Compositional and Process Effects on Structures and Properties of Fe-Nd-B-Based Ribbons and Magnets Produced by the Melt Spinning Route

The effects of alloy composition and of process variables such as roll material and velocity, ribbon thickness, annealing temperature and pressing conditions on the microstructure and magnetic properties of chill-block melt spun FeNdB-based ribbons and of magnets derived by hot-pressing the ribbons have been studied. Measurements by X-ray diffraction line broadening analysis indicate that a very small grain size (typically 30-80nm) plays a major role in promoting high coercivity iHc and energy product (BH)Max but they also suggest that other, less identifiable, factors also play a role. Substitution of Fe by Co leads to generally improved properties at elevated temperatures for hot pressed magnets as well as for the as-spun ribbon. Small additions of niobium and of silicon can lead to substantial improvements in coercivity and to remanence respectively, although the effect of the silicon appears to be particularly sensitive to the melt spinning parameters. The morphology of the microcrystallites is also, correspondingly, changed markedly by the silicon additions but the role of this in the enhancement of energy product requires further clarification.