MICROSTRUCTURE AND COMPOSITION IN RAPIDLY QUENCHED NDFEB-BASED HARD MAGNET ALLOYS

A detailed study of the microstructure and composition in hot-pressed (MQ-2) and die-upset (MQ-3) magnet alloys based on the Nd2Fe14B compos ition, utilizing high resolution and analytical transmission electron microscopy, is reported. The initial magnetic properties of the two sa mples show different behaviors, which are attributed to the difference in the anisotropy of the grain structure and the grain boundaries. Th e hot-pressed sample shows faceted grains of the 2-14-1 phase, while d ie-upset sample shows plate-like grains, together with larger equiaxed grains that contain a speckling of precipitates in the grain interior . The grain structure and composition remain rather similar in the two samples. The grain boundary phase averages similar to 1->10 nm in wid th. The thicker grain boundaries are Nd-rich, while the thinner grain boundaries in the hot-pressed sample exhibit an Fe-rich composition ne ar that of the NdFe3 phase. Nd-rich phases are found at the grain boun dary junctions of both samples, with the Nd:Fe ratio near 7:3 in the d ie-upset sample, and up to 3:2 in the hot-pressed sample. The signific ance of the microstructure and the grain boundary phases on the magnet ic behavior in the two samples is discussed. (C) 1996 American Institu te of Physics.