Further studies of anisotropic hydrogen decrepitation in Nd16Fe76B8 sintered magnets

Nd16Fe76B8 sintered magnets were produced in aligned and unaligned forms. The magnets were prepared by isostatic pressing and finished with a centreless grinder; no coatings were applied and the samples were left unmagnetised. These magnets differed only in the orientation of the Nd2Fe14B grains. Magnets were exposed to hydrogen and the decrepitation behaviour observed. At room temperature the aligned samples were found to decrepitate exclusively from the ends of the rods, with the decrepitation taking place in two distinct stages. It was found that only elevated temperatures, electrolytic charging or application of special coatings could initiate decrepitation away from the ends of the aligned sample. X-ray diffraction data have provided evidence for very high uptakes of hydrogen in the case of electrolytic charging of the aligned sintered sample. As a result of these studies, anisotropic hydrogen decrepitation was attributed to differences in the activities of the ends and sides of the aligned samples.