| Summary: | 碩士 === 國立中央大學 === 機械工程研究所 === 91 ===
Abstract
Solidification process is generally applied to the industrial material manufacturing. In particular, the material is produced by directional solidification process with better mechanical properties. So it is usually adopted in the manufacture of turbine blades. However, in some situations, casting alloys may have the non-uniform defects, which are induced in the process of directional solidification. Casting alloy with defects cannot fulfill the demand of industry because these defects decrease casting alloy’s mechanical properties.
It is believed the appearance of non-uniform defects comes from the supercooling area adjacent to the solid/liquid interface. The liquid near the interface encounters the supercooling effects and thus makes the morphological instability of solid/liquid interface. Many scholars are engaged in correlative investigations. They observed the variation of the solidification flow field by changing some correlative physical parameter, and hope to find a method that the morphological instability can be successfully inhabited; hence, the casting alloys will have better quality.
The main goal of this thesis is to probe into the influences of temperature modulation on the morphological stability of solid/liquid interface. We hope that the morphological instability can be successfully inhabited by means of the temperature modulation. Using theoretical analysis and numerical simulation to find stable region of the system, my analysis approach is as follows:
First, we drive the basic solution. Based on the analytical solution, we are able to identify the characteristics of basic state with temperature modulation. Then, we apply linear stability analysis to investigate the stability of the basic state. We found that the morphological instability can occur with the synchronous and subharmonic modes. The stability regions for specific modulation frequencies and amplitude were also studied.
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