Investigation of segregation and density profiles in the mushy zone of CMSX-4 superalloys solidified during downward and upward directional solidification processes
Investigation of segregation and density profiles in the mushy zone of CMSX-4 superalloys solidified during downward and upward directional solidification processes
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DOI：
10.1016/j.jallcom.2014.09.103
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发表时间：
2015-01
影响因子：
6.2
通讯作者：
Fu Wang;D. Ma;Jun Zhang;A. Bührig-Polaczek
中科院分区：
文献类型：
--
作者：
Fu Wang;D. Ma;Jun Zhang;A. Bührig-Polaczek
采用向下定向凝固（DWDS）和向上定向凝固（Bridgman）工艺制备了CMSX-4单晶高温合金棒材。测量了淬火试样沿着糊状区的枝晶间偏析，并给出了相应的浓度分布。使用数值模型将该剖面转化为液体密度剖面。从这一观察推断，沿着DWDS凝固样品的糊状区，元素Al的含量随着距离枝晶尖端的增加而增加，但Re和W逐渐减少。Bridgman凝固试样中这些合金元素的偏析分布也表现出相同的趋势。密度计算结果表明，枝晶间熔体在Bridgman凝固试样的糊状区随着深度的增加而变轻。这表明发生了密度反转。DWDS固化样品中的密度分布显示出类似的趋势。但是，由于生长方向相反，DWDS样品中没有出现密度反转。这表明DWDS工艺可以从根本上避免由密度反转引起的雀斑的出现，这是单晶高温合金涡轮机叶片中的严重宏观缺陷。
Single-crystal CMSX-4 superalloy bars were casted by using downward (DWDS) and upward (Bridgman) directional solidification processes. The interdendritic segregation along the mushy zone of the quenched samples was measured and the corresponding concentration profiles are comparatively presented. The profiles are translated into liquid density profiles using a numerical model. It was deduced from this observation that, along the mushy zone of DWDS solidified samples, the content of elemental Al increased with increasing distance from the tip of the dendrites, but Re and W gradually decreased. The segregation profiles of these alloying elements in the Bridgman solidified samples demonstrated the same tendency. The results of density calculations suggest that the interdendritic melt becomes lighter with increasing depth in the mushy zone of the Bridgman solidified samples. This indicates that density inversion occurred. The density profiles in the DWDS solidified samples showed an analogous tendency. However, due to the opposite direction of growth, the density inversion did not appear in the DWDSs′ samples. This suggests that the DWDS process can essentially avoid the occurrence of freckles, caused by density inversion, which are serious macro-defects in single-crystal superalloy turbine blade.