Improvement of magnetic properties for V-substituted Fe73.5Si13.5B9Cu1Nb3−xVx nanocrystalline alloys

The effects of V element on microstructural evolution and soft magnetic properties of Fe73.5Si13.5B9Cu1Nb3−xVx (x = 0, 0.5,1, 1.5 and 2, at.%) nanocrystalline alloys annealed at one-step and two-step state were investigated. As a result of an adequate addition of V, the microstructure and soft magnetic properties of the nanocrystalline alloys have greatly changed. The alloys with higher V content are prone to form large grain size nanocomposite structure with better thermal stability but slightly worsen soft magnetic properties. However, the strategy of two-step annealing technique effectively refines grain and thereby improves the soft magnetic properties of the alloys. The nanocrystalline alloy with V = 1.5 after two-step annealing exhibits combined excellent soft magnetic properties, including a lower coercivity (Hc= 0.89 A/m), enhanced saturation magnetization (Bs over 1.3 T), high effective permeability? µe = 26,400 at 1 kHz) and low core loss. The work shows that adopting a preheating procedure before the primary nanocrystallization stage, viz. to use two-step annealing technique instead of the routinely used one-step nanocrystallization stage,is an effective solution to the disadvantage of the decrease of Nb.