Effect of Cu additions on the magnetic properties and microstructure of FeCoNbB nanocrystalline alloy

The influence of Cu content and the annealing conditions in the (Fe0.5Co0.5)85−xNb7B8Cux (x=0.5, 1.0, 1.5) soft magnetic alloys on the magnetic properties and microstructure were investigated. The additions of Cu lower the primary and secondary crystallization temperatures and the α→γ phase transformation temperature of the FeCoNbB alloys. The (Fe0.5Co0.5)84Nb7B8Cu1 alloy annealed at 873 K for 3.6 ks, in which α-(Fe, Co) nanocrystalline phase with diameter of 5 nm precipitated from the amorphous matrix, shows the best soft magnetic properties. The resulting (Fe0.5Co0.5)84Nb7B8Cu1 nanocrystalline alloy exhibits a high saturation flux density of 1.88 T, low coercivity of 42 A/m, very high Curie temperature of 1240 K, as well as low core loss of 770 W/kg at 10 kHz under maximum magnetization of 1 T.