二元层片共晶凝固过程的特征尺度选择

Characteristic scale selection of lamellar spacings in binary eutectic solidification

基于Jackson和Hunt二元规则共晶稳态生长理论,在共晶两相的界面溶质守恒条件中引入密度修正项,改进了共晶两相的界面溶质守恒条件.在此基础上,根据二元层片共晶常规凝固过程中层片组织稳态生长时Gibbs自由能的变化,运用极值形态选择原理确定二元层片共晶凝固过程中层片间距特征尺度选择准则.理论分析表明,对于给定二元共晶合金,在常规凝固条件下的层片间距选择通常为一有限区间.此外,理论分析还表明,二元层片共晶稳态生长时其特征尺度的选择可以呈现超稳定性,而且在给定的凝固条件下超稳定性只和给定合金系的物性参数有关.将该形态选择准则分别运用于物性参数精确已知的Al-Al2Cu,Sn-Pb和CBr4-C2Cl6合金系,表明计算结果与实验结果相符合.

The lamellar spacing, which is formed by solidified melt of eutectic or near-eutectic composition, plays a very important role in determining the properties of final products. In this study, the lamellar spacing of eutectic growth in steady-state is predicted by the method which is established based on the classical Jackson-Hunt theory, and completed by considering the free energy change during eutectic solidification at small undercooling. The density difference between the solid phases is also considered when calculating the diffusion field in the liquid. It is found that a band of lamellar spacings would be generally selected for a given alloy under fixed growth conditions. In addition, the lamellar spacing can be morphologically stable below the minimum undercooling value, and this overstabilization is only dependent on the intrinsic characteristic properties of a given system at a fixed growth velocity. The analysis results are found to be in reasonable agreement with experimental data of Al-Al2Cu, Sn-Pb and CBr4-C2Cl6 systems available from the literature.