(北京航空材料研究院 先进高温结构材料重点实验室，北京 100095)
摘 要: 通过在高速凝固法(HRS)定向凝固过程中调整隔热挡板与壳型之间的间隙，获得了较低的定向凝固温度梯度(~30？℃/cm)，制备了含有雀斑组织的单晶高温合金试棒。结果表明：采用常规HRS工艺(温度梯度~50？℃/cm)制备的合金一次枝晶间距为323？μm，含有1.70%铸态共晶；而采用较低温度梯度HRS工艺制备的合金一次枝晶间距达到了704？μm，是常规HRS工艺的2.2倍，并且合金的二次枝晶及三次枝晶较为发达；此外，雀斑组织区域包含较多平均晶粒尺寸为200？μm的等轴晶晶粒和4.64%的铸态共晶，同时分布着富集Ta元素的MC碳化物。定向凝固过程中较低的温度梯度增大了合金的一次枝晶间距并使合金元素的凝固偏析加重，导致糊状区液相发生对流的倾向增大，从而促进了雀斑组织的形成。
关键字: 高温合金；低温度梯度；定向凝固缺陷；雀斑；凝固偏析
（Science and Technology on Advanced High Temperature Structural Materials Laboratory, Beijing Institute of Aeronautical Materials, Beijing 100095, China）
Abstract:The low thermal gradient during directional solidification was obtained by adjusting the distance between the baffle and the shell mold during traditional Bridgman (HRS) directional solidification process, and the single crystal superalloy bars containing freckles were prepared. The results show that the primary dendrite arm spacing of the normal HRS process alloy is 323？μm, which contains 1.70% cast eutectic. The primary dendrite arm spacing of the alloy prepared by lower temperature gradient HRS process reaches 704？μm，which is 2.2 times of that prepared by the normal HRS process. In addition, the secondary dendrite arm and thirdly dendrite arm are extremely developed under the low temperature gradient HRS process. The region of the freckles contains a large amount of equiaxed grains with a grain size of about 200？μm and 4.64% eutectic, and there are MC carbides enriched in Ta. The coarsen primary dendrite arm spacing and aggravated solidification segregation, caused by low thermal gradient during directional solidification, increase the tendency of convection of the liquid phase in the mushy zone, and promote the formation of freckles.
Key words: superalloy; low thermal gradient; directional solidification defects; freckle; solidification segregation
