Characterization of nanostructured Nd-Fe-Al permanent magnets

Rapidly solidified Nd60Fe30Al10 alloys produced in the form or ribbons or 1 and 5 mm diameter rods were examined using transmission electron microscopy (TEM), XRD, magnetic measurements, and Mossbauer spectroscopy. Strong dependence of the structure and magnetic properties on cooling rate was proved. The present work concerns the microstructure on the nanometric level (HRTEM) of the Nd60Fe30Al10 alloy. The specimens were in a form of 1 and 5 mm diameter rods and a rapidly solidified ribbons, prepared at a roll speed of 30 m/s. The high-resolution images shown large regions where the crystalline phase is present. The size of the crystallites depends on the quenching rate, which also influences the composition of the amorphous phase. In both, ribbon and rod samples, well defined boundaries of nanoscale grains of similar crystallographic orientations were observed. Basing on the observations in the dark field, we can say that the precipitates often form agglomerates whose components maintain the same crystallographic orientations. The studies revealed that the crystalline grains are frequently separated by a narrow layer of an intermediate phase. The EDS examinations reveal that the individual crystallites differ in their chemical composition, but in all nano-regions examined, all the components of the alloy occur simultaneously, in the proportions varying around the average composition of the alloy. (C) 2011 Elsevier B.V. All rights reserved.