반복 열처리한 Nd-Fe-B 소결 자석의 미세구조 제어 및 자성특성 평가

Abstract

Sintered Nd-Fe-B magnets have been widely used due to their excellent magnetic properties, especially for driving motors of hybrid and electric vehicles. The microstructure of Nd-Fe-B magnets strongly affects their magnetic properties, in particular the coercivity. Therefore, a post-sintering process like heat-treatment is required for improving the magnetic properties of Nd-Fe-B sintered magnets. In this study, cyclic heat treatment was performed at temperatures between 350oC and 450oC up to 16 cycles in order to control microstructures such as size and shape of the Nd-rich phase without grain growth of the Nd2Fe14B phase. The 2 cycles specimen at this temperature range showed more homogeneous microstructure which leads to higher coercivity of 35 kOe than as-sintered one.