Structural-Phase Changes of the Fe3C/Fe7C3/P-Phase/Cam Mechanocomposite at Heating.

The effect of the action of temperature on the structure and phase composition of an Fe₃C/Fe₇C₃/P-phase/C_am composite obtained by mechanosynthesis of Fe–75 at % C has been studied by the methods of X‑ray diffraction, Mössbauer spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. It is shown that the structural and phase changes at heating have a multistage character. In the temperature range 315–400°C crystallization of the paramagnetic P-phase with generation of Fe₃C and/or Fe₇C₃ occur. In the course of heating to higher temperatures, complete decomposition of carbide Fe₇C₃ (in the range 450–550°C) and partial decomposition of Fe₃C (at 600°C and above) are observed. After cooling from 800–1000°C the mechanocomposite consists of α-Fe, cementite Fe₃C, and graphite. The phase transformations are accompanied by the processes of composite oxidation with the formation of Fe₃O₄ oxide and its subsequent reduction. The P-phase is a disorded amorphous carbide Fe_{1 – x}C_x, which is characterized by magnetic ordering at the temperature of liquid nitrogen. [ABSTRACT FROM AUTHOR]