Nanostructural evolution and improved magnetic performance of high saturation-induction Fe-based alloy via two-step combination crystallization

Abstract

Refining nanoparticles and reducing the average random anisotropy constant (<K1>) are crucial for improving the magnetic properties of nanocrystalline alloys with high magnetic saturation induction. This study systematically investigates the evolution of nanostructure and soft magnetic performance during two-step combination annealing, which includes stress annealing at a flash heating rate followed by normal-annealing. Stress-annealing at 500 °C prior to crystallization reduces the area of the FeB-like short-range-order structure and effectively increases the number density of Cu clusters that act as heterogeneous nucleation sites for α-Fe(Si) nanoparticles. Stress-annealing at 500 °C precipitates tiny (∼ 5 nm) Fe3Si nanoparticles (A6 structure) dispersed in an amorphous matrix, resulting in more Fe clusters in the amorphous matrix and superior crystallinity following the second-step annealing process. The two-step combination annealing process increases the magnetic saturation induction (by ∼3%) and permeability (by∼62%) at 10 kHz in comparison with those obtained for the one-step annealed sample. Moreover, we propose a model for nanostructural evolution and the observed correlation with magnetic performances.