MICROSTRUCTURE AND MAGNETIC-PROPERTIES OF MECHANICALLY ALLOYED ANISOTROPIC ND-FE-B

Mechanically alloyed Nd-Fe-B powders with additions of Dy, Co, and Ga were hot compacted to magnetically isotropic materials and then deformed by die upsetting to obtain anisotropic magnets. Magnets can be processed either with a medium coercivity Hci of 7.8 kA/cm but with a high-energy product (BH)max of 330 kJ/m3 or with a coercivity of 21.2 kA/cm and a lower (BH)max of 192 kJ/m3. Plane-view transmission electron microscopy (TEM) pictures show nearly equiaxed Nd2Fe 14B grains. In cross section, the grains display the typical platelet form known from MQ 3-type magnets with a length of about 300 nm and a height of 100 nm. Characteristic for mechanically alloyed materials are up to 500 nm large globular NdOx particles distributed regularly throughout the microstructure which inhibit the anisotropic grain growth. In addition 5-20 nm small NdOx precipitates are found within some Nd2Fe 14B grains. X-ray diffraction studies also indicate that the degree of texturing after die upsetting is smaller for mechanically alloyed than for melt-spun materials. High-resolution TEM experiments did not show any grain boundary phase usually found in melt-spun materials; however, this needs to be confirmed.