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的和/或密集的原子组合，并释放聚变潜热。从潜热提取方式的角度来看，凝固过程与冷却速率的关系大致可分为三种类型。在低冷却速率下，潜热通过传热排出，凝固过程准稳定进行，固液界面保持在平衡温度。在高冷却速率下，对于“材料加工的快速凝固”，容易出现过冷状态，这是由于晶核引发的晶体生长导致的大量凝固。过冷使快速原位凝固成为可能，可能导致新的亚稳定相结晶和非晶的形成。在中等冷却速率下，也出现过冷现象，并分布在从冷却表面到内部某个平衡位置的封闭区域内。这表明凝固过程在两种热源下进行；初始分布过冷和外部冷却。讨论的重点是外换热冷却下过冷混合物凝固的基本原理：凝固过程、固体中微观组织和微偏析的出现以及传热与凝固的宏观-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.