Magnetic properties, phase evolution and microstructure of directly quenched bulk Pr-Fe-B-Nb magnets

The magnetic properties, phase evolution and microstructure of directly quenched bulk Pr9.5Fe90.5-x-yNbxBy magnets have been studied. Proper Nb substitution for Fe at a high B concentration can greatly modify the phase constitution and refine the grain size from the micrometer scale to 50-150nm. Optimal magnetic properties, i.e. J(r)=0.57T, H-i(c) = 1296 kA m(-1) and (BH)(max) = 56.8 kJ m(-3), were achieved for Pr9.5Fe71.5Nb4B15. The high coercivity results from the large volume fraction of the 2:14:1 phase, fine grains and the appearance of a grain boundary phase in the magnet. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.