Structural Evolution In Fe-Si Binary Alloy Under Far From Equilibrium Conditions And β-FeSi₂ Phase Formation

Under various conditions, such as high pressure, free falling, and ion beam sputtering, the structural evolution in Fe-Si binary alloy under far from equilibrium conditions and the β-FeSi₂ phase formation have been investigated. Solidification behaviors of the Fe-66.7at.%Si alloy under high pressure and during free falling were investigated. Different from the eutectic structure of the Fe-66.7at.%Si alloy solidified at ambient pressure, the microstructures of the alloy solidified at high pressures are composed of the dendritic primary phase and the anomalous eutectic. The significant changes in microstructure result from the change of phase diagram and the solute atom diffusion induced by high pressure. By introducing the pressure parameter, the correctional composition undercooling criterion was attained. Formation mechanism of the dendritic primary phase under high pressure was analyzed according to the correctional criterion. Containless solidification of the Fe-66.7at.%Si alloy was achieved in a 3 m drop tube. With decreasing droplet diameter, the growth mode of the primary phase α changes from faceted to nonfaceted growth and the eutectic changes from needle-like to anomalous eutectic. At the different sites of the droplet with the diameter of 0.2 mm, the same growth mode transition occurs. The different cooling rates and undercooling levels are responsible for the morphology changes. β-FeSi₂ single crystals were prepared by chemical vapor transport technique at substrate temperature 1023 K and source FeSi₂ temperature 1323 K. Influences of the temperature distribution and the carrier gas pressure on crystal growth were investigated. Different kinds of iron silicides were prepared at different Si(111) substrate temperatures by ion beam sputtering with an iron target. The β-FeSi₂ film with the thickness of 500 nm was obtained when the Si(111) substrate was heated to 973 K. The β-FeSi₂ film obtained was locally epitaxial and the interface between the film and the substrate was sharp. Monophase β-FeSi₂ films 360 nm and 850 nm in thickness were also successfully prepared by post-annealing 4-period and 10-period [20 nm Fe/64 nm Si] multilayers at 973 K for 60 minutes. The structural properties and interdiffusion of Fe/Si multilayers were investigated by in-situ X-ray diffraction method. Diffusivities at low temperature(573K-623K) can be described as: D_L (T )= 4.53×10_-22 exp(-0.16eV/K_BT) [m²/s]...