定向凝固过程中的不规则固液界面形貌

固液界面通常为规则界面, 但有时为不规则界面,如倾斜枝晶、退化枝晶和海藻状晶体界面.以琥珀腈为研究对象,用设计的定向凝固实验体系, 研究了不同温度梯度和界面生长速度对固液界面形貌的影响.实验结果表明:界面生长速度一定时,增加温度梯度界面由倾斜枝晶逐渐转变为退化枝晶,最终成为海藻状晶体;温度梯度一定时,降低界面生长速度界面会发生类似的变化.温度梯度和界面生长条件在一定范围内变化时,界面可以从一种生长方式变为另一种方式,如可以从海藻状晶体连续地变为倾斜枝晶.在某些条件下,海藻状晶体和倾斜枝晶可能同时出现在界面上,并竞相生长.退化枝晶界面处于动态变化中,二次枝晶臂不断地改变着生长方向.

Characteristics of Irregular Interface Pattern during Unidirectional Solidification

Besides normal interface morphologies, irregular morphologies such as titled dendritic, degenerate, and seaweed patterns can be observed in experiments. The effects of temperature gradient and interfacial growth velocity on solid-liquid interface morphology were studied with succinonitrile under the unidirectional solidification system. Experimental results show that, for any given interface growth velocity, increasing the temperature gradient changes the interface pattern first from titled dendrites to a degenerate pattern and eventually to a seaweed pattern, and the similar change in the solidification pattern exists by decreasing the interface growth velocity with a fixed temperature gradient. Transition from one pattern to another occurs at a range of temperature gradients and interface growth conditions. The solidification pattern is then unstable, with the interface developing continuously from seaweed into tilted dendritic pattern or from seaweed to tilted dendrites. In some cases, these two different patterns compete at the same time. In addition, solidification with a degenerate pattern shows a transient feature with a continuous variation in the angle of the second arm with respect to the heat flux direction.