| 1. |
- Gorbatov, O. I., et al.
(author)
-
Vacancy-solute interactions in ferromagnetic and paramagnetic bcc iron : Ab initio calculations
- 2011
-
In: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 419:1-3, s. 248-255
-
Journal article (peer-reviewed)abstract
- Vacancy-solute interactions play a crucial role in diffusion-controlled processes, such as ordering or decomposition, which occur in alloys under heat treatment or under irradiation. Detailed knowledge of these interactions is important for predicting long-term behavior of nuclear materials (such as reactor steels and nuclear-waste containers) as well as for advancing our general understanding of kinetic processes in alloys. Using first-principles calculations based on the density functional theory and employing the locally self-consistent Green's function technique, we develop a database of vacancy-solute interactions in dilute alloys of bcc Fe with 3p (Al, Si, P, S), 3d (Sc-Cu), and 4d (Y-Ag) elements. Unrelaxed interactions within the first three coordination shells have been computed in the ferromagnetic state as well as in the paramagnetic (disordered local moment) state of the iron matrix. Magnetism is found to have a strong effect on the vacancy-solute interactions. Implications of the obtained results for interpreting the effects of vacancy trapping and enhanced impurity diffusion are discussed.
|
|
| 2. |
- Kabliman, Evgeniya, et al.
(author)
-
Ab initio-based mean-field theory of the site occupation in the Fe-Cr sigma-phase
- 2011
-
In: Physical Review B. Condensed Matter and Materials Physics. - : AMER PHYSICAL SOC. - 1098-0121 .- 1550-235X. ; 83:9, s. 092201-
-
Journal article (peer-reviewed)abstract
- An efficient first-principles-based mean-field theory is applied to study the site occupations in the Fe-Cr sigma phase. It is based on the expansion of the total energy of a random alloy close to the equiatomic composition in the paramagnetic state in terms of the effective on-site interactions and takes into account longitudinal spin fluctuations at high temperatures. The calculated site occupation is in very good agreement with the existing experimental data.
|
|
| 3. |
- Kabliman, Evgeniya, et al.
(author)
-
Configurational thermodynamics of the Fe-Cr sigma phase
- 2011
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 84:18, s. 184206-
-
Journal article (peer-reviewed)abstract
- Configurational thermodynamics of the Fe-Cr sigma phase is investigated on the basis of an Ising-type configurational Hamiltonian and a single-site mean-field model for the free energy. The parameters of the statistical models are obtained from efficient first-principles calculations using different computational techniques. We demonstrate that the effective pair and multisite interactions in the sigma phase are relatively small, which allows using a simplified model for distributing Fe and Cr atoms among sublattices. We also show that this system exhibits a nontrivial magnetic behavior at high temperatures, which affects the site occupation by Fe and Cr atoms. The structural variation (volume and c/a) that might be present due to neutron irradiation and thermal expansion can lead to an additional atomic redistribution.
|
|
| 4. |
- Rahaman, Moshiour, et al.
(author)
-
Magnetic state effect upon the order-disorder phase transition in Fe-Co alloys : A first-principles study
- 2011
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 83:5, s. 054202-
-
Journal article (peer-reviewed)abstract
- We investigate the effect of global magnetization on the effective cluster interactions and order-disorder phase transition in FexCo1-x alloys. The effective cluster interactions are obtained by the screened generalized perturbation method as it is implemented in the exact muffin-tin orbitals formalism within the coherent potential approximation. The ordering transition from the high-temperature disordered body-centered cubic alloy to the ordered B2 phase is determined by Monte Carlo simulations. The calculated transition temperatures are in good agreement with the available experimental data for the effective interactions, which correspond to the experimentally observed magnetization at the order-disorder phase transition.
|
|
| 5. |
- Ruban, Andrei, et al.
(author)
-
Ab initio based investigation of the oxygen and nitrogen interstitial ordering in hcp Hf, Zr, and Ti : An ab initio study
- 2010
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 82:13, s. 134110-
-
Journal article (peer-reviewed)abstract
- We investigate the ordering of oxygen and nitrogen interstitials in hcp Zr, Hf, and Ti using the corresponding oxygen-oxygen and nitrogen-nitrogen interactions obtained in the state-of-the-art first-principles calculations. Two main contributions, chemical and strain induced, to the interstitial-interstitial interactions are obtained by different techniques. We find that there is the strong repulsion between interstitial atoms at the nearest-and next-nearest-neighbor coordination shells, which is solely determined by the chemical interaction determined on a fixed ideal lattice, while both contributions are important for more distant coordination shells. The Monte Carlo simulations reveal the existence of three stoichiometric compositions, MeI1/6, MeI1/3, and MeI1/2, for the ground-state structures of interstitials, having different ordering types. Our results for the structures of oxygen interstitials are in good agreement with existing experimental data for the Ti and Hf alloys. In the case of Zr-O interstitial alloys, we correctly predict the general type of ordering, although the detailed structure is at variance the experimental observations. The ordering transition temperatures in some cases are overestimated by a factor of 2. We also predict the ordering type of nitrogen interstitials in hcp Ti, Zr, and Hf, which are similar to those in the case of oxygen interstitials.
|
|
