Development of Composite-and-Functional Gradient Material by using Supercooling

凝固是由于液体分子的旋转运动受到限制，导致固体结构固定为规则和/或致密的原子组装体，并释放熔化潜热。从潜热提取方式的角度看，与冷却速度有关的凝固大致可分为三种类型：在低冷却速度下，潜热通过传热被带走，凝固过程在固液界面保持平衡温度的情况下准稳态进行;在高冷却速率下，对于“材料快速凝固加工”，由于形核引发晶体生长，容易出现过冷状态，导致大块凝固。过冷使快速原位凝固成为可能，可能导致新的亚稳结晶相和非晶相的形成。在中等冷却速度下，也出现过冷，且过冷分布在冷却表面到内部某个平衡位置的较近区域。本文着重讨论了外部传热冷却条件下过冷混合物凝固过程的基本原理：凝固过程、凝固过程中微观结构和微观偏析的出现以及传热与凝固的宏微观耦合。

Solidification is due to the restriction of rotational motion of liquid molecules and results in the fixation of solid structure as a regular and/or dense assembly of atoms with release of latent heat of fusion. From the viewpoint of the way that the latent-heat extraction should be, the solidification can be largely classified into three types in relating with cooling rates.In low cooling rate, the latent heat is removed out by heat transfer and solidification proceeds quasisteadily with a solid-liquid interface kept at an equilibrium temperature. In high cooling rate, as for "rapid solidification of material processing", a supercooling state easily appears and this brings massive solidification due to crystal growth initiated by nucleation. The supercooling which makes a rapid and insitu solidification possible, may result in the formation of new meta-stable phases of crystalline and of amorphous. In intermediate cooling rate, the supercooling also appears and distributes in close region from the cooling surface to some internal position being equilibrium. These imply that the solidification proceeds under two kinds of heat extraction sources ; the initially distributed supercooling and the external cooling.The emphasis in the discussion is on fundamentals of solidification of mixtures with supercooling under external heat transfer cooling : solidification process, appearance of micro-structure and microsegregation in the solid, and macro-micro conjugation of heat transfer with the solidification.