1. Investigation on freckle formation and evolution of single-crystal nickel-based superalloy specimens with different thicknesses and abrupt cross-section changes.
- Author
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Han, Dongyu, Jiang, Weiguo, Xiao, Jiuhan, Li, Kaiwen, Lu, Yuzhang, Zheng, Wei, Zhang, Shaohua, and Lou, Langhong
- Subjects
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NICKEL alloys , *RADIAL flow , *HEAT resistant alloys , *SCANNING electron microscopes , *OXYGEN carriers , *OPTICAL microscopes , *ELECTRON diffraction - Abstract
The freckle formation and evolution in directionally solidified single-crystal specimens with different thicknesses and abruptly expanding rectangular cross-section were investigated at different withdrawal rates. The microstructure was studied by optical microscope (OP) and scanning electron microscope (SEM), and the crystallographic orientation in freckle areas was characterized by electron backscattered diffraction (EBSD). The experimental results showed that the freckle was the most severe in specimens with a thickness of 10 mm at the same withdrawal rate, and the freckle chain was observed to form below an abruptly expanding cross-section ended at the expanding step. It was found that freckles formed exclusively on the edges of casting facing the central sprue of the shell mould. Findings reveal that freckles tend to form at the highest position of the mushy zone, mainly due to the thermosolutal convection and the radial flow caused by feeding behavior in the mushy zone. The freckle formation is pronounced at a low withdrawal rate, and can further generate stray grains. • Freckle formation is more pronounced at a low withdrawal rate of 1 mm/min. • Freckles form exclusively on the edges facing the central sprue of the shell mould. • Radial flow and feeding behavior play a major role in freckle position. • Freckle grains can evolve into stray grains at a low withdrawal rate of 1 mm/min. [ABSTRACT FROM AUTHOR]
- Published
- 2019
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