Papers by Author: Andriy Ostapovets

Abstract: Stability of the crystal structure is determined by the competition between attractive and repulsive interatomic forces. Using many-body exponential potentials it can be shown that the bcc structure corresponding to austenitic phases is more stable for low values of the q-parameter characterising the attractive forces for a fixed value of the p-parameter describing the repulsive forces. The structural stability can be changed with the acting pressure that may alter the martensitic transformations from the bcc-austenite to a close-packed structure. The effect of pressure is examined in a generic model employing many-body potentials and the results are compared with ab initio calculations for zirconium representing a monoatomic material with displacive phase transformation.

Abstract: The structures of {121} twin boundary in orthorhombic 2H martensite are modeled using Finnis-Sinclair type many-body interatomic potentials. The boundary corresponds to type-I twinning in 2H martensite of Cu-Al-Ni, Cu-Zn-Al and Au-Cd alloys. Three possible configurations of the {121} boundary are found. The structure with the lowest energy possesses a non-corrugated central {121} plane.

Abstract: Shear deformation and shuffling of atomic planes are elementary mechanisms of collective atomic motion that take place during displacive phase transformations. General displacements of atomic planes are examined, i.e. -surface type calculations extensively used for the stacking faults and crystal dislocations are applied to single plane shuffling and alternate shuffling of every other atomic plane producing in combination with homogeneous deformation the hcp structure (martensitic type) from the initial bcc structure (austenitic type). Similar approach considering shear type planar displacements leads to the Zener path between the bcc and fcc lattices. The effect of additional deformation required to obtain the close-packed atomic arrangements is examined as well. Finally, the influence of volume modification on phase transitions is investigated. The energies of various structural configurations are calculated using many-body potentials for the description of interatomic forces. Such atomic models are tested to check their suitability for investigation of the role of interfaces in the displacive structural transitions.

Abstract: The parameters of exponential many-body Finnis-Sinclair potentials corresponding to qualitatively different crystal lattice stability were selected and their behaviour was studied. Furthermore, a model with pairwise Lennard-Jones potential was also considered. The attention was paid to the stability of different crystal structures and the properties of simple interfaces such as stacking faults and twin boundaries were investigated.