In   situ and dynamic observation of NdFeCoB magnet by high voltage transmission electron microscope (abstract)

In situ and dynamic observation of microstructural characteristics of sintered Nd-Fe-Co-B magnet has been carried out using JEM-1000X high voltage transmission electron microscope (HVTEM). Magnetic properties of the sample studied are as follows: Br=1.28 T, Hc=589 kA/m, (BH)max=302.4 kJ/m3. HVTEM observation results are as follows: (1) At room temperature, the grains of the matrix phase are found to be nearly perfect crystals. In some grains, there exist some spherical inclusions that are embedded in the matrix. Structural analysis of these inclusions has been made by electron diffraction. (2) When the temperature is lower than 400 °C, we found no obvious changes. (3) When the temperature is higher than 400 °C, some small precipitates began to occur in the matrix. (4) When the temperature reaches 500 °C, the precipitates grow and become needlelike and perpendicular to each other. (5) When the temperature reaches 700 °C, the tetragonal symmetry of the matrix phase is completely damaged. (6) No remarkable changes were found for the Nd-rich grain boundary phase when the temperature increases from 25 to 600 °C. (7) Temperature dependence of coercivities of the sample has been explained by the structure changes.