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/Nd₂ Fe₁₄B nanocomposite permanent magnet. Optimum magnetic properties with B_r=1.25 T, H_cJ=273 kA/m and (BH) _max=125 kJ/m³ were obtained by annealing a melt-spun Nd_4.5Fe_75.8B_18.5Cu_0.2 Nb₁ amorphous ribbon at 660°C for 6 min. Compared with a ternary Nd_4.5Fe₇₇B_18.5 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