Nanocrystallization and microstructure of (FeCo)_(73.5)Cu_1Nb_3Si_(13.5)B_9

Amorphous ribbons with 4 mm in width,30 μm in thickness were obtained by the melt spinning technique with nominal compositions(FeCo)73.5Cu1Nb3Si13.5B9,and the microstructure features were investigated by using TEM and XRD.The magnet annealed at 600 ℃ for 1 5 min shows the highest saturation magnetization of 1.30 T and low coercivity of 4.61 A/m.The soft magnetic properties of the alloy are deteriorated by increasing the annealing temperature to 700 ℃,saturation magnetization decreases to 1.02 T and coercivity increases to 1.95 kA/m.After annealing at 600 ℃ for 5 min,amorphous structure is kept with little α-Fe(Si) nanocrystallites embedded in it.The alloy annealed at 600 ℃ for 15 min is characterized mainly by the precipitation of randomly oriented α-Fe(Si) nanocrystals embedded in a residual amorphous matrix,and the grain size of α-Fe(Si) phase is about 15 nm.When amorphous alloy is annealed at 700 ℃ for 15 min,this nanocrystalline material consists of α-Fe(Si) phase,amorphous structure,and little Fe3B phase.The grain size of α-Fe(Si) phase increases to about 27.9 nm.The formation of Fe3B phase,the grain coarsening of α-Fe(Si) phase and the increase of crystal lattice constant decrease the soft magnetic properties of the magnets.