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Session Chairs: R.G. Reddy, Department of Metallurgical and Materials Engineering, The University of Alabama, Tuscaloosa, AL 35487; D.J. Fray, Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB2 3QZ, United Kingdom
STABILITY ANALYSIS OF MICROSTRUCTURE EVOLUTION PROCESSES: W.M. Mullins, Wright Laboratory, WL/MLIM-TMCI, Bldg. 653, 2977 P St., WPAFB, OH 45433-7746; R.D. Irwin, E.A. Medina, Department of Electrical and Computer Engineering, Stocker Center, Ohio University, Athens, OH 45701
Various stability criteria are introduced and thermo-kinetic models for metallurgical processes are used as concrete examples for evaluation. Kinetic criteria for the process of dynamic recrystallization are proposed. These criteria are compared to the non-equilibrium thermodynamic approaches discussed in the literature. The application of macroscopic stability criteria to materials processing is then discussed.
STATISTICAL ANALYSIS OF INTERFACE DYNAMICS IN NON-SPHERICAL MORPHOLOGIES: S.P. Marsh, Code 6325, Naval Research Laboratory, Washington, D.C. 20375-5000; M.E. Glicksman, Rensselaer Polytechnic Institute, Troy, NY
Complex interfaces can be described as a distribution of interfacial patches, each having a differential area. The patches are fully characterized by a mean curvature, a dimensionless shape factor, and an extensive variable such as solid angle or area. Using this approach, a statistical theory of Ostwald ripening has been extended to describe the diffusion-limited coarsening of non-spherical convex interfaces. Coarsening rate constants are calculated as a function of both the precipitate volume fraction and the geometric shape factor. Application of these results to ripening of ellipsoidal precipitates and other morphologies will be discussed.
ULTRA FINE PRECIPITATES IN REACTOR PRESSURE VESSEL STEELS INVESTIGATED BY MONTE CARLO SIMULATIONS: STRUCTURE, COMPOSITION, AND MORPHOLOGY: C.L. Liu, G.R. Odette, B.D. Wirth, and G.E. Lucas, Dept. of Chemical Engineering, University of California Santa Barbara, Santa Barbara, CA 93106
Ultra fine scale precipitates are the leading cause to the irradiation embrittlement of reactor pressure vessel (RPV) steels and may limit the continued operation or extended life of a number of nuclear power plants around the world. Tremendous effort in studying these precipitates has been made using various experimental techniques such as small angle neutron scattering (SANS) and atom probe field ion microscope (APFIM). However, detailed identity and characteristic of the precipitates o atomic scale are not well known. We propose a self-consistent model, combining advanced thermodynamics, small angle neutron scattering measurements, and Lattice Monte Carlo simulations, to examine detailed identity and characteristic of the ultra fine precipitates on atomic scale in Fe-based multicomponent systems Fe-Cu-Ni-Mn and Fe-Cu-Ni-Mn-Si. A systematic parametric study using both the metallurgical and simulation variables is carried out. Interaction parameters in an extended regular solution treatment, composition, and temperature as the metallurgical variables, and starting configurations, sizes of simulation cells, and simulation duration as the simulation variables, are exercised. The results from the simulations are in good agreement with those from SANS and APFIM.
OBSERVATION AND CALCULATION OF MARANGONI CONVECTION INDUCED THERMALLY IN A MOLTEN SALT: T. Takasu, J.M. Toguri, Dept of Metallurgy and Materials Science, University of Toronto, 184 College Street, Toronto, Ontario, Canada, M5S 1A4; H. Itou, T. Nakamura, Dept of Materials Science & Engineering, Kyushu Institute of Technology, Secsui-cho 1-1, Tobata-ku, Kitakyushu, 804 Japan
Marangoni convection has a large effect on materials processing since it remarkably promotes heat and mass transport near the free interface. In order to clarify the behavior of marangoni convection in a molten salt, observation and calculation of the thermal convection in a column held between a pair of Pt disks (2mm in diameter) which were fixed to hot thermocouples, were carried out. Calculated flow patterns and absolute values of fluid velocity agreed well with the observed results. When the temperatures of both disks were set equal and the height of liquid bridge was 2.4mm, four vortexes were generated on the longitudinal plane and typical velocity was 15mm/s. From the calculated isothermal lines the behavior of promotion of heat transport is obvious; fluid heated at the disks was conveyed to the free surface and fluid cooled at the surface was conveyed to the inner region. Increase in the height of column and/or increase in the absolute value of applied temperature difference lead to increase in fluid velocity lineally in this calculation range.
