a floating ceramic baffle. A mold geometry was designed to evaluate a range of thermal conditions during Solidification and assess the tendency for lateral growth. Correlations between dendritic structure, Solidification-front curvature, Solidification rate and thermal gradients have been analyzed. A criterion for predicting the onset of lateral growth based on the inclination of the Solidification front at the casting surface is demonstrated.
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the effect of processing conditions on heat transfer during directional Solidification via the bridgman and liquid metal cooling processes
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2014Co-Authors: J D Miller, Tresa M PollockAbstract:Finite-element-based Solidification Modeling was used to investigate the thermal characteristics of the Bridgman and liquid metal cooling (LMC) directional Solidification (DS) processes. Physically representative boundary conditions were implemented within a finite-element model to test its applicability to a broad range of processing conditions. The dominant heat-transfer step for each case was identified. Relationships between the thermal gradient and the solid–liquid interface position relative to the transition region of the furnace were developed. The Solidification rate, the local velocity of the solid–liquid interface, and the cooling rate as a function of withdrawal rate were analyzed. The curvature of the solid–liquid interface varies with the processing conditions and influences the local thermal condition and, therefore, the morphological development of dendritic structure during Solidification. An extensive sensitivity analysis of process conditions was conducted for both the Bridgman and LMC techniques. The relative importance of process parameters on the resulting thermal conditions during Solidification was identified. A protocol for determination of preferred process conditions was defined. The maximum axial thermal gradient at the surface of the casting occurs when the solid–liquid interface is just above the baffle for both the Bridgman and LMC DS processes, independent of casting geometry or mold-heater temperature.
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development and application of an optimization protocol for directional Solidification integrating fundamental theory experimentation and Modeling tools
Superalloys, 2012Co-Authors: J D Miller, Tresa M PollockAbstract:A protocol for identifying the preferred process conditions for directional Solidification has been developed using the axial thermal gradient at the surface of the casting during Solidification. Solidification Modeling has been utilized to predict local thermal conditions during Solidification for a broad range of geometrical configurations, alloy compositions and heat-extraction conditions. Three different mold configurations were evaluated for three alloy compositions using both conventional and high-gradient directional Solidification processes. The high-gradient directional Solidification process investigated was the Liquid Metal Cooling (LMC) process that utilizes a liquid-metal coolant in the cold zone of the directional-Solidification furnace. Process conditions associated with the development of dendritic structure and Solidification defects have been analyzed in detail for each configuration. Classical defect maps have been extended to consider the important effects of solid-liquid interface curvature. The utilization of the surface maximum axial thermal gradient as a means to identify preferred processing conditions is applicable to a range of Solidification conditions, and accounts for changes in casting geometry, alloy composition or degree of heat-extraction. Experiments have been conducted to validate model predictions and improve the understanding of the role of solid-liquid interface curvature on dendrite-growth morphology. The optimization technique has been demonstrated for an atypical casting configuration and applied to a complex geometry, in which timedependent process conditions were required to maintain desired single-crystal growth.
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process simulation for the directional Solidification of a tri crystal ring segment via the bridgman and liquid metal cooling processes
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2012Co-Authors: J D Miller, Tresa M PollockAbstract:The feasibility of a monocrystalline ring comprised of a multiply-seeded, SX ring separated by low-angle boundaries was investigated for two thicknesses and two processing techniques. In particular, Solidification experiments using 1.9- and 5.1-cm-thick tri-crystal castings were conducted in a furnace capable of either the Bridgman or liquid metal cooling (LMC) mode. LMC is a high-gradient directional Solidification process that provides refinement of dendritic structure by submerging the casting in a liquid-metal-coolant bath upon withdrawal from the mold heater. The degree of structure refinement was investigated in these castings with varying cross-sectional areas. Solidification Modeling was used to optimize process conditions and investigate the thermal characteristics of each process for both casting configurations. Predicted relationships between dendritic structure, cooling rate, and thermal gradients in the axial and transverse directions are presented. A model for the prediction of thermal behavior for Bridgman and LMC techniques using complex casting configurations with section-thickness variations, encompassing a broad range of thermal conditions, was validated. A viable processing route for a monocrystalline ring was identified using the LMC technique, which mitigates the detrimental effects of radiation view factors present in the Bridgman process. Solidification Modeling identified the process conditions required to produce a new casting configuration with minimal casting trials.
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development and application of a protocol for definition of process conditions for directional Solidification integrating fundamental theory experimentation and Modeling tools preprint
2012Co-Authors: J D Miller, Tresa M PollockAbstract:Abstract : Solidification Modeling has been utilized to predict local thermal conditions during Solidification for a broad range of geometrical configurations, alloy compositions and heat-extraction conditions. Three different mold configurations were evaluated for three alloy compositions using both conventional and high-gradient directional Solidification processes. The high-gradient directional Solidification process investigated was the Liquid Metal Cooling (LMC) process that utilizes a liquid-metal coolant in the cold zone of the directional-Solidification furnace. Predictions of Solidification conditions have been compared to classical defect formation criteria to determine Solidification-model applicability. The classical defect maps and dendrite-growth models have been extended to accommodate curvature of the solid-liquid interface, which has not been well understood to date. Experiments have been conducted to validate model predictions and improve the understanding of the role of solid-liquid interface curvature on dendrite-growth morphology.
