Microstructural evolution of Fe3B/Nd2Fe14B nanocomposite magnets microalloyed with Cu and Nb

The microalloying effect of Cu and Nb on the microstructure and magnetic pr operties of an Fe3B/Nd2Fe14B nanocomposite permanent magnet has been studie d by transmission electron microscopy (TEM) and atom probe field ion micros copy (APFIM). Additions of Cu are effective in refining the nanocomposite m icrostructure and the temperature range of the heat treatment to optimize t he hard magnetic properties is significantly extended compared with that of the ternary alloy. Combined addition of Cu and Nb is further effective in reducing the grain size. Optimum magnetic properties obtained by annealing a melt-spun Nd4.5Fe75.8B18.5Cu0.2Nb1 amorphous ribbon at 660 degrees C for 6 min are B-r = 1.25T, H-cJ = 273 kA/m and (BH)(max) = 125 kJ/m(3). The sof t magnetic Fe23B6 phase coexists with the Fe3B and Nd2Fe14B phases in the o ptimum microstructure of the Cu and Nb containing quinternary alloy. Three- dimensional atom probe (3DAP) results show that the finer microstructure is due to the formation of a high number density of Cu clusters prior to the crystallization reaction, which promote the nucleation of the Fe3B phase. T he Nb atoms appear to induce the formation of the Fe23B6 phase when the rem aining amorphous phase is crystallized. (C) 1999 Acta Metallurgica Inc. Pub lished by Elsevier Science Ltd. All rights reserved.