Microalloying effect of Cu and Nb on the microstructure and magnetic properties of Fe3B/Nd2Fe14B nanocomposite permanent magnets

This paper reports the microalloying effect of Cu and Nb on the microstructure and magnetic properties of a Fe3B/Nd2Fe14B nanocomposite permanent magnet. Optimum magnetic properties with B-r= 1.25 T, H-cJ = 273 kA/m and (BH)(max) =125 kJ/m(3) were obtained by annealing a melt-spun Nd4.5Fe75.8B18.5Cu0.2Nb1 amorphous ribbon at 660 degrees C for 6 min. Compared with a ternary Nd4.5Fe77B18.5 alloy, the grain size is much finer in the optimum microstructure of the Cu and Nb containing alloys, and the temperature range of the heat-treatment for obtaining optimum hard magnetic properties was significantly extended. The soft magnetic Fe23B6 phase coexists with Fe3B and Nd2Fe14B phases in the optimum microstructure, Three-dimensional atom probe (3DAP) analysis results have revealed that the finer microstructure is due to the formation of a high number density of Cu clusters, which promote the nucleation of the Fe3B phase. The Nb atoms appear to induce the formation of the Fe23B6 phase and stabilize it by partitioning into this phase.