CHARACTERIZATION OF ND2FE14B FINE POWDERS PRODUCED BY ULTRA-HIGH-PRESSURE GAS ATOMIZATION

By using ultra-high-pressure gas atomization, it is possible to produc e fine powders of the rare earth permanent magnet material Nd2Fe14B wi th the particle size below 30 mu m. The grain size, impurity phase con tent and magnetic properties of these powders have been analyzed as a function of particle size. Rietveld analysis of X-ray diffraction patt erns is used to determine the average grain size and to identify the s econd phases. The average grain size is confirmed by using transmissio n electron microscopy. The grain size is found to be decreased as the classified particle size decreased. For particle sizes smaller than 5 mu m, the particles exhibit more second phase of NdFe4B4. Magnetic mea surements indicate that the coercivity increased as the particle size decreased to 5 mu m and then dropped significantly for finer particles .