Effects of Ribbon Thickness on Structure and Soft Magnetic Properties of a High-Cu-Content FeBCuNb Nanocrystalline Alloy

The effects of ribbon thickness (t) on the structure and magnetic properties of a Fe82.3B13Cu1.7Nb3 alloy in melt-spun and annealed states have been investigated. Increasing the t from 15 to 23 mu m changes the structure of the melt-spun ribbons from a single amorphous phase to a composite with dense alpha-Fe nanograins embedded in the amorphous matrix. The grain size (D alpha-Fe) of the alpha-Fe near the free surface of the ribbon is about 6.7 nm, and it gradually decreases along the cross section toward the wheel-contacted surface. Further increasing the t to 32 mu m coarsens the D alpha-Fe near the free surface to 15.2 nm and aggravates the D alpha-Fe ramp along the cross section. After annealing, the ribbon with t = 15 mu m has relatively large alpha-Fe grains with D alpha-Fe > 30 nm, while the thicker ribbons possessing the pre-existing nanograins form a finer nanostructure with D alpha-Fe < 16 nm. The structural uniformity of the ribbon with t = 23 mu m is better than that of the ribbon with t = 32 mu m. The annealed ribbons with t = 23 and 32 mu m possess superior soft magnetic properties to the ribbon with t = 15 mu m. The ribbon with t = 23 mu m exhibits a high saturation magnetic flux density of 1.68 T, low coercivity of 9.6 A/m, and high effective permeability at 1 kHz of 15,000. The ribbon with t = 32 mu m has a slightly larger coercivity due to the lower structural uniformity. The formation mechanism of the fine nanostructure for the ribbons with suitable t has been discussed in terms of the competitive growth effect among the pre-existing alpha-Fe nanograins.

Automated summary

The effects of ribbon thickness on the structure and magnetic properties of Fe82.3B13Cu1.7Nb3 alloy were investigated, revealing that increasing thickness led to different nanostructures and changes in magnetic properties.