Characterization of Melt-Spun NdFeB Magnets Prepared by Explosive Compaction

Abstract

Explosive compaction processing is applied to prepare NdFeB magnets with melt-spun powders. It is found that shock consolidation processing could result in the magnetic properties, compressed strength and density of NdFeB bulk better than that of the conventional resin-bonded magnet. Scanning electron microscope (SEM) observation shows the melted areas and a mass of the micro-cracks in the close-packed particles resulted from the shock wave. The small Nd2Fe14B grains less than 100 nm, existing inside the powder particle without appreciable change of the original grain size, are revealed using the field emission scanning electron microscope (FE-SEM). The corresponding magnetic structure consisting of the very fine magnetic domains is also revealed with magnetic force microscopy (MFM). The results indicate that not only the microstructure but also the magnetic domain structure of the original powder are kept after explosive compaction. Although there are many micro-cracks in particles, the excellent magnetic properties are still obtained because the magnetic domain structure is so fine that seems not to be affected by the micro-cracks. The compression strength is also 40% higher than that of the polymer-bonded NdFeB magnet for its increased density.