Arrangement of Atoms of Interstitial Impurity in the Crystal Lattice of Iron Austenite and Mechanism of their Diffusion Jump

• Published in: Metal science and heat treatment Vol. 65; no. 5-6; pp. 272 - 278
• Main Authors: Semenov, M. Yu, Kraposhin, V. S., Arestov, V., Pancho-Ramirez, V. A., Talis, A. L.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.09.2023; Springer Nature B.V
• Subjects: Adequacy; Austenite; Carbon; Cementite; Characterization and Evaluation of Materials; Chemistry and Materials Science; Classical Mechanics; Crystal lattices; Crystal structure; Crystallinity; Diamonds; Engineering Thermodynamics; Enthalpy; Heat and Mass Transfer; Interstitial impurities; Iron; Materials Science; Metallic Materials; Octahedrons; Tetrahedra; cementite; diffusion; activation enthalpy; dissolution of carbon; austenite; carbon cluster
• ISSN: 0026-0673; 1573-8973
• DOI: 10.1007/s11041-023-00925-y

A model of the arrangement of atoms of interstitial impurity in iron austenite is developed, according to which an introduction of an interstitial impurity atom causes transformation of a regular close packing (CP or FCC) composed of octahedrons and tetrahedrons into a cementite-type local prismatic packing by diagonal flipping. Carbon dissolves in the crystalline structure of iron austenite as a centered five-atom tetrahedral cluster, which represents a fragment of the carbon packing in the crystalline structure of diamond. The diffusion of the impurity atom is accompanied by a transformation into a prism in the neighboring lattice period, while the prismatic packing in the initial location of the impurity atom is reconstructed back into a conventional interstitial void. To check the adequacy of the proposed model, theoretical calculations of the activation enthalpy of carbon and nitrogen diffusion in austenite were performed, according to which the activation enthalpy values are 149 ± 20 and 155 ± 20 kJ/mol, respectively, which is fairly consistent with the experimental data reported in the literature (153 and 169 kJ/mol).