Development of Insulation Nano-coating on Nanocrystalline FINEMET Foils

In the present research¡ amorphous Fe73.5Si13.5B9Cu1Nb3 FINEMET foils¡ 21 μm in thickness and 5 mm in width¡ were prepared by planar flow casting (PFC) process. Wound cores of amorphous FINEMET foils were simultaneously annealed and heat treated at 540°C for 60 minutes in steam and air flow to form oxide insulating coating layer on both surfaces of the foils. The structure of nanocrystalline foils was examined by X-ray diffraction and transmission electron microscopy (TEM). The thickness and chemical composition of the insulating coating layer were studied by FE-SEM¡ GI-XRD and FTIR techniques. The results show that the coating thickness formed on air and wheel surfaces of the foil was 65 and 145 nm¡ respectively¡ and these thin coating layers contain a mixture of iron¡ silicon¡ boron and niobium oxides. The study of magnetic properties in amorphous and nanocrystalline states revealed that nanocrystalline cores have superior soft magnetic properties compared with the amorphous ones. In other words¡ the heat treatment gives rise to a decrease in coercivity and a significant increase in saturation induction and magnetic permeabilities.