Microstructure Control of Nd-Fe-B Sintered Magnets by Two-Step Sintering

Abstract

Nd-Fe-B sintered magnets have been widely applied to a high performance permanent magnet. Nd-Fe-B sintered magnets are normally composed of Nd2Fe14B hard magnet phase as a matrix and Nd-rich phase on grain boundary. Many researchers have shown that the coercivity of Nd-Fe-B magnets was sensitive to microstructure. Therefore, modifying a sintering process has been an important method for homogeneous microstructure. In this study, Nd-Fe-B powder was fabricated by strip-casting and jet-milling. The powder was compacted under magnetic field. After that, the green compact was sintered at temperature between 950oC and 1050oC. Two-step process was employed for the sintering of Nd-Fe-B powder to obtain homogeneous grain size and control grain growth in bulk part. The microstructure was investigated by SEM and EPMA. Magnetic properties were measured by a B-H loop tracer.