Atom probe studies of microstructural evolution in Nd–Fe–B-based nanocomposite magnets

The effect of Cu and Nb additions on the nanocrystallization process of Nd–Fe–B-based alloys are discussed based on recent atom probe results. Cu atom clusters are formed on annealing the amorphous precursors prior to the primary crystallization reaction in Nd–Fe–B-based amorphous alloys. These Cu clusters serve as heterogeneous nucleation sites for Fe3B primary crystals, thereby reducing the grain size of Fe3B/Nd2Fe14B nanocomposites. However, Cu addition does not give any influence on the grain size of α-Fe/Nd2Fe14B nanocomposite. In the latter case, Nb does play an essential role as the grain growth inhibitor. The reason for the variations of the effect of Cu and Nb in Nd–Fe–B-based amorphous alloys is discussed based on atom probe results.