Crystallization kinetics of amorphous Nd3.6Pr5.4Fe83Co3B5 and preparation of α-Fe/Nd2Fe14B nanocomposite magnets by controlled melt-solidification technique

Abstract

The crystallization kinetics of amorphous Nd3.6Pr5.4Fe83Co3B5 and the preparation of α-Fe/Nd2Fe14 B nanocomposite magnets by controlled melt-solidification of Nd3.6Pr5.4Fe83Co3B5 was investigated by employing DTA, XRD, and TEM. The results show that a metastable intermediate phase Nd8Fe27B24 prior to α-Fe and Nd2Fe14B phases is crystallized as the amorphous Nd3.6Pr5.4Fe83Co3B5 is heated to 1 223 K. The crystallization activation energy of α-Fe and Nd8Fe27B24 phases is larger at the beginning stage of crystallization, and then it decreases with crystallized fraction x for the former and has little change when x is below 70% for the latter, which essentially results in an α-Fe/Nd2Fe14B microstructure with a relatively coarse grain size about 20–60 nm and a non-uniform distribution of grain size in the annealed alloy. The α-Fe/Nd2Fe14B nanocomposite magnets with a small average grain size about 14 nm and a quite uniform grain size distribution were prepared by controlled melt-solidification of Nd3.6Pr5.4Fe83Co3B5 at a wheel speed of 20 m · s−1 during melt-spinning. The magnets show a high maximum energy product of (BH)max=194 kJ · m−3, which is nearly twice of that of the nanocomposite magnets made by annealing the amorphous Nd3.6Pr5.4Fe83Co3B5 precursor alloy.