Self-point defects diffusion in BCC iron

Full text of publication follows: The study of diffusion mechanisms of self-interstitial atom (SIA) and vacancy in bcc iron has been carried out using molecular statics and molecular dynamics simulations. Temperature dependences of defects diffusion Dd(T) and corresponding self diffusion D*(T) coefficients and tracer correlation factor ftr have been calculated in temperature ranges (1000 - 1800) K and (250 - 1800) K for vacancy and SIA, respectively. The obtained temperature dependences of vacancy diffusion coefficients are described well by Arrhenius equation: Dd(T) = 8.49. 10-3 exp(-0.733 eV/kBT) cm2 /s, D*(T) = 5.35. 10-3 exp(-0.720 eV/kBT) cm2/s, kB is Boltzmann constant. Additional migration mechanisms are activated at high temperatures, at which the vacancy migrates to the 3. and the 5. nearest neighbors (nn) positions, besides the ordinary mechanism of migration to the 1. nn position. The approximation of the temperature dependences of jump frequencies, corresponding to these migration mechanisms, by Arrhenius equation gives the values of the activation energies: 0.730 eV, 1.401 eV and 1.664 eV for the jumps to the 1., 5. and 3. nn positions, respectively. These values agree with the corresponding static barriers: 0.735 eV, 1.406 eV and 1.743 eV. The calculated value of ftr agrees with its theoretical value 0.727 within the limits of inaccuracy at T≤1600 K. At higher temperatures, some weak systematic decrease of ftr is observed which is concerned with the activation of two mentioned above less energetically favorable migration mechanisms. The temperature dependences of SIA diffusion coefficients sufficiently differ from Arrhenius type in the considered temperature range. The effective migration energies are ∼(0.22 - 0.23) eV at T < 300 K. These values are close to the calculated values of static barriers of <110> dumbbell migration and <110> to <111> dumbbell reorientation processes (0.246 eV and 0.250 eV, respectively) and in agreement with the experimental value ∼(0.25 - 0.30) eV. The effective migration energy decreases with the temperature reaching the value 0.09 eV at T ∼ 1000 K. The SIA has a complex 1D and 3D migration mechanism. The value of ftr is constant within the limits of inaccuracy through the considered temperature range and equals to 0.27, which is the evidence of the complex diffusion mechanism not changing with the temperature. (authors)