Core Losses and Soft Magnetic Properties of Nanocrystalline Fe-Zr-Nb-B Alloys with Zero-Magnetostriction

Abstract

AbstractThe structure, the soft magnetic properties and the core losses for Fe-Zr-Nb-B(-Cu) nanocrystalline alloys were investigated. It has been already reported that the typical ternary nanocrystalline Fe90Zr7B3 and Fe84Nb7B9 alloys exhibit good soft magnetic properties and a small negative and a small positive magnetostriction (λs), respectively. The soft magnetic properties of the nanocrystalline Fe84–90(Zr, Nb)7B3–9 quaternary alloys with mixed compositions of Fe90Zr7B3 and Fe84Nb7B9 cannot be improved whereas very small magnetostrictions are obtained. The quaternary alloys with 7 at% (Zr + Nb) have structures of an amorphous with α-Fe phases on the free and roll-contacted surfaces at an as-quenched state. The crystalline surface layers deteriorate the soft magnetic properties at a crystallized state. The high saturation magnetic induction of 1.64 T, the high permeability of 60,000 at 1 kHz and the very low core loss of 0.9 W/kg at 1.4 T and 50 Hz are obtained for the Fe85.5(Zr1/3Nb2/3)6B8.5 alloy containing 6 at% of (Zr + Nb) content with nearly zero-λs produced by crystallizing the single amorphous phase without the crystalline surface layers. The thermal stability of the core loss of the quaternary alloy is significantly higher than that of the Fe78Si9B13 amorphous alloy. The crystalline surface layers of the Fe84–90(Zr, Nb)7B3–9 quaternary alloys disappear by 1 at% Cu addition, which results in significant improvement of the soft magnetic properties at a crystallized state.