PROPERTIES OF ND-FE-B MAGNET PROCESSED BY THE HYDROGEN DECREPITATION TECHNIQUE

The magnetic hysteresis loops and the temperature dependence of the coercive field are investigated for aligned sintered permanent magnets of ternary and Al‐substituted NdFeB alloys produced by a hydrogen decrepitation (HD) technique. The microstructure and the domain structure of magnets containing various fractions of HD powder are analysed. It is shown that the coercivity of the magnets is enhanced with increasing HD powder fraction, but the hardening of the coercivity is still determined by the nucleation mechanism, as in conventionally sintered magnets. The coercive field can be improved by fining the HD powder and by a perfect alignment of grains. The microstructure of the HD magnet shows that small permanent magnetic (pm) grains of Nd2Fe14B are well isolated by a nonmagnetic Nd‐rich phase or a (Fe, Al)2Nd phase. The coercivity of HD magnet is found to be very sensitive to the processing conditions. Copyright © 1990 WILEY‐VCH Verlag GmbH & Co. KGaA