Coercivity and Grain Boundary Morphology in Nd–Fe–B Sintered Magnets

Abstract

The microstructure of Nd 15 Fe 77 B 8 sintered permanent magnets has been investigated under a 400 kV high-resolution transmission electron microscope. With particular concern about the microstructural changes in the Nd–Nd 2 Fe 14 B interfaces, the effects of isothermal heat treatment at 870 K have been studied for a more comprehensive understanding of the coercivity-microstructure relationship in the Nd–Fe–B sintered magnets. The atomic-scale steps along the grain boundary can be observed in as-sintered samples. The steps disappear after heat treatment, and very flat interfaces are formed. This atomic-scale alignment at the grain boundary, therefore, is one of the factors affecting the coercivity of Nd–Fe–B sintered magnets.