Laws of thermally induced formation of phases in α-Fe with a titanium coating upon isochronous annealings

Abstract

Mossbauer spectroscopy and X-ray diffraction were used to study thermally induced processes of diffusion and phase transformations in nonequilibrium layered systems Fe (10 μm)-Ti (2 μm) and Fe0.966Ti0.034 (10 μm)-Ti (2 μm) upon isochronous annealing. The relative concentrations of phases have been determined and the sequence of phase transformations in the near-surface layers and in the bulk of samples have been established. It has been shown that the interdiffusion of components results in the formation of intermetallic compounds FeTi and Fe2Ti in the contact layer between the coating and the substrate. Titanium diffusing into the matrix of the substrate forms a solid solution on the basis of α-Fe. The kinetics of phase formation in α-Fe and in the Fe0.966Ti0.034 alloy with a titanium coating occurs by the same mechanism without fundamental differences; however, the process of the formation of phases in the alloy occurs at higher temperatures. The difference is only in the phase relationship at different stages of annealing. A correlated change in the average value and dispersion of the distribution function of the hyperfine magnetic field at the 57Fe nuclei in the α-Fe(Ti) solid solution with a change in the impurity concentration has been found. A method has been suggested for determining the concentration of substitutional impurity in the α-Fe solid solution from the average value of the hyperfine magnetic field \( \bar H_n \) at 57Fe nuclei. In the process of sequential thermal anneals, both systems remain layered and consist of the solid solution of Ti in α-Fe with the limiting concentration on the substrate side, and of an intermetallic compound Fe2 + xTi1 − x enriched in iron on the coating side.