Coercivity Enhancement of Nd-Fe-B Sintered Magnets by Two-Step Sintering

Abstract

Nd-Fe-B sintered magnets are normally composed of Nd2Fe14B hard magnet phase as matrix and Nd-rich phase on grain boundary. Many researchers have shown that the coercivity of Nd-Fe-B magnets was sensitive to microstructure, such as the grain boundary phases and grain size, etc. Therefore, modifying a sintering process has been an important method for better homogeneous microstructure. In this study, Nd-Fe-B powder was compacted under magnetic field of 20kOe. After that, the green compact was sintered at 950°C for 4h as firststep and second-step sintering was performed as 1050°C. The microstructure was investigated by TEM and EPMA. Magnetic properties were measured by a B-H tracer. Densification over 99% could be obtained by the two-step sintering of Nd-Fe-B powder under 6μm in Nd2Fe14B phase and the Nd-rich phase was homogeneously distributed around Nd2Fe14B phases. Moreover, the two-step sintering process led to uniform grain size distribution which had the improved magnetic properties. This research was supported by a grant from the Fundamental R&D Program for Core Technology of Materials funded by the Ministry of Knowledge Economy, Republic of Korea.