Study of Structural Kinetics in the Effect of Partly Substitution of Fe by Co in FINEMET

Abstract

This thesis is based on the experimental investigation of nanocrystalline formation partly substitution Fe by Co in FINEMET with composition (Fe0.9 Co0.1)73.5Cu1Nb3Si13.5B9 alloy in the amorphous and annealed states. The sample has been prepared from high purity in gradients by rapid solidification technique using a method spinning technique and their amorphous nature has been confirmed by X-ray diffraction (XRD). The crystallization kinetics and the nanocrystal formation have been studied by differential thermal analysis (DTA) and XRD. Magnetization measurements have been carried out using vibrating sample magnetometer (VSM). The alloy has been annealed in a controlled way in the temperature range of 400 - 650 o C for constant annealing time one hour. The kinetics of primary crystallization α- FeCo(Si) phase and secondary crystallization Fe2B phase in composition is studied as affected DTA and confirmed by XRD. The sample annealed at 450oC at constant annealing time is almost unchanged is still lower than DTA scan that of primary crystallization phase but the same condition sample annealed at 600oC completely diffused primary crystallization α-FeCo(Si) phase has already vanish. Thermal analysis experiment and from the obtained data activation energy of α-FeCo(Si) is 4.1eV and Fe2B is 6.31eV. In the optimized annealing condition the grain size has been obtained in the range of 12 - 15 nm. The peak shifts indicate the change of the values of Si-content of nanograins and therefore, the change of the values of lattice parameter of nanograins. Saturation magnetization is maximum value is observed annealed at 6000C. The MS initially decreases with increasing annealing temperature and again increase MS further decrease with increase annealing temperature may be connected with the enrichment of the residual amorphous phase with Nb that weakens the coupling between ferromagnetic nanograins. Lower applied field suffices to produce saturation the nanocrystalline material is said to be magnetically soft.