Cyclic heat treatment of sintered Nd-Fe-B magnet

Abstract

Sintered Nd-Fe-B magnets have been wildly used due to their excellent magnetic properties. However, the inhomogeneous microstructure of Nd-Fe-B magnet is an important factor limiting their magnetic property. Therefore, modifying a post-sintering process, such as heat treatment, has been important method for better homogeneous microstructure of the sintered Nd-Fe-B magnets. In this study, Nd-Fe-B magnet was fabricated by compaction in a magnetic field and sintering at 1100oC with Nd-Fe-B powder synthesized by strip-casting and jet milling. To modulate size and shape of Ndrich phase without growth of Nd2Fe14B phase, cyclic heat treatment was performed at temperature from 500oC to 700oC up to 32 cycles. The microstructure of heat treated sample was observed by optical microscopy and distribution of Nd-rich phase was measured using an Image Analyzer. Magnetic properties were analyzed by B-H curve analyzer and discussed relating with Nd-rich phase distribution.