Temperature stability and corrosion behavior of sintered Nd-Dy-Fe-Co-TM-B magnets, TM:V,Mo (abstract)

By simultaneous additions of Co and V or of Co and Mo the temperature stability of sintered Nd-Fe-Al-B magnets can be improved.1--3 A partial substitution of Nd by Dy increases the coercivity by 1.4 kA/cm per wt. % Dy in the alloy, which results in strong coercivities at high temperatures. At 150 degree C, for instance, coercivities of about 9 kA/cm can be achieved. The magnetizing behavior is determined by nucleation of reversed domains. A complete magnetization requires a magnetizing field strength of about 25 kA/cm and does not depend on the coercive field strength. Although in Nd-Dy-Fe-Co-Mo-B magnets the Nd-rich Fe eutectic and the Nd1.1Fe4B4 boride are replaced by the Nd3Co compound and the Mo2FeB2 boride, respectively, the corrosion is similar to sintered Nd-Dy-Fe-B magnets. The corrosion rate at the 85 degree C--85% relative humidity test is much more determined by the surface treatment of the magnets