Heating rate dependence of coercivity and microstructure of Fe-B-P-Cu nanocrystalline soft magnetic materials

The nanocrystalline structure and soft magnetic properties of melt-spun Fe-B-P-Cu ribbons are largely influenced by heating rates for crystallization of amorphous precursors. In this study, we investigated the structure and soft magnetic properties of Fe84.8O4.9P9.5Cu0.8 (P-rich) and Fe84.8O10.9P3.5Cu0.8 (B-rich) melt-spun ribbons crystallized at two different heating rates, 0.67 K/s and 6.7 K/s, using transmission electron microscopy (TEM) and atom probe tomography (APT). The P-rich ribbon shows smaller coercivity regardless of the heating rates, while the B-rich ribbon shows large heating rate dependence of the coercivity. APT analyses have revealed that the size of Cu clusters in the P-rich nanocrystalline ribbon is larger than that in the B-rich nanocrystalline ribbon while their number densities are nearly the same. Also, the high heating rate led to a larger size and higher Cu concentration of the Cu clusters in both samples, indicating that the Cu clusters are effective as nuclei for alpha-Fe only when they are larger than a critical size. The solute partitioning behaviors between alpha-Fe and residual amorphous phase determined by APT analyses are consistent with the tie-lines between alpha-Fe and liquid phase in a calculated Fe-P-B ternary phase diagram. P was found to segregate at amorphous/alpha-Fe interface, suggesting the grain growth is controlled by the volume diffusion of P in the amorphous phase during their crystallization process. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The nanocrystalline structure and soft magnetic properties of melt-spun Fe-B-P-Cu ribbons are greatly influenced by the heating rates during crystallization of amorphous precursors. Higher heating rates lead to larger size and higher Cu concentration of the Cu clusters in both P-rich and B-rich ribbons. Solute partitioning behaviors between alpha-Fe and residual amorphous phase are consistent with the Fe-P-B ternary phase diagram, with P segregating at the amorphous/alpha-Fe interface during crystallization.