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Sliver defect formation in single crystal Ni-based superalloy castings
Materials & Design ( IF 8.4 ) Pub Date : 2020-11-01 , DOI: 10.1016/j.matdes.2020.109138
Wenliang Xu , Fu Wang , Dexin Ma , Xintao Zhu , Dichen Li , Andreas Bührig-Polaczek

Abstract Sliver is a typical grain defect in single crystal Ni-based superalloy castings produced by Bridgman directional solidification. However, its formation mechanism has yet to be fully understood. In this study, the formation of sliver defects was investigated with respect to the defect morphological features, the microstructure of defect initiation points, and the solidification conditions. Experiment results showed that sliver defects were originated from fragmentation of dendrite trunks and could developed to various morphologies. The misorientation range of sliver grains was between 3.2° to 12°. Microstructural analysis results indicated that the dendrites fragmented abruptly without significant plastic deformation. And the dendrite fragmentation could be facilitated by oxide inclusions and solidification pores. It was also found that the sliver defects were prone to occur at the interface where primary dendrite converge to the mold inner wall. Based on the low misorientation level of sliver grains in the experimental observation, the critical solid volume fraction range for fragmentation was suggested to be 0.6–0.8. The dendrite fragmentation was attributed to the non-uniform stress distribution in dendrite during solidification. In addition, the effect of airfoil geometry of a typical blade casting and defect prevention methodology were discussed.

中文翻译:

单晶镍基高温合金铸件中长条缺陷的形成

摘要 条子是布里奇曼定向凝固法生产的单晶镍基高温合金铸件中的一种典型晶粒缺陷。然而,其形成机制尚未完全了解。本研究从缺陷形态特征、缺陷起始点的微观结构和凝固条件等方面研究了银条缺陷的形成。实验结果表明,条子缺陷起源于枝晶干的破碎,可以发展成各种形态。条子晶粒的错误取向范围在3.2°到12°之间。微观结构分析结果表明,枝晶突然破碎,没有明显的塑性变形。氧化物夹杂物和凝固孔可以促进枝晶破碎。还发现在初级枝晶会聚到模具内壁的界面处容易出现条子缺陷。基于实验观察中条子晶粒的低取向差水平,碎裂的临界固体体积分数范围建议为0.6-0.8。枝晶破碎是由于在凝固过程中枝晶中的应力分布不均匀。此外,还讨论了典型叶片铸造和缺陷预防方法的翼型几何形状的影响。枝晶破碎是由于在凝固过程中枝晶中的应力分布不均匀。此外,还讨论了典型叶片铸造和缺陷预防方法的翼型几何形状的影响。枝晶破碎是由于在凝固过程中枝晶中的应力分布不均匀。此外,还讨论了典型叶片铸造和缺陷预防方法的翼型几何形状的影响。
更新日期:2020-11-01
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