Improvement of magnetic properties, microstructure and magnetic structure of Fe73.5Cu1Nb3Si15.5B7 nanocrystalline alloys by two-step annealing process

Fe73.5Cu1Nb3Si15.5B7 nanocrystalline alloys were prepared by using conventional one-step annealing process and two-step annealing process. It was found that two-step annealing process can effectively improve soft magnetic properties and optimize microstructure. By separately controlling the formation of Cu clusters and further optimize the nanocrystalline structure, Bcc alpha-Fe with the grain size of 13 nm is formed in samples pretreated at 400 A degrees C and nanocrystallized at 560 A degrees C for 1 h. The samples exhibit excellent magnetic properties, such as lower coercive force of 0.7 A/m, higher initial permeability of 9.16 x 10(4), lower core loss of 0.18 W/kg at 0.7 T and 400 Hz, and 0.5 W/kg at 0.7 T and 1 kHz, respectively. The microstructure and magnetic structure evolution during different annealing processes were investigated. Correlation among the magnetic properties, magnetic structures and the microstructures changes in two different crystallization processes was studied systematically.