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This work is devoted to the study of the point defect diffusion features in metals. In particular, we propose the model, which allows calculating activation volumes that describe the influence of pressure on the diffusion processes in solids. Our model realizes a new approach that makes it possible to self-consistently determine atomic structure near defect and constants characterizing the displacement of atoms in an elastic matrix around computational cell. Also we take into consideration that the energy of perfect system and system with a defect differently depends on the outer pressure, and this gives an addition to the values of migration and formation volumes. This addition can comprise a considerable part of activation volume. Moreover, we take into account that the atomic jump is a momentary process and so we carry out only partial relaxation of the atomic structure in the vicinity of a defect. The formation and migration energies and formation and migration volumes have been calculated for vacancies, di-vacancies and interstitials in bcc iron and tungsten using pair and many-body potentials.

This work is devoted to the evaluation of a change in the barrier height in the case of an atom jump to the nearest vacancy site under strain and to obtaining the vacancy diffusion equation taking into consideration the strain influence. Earlier, we suggested a new approach to solving the problem of the influence of elastic stress on the vacancy jump rate for atomic diffusion in crystals. It was based on the simple observation that a stress field alters the surrounding configuration and on the assumption that the height of the activation barrier should be altered accordingly. The change of the activation barrier was shown to depend on the displacement field, the symmetry of the crystal, the atomic structure near point defects and the interatomic potential. Knowledge of this change makes it possible to calculate the jump rate. The expression for the vacancy flux was obtained with the help of the 'hole gas' method, by using the jump rate. In these nonlinear equations, the influence of the strain tensor component on diffusion flux is determined by coefficients, which depend on the atomic interaction and atomic structure of the saddle-point configuration. One of the aims of the present work is to generalize our approach taking into account N-body interatomic interaction. Now we present the diffusion equation for vacancy in FCC and BCC metals, obtained in a more general and convenient form.