Tailoring Microstructure and Microsegregation in a Directionally Solidified Ni-Based SX Superalloy by a Weak Transverse Static Magnetic Field

摘要

A weak transverse static magnetic field(WTSMF,0–0.5 T)is applied to the directional solidification process of a DD3 Ni-based SX superalloy,aiming to tailor the microstructure and microsegregation of alloys.The mechanisms of microstructural refinement and microsegregation distribution caused by a WTSMF during directional solidification are discussed.It is shown that the primary dendrite arm spacing is rapidly reduced from 181 to 143μm,and the average size ofγ′phase is significantly refined from 0.85 to 0.25μm as the magnetic field increases from 0 to 0.5 T.At the same time,the volumefractions ofγ/γ′eutectic and the segregation coefficient are also gradually decreased.The 3D numerical simulations of the multiscale convection in liquid phase show that the modifications of the microstructure and microsegregation in DD3 are mainly attributed to the enhanced liquid flow caused by thermoelectric magnetic convection(TEMC)at dendrite/sample scale under the WTSMF.The maximum of the TEMC increases with increasing the magnetic field intensity.This work paves a simple way to optimize the microstructure and microsegregation in directionally solidified Ni-based SX superalloys without changing the processing parameters and composition.