J D Miller - One of the best experts on this subject based on the ideXlab platform.
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stability of dendrite growth during directional Solidification in the presence of a non axial thermal field
Acta Materialia, 2014Co-Authors: J D Miller, Tresa M PollockAbstract:Abstract The liquid–metal-cooling (LMC) directional-Solidification process offers refinement of dendritic structure due to the increased cooling rate from enhanced heat extraction. However, under some conditions in the LMC process substantial lateral heat extraction occurs that leads to a change in dendrite morphology, resulting in grain nucleation or lateral growth – the formation of long secondary dendrite arms overgrowing favorably aligned primary dendrites. The conditions under which lateral growth occurs during Solidification of alloys CMSX-486 and Rene-N4 have been studied experimentally and via Solidification Modeling. Solidification experiments have been conducted in a LMC furnace that utilizes liquid tin as the cooling medium and a floating ceramic baffle. A mold geometry was designed to evaluate a range of thermal conditions during Solidification and assess the tendency for lateral growth. Correlations between dendritic structure, Solidification-front curvature, Solidification rate and thermal gradients have been analyzed. A criterion for predicting the onset of lateral growth based on the inclination of the Solidification front at the casting surface is demonstrated.
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the effect of processing conditions on heat transfer during directional Solidification via the bridgman and liquid metal cooling processes
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2014Co-Authors: J D Miller, Tresa M PollockAbstract:Finite-element-based Solidification Modeling was used to investigate the thermal characteristics of the Bridgman and liquid metal cooling (LMC) directional Solidification (DS) processes. Physically representative boundary conditions were implemented within a finite-element model to test its applicability to a broad range of processing conditions. The dominant heat-transfer step for each case was identified. Relationships between the thermal gradient and the solid–liquid interface position relative to the transition region of the furnace were developed. The Solidification rate, the local velocity of the solid–liquid interface, and the cooling rate as a function of withdrawal rate were analyzed. The curvature of the solid–liquid interface varies with the processing conditions and influences the local thermal condition and, therefore, the morphological development of dendritic structure during Solidification. An extensive sensitivity analysis of process conditions was conducted for both the Bridgman and LMC techniques. The relative importance of process parameters on the resulting thermal conditions during Solidification was identified. A protocol for determination of preferred process conditions was defined. The maximum axial thermal gradient at the surface of the casting occurs when the solid–liquid interface is just above the baffle for both the Bridgman and LMC DS processes, independent of casting geometry or mold-heater temperature.
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development and application of an optimization protocol for directional Solidification integrating fundamental theory experimentation and Modeling tools
Superalloys, 2012Co-Authors: J D Miller, Tresa M PollockAbstract:A protocol for identifying the preferred process conditions for directional Solidification has been developed using the axial thermal gradient at the surface of the casting during Solidification. Solidification Modeling has been utilized to predict local thermal conditions during Solidification for a broad range of geometrical configurations, alloy compositions and heat-extraction conditions. Three different mold configurations were evaluated for three alloy compositions using both conventional and high-gradient directional Solidification processes. The high-gradient directional Solidification process investigated was the Liquid Metal Cooling (LMC) process that utilizes a liquid-metal coolant in the cold zone of the directional-Solidification furnace. Process conditions associated with the development of dendritic structure and Solidification defects have been analyzed in detail for each configuration. Classical defect maps have been extended to consider the important effects of solid-liquid interface curvature. The utilization of the surface maximum axial thermal gradient as a means to identify preferred processing conditions is applicable to a range of Solidification conditions, and accounts for changes in casting geometry, alloy composition or degree of heat-extraction. Experiments have been conducted to validate model predictions and improve the understanding of the role of solid-liquid interface curvature on dendrite-growth morphology. The optimization technique has been demonstrated for an atypical casting configuration and applied to a complex geometry, in which timedependent process conditions were required to maintain desired single-crystal growth.
