The Local Structure Evolution Of FeBPCu(Si) Alloys During Relaxation And Crystallization And Its Effect On Magnetic Properties

In this study,the evolution of local structure and its effect on the magnetic properties during the structural relaxation and nanocrystallization are investigated to search for the beneficial structures in Fe amorphous alloys which can realize the effective improvement of magnetic properties.By controlling the annealing temperature or the holding time,the evolution of local structure in the Fe_80.8B₁₀P₈Cu_1.2 amorphous alloy during the structural relaxation and its effect on soft magnetic properties are characterized.Atomic regions in the amorphous structure tend to transform from Fe₃B-to FeB-like chemical short-range order with the annealing temperature increasing,where the exhausted Fe atoms gradually assemble together resulting in the increase of Fe clusters in the amorphous matrix.Meanwhile,CuP clusters gradually form which can refine nanograins during the nanocrystallization.When the annealing temperature reaches 660 K,the dramatic increase of inhomogeneity in the amorphous matrix contributes to the enhancement of magnetic anisotropy in the amorphous alloy and the coarsening of nanograins in the nanocrystalline alloy.Then,the similar evolution tendency of local structure is proved in the Fe_80.8B₁₀P₈Cu_1.2 amorphous alloy with the annealing time proceeding at 660 K.The content of CuP and Fe clusters in the Fe_80.8B₁₀P₈Cu_1.2amorphous matrix can be adjusted by two-step annealing to promote the nanocrystallization and refine the nanograins,which eventually enhances soft magnetic properties of the nanocrystalline alloy.Compared with the conventional annealing,the saturation magnetic flux density of the two step annealing increases from 1.66 T to 1.69 T,and the coercivity decreases from 15.4 A/m to 12.5 A/m.With Si superseding P in the Fe₈₁Si_xB₁₀P_8-xCu₁?x=0⁸?alloys,we study the effect of nonmagnetic element substitution on local structure,crystallization behavior and magnetic properties,especially the change in the density of heterogeneous nucleation sites.The moderate ratio of Si and P content can significantly strengthen the magnetic interaction and reduce the magnetic anisotropy which enhances magnetic properties of the FeSiBPCu melt spun alloy.At the early stage of crystallization,the density of nucleation sites in the Fe₈₁Si_xB₁₀P_8-xCu₁ amorphous matrix gradually decreases in the substitution of P by Si,which results in the coarsening of nanograins and the increase of the coercivity after the crystallization.Moreover,various site occupancies of Si are observed in the nanocrystallites causing the decrease in the average magnetic moment of nanograins,but the crystallinity increases contributing to the gradual improvement of saturation magnetic flux density after the nanocrystallization.When x reaches 6,the precipitated nanograins obviously coarsen,which causes soft magnetic properties of the nanocrystalline alloy conspicuously deteriorating.By comparison,the size and content of nanograins simultaneously achieve the optimum in the Fe₈₁Si₄B₁₀P₄Cu₁ nanocrystalline alloy and thus it possesses relatively outstanding magnetic properties.Finally,local structure in the Fe₈₁Si₄B₁₀P₄Cu₁ amorphous alloy is tuned by controlling the annealing temperature to further improve soft magnetic properties of the nanocrystalline alloy.It is found that the beneficial local structure of the Fe₈₁Si₄B₁₀P₄Cu₁ amorphous alloy is acquired by pre-annealing at 637 K for 5 min.The best saturation magnetic flux density and coercivity in the two-step annealing are 1.74 T and 10.7 A/m,respectively,superior to the conventional annealing where the corresponding values are 1.71 T and 12.6 A/m,respectively.