Quantitative phase field modeling of directional solidification of a binary alloy
Date Issued
2004
Date
2004
Author(s)
Shih, Chih-Jen
DOI
en-US
Abstract
Directional solidification is a process describing that an alloy solution undergoes phase transformation from melt to solid toward a specific direction. During this process, if the solidification speed is high enough to overcome the stabilizing effects of the thermal gradient and interfacial tension, the planar interface becomes unstable and wrinkled. As observed in the experiments, once the instability starts, shallow cellular structures grow initially followed by deep cells and then dendrites with the increasing speed. By controlling the interfacial morphology during freezing of an alloy, one can design its mechanical properties for many industrial applications. Also, in terms of theoretical aspects, the structural wavelength shows some nonlinear dependence with the control parameters. So far, the directional solidification of an alloy is a popular topic both in physics and material science in past few decades.
The purpose of the research presented in this thesis is to simulate alloy solidification by using the phase field model. The phase field model has emerged as a powerful tool to simulate microstructure evolution in solidification. However, limited by computation and inherent numerical nature, the phase field model has encountered many difficulties to perform quantitative simulation; one of them is the effect of solute trapping due to the diffusive interface. To mend this discrepancy, the anti-trapping current proposed by Karma is added to the standard WBM model to model solidifications of lower concentration. For ones with higher concentration, we introduce a simple interface model to restore the local equilibrium, and the solute trapping is totally eliminated. By using these modifications, the phase field modeling of alloy solidification is simulated quantitatively for the first time.
Based on the models presented here, we observe many interesting morphological evolutions, which have never been simulated. In addition, they also fit nicely to the classical theories. A long-time scale structural transition, which is extremely difficult to observe in real experiments, is also been performed. Consequently, a one-to-one comparison with experiments is quite promising in the future. Our work contributed in this thesis indeed opens a window for the research of alloy solidification.
Subjects
相場模擬
合金
凝固
alloy
solidification
Phase-field
Type
thesis
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