Formation and Evolution of Stray Grains on Remelted Interface in the Seed Crystal During the Directional Solidification of Single-Crystal Superalloys Assisted by Vertical Static Magnetic Field
Nickel-based superalloys,especially single-crystal(SC)ones,have long been recognized as important materials for turbine blades used in aerospace and gas engines.Static magnetic fields are effective at controlling the material forming.The use of static magnetic fields during solidification has evolved as a sophisticated approach for efficiently controlling the microstructures and mechanical perfor-mance of metallic materials.In recent years,studies have shown that static magnetic fields have a com-plex effect on dendrites in SC superalloys.However,the mechanism of static magnetic fields regulating stray grains on remelted interface needs to be investigated further.This work studied the generation of stray grains near the seed remelted zone and the evolution mechanism during the directional solidifica-tion of the SC superalloy assisted by a magnetic field by tracing the solidification microstructure.The stray grains of large orientation that deviated from the<001>direction appeared on the remelted zone in-terface of the solidification microstructure when the magnetic field was applied,accompanied by the for-mation of a large-angle grain boundary(LAGB).Most of the stray grains were distributed at the sample edge.The increase in magnetic field intensity and pulling speed increased the number of stray grains and the length of the LAGB.As the solidification progressed,the large-orientation stray grains and the LAGBs were eliminated at a fast speed and evolved into small-orientation dendrites.During the following solidifi-cation,the orientation of the dendrites became even smaller and the evolution speed decreased sharply.The increase in withdrawal speed intensified the evolution process.The stray grains formed in the remelt-ed zone can be attributed to the twisting dendrite by the thermoelectric magnetic force.The distribution of more stray grains around the sample was caused by the circulation from thermoelectric magnetic convec-tion at the macroscopic scale.
single-crystal superalloyvertical static magnetic fielddirectional solidificationstray grain
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