Morphological peculiarities of R–Fe–B (R = Nd, Pr) alloys formed upon solidification by strip-casting

Abstract

X-ray diffraction analysis, scanning electron microscopy, and atomic force microscopy are used to study the phase composition, texture, and peculiarities of the morphology of R-Fe-B (R = Nd, Pr, Dy) alloys prepared by strip-casting technology. Along with the traditional structural components of the alloys, namely, areas characterized by randomly oriented fine grains of the main magnetic phase with the Nd2Fe14B-type structure (which are formed near the contact surface of flakes) and coarse extended textured grains of the phase (in the volume of flakes), wide areas characterized by uniform distribution of rare-earth metal-rich phase with a period of 2-4 mu m were also found. The formation of these areas takes place in the absence of coarse dendritic crystallites and, according to the suggested mechanism, is related to the solidification of the melt under conditions of its motion upon quenching on a cooled cylindrical surface. Data indicating the melt twisting upon solidification, which favors the formation of the structure with the aforementioned distribution of intergranular phase, are reported. The data obtained are discussed from the viewpoint of their practical utility for the improvement of the structure of alloys prepared by strip-casting and powders for manufacturing Nd-Fe-B permanent magnets.