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process simulation for the directional Solidification of a tri crystal ring segment via the bridgman and liquid metal cooling processes
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2012Co-Authors: J D Miller, Tresa M PollockAbstract:The feasibility of a monocrystalline ring comprised of a multiply-seeded, SX ring separated by low-angle boundaries was investigated for two thicknesses and two processing techniques. In particular, Solidification experiments using 1.9- and 5.1-cm-thick tri-crystal castings were conducted in a furnace capable of either the Bridgman or liquid metal cooling (LMC) mode. LMC is a high-gradient directional Solidification process that provides refinement of dendritic structure by submerging the casting in a liquid-metal-coolant bath upon withdrawal from the mold heater. The degree of structure refinement was investigated in these castings with varying cross-sectional areas. Solidification Modeling was used to optimize process conditions and investigate the thermal characteristics of each process for both casting configurations. Predicted relationships between dendritic structure, cooling rate, and thermal gradients in the axial and transverse directions are presented. A model for the prediction of thermal behavior for Bridgman and LMC techniques using complex casting configurations with section-thickness variations, encompassing a broad range of thermal conditions, was validated. A viable processing route for a monocrystalline ring was identified using the LMC technique, which mitigates the detrimental effects of radiation view factors present in the Bridgman process. Solidification Modeling identified the process conditions required to produce a new casting configuration with minimal casting trials.
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development and application of a protocol for definition of process conditions for directional Solidification integrating fundamental theory experimentation and Modeling tools preprint
2012Co-Authors: J D Miller, Tresa M PollockAbstract:Abstract : Solidification Modeling has been utilized to predict local thermal conditions during Solidification for a broad range of geometrical configurations, alloy compositions and heat-extraction conditions. Three different mold configurations were evaluated for three alloy compositions using both conventional and high-gradient directional Solidification processes. The high-gradient directional Solidification process investigated was the Liquid Metal Cooling (LMC) process that utilizes a liquid-metal coolant in the cold zone of the directional-Solidification furnace. Predictions of Solidification conditions have been compared to classical defect formation criteria to determine Solidification-model applicability. The classical defect maps and dendrite-growth models have been extended to accommodate curvature of the solid-liquid interface, which has not been well understood to date. Experiments have been conducted to validate model predictions and improve the understanding of the role of solid-liquid interface curvature on dendrite-growth morphology.
Markus Apel - One of the best experts on this subject based on the ideXlab platform.
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theory training deep neural networks for an alloy Solidification benchmark problem
Computational Materials Science, 2020Co-Authors: Torabi M Rad, A Viardin, Georg Schmitz, Markus ApelAbstract:Abstract Deep neural networks are machine learning tools that are transforming fields ranging from speech recognition to computational medicine. In this study, we extend their application to the field of alloy Solidification Modeling. To that end, and for the first time in the field, theory-trained deep neural networks (TTNs) for Solidification are introduced. These networks are trained using the framework founded by Raissi et al. [1] , [2] , [3] and a theory that consists of a mathematical macroscale Solidification model and the boundary and initial conditions of a well-known Solidification benchmark problem. One of the main advantages of TTNs is that they do not need any prior knowledge of the solution of the governing equations or any external data for training. Using the built-in capabilities in TensorFlow, networks with different widths and depths are trained, and their predictions are examined in detail to verify that they satisfy both the model equations and the initial/boundary conditions of the benchmark problem. Issues that are critical in theory-training are identified, and guidelines that can be used in the future for successful and efficient training of similar networks are proposed. Through this study, theory-trained deep neural networks are shown to be a viable tool to simulate alloy Solidification problems.
Michael L Santella - One of the best experts on this subject based on the ideXlab platform.
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advances in processing of ni3al based intermetallics and applications
Intermetallics, 2000Co-Authors: V K Sikka, Seetharama C Deevi, S Viswanathan, Robert W Swindeman, Michael L SantellaAbstract:Abstract The intermetallic-based alloys for structural applications have been an active field of research around the world for the last 20 years. Several major breakthroughs have occurred in this field during this time period. These breakthroughs include: (1) the dramatic effects of boron on ductility improvement for Ni3Al at ambient and high temperatures, (2) effect of chromium addition for intermediate temperature ductility improvement of Ni3Al, and (3) identification of an environmental effect from hydrogen generated by the reduction of moisture in air by aluminum in the aluminides. The knowledge of the compositional effects has led to the development of Ni3Al-based alloys, which allowed them to be taken from laboratory-size melts to commercial applications. This paper will describe the advances in melting practice, casting practices, Solidification Modeling as it applies to static and centrifugal castings and weld repairs, and welding of castings. This paper will also describe various applications of Ni3Al-based alloys and their current status of commercialization.
Tianyou Huang - One of the best experts on this subject based on the ideXlab platform.
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Solidification Modeling in continuous casting by finite point method
Journal of Materials Processing Technology, 2007Co-Authors: Lei Zhang, Yiming Rong, Houfa Shen, Tianyou HuangAbstract:Abstract In this paper, a meshless method, finite point method, is studied and applied to model metal Solidification processes in continuous casting. An additional term is added to stabilize the computation with Neumann boundary. The enthalpy method is used to calculate the latent heat and the corresponding iterative solution is given. An iteration scheme for nonlinear material calculation is also constructed. The model is verified by the classical Stefan problem and a 2D FEM Solidification example. And then it is applied to the simulation of the solid shell growth in the continuous casting of a large square bland in mold. The result is coincided with the measurement.