Changes in the Properties of Iron during BCC–FCC Phase Transition

Abstract

The thermodynamic properties of bcc and fcc iron phases are calculated at the temperature of the polymorphic bcc–fcc phase transition using the method of calculating properties of a crystal developed before on the base of the Mie–Lenard-Jones pairwise potential. 23 properties of iron and their changes during the bcc–fcc transition have been calculated. The calculations show that the properties, such as: the Gruneisen parameter, the thermal expansion coefficient, and the specific heat are only slightly changed during the bcc–fcc transition. The modulus of elasticity, the specific entropy, the Poisson ratio, and the specific surface energy are changed as well as the molar volume, i.e., within the limit of 1%. The Debye temperature and its pressure derivative decrease during the bcc–fcc transition in the same manner as the distance between the centers of the nearest atoms, i.e., within 2–3%. The analysis of the available experimental data shows that even comparatively correctly measured parameters, such as the thermal expansion coefficient and the modulus of elasticity, are measured with an error higher than the jumps of these parameters during the bcc–fcc transition. It is shown that amorphization or the nanostructurization of a certain iron fraction during the bcc–fcc transition is indicated can contribute to the changes in the iron properties during this phase tr-ansition.