Calculation Of The Iron Properties At Polymorphic Phase Transition

Mahach N. Magomedov

Institute for geothermal problems and renewable energy, Branch of the Joint Institute of
High Temperatures of the Russian Academy of Sciences, 39-a Shamil str.,
Makhachkala, Republic of Dagestan, 367030, (RUSSIA)

PAGE NO: 066-077

ABSTRACT – DOI: https://dx.doi.org/10.47204/EMSR.4.1.2022.066-077

To calculate the properties of iron, an analytical method for calculating the properties of a crystal is used, which is based on the pair potential of the Mie–Lennard-Jones interatomic interaction. The parameters of the pairwise potential were determined both for the bcc and fcc phases of iron. Based on these parameters, 23 thermodynamic properties of iron at the temperature of the polymorphic bcc-fcc phase transition are calculated. Calculations have shown that properties such as the Gruneisen parameter, the coefficient of thermal expansion,
and the heat capacity practically do not change during the bcc-fcc transition. The elastic modulus, specific entropy, Poisson’s ratio, and specific surface energy change in the same way as the molar volume, i.e. within 1%. The Debye temperature and its pressure derivative decrease at the bcc-fcc transition in the same way as the distance between the centers of the nearest atoms increases, i.e. within 2-3%. Based on the analysis of experimental data known from the literature, it is shown that even relatively accurately measured parameters such as the coefficient of thermal expansion and elastic modulus are measured with an error exceeding the values of jumps in these parameters at the bcc-fcc transition. It is indicated that amorphization or nanostructuring of a certain portion of iron during the bcc-fcc transition can contribute to changes in the properties of iron during this phase transition. It is shown that in the fcc-Fe, the proportion of vacancies and delocalized atoms is greater than in the bcc-Fe.