The microstructure of sintered Sm(Co0.72Fe0.20Cu0.055Zr0.025)7.5 permanent magnet studied by atom probe Original Research Article

The microstructure and the compositions of the constituent phases in a sintered Sm(Co0.72Fe0.20Cu0.055Zr0.025)7.5 permanent magnet with different cooling processes have been investigated by transmission electron microscopy and the three-dimensional atom probe (3DAP) technique. The Cu concentration in the SmCo5 phase increases during slow cooling from 820 to 520 °C, having a wider concentration profile than that of Sm at cell boundaries. Enrichment of Cu at the triple junction of cell boundaries was also found. These results explain the substantial increase in coercivity during the slow cooling process. High resolution transmission electron microscopy and nano-beam electron diffraction analysis have confirmed that the Z-phase is Zr(Co, Fe)3, having the Be3Nb structure with a≈0.5 nm, c≈2.4 nm. In the Z-phase, Sm is almost completely replaced with Zr during slow cooling.