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 microstruct ure and magnetic properties of a Fe3B/Nd2Fe14B nanocomposite permanent magn et. 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 Nd4.5Fe75.8B18.5Cu 0.2Nb1 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 microstr ucture of the Cu and Nb containing alloys, and the temperature range of the heat-treatment for obtaining optimum hard magnetic properties was signific antly extended. The soft magnetic Fe23B6 phase coexists with Fe3B and Nd2Fe 14B phases in the optimum microstructure, Three-dimensional atom probe (3DA P) analysis results have revealed that the finer microstructure is due to t he formation of a high number density of Cu clusters, which promote the nuc leation of the Fe3B phase. The Nb atoms appear to induce the formation of t he Fe23B6 phase and stabilize it by partitioning into this phase.