A first-principles model for anomalous segregation in dilute ternary tungsten-rhenium-vacancy alloys.

Title A first-principles model for anomalous segregation in dilute ternary tungsten-rhenium-vacancy alloys.
Authors J.S. Wróbel; D. Nguyen-Manh; K.J. Kurzyd?owski; S.L. Dudarev
Journal J Phys Condens Matter
DOI 10.1088/1361-648X/aa5f37
Abstract

The occurrence of segregation in dilute alloys under irradiation is a highly unusual phenomenon that has recently attracted attention, stimulated by the interest in the fundamental properties of alloys as well as by their applications. The fact that solute atoms segregate in alloys that, according to equilibrium thermodynamics, should exhibit full solubility, has significant practical implications, as the formation of precipitates strongly affects physical and mechanical properties of alloys. A lattice Hamiltonian, generalizing the so-called 'ABV' Ising model and including collective many-body inter-atomic interactions, has been developed to treat rhenium solute atoms and vacancies in tungsten as components of a ternary alloy. The phase stability of W-Re-vacancy alloys is assessed using a combination of density functional theory (DFT) calculations and cluster expansion (CE) simulations. The accuracy of CE parametrization is evaluated against the DFT data, and the cross-validation error is found to be less than 4.2 meV/atom. The free energy of W-Re-vacancy ternary alloys is computed as a function of temperature using quasi-canonical Monte Carlo simulations, using effective two, three and four-body interactions. In the low rhenium concentration range (<5 at.Re), solute segregation is found to occur in the form of voids decorated by Re atoms. These vacancy-rhenium clusters remain stable over a broad temperature range from 800?K to 1600?K. At lower temperatures, simulations predict the formation of Re-rich rhenium-vacancy clusters taking the form of sponge-like configurations that contain from 30 to 50 at.Re. The anomalous vacancy-mediated segregation of Re atoms in W can be rationalized by analyzing binding energy dependence as a function of Re to vacancy ratio as well as chemical Re-W and Re-vacancy interactions and short-range order parameters. DFT calculations show that rhenium-vacancy binding energies can be as high as 1.5?eV if the rhenium/vacancy ratio is in the range from 2.4 to 6.6. The predicted Re clustering agrees with experimental observations of precipitation in self-ion irradiated W-2 Re alloys and neutron-irradiated alloys containing 1.4 at.Re.

Citation J.S. Wróbel; D. Nguyen-Manh; K.J. Kurzyd?owski; S.L. Dudarev.A first-principles model for anomalous segregation in dilute ternary tungsten-rhenium-vacancy alloys.. J Phys Condens Matter. 2017;29(14):145403. doi:10.1088/1361-648X/aa5f37

Related Elements

Rhenium

See more Rhenium products. Rhenium (atomic symbol: Re, atomic number: 75) is a Block D, Group 7, Period 6 element with an atomic weight of 186.207. The number of electrons in each of rhenium's shells is 2, 8, 18, 32, 13, 2 and its electron configuration is [Xe] 4f14 5d5 6s2. Rhenium Bohr ModelThe rhenium atom has a radius of 137 pm and a Van der Waals radius of 217 pm. Rhenium was discovered and first isolated by Masataka Ogawa in 1908. In its elemental form, rhenium has a silvery-white appearance. Rhenium is the fourth densest element exceeded only by platinum, iridium, and osmium. Rhenium's high melting point is exceeded only by those of tungsten and carbon.Elemental Rhenium Rhenium is found in small amounts in gadolinite and molybdenite. It is usually extracted from the flue dusts of molybdenum smelters. The name Rhenium originates from the Latin word 'Rhenus' meaning "Rhine" after the place of discovery.

Tungsten

See more Tungsten products. Tungsten (atomic symbol: W, atomic number: 74) is a Block D, Group 6, Period 6 element with an atomic weight of 183.84. The number of electrons in each of tungsten's shells is [2, 8, 18, 32, 12, 2] and its electron configuration is [Xe] 4f14 5d4 6s2. Tungsten Bohr ModelThe tungsten atom has a radius of 139 pm and a Van der Waals radius of 210 pm. Tungsten was discovered by Torbern Bergman in 1781 and first isolated by Juan José Elhuyar and Fausto Elhuyar in 1783. In its elemental form, tungsten has a grayish white, lustrous appearance. Elemental TungstenTungsten has the highest melting point of all the metallic elements and a density comparable to that or uranium or gold and about 1.7 times that of lead. Tungsten alloys are often used to make filaments and targets of x-ray tubes. It is found in the minerals scheelite (CaWO4) and wolframite [(Fe,Mn)WO4]. In reference to its density, Tungsten gets its name from the Swedish words tung and sten, meaning heavy stone.

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