非稳态过程与凝固界面形态选择

以透明模型合金丁二腈－乙醇系为实验系统，直接观察其单相凝固过程中界面形态的非稳态演化过程，从三个方面：①平胞转变②胞枝转变③枝晶一次间距，系统地考察了凝固界面形态选择的时间相关性和历史相关性。结果表明：①导出了凝固初始过渡区溶质再分配的一个新公式；②提出了确定平界面稳定性临界条件的可测判据和实验方法；③从实验上和理论上解释了胞枝转变行为；④揭示了枝晶一次间距的历史相关性；⑤发现凝固形态选择的历史相

EFFECTS OF NON-STEADY STATE PROCESS ON THE INTERFACE PATTERN SELECTION DURING UNIDIRECTIONAL SOLIDIFICATION

In situ observation of non-steady state process of interface pattern formation during unidirectional solidification were performed by using a typical transparent model alloy system------succinonitrile Time-dependent development and history-dependent steady-state selection of two important critical points of interface pattern transition(planar to cellular and cellular to dendritic transition) and one important characteristic scale(primary dendritic spacing)during constrained crystal growth of a single phase alloy were systematically investigated. The main results are as follows f (1) a new equation of initial transient solute redistribution was deduced: (2) a new experimental method was developed to identify the critical condition for interface instability. (3) a new equation for cell-dendrite transition point. which was deduced from a qusi-dynamical analysis of the pattern developing process. agrees excellently with the experimental observation: (4) selection of average primary dendritic spacings is considerably history-dependent; (5) history-dependence of interface pattern selection is related to the degree that the system deviates from equilibrium.