Abstract
High-speed optical temperature measurement and digital imaging elucidated the solidification behavior of undercooled Nd2Fe14B melt through containerless processing by an electromagnetic levitation method. The Fe phase solidified primarily from the melt. Subsequently, the remaining melt was undercooled below the peritectic temperature and the Nd2Fe14B phase surrounded the primary Fe dendrites, yielding the recalescence. The clear interface of the thermal field propagated and covered the entire sample. Detailed microstructural observation showed that the Nd2Fe14B phase surrounding the different Fe dendrites mutually came into contact with the several points. This suggested that many sites for nucleation of the Nd2Fe14B phase are not necessary for the successive growth of the Nd2Fe14B phase that was maintained by the spread of the Nd2Fe14B phase to the different primary Fe dendrites. This resulted in the macroscopic interface of the thermal field during recalescence. Moreover, the undercooled melt was dropped from the levitation coil and quenched by a pair of copper chill plates with moulds, the shape of which is a hemisphere cap, in order to obtain a small bulk sample for industrial purpose. The spherical sample with the diameter of 5 mm was successively obtained without decreasing the cooling rate. This result suggests the possibility of the net shaping of a small magnet from the melt.
