No abstract

No abstract

The effect of carbon and oxygen impurity atoms on the migration rate of tilt boundaries with the <100> and <111> misorientation axes in fcc metals Ni, Ag, Al was studied by means of the molecular dynamics method. It is shown that the introduction of impurity atoms of light elements led to a significant inhibition of the migration of grain boundaries: with the introduction of 5 % by almost an order of magnitude, 10 % -by two orders of magnitude. Carbon atoms tend to form aggregates, which, being fixed on the grain boundary, become effective stoppers that prevent the boundary moving. Oxygen atoms did not form aggregates, but because of the high values of the binding energy with the boundaries, they also effectively hampered their migration. In contrast to the formation of aggregates by carbon atoms, in the case of oxygen impurity, another effect takes place -"loosening" and an increase in the width of the boundary. For impurity atoms of carbon and oxygen, the binding energies with grain-boundary edge dislocations in the metals under consideration were calculated. The obtained values correlate well with the dependences of the grain boundary migration rate on the impurity concentration: the greatest effect of impurities on the boundary migration rate and the value of the binding energy were obtained for the Al-C system, the smallest -for Ag-O.

No abstract

The features and migration mechanism of tilt boundaries with the misorientation axis <110> in an fcc crystal using nickel as an example were studied by the method of molecular dynamics. The dependences of the boundaries energy and the rate of their migration at a temperature of 1700 K on the misorientation angle are obtained. It is shown that the migration rate of <110> tilt boundaries under the same conditions is an order of magnitude lower than the migration rate of <111> and <100> boundaries, which is primarily due to the relatively low energy of <110> boundaries. In addition, the low-angle <110> tilt boundaries are unique compared to other tilt boundaries-grain boundary dislocations in them are ordinary perfect edge dislocations with straight cores that do not contain jogs periodically located on them, as in <111> and <100> boundaries. In <110> boundaries, as well as in <111> and <100> boundaries, there are two different sets of dislocations, but they are not always combined, as is often the case in <111> and <100> boundaries. Combined dislocations in <110> boundaries turned out to be less mobile during boundary migration than non-combined ones. An analogy of migration mechanisms of low-angle <110> boundaries with the previously considered <111> and <100> boundaries was noted. During migration, in the grain towards which the migration took place, regions of the same shape orderly rotated through the angle of misorientation were formed, the size of which depended on the distance between neighboring grain boundary dislocations.

No abstract

Potentials for describing interatomic interactions in a γFe-Mn-C-N multicomponent system, modified Hadfield steel, where face-centered cubic (f.c.c.) iron is the main component, are proposed. To describe the Fe-Fe interactions in austenite, it is proposed to use Lau EAM potential. For all other interactions, Morse potentials are proposed, the parameters of which were found from various experimental characteristics: in particular, the energy of dissolution and migration of an impurity in an f.c.c. iron crystal, the radius of atoms, their electronegativity, mutual binding energy, etc. The found potentials are intended for modeling the atomic structures and processes occurring at the atomic level in Hadfield steel using relatively large computational cells by the molecular dynamics method.

The interaction of impurity atoms of light elements C, N, O with self-interstitials in fcc metals Ni, Ag and Al was studied by the molecular dynamics method. It is shown that the self-interstitial atom in fcc metals migrates through at least two mechanisms: by the displacement and rotation of the <100> dumbbell and by the crowdion mechanism. The first mechanism is characterized by broken trajectories of atomic displacements, the second-by straight ones along close-packed directions in the crystal. The binding energies of impurity atoms with self-interstitials in Ni, Ag and Al have been calculated. It is shown that impurity atoms are effective "traps" for interstitial atoms that migrate relatively quickly in a crystal. When a self-interstitial atom and an impurity atom interact, the interstitial atom forms a dumbbell configuration with the axis along the <100> direction, and the impurity atom is located in the nearest octahedral pore. To analyze the effect of impurities on the diffusion mobility of interstitial atoms, we calculated the activation energy of migration of the interstitial atom in pure metals and metals containing 10 % of impurity atoms. It was found that the mobility of interstitial atoms is significantly reduced due to the presence of impurities in the metal. At the same time, the contribution of the crowdion mechanism also decreased.