Nd-Fe-B permanent magnets fabricated by low temperature sintering process

Abstract

Fabrication of 13Nd-2Dy-6B-bal. Fe (at.%) sintered magnets by low temperature sintering was demonstrated, focusing on grain size control. A magnet with a density higher than 99% was successfully obtained by sintering a Nd-Fe-B powder compact at 970 degrees C for 20 h. The average grain size of the magnet was 5.5 mu m, which was similar to that of the initial powder size (5 mu m). Compared with a conventionally sintered specimen (1070 degrees C/4 h), the coercivity of the magnet increased from 1672 kA/m to 1823 kA/m upon low temperature sintering. Consequently, the low temperature sintering process enabled us to suppress grain growth and to distribute the grains more uniformly, which resulted in improved magnetic properties, in particular improved intrinsic coercivity. The grain-size reduction through the low temperature sintering was explained by analyzing microstructures in relation to sintering behavior.