Hemijska Industrija (Jan 2012)
Influence of thermal treatment on structure and properties of Fe75Ni2Si8B13C2 amorphous alloy
Abstract
Iron-based amorphous alloys have been a focus of considerable scientific interest in recent years, both from fundamental and practical point of view. Comprehensive study of Fe75Ni2Si8B13C2 amorphous alloy investigated its thermal stability and thermally induced changes of the electrical, magnetic and mechanical properties and correlated them with microstructural changes. The alloy was investigated in 25-1000°C temperature range. Thermally induced structural transformations had been investigated using the DSC and the thermomagnetic measurements, revealing that the alloy exhibits the Curie temperature, glass transition, multi-step crystallization and recrystallization. The crystallization kinetics was determined, under non-isothermal conditions, to include three processes, corresponding to crystallization of α-Fe, Fe3B and Fe2B phases, respectively. Microstructural analysis using the XRD and the Mössbauer spectroscopy suggests that Fe3B acts as an intermediate in the formation of Fe2B. The microstructure was investigated on both the surface of the alloy ribbon and on the cross-section, using SEM to determine structural changes of the alloy after thermal treatment. Additionally, the XRD spectra were analyzed to determine the change in microstructural parameters of the alloy caused by the thermal treatment and the structural transformations. The Mössbauer spectroscopy was used to determine the distribution of iron atoms between the individual crystalline phases and the amorphous matrix. The functional properties were investigated using measurements of the magnetic susceptibility, electrical resistivity and microhardness and these results were correlated with changes in the microstructural parameters (average crystalline size, microstrain) and the phase composition. The measurements were performed, where possible, both during heating cycles to observe the change of these properties with temperature, and at room temperature, after individual heating cycles to determine the change in properties caused by annealing at different temperatures.
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