切向流动作用下SCN-3wt% H2O枝晶定向生长过程研究

实时观察了切向流动作用下SCN-3wt% H₂O合金的定向凝固过程，研究了该合金枝晶生长方向、尖端半径、枝晶一次臂间距以及二次臂生长速度的变化规律.实验观察到能够代表枝晶尖端溶质边界层的“亮带”，该亮带在流动作用下的非对称性证实了切向流动能够改变枝晶前沿溶质的对称分布，使溶质边界层厚度沿背流侧向迎流侧逐渐减薄，枝晶生长发生迎流偏转，且偏转角度随抽拉速度的提高而减小.同时，流场与浓度场的耦合促进枝晶间的优胜劣汰，枝晶一次臂间距显著增大.固液界面处的强迫流动还能够引发相邻枝晶间环流，加速迎流处二次臂生长而抑制背流处生长. 关键词： 定向凝固 枝晶生长 切向流动

Directional dendrite growth of SCN-3wt% H2O under shear flow

Directional solidification of SCN-3wt% H₂O was carried out under externally imposed parallel shear flow, and the growth characteristics of dendritic tips, primary arms and secondary arms were investigated. A bright band related to solute boundary layer along the dendritic tip is observed for the first time. It was confirmed that the left-right symmetry of the dendritic tip is broken up by the shear flow, with the dendritic tip tilting toward the upstream side. The tilting angle increases with the pulling rate. Compared with the case of static condition, the primary spacing becomes lager under shear flow, and this is due to the coupling effect of flow and solute fields. The growth of secondary arm is promoted at the upstream side whereas greatly restrained at the downstream side, which is caused by the circumfluence among dendrites produced by force flow.