Influence of an Axial Magnetic Field on Microstructures and Alignment in Directionally Solidified Ni-based Superalloy

The effect of an axial magnetic field on the dendrite morphology in directionally solidified Ni-based superalloy was investigated experimentally. Results show that an application of the magnetic field modified the morphology of the dendrite remarkably. Under a relatively weak magnetic field (B<0.5 T), the primary dendrite spacing decreases with the increase of magnetic field intensity. However, under a relatively high magnetic field (B >= 2T), the primary dendrite spacing increases with the increase of magnetic field intensity. Moreover, it was found that the strong magnetic field is capable of inducing the fracture of the dendrite and the columnar to equiaxed transition (CET). With the increase of the magnetic field and the decrease of the growth speed, the fracture of the dendrite and the CET under the magnetic field is enhanced. The above results may be attributed to the TE magnetic convection in the liquid and the TE magnetic force acting on the dendrite.