Diffusion Constants for the Vacancy Mechanism in Mg and α‐Zr Calculation

Abstract

Calculation BY A. M. MONTISelf-diffusion coeficients for the monovacancy mechanism described in terms of the Arrhenius law a: calculated in Mg and a-Zr from computer simulation results. Different short-range pair interatom potentials which reproduce some material properties are used. Special interest is devoted to the resul obtained for the a-Zr lattice; by assuming a vacancy-formation energy value E' = 1.8 eV, a self-diffusic energy value Q = 3.3 eV and a pre-exponential factor Do = 5 x lo-' m2 s -l are obtained. The: numbers indirectly support some ideas proposed in the literature to understand the self-diffusic behaviour shown by experimental results, as well as some predictions made by other authors. Aus Computersimulationsergebnissen werden Selbstdiffusionskoeffizienten fur den

Dipole Tensors and Volume Changes of Point Defects in H.C.P. Lattices

“…The more repulsive interatomic potentials, P6C-type and P3C-Zr0, cause higher relaxation than the other P3C. P4C-Mg gives negative interstitial relaxation volumes [4] due to its smooth barrier at the interstitial distance range. In case (i), the volume change induced by the BO interstitial is almost three times higher than that for the octahedral one.…”

“…The so-obtained entropy S, has to be corrected with respect to the "true" constantpressure entropy s,. To evaluate the correction term, see (10) in [4], the lattice-volume change induced by the defect is required. To calculate the defect-volume change taking into account the displacement field induced in the anharmonically relaxed lattice, the defectdipole tensor must be previously determined.…”

“…The present results have been used (i) in [5] to study in the Mg and a-Zr lattices, through the dependence shown in (l), the effect of a stress field on the anisotropic diffusion of vacancies and interstitials; (ii) in [4] to correct vibrational entropies for the vacancy at both, equilibrium and activated states, in order to evaluate diffusion constants for a monovacancy mechanism in those lattices.…”

Void Sink Strength in H.C.P. Materials

“…When the P3C potentials are considered and B, and D are taken as stable interstitials, by replacing (Al) in (5), we obtain for the interstitial diffusivity were done by using the results corresponding to the five interatomic potentials given by Monti et al [19] and Monti [27] In Fig. 2 we plot the ratio DJD, for the vacancy and the interstitials as a function of strain and for the five potentials considered in this work.…”

“…For the purpose of calculation the diffusivity is taken at 560 K, which is approximately the reactor operating temperature and elastic strains up to E = are considered. The dipole tensors used are reported by Monti [27]. It can be seen that for the vacancy case, tensile extension along c always decreases the ratio DJD,, while compression increases it.…”