Optimization of the structure and soft magnetic properties of a Fe87B13 nanocrystalline alloy by additions of Cu and Nb

Abstract The effects of Cu and Nb additions on the structure and magnetic properties of a Fe87B13 alloy in melt-spun and annealed states were investigated. Increase in Cu content from 1.0 to 1.7 at.% changes the melt-spun Fe87-xB13Cux alloy ribbons from a single amorphous phase to a composite of high-number-density nano-order α-Fe phase with an average grain size (Dα-Fe) of 12.1 nm dispersing in the amorphous matrix. The crystallized structure after annealing gets refined with increasing the Cu content, and a small Dα-Fe of 18.1 nm is obtained for the Fe85.3B13Cu1.7 alloy, which possesses a low coercivity (Hc) of 32.6 A/m and high saturation magnetic flux density (Bs) of 1.87 T. Minor addition of Nb reduces the Dα-Fe in melt-spun Fe85.3-yB13Cu1.7Nby alloys but not obviously lowers the number density, while 3 at.% Nb makes the formation of fully amorphous phase. The Dα-Fe in the crystallized alloys is decreased to 15.3 nm by alloying 2 at.% Nb, but increased to 31.4 nm with 3 at.% Nb. The Fe83.3B13Cu1.7Nb2 nanocrystalline alloy exhibits a lower Hc of 9.5 A/m combined with high Bs and effective permeability at 1 kHz of 1.75 T and 15000, respectively. The combination effects of competitive growth of the pre-existing nano-order α-Fe particles and Nb-inhibited atoms diffusion contributes to the refinement of the nanocrystalline structure.