TEM STUDY OF NANOCRYSTALLINE NDFEB

A detailed study is reported of the microstructure in a nanocrystallin e alloy, Nd4Fe78B18, consisting of a mixture of hard (Nd2Fe14B) and so ft (Fe3B) magnetic phases, utilizing conventional and analytical trans mission electron microscopy (TEM). The nanocrystalline microstructures were fabricated by annealing the melt-spun amorphous Nd4Fe78B18 ribbo ns by means of conventional (furnace) annealing techniques and also by the so-called flash-annealing process. Enhanced remanence and coerciv ity were reported previously for the flash-annealed alloys. Furnace-an nealed ribbons contained 20-30 nm equiaxed grains with Fe/Nd = 17-19.6 . Also observed were large (50-100 nm) equiaxed grains of alpha-Fe. Fo r flash-annealed ribbons, significant amounts of Nd2Fe23B3, a metastab le cubic phase, were observed, as well as a marked difference in the s econd phase morphology. For the flash-annealed ribbon whose hysteresis loop showed good coupling of the magnetic phases, a refined microstru cture was found and the large alpha-Fe grains were absent.