Effect of local cooling rates on the microstructures of single crystal CMSX-6 superalloy: A comparative assessment of the Bridgman and the downward directional solidification processes
Effect of local cooling rates on the microstructures of single crystal CMSX-6 superalloy: A comparative assessment of the Bridgman and the downward directional solidification processes
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DOI：
10.1016/j.jallcom.2014.07.084
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发表时间：
2014-12-15
影响因子：
6.2
通讯作者：
Buehrig-Polaczek, Andreas
中科院分区：
文献类型：
--
作者：
Wang, Fu;Ma, Dexin;Buehrig-Polaczek, Andreas
采用新型定向凝固工艺-向下定向凝固工艺和Bridgman定向凝固工艺，对单晶镍基CMSX-6高温合金棒材进行了等速定向凝固。对于使用两种工艺铸造的棒材，在凝固前沿和冷却端之间的5.5 cm和12.5 cm位置测量了局部冷却速率。随着离冷点距离的增加，冷却速率在1.21 ~ 1.08 K/s之间变化，变化速率为10.74%。与此相反，Bridgman工艺的冷却速率从0.15到0.08 K/s变化，变化速率为46.67%。对比研究了两种工艺的微观组织演变与冷却速率的关系。与Bridgman工艺相比，在新工艺铸棒的两个位置均观察到细化的γ枝晶结构、更小的γ / γ共晶岛尺寸、枝晶核心中细化的γ析出物和更小的微孔平均尺寸。此外，随着枝晶间距从5.5 cm增加到12.5 cm，枝晶芯中初生枝晶和次生枝晶臂间距、γ / γ′共晶岛尺寸和γ′析出相尺寸的变化均小于Bridgman过程。这表明向下定向凝固工艺可以铸造出组织更加均匀的棒材。此外，与Bridgman工艺相比，大多数微孔的直径更小，冷端和远端之间微孔的最大尺寸变化和平均直径都更小；在布里奇曼过程中发现的情况正好相反。(C) 2014 Elsevier B.V.版权所有
Single-crystal nickel-based CMSX-6 superalloy rods were directionally solidified at a constant withdrawal rate by employing a novel directional solidification process the downward directional solidification process and the Bridgman process. For the rods cast using both processes, the local cooling rates were measured at the 5.5 cm and 12.5 cm locations between the solidification front and the chill end. With an increasing distance from the chill, the cooling rate varied from 1.21 to 1.08 K/s giving a change in the rate of 10.74% in the novel process. In contrast to this, the cooling rates in the Bridgman process varied from 0.15 to 0.08 K/s giving a change in the rate of 46.67%. The microstructural evolution was comparatively investigated for the two processes as a function of the cooling rates. In comparison to the Bridgman process, refined gamma dendrite structures, smaller size of gamma/gamma' eutectic island, refined gamma' precipitates in the dendritic core and a smaller average size of microporosities were observed in both locations of the rods cast by using the novel process. In addition to this, the variations of the primary and secondary dendrite arm spacings, the size of gamma/gamma' eutectic island, and the size of gamma' precipitates in the dendrite core were smaller than those in the Bridgman process with increasing the distance from 5.5 cm to 12.5 cm. This indicates that the downward directional solidification process can cast a rod possessing more homogeneous microstructures. Moreover in comparison to the Bridgman process, the majority of the micropores have smaller diameters and both the variation in the maximum size of microporosity as well as the average diameter of these micropores located between positions near to the chill end and the distant end were smaller in the rods cast by using the novel process; the opposite is found in the Bridgman process. (C) 2014 Elsevier B.V. All rights reserved.