Role of P in Nanocrystallization of ${\rm Fe}_{85}{\rm Si}_{2}{\rm B}_{8}{\rm P}_{4}{\rm Cu}_{1}$

The role of P in the nanocrystallization of a newly developed Fe-based ${\rm Fe}_{85}{\rm Si}_{{2}}{\rm B}_{{8}}{\rm P}_{{4}}{\rm Cu}_{{1}}$ soft magnet (NANOMET) is investigated by differential scanning calorimetry (DSC), high-energy X-ray diffraction (XRD), and transmission electron microscope. DSC results show that addition of P into ${\rm Fe}_{85}{\rm Si}_{{2}}{\rm B}_{12}{\rm Cu}_{{1}}$ retards growth of $\alpha$ -Fe precipitates and also hinders the onset of crystallization of the residual amorphous phase. High-energy XRD results indicate that a lattice parameter of the precipitated $\alpha$ -Fe is 2.86652 ${\rm\AA}$ , which is very close to that of pure bcc Fe. A small amount of P and/or Si, however, are resolved in nanocrystalline Fe, which causes Curie temperature $(T_{{C}})$ of the precipitated $\alpha$ -Fe to decrease by $\Delta T_{{C}}=31~{\rm K}$ lower than the value of pure bcc Fe. With increase in the volume fraction of the precipitated $\alpha$ -Fe, the concentration of residual amorphous becomes close to that of the most stable amorphous alloy, i.e., ${\rm Fe}_{{76}}{\rm Si}_{{9}}{\rm B}_{{10}}{\rm P}_{{5}}$ when the volume fraction approaches to 40%. P in NANOMET contributes to hinder the formation of Fe-B(Si,P) compounds by stabilizing residual amorphous phase.