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Alloying elements play an important role in adjusting the magnetic and thermal properties of Fe-based amorphous alloys. In this work, the effect of Mo addition on the thermal stability, structural evolution, and magnetic properties of Fe76Si9B10P5 metallic glass was studied. The study revealed that the substitution of a small amount of Mo (1 at.%) for Si enhances the glass-forming ability (GFA) but reduces the thermal stability of the alloy, causing a reduction of the supercooled liquid region. Substitution of up to 3 at.% Mo for Si lowers the Curie temperature from 677 to 550 K and the saturation magnetization drops from 160 to 138 Am2/kg. The structural evolution was evaluated by annealing the glassy samples at different temperatures, revealing that the crystallization proceeds in multiple steps, beginning with the formation of different iron borides (FeB, Fe2B, FeB2 and Fe23B6) followed by transformation to a mixture of more stable phases.

In the present study, FeSiBP and FeCoSiBP ribbons with a fully amorphous structure were made by melt spinning technique. A detailed analysis of the isochronal crystallization behavior is presented in this paper. The influence of cobalt on the crystallization kinetics of the alloys was studied under isochronal conditions using differential scanning calorimetry (DSC). Apparent and local activation energy values were determined by Kissinger, Ozawa and Kissinger-Akahira-Sunose (KAS) methods. The results indicate that appropriate amounts of cobalt can significantly enhance the thermal stability of Fe-based alloys, through an increase in nucleation activation energy from 538kJ/mol to 701kJ/mol, obtained by Kissinger method. Furthermore, with the method proposed by Matusita, it was possible to obtain global values for the Avrami exponent, noting that from a general perspective, Co changes the mechanism from diffusion controlled to interface controlled. This leads to the conclusion that the crystallization process is complex and takes place in more than one stage. Therefore, the determination of nucleation mechanisms and dimensional growth is difficult due to the inapplicability of the Johnson-Melh-Avrami (JMA) model. As such, a study under isothermal conditions is suggested, in order to achieve a full understanding of the mechanisms involved.

In the current work, a new variation of the FeSiBPCu system with good glass forming ability and soft magnetic properties was developed and investigated. The effect of copper addition on the FeSiBP base alloy was studied in the system (Fe0.77Si0.08B0.1P0.05)100-xCux with x = 0, 0.25, 0.5, 0.75 and 1.0 at%. Microstructural evolution upon the annealing process was evaluated by XRD and TEM, revealing the formation of α-Fe(Si), Fe2B and Fe3(B,P) crystalline phases. VSM allowed to determine that the combination of chemical composition and microstructure with the best soft magnetic properties after the annealing corresponds with the alloy with 0.75% Cu. In addition, activation energy for glass transition and the first crystallization event were calculated using the Kissinger method. The research findings demonstrated that maintaining the relationship between the main elements, it is possible to keep the good glass forming ability with the possibility of developing a nanocrystalline structure with soft magnetic performance. Graphical abstract