Molecular Dynamic Studies of the Vacancies Interaction with the Grain Boundaries

Abstract

In this paper the method of molecular dynamics used to study the interaction of lattice vacancies with symmetric tilt grain boundaries (GBs) in aluminum. A linear dependence between the number of captured vacancies and the distance to the GB's plane was found. The average rate of vacancy migration to the border decreases exponentially with increasing distance between the plane of the GB and the vacancy. Capture's radius is limited to 2-3 lattice parameters and increases with increasing temperature. Defined four types of boundaries in different ways of interacting with lattice vacancies. For quite a long time by various experimental techniques, such as (1-3) have shown that grain boundaries (GB) act ing as sources and sinks of vacancies. By now also experimentally found that the effectiveness of the boundaries as sources (sinks) of vacancies depends on the type boundaries: the boundary are highly arbitrary sources (sinks) even with vacancy's low chemical potential and special GB wh ich do not act as potential sinks (4). Ho wever, at very high chemical potential even coherent twin boundaries are sources (sinks) vacancies, although their effectiveness is less than the arbitrary boundaries (2). Modern researches have also shown that GB actively interacts with point defects in poly crystals. For examp le in (5) by computer simulat ion discussed interaction of vacancies with special grain boundaries. It is shown that the interaction of vacancies with GB essentially depends on the atomic structure of GB. Found on GB reg ions of alternating tension and compression leads to an oscillatory dependence of the interaction energy of vacancies fro m the distance fro m the border. The interaction energy of vacancy with GB is negative, i.e., border is a sink of vacancies. A similar result was obtained in (6) who studied the energy of format ion and migrat ion mechanisms of vacancies near the plane of the special GBs. Co mputer modeling was carried out by using mo lecular static, mo lecular dynamic and Monte Carlo method. The authors note that the vacancies can be moved by simp le ju mps and through collective atomic d isplacements. In (7-8) studied energy of format ion and the activation energy for vacancy migration. Calculations showed that the vacancy formation energy in all investigated borders does not depend on the applied external tensile, but the volu me and enthalpy of formation can vary considerably. In all shown examp les, it is a vacancy which is close to the plane of GB, i.e. actually are elements of the structure of the border. In our paper we present the results of computer simu lation of the interaction tilt boundaries with lattice vacancies placed in the bulk grain. II. MODEL