晶体取向对定向凝固平界面失稳行为的影响

采用丁二腈-丙酮透明模型合金研究了不同晶体取向的晶粒在定向凝固条件下的平界面失稳过程.实验选择了三个界面失稳后具有不同生长形态的典型晶粒作为研究对象, 分别为择优生长枝晶、倾斜枝晶和海藻晶.结果表明可发展为择优生长枝晶的晶粒的平界面失稳孕育时间和初始扰动波长最小,海藻晶次之, 倾斜枝晶最大,这与以往的解析结果和相场模拟结果一致. 同时,实验观察发现可发展为择优生长枝晶和倾斜枝晶的晶粒的界面非稳态演化过程与海藻晶显著不同,这表明平界面失稳的非稳态演化过程与晶体取向相关.

Effect of crystallographic orientation on instability behavior of planar interface in directional solidification

The instability process of planar interface in directional solidification with respect to the crystallographic orientation is studied using a transparent model alloy—succinonitrile-acetone.Three typical crystal grains which have preferred dendrite,tilted dendrite and seaweed patterns at rapid pulling velocity respectively are chosen in our experiment.The experimental results show that the prefened dendrite grain has the shortest incubation time and the smallest initial perturbation wavelength of planar interface instability, the tilted dendrite grain has the largest ones and the seaweed grain has median ones.These results accord qualitatively with previous analytical results and phase-field simulation results.It is also found that the interfacial non-steady-state evolution behaviors of the preferred dendrite grain and the tilted dendrite grain are significantly different from that of the seaweed grain,suggesting that the non-steady-state evolution behavior of planar interface instability is closely related to the crystallographic orientation.