10:10 am BREAK
MIXING PHENOMENA PERTINENT TO FERROALLOY REFINING USING WATER MODELS: G. Akdogan, R.H. Eric, School of Process and Materials Engineering, University of the Witwatersraind, Johannesburg, Private Bag 3, Wits 2050 South Africa
Mixing phenomena in a bottom blown air-stirred one-seventh water model of CLU (Creusot-Loire Uddeholm) reactor was studied using three different configurations of straight circular nozzles fitted axially at the bottom of the vessel. The mixing time has been experimentally determined utilizing acid injection and pH measurements at various gas flow rates, bath heights and nozzle orientations in the presence and in the absence of a second phase. High air flow rates were utilized usually above the range of ordinary flow meters. During experiments the air flow rates varied from 0.00599m3/sec to 0.01465m3/sec. An integral orifice plate assembly, which is coupled to two pressure transmitters, was constructed to calculate gas flow rates from pressure readings. Experimental results reveal that the mixing time decreases with increasing gas flow rate. A critical gas flow rate exists after which the mixing time tends to increase for all tuyere configurations studied. For a given gas flow rate the mixing time increases non-linearly with increasing bath height. Off-center configuration gives slightly lower mixing times as compared to center configuration. The presence of an upper oil layer increases the mixing time significantly for all configurations showing its resistance to the recirculatory velocity of fluid near the surface of the bath. Under the very high flow rates employed in this investigation, it is found that the contribution of buoyancy to the total stirring energy density is very small, but its contribution increases with increasing bath height.
DIMENSIONAL ANALYSIS FOR PREDICTING THE STRESSES IN FORGING: T. Robert N., Congreso 128-A204, Col. La Joya, Del. Tlalpan, Mexico, D.F., 14090; J. Navarrete M., J. Ramirez V., G. Salas B., M. Noguez A., Departamento de Ing. Metalurgica, Facultad de Quimica, Universidad Nal. Autonoma de Mexico, Cuidad Universitaria, 04510 Mexico, D.F.
The stresses required in an axial closed die forging are determined by the geometry of the blank and that of the die, the yield stress of the working material and the process variables like temperature, strain, strain rate, friction, etc. Five adimensional groups of the mentioned parameters are proposed. Like the Reynolds number, they permit the characterization and evaluation of almost any axial forging process. A wide data base is experimentally obtained, which validates the model. This dimensional analysis is an alternative to the traditional methods for calculating the stresses in metal forming.
MODELING OF LIQUIDUS TEMPERATURE AND ELECTRICAL CONDUCTIVITIES OF MANGANESE SMELTING SLAGS BY THE USE OF NEURAL NETS: M.A. Reuter, Faculty of Mining and Petroleum Engineering, Delft University of Technology, Delft, The Netherlands, R H. Eric, A.A. Hejja, School of Process and Materials Engineering, University of the Witwatersrand, Johannesburg, Private Bag 3, WITS 2050, South Africa
Liquidus temperature and electrical conductivity data measured on synthetic slags were modeled by the use of neural nets(NN). In this work the applied multilayer feedforward NNs were trained by a conjugate-gradient optimization for which a three layer formulation was used. Very good fits were obtained for both the liquidus temperature and the conductivity data. The synthetic slags were prepared from pure oxides to represent a wide range of compositions likely to be encountered in ferromanganese and silicomanganese smelting. The slag constituents were in the following range: MnO, 5-30%; CaO, 20-35%; MgO, 5-15%; SiO2, 27-58%; and Al2O3, 5%. Liquidus temperatures varied from 1300°C to 1380°C and increased with increasing basicity ratio. The electrical resistivity of slags decreased with the increase of basicity ratio from 0.55 to 1.1 but above 1.1 basicity ratio the resistivity tended to increase depending upon the MnO content.
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