Abstract
Abstract A detailed study is reported of the microstructure in a nanocrystalline alloy, Nd4Fe78B18, consisting of a mixture of hard (Nd2Fe14B) and soft (Fe3B) magnetic phases, utilizing conventional and analytical transmission electron microscopy (TEM). The nanocrystalline microstructures were fabricated by annealing the melt-spun amorphous Nd4Fe78B18 ribbons by means of conventional (furnace) annealing techniques and also by the so-called flash-annealing process. Enhanced remanence and coercivity were reported previously for the flash-annealed alloys. Furnace-annealed ribbons contained 20–30 nm equiaxed grains with Fe/Nd = 17–19.6. Also observed were large (50–100 nm) equiaxed grains of α-Fe. For flash-annealed ribbons, significant amounts of Nd2Fe23B3, a metastable cubic phase, were observed, as well as a marked difference in the second phase morphology. For the flash-annealed ribbon whose hysteresis loop showed good coupling of the magnetic phases, a refined microstructure was found and the large α-Fe grains were absent.
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