ドロップチューブ法を用いたNd-Fe 系合金の準安定相生成と高保磁力発現

抄録

The Nd-Fe and Nd-Fe-Al alloys were containerlessly solidified by using two types of drop-tubes: short and long ones, the free fall lengths of which are 3 m and 26 m, respectively. The diameters of as-dropped samples formed by using these short and long drop-tubes are ranged 100-1000 and 100-2300 mms, respectively. The coercivities of the as-dropped Nd-Fe-Al samples formed in the long drop-tube increased with decrease of the diameters, but in the samples with diameters less than the critical one, the coercivities decreased whereas the saturation of the magnetization increased. The reason for this phenomenon is ascribed to the formation of soft magnetic phases such as an amorphous phase due to the high cooling rates. In Nd-Fe alloys, on the other hand, all of the as-dropped samples exhibited hard magnetic properties, Hc = 4.6 kOe. The microstructures of the as-dropped 90Nd-10Fe samples consisted of primary a-Nd and the included metastable phases. In as-dropped 70Nd-30Fe samples with diameters of 212-300 mms, the microstructure consisted of primary metastable phases and fine a-Nd. Considering the previous experimental results using the gas-jet electromagnetic levitator, it can be concluded that the high coercivities of the as-dropped Nd-Fe samples are attributed to this fine metastable phase and a-Nd. Key Words: Containerless process, Short drop tube, Microgravity, Size effect, Non-equilibrium solidification.