Diffusion of Si impurities in Ni under stress: A first-principles study

Abstract

We perform a first-principles study of the effect of strain on the migration of Si atoms in Ni. For that purpose, migration barriers are computed using the nudged elastic band method and attempt frequencies are computed using the direct force method. Good agreement is found with tracer diffusion experiments. We used the elastic dipole model to calculate effects of strain on migration barriers by performing calculations on unstrained cells, therefore reducing significantly the computing time. We validate this approach by comparing results with migration barriers calculated on strained cells and obtain an excellent agreement up to a strain of 1%. Computing all the jump frequencies in the neighborhood of Si solutes, the effect of strain is found to be nearly independent of the relative position of the solute atom. A simple elastic analysis models the changes in the vacancy jump with strain; this correlates with the changes in geometry for the "cage" of atoms surrounding the hopping atom at the saddle point.

Calculation of strain effects on vacancy-mediated diffusion of impurities in fcc structures: General approach and application toNi1−xSix

“…Previously, atomic-scale migration properties of Si impurities in Ni were computed using DFT 28 . In this fcc alloy, non-negligible solute-vacancy interactions are found up to the third NN sites thus requiring the calculation of sixteen frequencies to describe diffusion.…”

“…We compute the elasto-diffusion tensor using the SCMF method. In the Ni(Si) alloy, the cross terms of the elastic dipole-which quantifies the effect of ε 12 shear strain on diffusionare all an order of magnitude smaller than the diagonal terms 28 . It was assumed in Ref.…”

“…Ref. 28 details how the effect of strain on migration barriers for atomic jumps leading to diffusion can be calculated with DFT for this alloy. Here we demonstrate how these results can be used to compute the full Onsager matrix of an anisotropic system to produce the strain-dependent mesoscopic diffusion properties.…”

Mesoscale modeling of vacancy-mediated Si segregation near an edge dislocation in Ni under irradiation

“…Silicon and nickel vacancies have interactions out to the third shell. Garnier et al 28 found an attractive ∆g 1 = −0.0996 eV (Z 1 = 12), a small ∆g 2 = 0.0120 eV (Z 2 = 6) and a repulsive ∆g 3 = 0.0452 eV (Z 3 = 24).…”

“…Indeed, for the special case of Ni-Si alloy, Garnier et al 28 have showed an interesting result that the derivatives of migration barriers with respect to volumetric strain ∂E m /∂ v is a constant for all types of atomic jumps in the system. Since the migration barriers have good linear dependences on the volumetric strain v in a larger strain range than that for L AB 28,29 , we use the following expression instead of Eqn.…”