HDDR PROCESSING OF DIRECT-REDUCED ND15FE77-XB8GAX POWDERS

Direct-reduced (DR) Nd15Fe77B8 and Nd15Fe77-xB8Gax powders with x = 0. 5, 1, 2 and 4, were treated by the HDDR process at various temperature s in order to optimise the processing parameters. The investigation of the magnetic properties was carried out on wax-bonded samples on a vi brating sample magnetometer (VSM) and polymer-bonded magnets on a perm eameter. The influence of Ga additions on the microstructure of direct -reduced Nd-Fe-B-type material was investigated by means of scanning e lectron microscopy (SEM) and transmission electron microscopy (TEM). I t was found that the direct-reduced Nd-Fe-B powders containing Ga addi tions show significantly increased intrinsic coercivities of up to 895 kAm(-1) compared to those of the ternary alloy or those of direct-red uced powders with Zr additions. The remanence appears to be, for Nd15F e77-xB8Ga2, with x = 0.5, 1 and 2, relatively constant over a processi ng temperature range of similar to 50 degrees C; with remanence values of up to 720 mT. The maximum remanence values decrease with increasin g Ga content. Under the conditions employed in these experiments, the HDDR treatment removes existing anisotropy in the as-received coarse g rain material, thus leading to predominantly isotropic behaviour.