Revealing the effect of rapid annealing on nano-crystallization behavior and soft magnetic properties of Fe–Co–B amorphous alloy

Rapid annealing (RA), or the application of a high temperature for a short duration, is an efficient strategy to promote the nano-crystallization of Fe-based amorphous alloys and improve their soft magnetic properties. Herein, the ternary Fe–Co–B amorphous alloy is investigated as a typical system to reveal the effect of RA on crystallization behavior and soft magnetic properties. It is found that the large superheating generated during RA significantly increases the homogenous nucleation rate of nanocrystals, while the short duration greatly inhibits the growth kinetics, yielding fine and dense nanograins in the amorphous matrix. The Fe–Co–B alloy shows optimized properties of low coercivity (5.6 A/m) and high saturation magnetization (1.87 T) after RA at 813 K for 3 s. In contrast, all superheating and long duration used in conventional annealing produce large and sparse grains with single crystal morphology and large coercivity above 30 A/m. This work reveals the thermodynamic and kinetic effects of RA on the nano-crystallization behavior of Fe-based amorphous alloys, showing that the RA treatment (high annealing temperature and short annealing time) can induce in-situ homogeneous nucleation and growth, which may help guide the design of Cu-free amorphous/nanocrystalline alloys with desirable soft magnetic properties.