Optimization of crystallization, microstructure and soft magnetic properties of Fe-B-Cu alloys by rapid cyclic annealing

Fe83.5B16.5-xCux (x = 0, 0.7, 1.2, 1.5) amorphous alloys were rapidly annealed under various cyclic numbers (C). The crystallization behavior and its effects on the microstructure and soft magnetic properties of nanocrystalline alloys have been investigated. It is found that the cyclic annealing is more effective to refine and uniform α-Fe grains by introducing multiple rapid heating than the non-cyclic annealing. The saturation magnetic flux density of the Fe83.5B15Cu1.5 nanocrystalline alloy increases from 1.79 T to 1.82 T and the coercivity decreases from 13.1 A/m to 7.5 A/m simultaneously when the cyclic numbers change from C = 1 to 6. Moreover, the rapid cyclic annealing with C = 6 enlarges the annealing temperature ranges for the Fe83.5B16.5 and Fe83.5B15Cu1.5 nanocrystalline alloys with low HC by ∼20 K compared to that with C = 1. The Mössbauer spectroscopy confirms that the rapid cyclic annealing can inhibit the aggregation of B atoms in the amorphous matrix, which is beneficial to enhance the magnetic interaction between α-Fe nanocrystals. However, when the cyclic numbers further rise to C = 10, the mean grain size of the Fe83.5B15Cu1.5 nanocrystalline alloy begins to increase, resulting in the deterioration of soft magnetic properties.