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- Duong, T. C., et al.
(författare)
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A hierarchical computational thermodynamic and kinetic approach to discontinuous precipitation in the U-Nb system
- 2015
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Ingår i: PTM 2015 - Proceedings of the International Conference on Solid-Solid Phase Transformations in Inorganic Materials 2015. - : International Conference on Solid-Solid Phase Transformations in Inorganic Materials. - 9780692437360 ; , s. 887-894
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Konferensbidrag (refereegranskat)abstract
- U-Nb alloys decompose via discontinuous precipitation (DP) over a broad range of aging conditions, adversely affecting their properties. The growth kinetics, lamellar spacing, and Nb partitioning have been measured, but the thermodynamic and kinetic factors underlying these specific transformation characteristics and reaction paths, vis-a-vis the monotectoid reaction, are not fully resolved. In this work, a hierarchical computational thermodynamic and kinetic approach was carried out to investigate DP. The hierarchical approach started with density-functional theory (DFT) investigations of ground-state formation energies of bcc-based U-Nb alloys. The estimated energetic data was then utilized as an imposed first-principles-based constraint to improve the consistency of the CALPHAD thermodynamic and, subsequently, kinetic assessments of U-Nb. Phasefield simulations were then carried out to study DP's microstructure evolution using the assessed CALPHAD thermodynamic and kinetic representations. Good agreement with experiments on different physical/length scales was achieved, which validates the present theoretical contributions to a better understanding of DP in U-Nb alloys.
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- Abrikosov, I. A., et al.
(författare)
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Multiscale approach to theoretical simulations of materials for nuclear energy applications : Fe-Cr and Zr-based alloys
- 2013
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Ingår i: Advances in materials for nuclear energy. - : Materials Research Society. - 9781605114910 ; , s. 3-14
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Konferensbidrag (refereegranskat)abstract
- We review basic ideas behind state-of-the-art techniques for first-principles theoretical simulations of the phase stabilities and properties of alloys. We concentrate on methods that allow for an efficient treatment of compositional and thermal disorder effects. In particular, we present novel approach to evaluate free energy for strongly anharmonic systems. Theoretical tools are then employed in studies of two materials systems relevant for nuclear energy applications: Fe-Cr and Zr-based alloys. In particular, we investigate the effect of hydrostatic pressure and multicomponent alloying on the mixing enthalpy of Fe-Cr alloys, and show that in the ferromagnetic state both of them reduce the alloy stability at low Cr concentration. For Zr-Nb alloys, we demonstrate how microscopic parameters calculated from first-principles can be used in higher-level models.
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- Korzhavyi, Pavel A., 1966-, et al.
(författare)
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Constitutional and thermal point defects in B2 NiAl
- 2000
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 61:9, s. 6003-6018
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Tidskriftsartikel (refereegranskat)abstract
- The formation energies of point defects and the interaction energies of various defect pairs in NiAl are calculated from first principles within an order N, locally self-consistent Green's-function method in conjunction with multipole electrostatic corrections to the atomic sphere approximation. The theory correctly reproduces the ground state for the off-stoichiometric NiAl alloys. The constitutional defects (antisite Ni atoms and Ni vacancies in Ni-rich and Al-rich NiAl, respectively) are shown to form ordered structures in the ground state, in which they tend to avoid each other at the shortest distance on their sublattice. The dominant thermal defects in Ni-rich and stoichiometric NiAl are calculated to be triple defects. In Al-rich alloys another type of thermal defect dominates, where two Ni vacancies are replaced by one antisite Al atom. As a result, the vacancy concentration decreases with temperature in this region. The effective defect formation enthalpies for different concentration regions of NiAl are also obtained.
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- Korzhavyi, Pavel A., 1966-, et al.
(författare)
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First-principles calculations of the vacancy formation energy in transition and noble metals
- 1999
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 59:18, s. 11693-11703
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Tidskriftsartikel (refereegranskat)abstract
- The vacancy formation energy and the vacancy formation volume of the 3d, 4d, and 5d transition and noble metals have been calculated within the local-density approximation. The calculations employ the order-N locally self-consistent Green’s-function method in conjunction with a supercell approach and include electrostatic multipole corrections to the atomic sphere approximation. The results are in excellent agreement with available full-potential calculations and with the vacancy formation energies obtained in positron annihilation measurements. The variation of the vacancy formation energy through a transition-metal series and the effects of crystal and magnetic structure are investigated and discussed.
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- Serikov, V. V., et al.
(författare)
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Formation of solid solutions of gallium in Fe-Cr and Fe-Co alloys : Mossbauer studies and first-principles calculations
- 2014
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 614, s. 297-304
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Tidskriftsartikel (refereegranskat)abstract
- Investigation of Ga influence on the structure of Fe-Cr and Fe-Co alloys was performed with the use of Mossbauer spectroscopy and X-ray diffraction methods. The experimental results are compared with results of first-principles calculations of the mixing and solubility energies for Ga in an Fe-X (X = Co, Cr) alloy both in ferromagnetic and paramagnetic states. It is shown that Ga mainly goes into the solid solutions of the base alloys. In the alloys of the Fe-Cr system, doping with Ga handicaps the decomposition of solid solutions, observed in the binary alloys, and increases its stability. In the alloys with Co, Ga also favors the uniformity of solid solutions. The results of the first-principles calculations testify in favor of a preferable dissolution of Ga in the FeCo regions of a multicomponent structure rather than FeCr regions, both types of regions being in the ferromagnetic state at the temperature of annealing. The analysis of Mossbauer experiments gives some grounds to conclude that if, owing to liquation, clusterization, or initial stages of phase separation, there exist regions enriched in iron, some amount of Ga atoms prefer to enter the nearest surroundings of iron atoms, thus forming binary Fe-Ga regions (or phases).
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