HYDROGENATION DISPROPORTIONATION DESORPTION AND RECOMBINATION (HDDR) STUDIES ON DIRECT-REDUCED ND15FE77-XB8GAX POWDERS

Direct-reduced Nd-Fe-B powders with additions of 1.0% and 2.0% Ga were treated by the HDDR process at temperatures between 770 degrees C and 900 degrees C in order to optimise the processing parameters. The mic rostructures of the powders were investigated by scanning electron mic roscopy (SEM) on rotary forged Al bonded samples. The investigation of the magnetic properties was carried out on wax-bonded samples on a vi brating sample magnetometer (VSM). It was found that the direct-reduce d Nd-Fe-B powders containing Ga additions show significantly increased intrinsic coercivities of up to 895 kA/m compared to those of the ter nary alloy or those of powders with Zr additions [1]. The remanence ap pears to be, for both Nd15Fe76B8Ga1 and Nd15Fe75B8Ga2, relatively cons tant over a processing temperature range of similar to 50 degrees C wi th Nd15Fe76B8Ga1 exhibiting higher values of up to 680 mT. The disprop ortionation time has a significant influence on the magnetic propertie s of the material, higher processing temperatures requiring shorter ti mes in the disproportionated state, lower temperatures longer times. U nder the conditions employed in these experiments, the HDDR treatment removes existing anisotropy in the as-received coarse grain material, thus leading to predominantly isotropic behaviour.