| Summary: | The effect of the dilution gas flow rate on inorganic oxide insulating layers can improve fluidised bed chemical vapour deposition (FBCVD) in Fe–Si/inorganic-oxide soft magnetic composites and obtain excellent magnetic properties. Herein, Fe–Si/SiO<sub>2</sub> composite particles coated via FBCVD and deposited at a 125–350 mL/min Ar-dilution gas flow rate were prepared and sintered into soft magnetic composites. Results demonstrate that SiO<sub>2</sub> deposited on the Fe–Si substrate particle surface changed from submicron SiO<sub>2</sub> clusters (125 mL/min) to an incomplete SiO<sub>2</sub> film, then to a complete SiO<sub>2</sub> film, and finally to a porous SiO<sub>2</sub> film as the Ar-dilution gas flow rate increased. SiO<sub>2</sub> layers began to transform from the amorphous to the beta-cristobalite state with a hexagonal crystal structure between 1149.45 K and 1280.75 K. However, the SiO<sub>2</sub> amorphous layers’ crystallisation did not affect the Fe–Si substrate particles’ crystal structure. With the increasing Ar-dilution gas flow rate, the saturation magnetisation of Fe–Si/SiO<sub>2</sub> soft magnetic composites initially decreased and then increased. The electrical resistivity increased before 150 mL/min, followed by an increase between 150 and 250 mL/min and then decreased, whereas the total core loss exhibited the opposite trend. These results show that magnetic performance can be promoted by selecting a suitable dilution flow rate.
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