Effects of adding B element on amorphous forming ability, magnetic properties, and mechanical properties of FePBCCu alloy

Abstract

Fe-based amorphous alloys are widely used in power electronics fields such as transformers and reactors owing to their low coercivity, high permeability and low loss. However, the relatively low saturation magnetization (<em>B</em><sub>s</sub>) restricts their further application. Generally speaking, the adjustable magnetic Fe content as an effective strategy can ameliorate the magnetic properties, and the higher Fe content is, the much higher <em>B</em><sub>s</sub> can be obtained, but the decrease of the corresponding non-magnetic element content will lead to the drop of the amorphous forming ability of alloys, resulting in the deterioration of the magnetic softness and bending ductility of nanocrystalline alloys. To address this critical issue, in this work, based on the metal-metalloid hybridization, the FePBCCu amorphous ribbons with thickness of ~25 μm were prepared by the single-roller melt spinning method via 7 at.% B substitution for P, and the effects of B addition on the amorphous forming ability, magnetic properties and mechanical properties of ribbons were investigated. Thermodynamic behavior revealed that small size B addition can decline the structural heterogeneity of alloy and reduce the driving force of crystallization, thus effectively improving the thermal stability of the amorphous matrix. The melting and solidification curves showed that the B addition can promote alloy close to the eutectic composition and have a large degree of undercooling. As a result, the critical thickness of ribbons increased from ~21 μm for B-free alloy to ~30 μm for B-added alloy owing to the micro-alloying effect. The B addition increased the effective magnetic moment of magnetic atoms in alloy, resulting in the increase of the saturation magnetization. Furthermore, the results of nanoindentation tests showed that the reduced modulus value of the B-added alloy is larger and fluctuates in a smaller range than that of the B-free alloy, which is closely associated with the structural uniformity of the alloy.