Microstructural evolution of Fe 3B/Nd 2Fe 14B nanocomposite magnets microalloyed with Cu and Nb

Abstract

The microalloying effect of Cu and Nb on the microstructure and magnetic properties of an Fe 3B/Nd 2Fe 14B nanocomposite permanent magnet has been studied by transmission electron microscopy (TEM) and atom probe field ion microscopy (APFIM). Additions of Cu are effective in refining the nanocomposite microstructure and the temperature range of the heat treatment to optimize the 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 Nd 4.5Fe 75.8B 18.5Cu 0.2Nb 1 amorphous ribbon at 660°C for 6 min are B r=1.25 T, H cJ=273 kA/m and ( BH) max=125 kJ/m 3. The soft magnetic Fe 23B 6 phase coexists with the Fe 3B and Nd 2Fe 14B phases in the optimum 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 Fe 3B phase. The Nb atoms appear to induce the formation of the Fe 23B 6 phase when the remaining amorphous phase is crystallized.