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 deform ed by die upsetting to obtain anisotropic magnets. Magnets can be proc essed either with a medium coercivity H-ci of 7.8 kA/cm but with a hig h-energy product (BH)(max) of 330 kJ/m(3) or with a coercivity of 21.2 kA/cm and a lower (BH)(max) of 192 kJ/m(3). Plane-view transmission e lectron microscopy (TEM) pictures show nearly equiaxed Nd2Fe14B 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 50 0 nm large globular NdOx particles distributed regularly throughout th e microstructure which inhibit the anisotropic grain growth. In additi on 5-20 nm small NdOx precipitates are found within some Nd2Fe14B grai ns. X-ray diffraction studies also indicate that the degree of texturi ng after die upsetting is smaller for mechanically alloyed than for me lt-spun materials. High-resolution TEM experiments did not show any gr ain boundary phase usually found in melt-spun materials; however, this needs to be confirmed.