Phase selection and characterization of Fe-based multi-component amorphous composite

Phase selection and amorphous transition play a significant role for controlling of the microstructure and properties of multi-component alloys. In the present work, the solidified microstructure evolution of Fe_52-xCo₂₀Ni_xB₁₉Si₅Nb₄ (x = 7,12, labeled as 7 Ni, 12 Ni) alloys were studied in a wide range of cooling rate, and the effect of phase constitutions on the magnetic and micromechanical properties were systematically investigated. The results show that the microstructures of the two master alloys are composed of α-Fe, γ-Fe, Fe₂B and Nb₆Co₁₆Si₇ phases. As the solid solubility increases, the content of the intermetallic Nb₆Co₁₆Si₇ phase decreases or even disappears, while the metastable Fe₃B phase and Fe₂₃B₆ phase grow competitively. With the rise of the cooling rate, there is a transition from eutectic microstructure to internal amorphous structure plus peripheral crystalline/amorphous composite, and then to complete amorphous state in the two alloys. For the 7 Ni alloy, when the droplet diameter reduces, the coercivity of the alloy decreases continuously. As the content of the main magnetic α-Fe phase decreases, the saturation magnetization of the alloy diminishes firstly, and then slightly heightens when it is completely amorphous. From the perspective of solid solubility, the difference in hardness of the α-Fe and Fe₂B phases with the undercooling is clarified. The hardness of the amorphous phase is slightly lower than that of the Fe₂B phase. Finally, the nanoindentation technique was used to explore the indentation size effect and creep behavior of amorphous composite under different peak loads and different loading rates. As the peak load decreases or the loading rate increases, the hardness and elastic modulus of the alloy enhance, while the maximum creep displacement, stress factor and activation volume all increase with the rise of the peak load.