Carbonization of α-Fe upon mechanical alloying

• Published in: Physics of metals and metallography Vol. 115; no. 1; pp. 53 - 68
• Main Authors: Barinov, V. A., Tsurin, V. A., Kazantsev, V. A., Surikov, V. T.
• Format: Journal Article
• Language: English
• Published: Boston Springer US 2014; Springer
• Subjects: Analysis; Carbides; Carbon; Carbonization; Cementite; Chemistry and Materials Science; Decomposition; Diffusion; Hydrocarbons; Intermetallic compounds; Iron; Iron compounds; Materials Science; Metallic Materials; Phase Transformations; Phases; Powders; Solid solutions; Structure; Toluene; iron carbides; mechanosynthesis; iron-based solid solutions; hyperfine interaction parameters; magnetic susceptibility; toluene; Curie temperature
• ISSN: 0031-918X; 1555-6190
• DOI: 10.1134/S0031918X14010025

Methods of thermomagnetic analysis (TMA) and Mössbauer spectrometry (
57
Fe) have been used to study the processes of the carburizing of α-Fe under the conditions of mechanical milling in a medium of liquid hydrocarbons. It has been established that, under the chosen conditions of the mechanical synthesis of carbides, the process of carbonization at
T
< 375 K occurs through the decomposition of the deformation-induced martensite, i.e., the supersaturated bct solid solution α″-Fe(C) with the formation of transitional hcp ε and ε′ phases that precede the formation of cementite. The milling of the metallic iron in the toluene medium substantially enhances the catalytic capability of disperse powders of α-Fe in the process of conversion of cyclic structures of hydrocarbons into other chemical forms. The increase in the dispersity of the iron powder to a nanocrystalline state leads to an increase in the chemical activity of carbon and an increase in the rate of diffusion sufficient for the formation in the Fe-C mixture of both primary cementite (θ′) with an anomalously low Curie temperature
T
C
(θ′)(first stage) and secondary cementite (θ″) at the second stage of mechanosynthesis. The parameters of hyperfine interactions have been calculated for a number of synthesized carbides. It has been shown that the change in the carbon concentration in iron carbides is determined by the following inequality:
c
C
(θ′) >
c
C
(ε) >
c
C
(ε′). The boundary of the temperature stability of cementite has been established. The effect of the decomposition of the θ phase (Fe
3
C) upon thermal cycling θ ⇔ γ in the temperature range of 300 <
T
< 1075 K has been revealed. Based on the results obtained, a scheme of the sequence of phase transformations that occur in the Fe-C system under the conditions of low-temperature mechanosynthesis has been derived.