Determining the effect of casting geometric structure on freckle formation is important in designing the directional solidification parameter of single‐crystal superalloy castings. In this research, single‐crystal castings of a third‐generation nickel (Ni)‐based superalloy with different thicknesses and structures are prepared by conventional Bridgman high‐rate‐solidification technique at withdrawal rates of 1, 3, and 6 mm min^–1. The experimental results show that the freckles in castings with expansion structures are severer than those with contraction structures at a withdrawal rate of 1 mm min^–1, and vice versa at withdrawal rates of 3 and 6 mm min^–1. It is found that the larger casting thickness tends to promote the freckle formation at the same withdrawal rate. Furthermore, a lower tendency is displayed at the withdrawal rate of 3 mm min^–1 in freckle formation, whereas an increased tendency is displayed at the withdrawal rate of 6 mm min^–1. The different withdrawal rates, thicknesses, and structures of casting cause differences in cooling rate, shrinkage flow, and mushy zone morphology, which are believed to be responsible for the tendency of freckle formation.

中文翻译：

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镍基单晶高温合金定向凝固过程中铸件的几何结构和进给行为对雀斑形成的影响

确定铸件几何结构对雀斑形成的影响对于设计单晶高温合金铸件的定向凝固参数很重要。在这项研究中，采用传统的Bridgman高速凝固技术，以1、3和6 mm min ^–1的拉拔速率制备了具有不同厚度和结构的第三代镍（Ni）基高温合金单晶铸件。。实验结果表明，在1 mm min ^–1的拉拔速率下，具有膨胀结构的铸件中的雀斑比具有收缩结构的铸件中的雀斑更严重，而在3 mm和6 mm min ^–1的拔出速率下，其雀斑更严重。。已经发现，较大的铸件厚度倾向于在相同的排出速率下促进雀斑形成。此外，在雀斑形成中，以3 mm min ^–1的抽出速率显示出较低的趋势，而以6 mm min ^–1的抽取率显示出较高的趋势。铸造速率，厚度和铸件结构的不同会导致冷却速率，收缩流和糊状区形态的差异，这被认为是造成雀斑形成的原因。