This title appears in the Scientific Report :
1999
Please use the identifier:
http://hdl.handle.net/2128/20227 in citations.
The motion of the solidification front of a binary alloy with quenched disorder
The motion of the solidification front of a binary alloy with quenched disorder
In this work, we studied the motion of the solidification front of a disordered binary alloy. Here we assume that the atoms are frozen not only in die solid stete but also in the liquid state. This assumption is justified if the system is quenched from its melt so fast that the atoms in both phases...
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Personal Name(s): | Feng, X. (Corresponding author) |
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Contributing Institute: |
Institut für Festkörperforschung; IFF |
Imprint: |
Jülich
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
1999
|
Physical Description: |
127 p. |
Dissertation Note: |
Aachen, Techn. Hochsch., Diss., 1999 |
Document Type: |
Book Dissertation / PhD Thesis |
Research Program: |
ohne FE |
Series Title: |
Berichte des Forschungszentrums Jülich
3613 |
Subject (ZB): | |
Link: |
OpenAccess OpenAccess |
Publikationsportal JuSER |
In this work, we studied the motion of the solidification front of a disordered binary alloy. Here we assume that the atoms are frozen not only in die solid stete but also in the liquid state. This assumption is justified if the system is quenched from its melt so fast that the atoms in both phases do not have time to jump as the solidification front passes. Both analytical results and results obtained from MC-simulations are presented. The quenched disorder in the system, which is cansed by concentration fluctuatons, leads to spatial and temporal correlations through the propagation of the fluctuations, leads to spatial and temporal correlations through the propagaton of the solidification front. By investigating a two-dimensional lattice model, we found the non-trivial effects of the quenched disorder on the behavior of the solidification front. In the one-phase region of an equilibrium phase diagram, the interface moves with a constant velovity. However, in the two-phase region it demonstrates a complicated behavior, which strongly depends on the system parameters. The average displacement h of the interface as a function of time t obeys a power law, h(t) $\sim$ t$^{v}$, with the exponent v < 1. For very large bond energy, the exponent $\nu$ decreases to the value of a one-dimensional system; for moderate bond energy, the epxonent increases to about 1, and for small bond energy, it reverts to the value of a one-dimensional system. Therefore, the propagation of the solidification front is blocked by the quenched disorder at very small as well as very large bond energies. The energy range where $\nu$ =1 increases with increasing system size. For a very large system with finite bond energy tbe interface moves with a constant velocity. This movement corresponds to the thermal creep motion of the front. A finite temperature smears out the sharp pinning-depinning transition at zero temperature. The dynamic behavior of the front has been studied by means of a scaling theory. lt has been found that under small driving force, at low temperature or relatively high bond energy, the velocity $\nu$ of the front as a function of bond energy $\epsilon$ and concentration c can be factorized: $\nu(\epsilon$ . c) $\sim$ E$^{-eff}$ e$^{-\Delta /T(Co-c)}$ . Here $\Delta$ characterizes the relative strength of the disorder in the system and Co represents the concentration that separates the solid from liquid state in the equilibrium phase diagram. In addition to the diffusionless solidification we also studied the effects of the material diffusion on the motion of the front through MC-simulation of a onedimensional system. Without diffusion the exponent $\nu$has a value between 0 and 1. Typically, the exponent of a diffusion process is 0.5. The MC-simulation shows that the exponent $\nu$ increases to 0.5 for the concentration range where without diffusion $\nu$ would be smaller than 0.5. Here the diffusion process dominates. For other concentrations the exponent remains unchanged and the interface dynamics dominates. |