Effect of annealing on microstructural changes of Nd-rich phases and magnetic properties of Nd–Fe–B sintered magnet

Abstract

The microstructural changes of Nd-rich interface phases during postsintering annealing were investigated. A mixture of very fine (about 2–3 nm) crystallites of hexagonal h-Nd2O3, cubic Ia3¯-Nd2O3 (C-Nd2O3), and amorphous phases were observed at the interface phase in the as-sintered magnet and after the first postsintering annealing process. The transformation from h-Nd2O3 to C-Nd2O3 occurred during the second postsintering annealing process, and the resulting C-Nd2O3 has the proper crystallographic relation with the main phase. The reduced lattice mismatch between the (110) plane of C-Nd2O3 interface phase and the (001) or (100) plane of Nd–Fe–B main phase after the second postsintering annealing process is the primary reason for the enhancement in the magnetic properties.