Microstructure evolution of Nd-Fe-B alloys in consideration of magnetohydrodynamics

The solidification process and the resulting microstructure of Nd-Fe-B alloys in consideration of melt convection has been investigated experimentally with a specially designed floating-zone arrangement. A controlled influence on the melt flow is possible via tailored magnetic fields which enable enhancement or suppression of the melt convection. A specially designed magnetic two-phase stirrer offers a strong influence on the melt flow in the floating-zone facility. As a result, the microstructure pattern, mainly the volume fraction and grain size of the a-Fe phase, vary strongly with the strength of the internal flow motion. The melt flow is studied numerically under the additional effect of the two-phase stirrer taking into account the coupled heat and fluid flow fields. The electromagnetically driven flow during the inductive heating turned out to be of strong influence on the resulting microstructure.