On self-diffusion in iron at very strong compression of crystal

The dependences of the parameters of the formation of vacancies and self-diffusion have been calculated as functions of the degree of compression of iron crystals along isotherms of 300 and 3000 K. It has been shown that, in the range of 1 > V/V ₀ > (V/V ₀)_min, the suppression of the activation processes occurs upon isothermal compression and, upon isochoric heating, they are strengthened. Here, V/V ₀ is the ratio of the molar volume of the crystal at a pressure P and temperature T to that at P = 0 and T = 0. However, at V/V ₀ = (V/V ₀)_min = 0.0548, the probability of the formation of vacancies and the self-diffusion coefficient become minimum and, in the course of the further isothermal compression, the strengthening of activation processes occurs, and the activation parameters cease to depend on temperature. It is indicated that this is due to the quantum subbarrier tunneling of atoms over the volume of the crystal. It has been shown that, at V/V ₀ < (V/V ₀)_fr, the surface energy is negative, which should stimulate the process of the fragmentation of the crystal and that (V/V ₀)_fr > (V/V ₀)_min. The isothermal dependence of pressure in bcc iron has been estimated upon its compression to V/V ₀ = 0.001. Based on the calculated isotherms, the magnitudes of pressure at characteristic points of pressure dependences of the parameters of self-diffusion and surface energy have been estimated.