ND-FE-B-BASED MAGNETS - MAGNETIC-PROPERTIES AND MICROSTRUCTURAL APPEARANCE WITH COPPER ADDITION

The microstructure of sintered permanent magnets with a composition 17Nd-76.5Fe-5B-1.5Cu was investigated by optical microscopy, electron probe microanalysis and transmission electron microscopy. Using the hydrogen decrepitation processing route, maximum magnetic properties of H(cJ) = 950 kA m- 1 and (BH)max = 230 kJ m-3 were obtained after high temperature homogenization and low temperature annealing. The main effect of the heat treatment procedure was to change the proportion of phases in the four phase microstructure. In addition to PHI and a neodymium-rich phase, two new phases were found: an Nd1Cu1-type phase and a phase Nd30Fe65Cu5. The latter seems to play an important role in obtaining high coercivity.