确保柱状晶不向等轴晶转变，即避免CET发生，是激光修复单晶镍基高温合金表面缺陷的关键。基体晶向是影响CET的重要因素，由于单晶高温合金的各向异性，其基体晶向改变与采用哪一个方向作为旋转轴相关，但不同旋转轴条件下基体晶向对CET的作用并不清楚。已有研究主要集中在个别孤立基体晶向、功率和扫描速度对CET的影响方面，鲜有考虑不同旋转轴的作用，因此无法从本质上揭示基体晶向对CET的内在机理，亟待进行系统的研究。本项目以我国自行研制的DD系列合金为研究对象，采用激光表面熔凝技术，以不同晶体学取向为旋转轴为出发点，在此基础上改变基体晶向，探索熔池边界不同晶区的分布，研究不同晶区内的枝晶生长速度和温度梯度分量的变化，结合数值模拟计算，获得局部和整体CET因子，阐明不同旋转轴条件下基体晶向对于CET能力的影响规律，揭示不同旋转轴的作用机制，为修复镍基高温合金热端部件的表面缺陷提供理论依据。

Ensuring that the columnar dendrite does not evolve into equiaxed one, namely, avoiding the CET, is a key factor to laser repair of the surface defaults in Ni-based superalloy. The substrate orientation is one main parameter to influence the CET. Due to the anisotropy of the single crystal alloy, the variation of the substrate orientation can be performed by different rotation axes. However, the effect of the substrate orientation for different rotation axes is not clear. The previous works are mainly focused on the influences of the independent orientation, the laser power, or the laser scanning speed on CET. The impact of the different rotation axes has seldom been considered. This project will carry on investigations on this aspect.. For this purpose, the DD series superalloys developed in China will be selected as the research objects. On the basis of being performed via different rotation axes, the substrate orientation is changed. The variation in the distribution of different dendrite domains are checked under this condition. The solidification parameters, such as the dendrite growth velocity and the thermal gradient along the preferred dendrite growth direction, are examined. Furthermore, the local and overall CET are determined. The relative experiments will be done for the comparison to elucidate the mechanism of the rotation axis on the CET. The results of this project might provide an in-depth insight into the CET and be helpful for the laser repair of the Ni-based hot components.