Influence of gadolinium content on magnetic property and oxidation mechanism of Fe-B-Nb-Gd metallic glass

Abstract

In this work, we use the rapid solidification technique to prepare five kinds of metallic glasses with different Gd content, and investigate in depth the influences of Gd content on the amorphous formation capability, thermal stability, and magnetic properties of (Fe₇₃B₂₂Nb₅)_{100–<i>x</i>}Gd_<i>x</i> (<i>x</i> = 0, 0.5, 1.0, 1.5, 2.0) alloys. By comparing the microstructural morphology and solute distribution of oxidation products before adding Gd and those after adding Gd, the amorphous oxidation mechanism is analyzed systematically. With the addition of Gd, the atomic size difference of the alloys exceeds 13%, and the configuration entropy increases from 7.27 kJ/(mol·K) to 9.44 kJ/(mol·K). The glass-forming ability of the alloy is significantly improved. The increase of Gd content can increase the glass transition temperature of the alloy to 864 K, and the undercooled liquid region can reach 73 K, significantly enhancing the thermal stability of the metallic glasses. The Gd limits the local anisotropy of the alloy and reduces the density of quasi-dislocation dipole defects. This can effectively reduce the pinning sites that hinder the rotation of magnetic domain walls, thereby improving the soft magnetic property. By comparing with the metallic glasses without Gd, only 2% (atomic percentage) Gd can reduce the coercivity by 8%. Moreover, the Gd makes the metallic glasses more sensitive to temperature variation in the oxidation process, and the temperature of the maximum oxidation rate is reduced by 15 K. However, their antioxidant performance does not deteriorate. The Gd atoms are influenced by binding energy and migrate to the surface, forming Gd-rich oxides. They fill surface defects and occupy a large part of the top space, leading to the structure becoming more compact near the surface. This structure reduces the channels for oxygen atoms to diffuse through the microstructure interface, which helps to improve antioxidant capability. This work provides a new approach for designing high performance Fe-based metallic glasses.