The trapping effects of silicon and phosphorus on point defects in γ-Fe

Abstract

The addition of silicon (Si) and phosphorus (P) to austenitic stainless steel is observed to reduce swelling, but the inhibition mechanism has not been well understood. In this work, the solute properties of Si and P, their interaction with point defect, vacancy-mediated migration energies were obtained through first-principles calculations, and the diffusion behavior of solutes and vacancies are evaluated by both methods by solving the Onsager matrix. The solution energies of Si and P in the antiferromagnetic (001) double-layer with face-centered tetragonal structure (fct_afmD) Fe imply their relative high solubility. Vacancies can be attracted by Si and P at 1NN sites with the binding energies of 0.12 ∼ 0.19 eV, and 0.30 ∼ 0.42 eV, respectively. The vacancy wind and the ratio of tracer diffusion coefficient demonstrate that Si and P will be dragged by vacancy, diffuse faster than that of Fe, and strongly promote vacancy diffusion at low temperature while they have weak inhibition at high temperature. Simultaneously, as a function of temperature, compared to the phenomenological Manning method, the results of the Green-function method generally exhibit a left shift. Furthermore, Si and P are also found to attract the self-interstitial atoms (SIAs). Our results indicate that solutes Si and P can both welcome vacancies and SIAs, promote vacancy diffusion at low temperature, in which the effect of P is much stronger than that of Si. Therefore, their addition to austenitic steels may be beneficial to enhance recombination rates of vacancy and SIAs, drop of net defect concentrations and result in a reduction of the rates of void growth under irradiation.