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Microstructural evolution of directionally solidified DZ125 superalloy castings with different solidification methods

机译：不同凝固方式定向凝固DZ125高温合金铸件的组织演变

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The properties of Ni-base superalloy castings are closely related to the uniformity of their as-cast microstructure, and different solidification methods have serious effect on microstructural uniformity. In this paper, the influences of high rate solidification (HRS) process (with or without superheating) and liquid metal cooling (LMC) process on the microstructure of DZ125 superalloy were investigated. Blade-shape castings were solidified at rates of 40 μm·s-1 to 110 μm·s-1 using HRS process and a comparative experiment was carried out at a rate of 70 μm·s-1 by LMC process. The optical microscope (OM), scanning electron microscope (SEM) were used to observe the microstructure and the grain size was analyzed using electron back scattered diffraction (EBSD) technique. Results show that for the castings by either HRS or LMC process, the primary dendrite arm spacing and size of γ' precipitates decrease with increasing the withdrawal rate; the dendrites and γ' precipitates at the upper section of the blade are coarser than those in the middle, especially for the HRS castings without high superheating technique. When the withdrawal rate is 70 μm·s-1, the castings by HRS with high superheating technique have the smallest PDAS with fine γ' precipitates; while the size distribution of γ' precipitates is more homogenous in LMC castings, and the number of larger grains in LMC castings is smaller than that in the HRS castings. Moreover, high superheating technique yields smaller grains in the castings. Both the LMC method and HRS with high superheating technique can be used to prepare castings with reduced maximum grain size.
机译：镍基高温合金铸件的性能与其铸态组织的均匀性密切相关，不同的凝固方法对组织的均匀性有严重影响。本文研究了高速凝固（HRS）工艺（有或没有过热）和液态金属冷却（LMC）工艺对DZ125高温合金显微组织的影响。使用HRS工艺将叶片形铸件以40μm·s-1至110μm·s-1的速率凝固，并通过LMC工艺以70μm·s-1的速率进行对比实验。用光学显微镜（OM），扫描电子显微镜（SEM）观察其微观结构，并利用电子背散射衍射（EBSD）技术分析晶粒尺寸。结果表明，采用HRS或LMC工艺的铸件，初生枝晶臂间距和γ'析出物的尺寸随回撤率的增加而减小;叶片上部的枝晶和γ'析出物比中部的要粗，特别是对于没有高过热度技术的HRS铸件。当抽出率为70μm·s-1时，HRS高过热度铸件的PDAS最小，且有细的γ'析出物。而LMC铸件中γ'析出物的尺寸分布更均匀，而LMC铸件中的较大晶粒数量少于HRS铸件。而且，高过热技术在铸件中产生较小的晶粒。 LMC方法和具有高过热技术的HRS均可用于制备减小的最大晶粒尺寸的铸件。

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