Three-dimensional atom probe study of Fe-B-based nanocrystalline soft magnetic materials

Solute clustering and partitioning in new Fe-B-based soft magnetic materials with high saturation magnetic flux density (B-s), (Fe0.85B0.15)(100-x)Cu-x (x = 0.0, 1.0, and 1.5) and Fe82.65Cu1.35SiyB16-y (y = 0.0, 2.0, and 5.0) melt-spun alloys, were investigated by three-dimensional atom probe and transmission electron microscopy. Although Cu clusters form after annealing in all the samples, it was found that only the clusters of 4-6 nm can serve as heterogeneous nucleation sites for alpha-Fe. While annealing the Si-free alloys at 410 degrees C led to the precipitation of Fe3B, only alpha-Fe nanocrystals were observed in the Si-containing alloys. Lorenz TEM observation indicated the Fe3B particles pin magnetic domain walls. The Fe82.65Cu1.35SiyB16-y alloy with y = 2.0 crystallized by annealing at 400 degrees C exhibited optimal nanocrsytal/amorphous microstructure without the precipitation of Fe3B, which led to the lowest coercivity while keeping a high B-s similar to 1.85 T. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.