Preparation and properties of Fe@Si/Cu soft magnetic composites via in-situ transient liquid-phase sintering

Soft magnetic composites (SMCs) are promising for medium-to-high-frequency electromagnetic devices, but thermally unstable insulation layers hinder high-temperature densification and mechanical strength. In this work, SMCs were fabricated by mechanically ball milling Si and Cu powders onto surface-modified Fe powder to form a Si/Cu precursor coating, followed by compaction and transient liquid-phase sintering, aiming to develop an insulation layer suitable for high-temperature processing while promoting densification. The results show that a continuous insulation layer was successfully formed along the particle boundaries, mainly consisting of Fe₃Si and Si with a small amount of residual Cu. The optimum sample, prepared with 0.1 wt % Si/Cu at 1800 MPa and sintered at 1100 ℃ for 30 min, exhibited a B_s of 1.639 T, a maximum permeability of 1465, a coercivity of 179.6 A/m at 10 kA/m, a core loss of 1257 W/kg at 1 T and 400 Hz, and a transverse rupture strength of 73.5 MPa. Lower Si/Cu content and appropriate densification improved the magnetic performance, whereas excessive compaction pressure or sintering temperature impaired insulation integrity and increased core loss. These results indicate that transient liquid-phase sintering is an effective route for developing Fe-based SMCs with balanced magnetic and mechanical properties.