Microstructure and properties of nanocrystalline Fe–Zr–Nb–B soft magnetic alloys with low magnetostriction

We have investigated the microstructure–property relationship of nanocrystalline Fe85Zr1.2Nb5.8B8 and Fe85.5Zr2Nb4B8.5 soft magnetic alloys in order to understand the origin of drastic change in the permeability regardless of the zero magnetostriction in these two alloy compositions. Plan-view and cross-section transmission electron microscopy (TEM) observations showed strongly textured α-Fe particles on the free surface of the Fe85Zr1.2Nb5.8B8 alloy ribbon, while uniform nanocrystalline microstructure was observed in the Fe85.5Zr2Nb4B8.5 alloy ribbon. The high Zr content of the latter improves the glass forming ability, thereby suppressing the surface crystallization, resulting in higher permeability. By adding Cu in the Fe–Zr–Nb–B alloy, uniform nanocrystalline microstructure was obtained, from which superior soft magnetic properties with zero magnetostriction was achieved.