Effect of a Transverse Magnetic Field on Stray Grain Formation of Ni-Based Single Crystal Superalloy During Directional
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, owing to the excellent high temperature strength and creep durability, Ni-based superalloy single crystal turbine blades have been widely used in advanced aeroengines and industrial gas turbines. In industrial production, a single crystal turbine blade of Ni-based superalloy is usually obtained through a grain selector method, while an off-axial orientation dendrite may be formed because of the random nature of grain selector during directional solidification.[1–3] However, some work indicated that stray grains were easily formed on the edge of blade because of the primary dendrite with off-axial orientation in single crystal blades during directional solidification.[4–8] Due to the random orientation of stray grains, high-angle boundaries may be formed and decrease the mechanical properties. Therefore, many scientific research workers
WEIDONG XUAN, Materials Research Engineer, HUAN LIU, Ph.D. Student, JIAN LAN, Master, CHUANJUN LI, Associate Professor, and YUNBO ZHONG, XI LI, GUANGHUI CAO, and ZHONGMING REN, Professors, are with the State Key Laboratory of Advanced Special Steel & Shanghai Key Laboratory of Advanced Ferrometallurgy & School of Materials Science and Engineering, Shanghai University, Shanghai 200072, P.R. China. Contact e-mails: [email protected], [email protected] Manuscript submitted June 21, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
investigated the formation of stray grains during directional solidification,[4–25] and some methods of stray grain suppression are proposed, such as the optimization of cooling rate[26,27] and the application of spiral grain selector between the blade and the seed.[4,9] Unfortunately, stray grain formation is still a key defect that has not been effectively solved. A transverse magnetic field has been extensively used to improve material microstructures and properties during solidification. Some reports show that a transverse magnetic field could influence many aspects of solidification,[28–30] such as the solid/liquid interface shape, the mushy zone length, the dendrite spacing, and the solute distribution. However, Liu et al.[6,7] and our previous work[8] indicate that the formation of stray grains on the side the primary dendrite diverges from the mold wall (i.e., the diverging side) is derived from the enrichment of solute which leads to a large undercooling. According to these researches, utilizing a transverse magnetic field optimizes the microstructures and eliminates the stray grain defect of Ni-based single crystal superalloy. Up to date, the effect of a transverse magnetic field on stray grain formation on the edge side for Ni-based single crystal superalloy during directional solidification has rarely been reported. The aim of this work is to investigate the effect of the transverse magnetic field on stray grain formation of superalloy PWA1483 during directional solidification. Experimental results indicated that the transverse magnetic field effectively suppressed the stray grain formation on the diverging side of sample. The Ni-based single crystal superalloy PWA1483
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