为研究凝固条件对第二代单晶高温合金DD6铸态和热处理态组织演化的影响，采用高速凝固(HRS)法和液态金属冷却(LMC)法制备了[001]取向合金。结果表明，铸态HRS合金的枝晶干γ′相呈现较为规则的立方形态，而LMC合金为不规则立方形态。随着浇注温度的升高，HRS合金γ′相尺寸呈现出先增加后降低的趋势，在1560 ℃时达到最大值；而1590 ℃浇注温度条件下，LMC合金的γ′相尺寸比HRS合金的更小。热处理后，所有合金γ + γ′共晶组织含量(体积分数)均大幅减少，且铸态合金γ + γ′共晶组织尺寸越小，热处理后降低幅度越大，这与铸态合金γ + γ′共晶组织含量无关。热处理态HRS合金和LMC合金枝晶干和枝晶间γ′相分布均匀、排列规则，立方化程度良好；LMC合金γ′相的尺寸均匀性优于HRS合金。不同凝固条件下铸态合金的组织差异主要由定向凝固过程中的温度梯度引起，因此通过提高浇注温度或采用LMC工艺等提高温度梯度的方式有助于细化合金枝晶组织，减轻元素微观偏析，进而降低合金热处理的难度。

Single-crystal superalloys are widely used in aircraft engines owing to their excellent high-temperature performance. As key factors in controlling the formation of microstructures, solidification conditions directly influence the comprehensive properties of alloys. Therefore, it is of great significance to understand the mechanisms of alloy microstructure evolution under different solidification conditions and to optimize the solidification process to improve the performance of advanced aircraft engine hot-section components. To investigate the effects of the solidification conditions on the evolution of as-cast and heat-treated microstructures in the second-generation single-crystal superalloy DD6, single-crystal bars oriented along the [001] direction were prepared using high-rate solidification (HRS) and liquid metal cooling (LMC) processes. The results showed that in the as-cast state, the γ′ phases in the dendritic core of the HRS alloy exhibited a relatively regular cubic shape, whereas those in the LMC alloy were irregularly cubic; the γ′ phases in the interdendritic regions of the HRS and LMC alloys were irregularly cubic and larger in size than those in the dendritic core. As the pouring temperature increased, the size of γ′ phases in the HRS alloy first increased and then decreased, reaching a maximum at 1560 ^oC. At the same pouring temperature of 1590 ^oC, the size of the γ′ phases in the LMC alloy was smaller. After the heat treatment, the volume fraction of the γ + γ′ eutectic under all conditions decreased significantly. A trend was observed where the smaller the size of the γ + γ′ eutectic in the as-cast alloy, the greater the reduction in its content, regardless of the initial γ + γ′ eutectic content in the as-cast state. In the heat-treated HRS and LMC alloys, the γ′ phases in the dendritic core and interdendritic regions were uniformly distributed and regularly arranged, and they demonstrated good cubicity. Furthermore, the size uniformity of the γ′ particles in the LMC alloy was superior to that in the HRS alloy. The differences in the microstructures of the as-cast alloys were primarily caused by differences in the temperature gradient during directional solidification. Therefore, increasing the pouring temperature or employing LMC to enhance the temperature gradient helped to refine the dendritic structure of the alloy, reduce microsegregation, and this can simplify the alloy's heat treatment process.