STRUCTURE FEATURES OF THE Fe –Cu–Nb–Si–B BASED NANOCRYSTALLINE ALLOY RIBBON PRODUCED BY THE MELT SPINNING METHOD

Amorphous and nanocrystal magnetic soft Fe-based alloys are widely used for the shielding materials production, which are effective in the wide range of magnetic and electromagnetic fields. These alloys are obtained in ribbons by an ultra-quick quenching of the melt flow on the high-speed rotating refrigerator-disk. During the amorphous ribbons production process, melted in the high-frequency inductor metal is fed through the dye on the surface of the quenching disk, wherein the surface layers, contacted with the refrigerator-disk, of the forming amorphous ribbon are cooled quicker than the top ones, which are not in contact with the refrigerator-disk. As the result on the “contact” side of the ribbon the residual compression stresses can occur, wherein on the “free” side – the tension stresses. All these can lead to the structure anisotropy along the ribbon thickness, therefore also to the properties anisotropy during the further heat treatment. In the present paper, the results of the TEM structure analysis (planar geometry and transversal cut geometry) along the ribbon thickness of the AMAG200 alloy (Fe – Nb – Cu – Si – B system), obtained by the spinning method, are presented. The relation between the structure changes in the amorphous AMAG-200 alloy (Fe – Nb – Cu – Si – B system), which occurred during the process of the controlled crystallization, with the structure features of the amorphous ribbon, obtained by the ultra-quick quenching of the melt (with the cooling speed up to 106 K/s) is determined, explaining the structure anisotropy along the ribbon thickness. It is stated that the heat treatment under 530 °С forms high magnetic properties and lowers the destruction energy by the formation of the optimal amorphous-nanocrystallline structure in part of grains volume fraction and size. Using the SEM the fracture appearance analysis was performed, connected to the structure obtained during the ultra-quick quenching from the melt and after the heat treatment under 530  °С. It is stated that the fracture surface at the as-build state provide viscous type and after heat treatment-completely brittle type.