Effect of Heat Treatment Time on the Characteristics of Coating Formed on Nanocrystalline Finemet Foils

In the present research, amorphous Fe۷۳.۵Si۱۳.۵B۹Nb۳Cu۱ Finemet foils, ۲۱-۲۶µm in thickness and ۵mm in width, were prepared by Planar Flow Casting (PFC) process. Wound cores of amorphous Finemet foils were simultaneously annealed and heat treated at ۵۴۰°C for ۶۰, ۱۲۰ and ۲۴۰ 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 diffractometry (XRD). The thickness and chemical composition of the insulating coating layer were studied by Field Emission Scanning Electron Microscopy (FE-SEM), Grazing Incidence XRD (GI-XRD) and Fourier Transform Infrared Spectroscopy (FTIR) techniques. The results show that the coating thickness formed on air and wheel surfaces of the foil was in the range of ۶۵-۳۱۰ nm 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 hysteresis loss and a significant increase in saturation induction and magnetic permeabilities.

Keywords:

Planar Flow Casting (PFC) Process , Nanocrystalline Foil , Finemet , Insulating Coating , Magnetic Core