中文摘要：

研究了螺旋段在选晶过程中的作用．基于金相及EBSD实验结果，指出在晶粒竞争生长过程中，晶粒二次臂取向和初始位置分布特征综合决定了晶粒的竞争优势．总结提出了选晶过程的两个几何限制机理：水平方向的二次臂竞争促进作用和竖直方向的一次臂限制作用．两种模型成功解释了螺旋段对选晶过程的作用．采用修正的元胞自动机（MCA）技术，对螺旋段的晶粒竞争生长过程进行了模拟．研究了晶粒结构及晶体取向随定向凝固过程的变化规律，并与实验结果进行了对比，两者吻合较好．基于模拟与实验的研究，获得了螺旋参数对选晶行为的影响规律及作用机理，提出了选晶器螺旋段的设计准则．

英文摘要：

The spiral selector is the key part for the integrity of crystal, which mainly includes starter producing single crystal （SX） blades and ensures block and spiral part. In this work, the influence of spiral part on the grain selection process was studied. Both of the metallography results and EBSD results proved that the prior location and the special orientation of the second dendrite arms were important for the grains competitive growth during the directional solidification process. Based on the experimental results, two geometrical restrict mechanisms of grain selection were proposed. They were the competitive stimulating effect on the second dendrite arms in horizontal direction, which was resulted from the spiral arc shape, and the growing blocking effect on the primary dendrites in vertical direction, which was resulted from the take~off angle of the spiral part. These models could successfully explain the grain selecting effects of the spiral part. The modified cellular automaton（MCA） technology was used to simulate the grains＇ competitive growth in spiral part. The changes of grains structure and orientation as the grain growing oil were studied. The simulated and experimental results were compared and agreed well. Based on the simulated and experimental results, Influences of structural parameters on the grain selection behavior were proposed. The criteria for designing spiral part were also presented.