The effect of cyclic heat-treatment to microsturcture and magnetic property on Nd-Fe-B sintered magnets.

Abstract

ln this study, the microstructure which is known to be a crucial factor for coercivity was studied by applying cyclic heat-treatment. Cyclic heat-treatment leads to homogeneous distribution of Nd-rich phase, non-magnetic phase, around Nd2Fe14B phases, hard-magnet phase. Cyclic heat-treatment also leads to the formation of continuous Nd-rich layers along the grain boundaries. The Nd-rich phase at grain boundary junction was observed by optical microscopy (OM) and scanning electron microscopy (SEM) equipped with an energy dispersive X-ray spectrometer (EDS). It is confirmed that the facet shape of Nd-rich phase and continuous grain boundaries between Nd2Fe14B phases with thickness of about 10nm were fabricated. Magnetic properties were measured with a B-H loop tracer after cyclic heat-treatment, and showed about 33.5kOe of coercivity at 2 cycle heat-treated sample.