Gradient Nanostructure, Diffusion Mechanisms, and Performance of Fe–Si (6.5 wt.%) Alloy Powders Prepared Using a Green and Controllable Method

To reduce carbon emissions associated with the traditional preparation of Fe–Si (6.5 wt.%) alloy powder, the main precursor of high-frequency soft magnetic composites, this study developed a green, controllable, and melt-free powder-preparation methodology enabled by defect-architecture engineering. Hydrogen-reduced iron powders are first subjected to surface mechanical attrition treatment (SMAT) and subsequently processed via a dual-stage heat-treatment protocol, comprising low-temperature Si infiltration at 565°C followed by homogenization at 900°C, to achieve rapid alloying and uniform silicon distribution. SMAT generated a gradient nanostructure through high-strain-rate deformation via dislocation multiplication and grain-boundary rearrangement, providing short-circuit diffusion paths that lowered the silicon infiltration temperature to 565°C. After homogenization at 900°C, silicon was evenly distributed throughout the prepared Fe–Si alloy powder. As proof of method, Fe–Si@boron nitride soft magnetic composites prepared from this material exhibited low power loss (201.5 kW/m 3 at 100 kHz and 50 mT), and high permeability retention (>80% under a 7.96 kA/m DC bias), outperforming mainstream commercial counterparts. Overall, this defect-enabled route offers an energy-efficient strategy for scalable low-temperature diffusion alloying of metal powders and for fabricating high-performance soft magnetic composites.