Effect of magnetic field-assisted melt-spinning on the crystallization behavior and soft magnetic properties of Fe85.25B11.25P2Cu1.5 nanocrystalline alloy with high Fe and Cu contents

This work examines the effects of magnetic field-assisted melt-spinning on the precursor solidified structure, glass forming ability (GFA), nanocrystallization behavior, and soft magnetic properties (SMPs) of high Fe and Cu contents Fe85.25B11.25P2Cu1.5 nanocrystalline alloy (NA). Applying a moderate magnetic field (120–180 mT) during melt-spinning enhances GFA, refines grain size, and increases the density of pre-existing α-Fe crystals. However, a stronger magnetic field (240 mT) deteriorates GFA and forms coarse α-Fe grains. The refined pre-existing α-Fe crystals promote competitive growth during annealing, leading to superior SMPs. The alloy spun under a 180 mT field exhibits high-density α-Fe crystals (7.1 × 1022 m−3) with a small grain size of 10.5 nm. After annealing at 360°C for 60 minutes, the alloy exhibits fine α-Fe grains (23.1 nm) and excellent SMPs, including a high saturation magnetization of 1.85 T, low coercivity of 7.7 A/m, and high effective permeability of 10310 at 1 kHz. It is suggested that the appropriate magnetic field strength (120–180 mT) increases the viscosity of the molten alloy, promoting uniformity and inhibiting the formation of short-range ordered clusters, thus enhancing GFA. Conversely, excessive magnetic field strength (240 mT) induces eddy currents and Joule heating, leading to decreased GFA. The present study demonstrates that the magnetic field-assisted melt-spinning process is an effective method for producing high Fe and Cu contents Fe-based NAs with excellent SMPs.