Effects of Si on the microstructure, soft magnetic properties and bendability of rapidly-annealed nanocrystalline Fe–Si–B–P–Cu alloy ribbons

The high Fe-content Fe–Si–B–P–Cu nanocrystalline alloys obtained by annealing the amorphous/nanocrystalline precursors are brittle and their magnetic properties are sensitive to the annealing process, which are disadvantageous for the practical applications of the alloys. In this study, the effects of Si on microstructure, soft magnetic properties and bendability of the rapidly-annealed Fe₈₃Si_xB_14−xP₂Cu₁ (x = 2–6 at%) nanocrystalline ribbons were investigated, and the properties of the nanocrystalline alloys with different Si contents were discussed in correlation to the structural evolution and element distribution. It was found that the partial substitution B with Si in the Fe–Si–B–P–Cu alloy system could promote the primary crystallization of α-Fe(Si) grains and suppress the precipitation of the hard-magnetic Fe-metalloid phase, thus widening the optimum annealing temperature (T_op) ranges for preparing the alloys with high saturation magnetization (B_s) and low coercivity (H_c). The alloys rapidly annealed at T_op for 30 s possess fine and uniform amorphous/α-Fe(Si) nanocrystalline structure, and exhibit good soft magnetic properties including high B_s of 1.80–1.85 T and low H_c of 5.2–7.2 A/m. Furthermore, the atom probe tomography (APT) results indicated that the distribution of Si in the nanocrystalline alloys is more uniform than that of B. The substitution of B with Si could decrease the compositional inhomogeneity, contributing to an improvement of bendability for the alloys with higher Si contents.