Microstructure of melt spun Nd-FeCoB magnets

In this paper we report results on microstructural characterization of melt spun Nd17Fe77B6 and Nd15(Fe1-xCox)77B8 ribbons using high resolution electron microscopy, X-ray microanalysis and microdiffraction. In general, the microstructure consists of the hard magnetic Nd2Fe14B phase and one or more grain boundary phases. In all these materials no Nd1.1 Fe4B4 phase was observed. The grain boundary phase in the Co-free samples appear mainly at multi-grain junctions and is a Nd-rich, crystalline (f.c.c.) phase, whereas the Co-containing specimens comprise two different f.c.c. grain boundary phases. The structural and microchemical data indicate that these are likely to be ferromagnetic and that they contain significantly less Nd than the grain boundary phase of the Co-free samples. The average matrix grain diameter is about 80 nm, but there are always some areas in every specimen where the grain diameter is very small (about 20 nm) or very large (more than 300 nm) causing differences in the size of the grain boundary phases both at the triple grain junctions and between the grains. © 1989.