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Amouyal, Yaron; Mao, Zugang; Booth-Morrison, Christopher; Seidman, David N. |
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On the interplay between tungsten and tantalum atoms in Ni-based superalloys: An atom-probe tomographic and first-principles study |
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2009 |
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Applied Physics Letters |
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Appl. Phys. Lett. |
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94 |
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041917 |
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NU @ c-booth @ |
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10551 |
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Booth-Morrison, Christopher; Mao, Zugang; Noebe, Ronald D.; Seidman, David N. |
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Chromium and tantalum site substitution patterns in Ni3Al (L1[sub:2]) [gamma]’-precipitates |
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2008 |
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Applied Physics Letters |
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App. Phys. Let. |
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93 |
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033103 |
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Nickel-based superalloys; Site substitution; Atom-probe tomography; Tantalum; Nanostructures, First-principles calculations |
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The site substitution behavior of Cr and Ta in the Ni3Al (L12)-type gamma[prime]-precipitates of a Ni–Al–Cr–Ta alloy is investigated by atom-probe tomography (APT) and first-principles calculations. Measurements of the gamma[prime]-phase composition by APT suggest that Al, Cr, and Ta share the Al sublattice sites of the gamma[prime]-precipitates. The calculated substitutional energies of the solute atoms at the Ni and Al sublattice sites indicate that Ta has a strong preference for the Al sites, while Cr has a weak Al site preference. Furthermore, Ta is shown to replace Cr at the Al sublattice sites of the gamma[prime]-precipitates, altering the elemental phase partitioning behavior of the Ni–Al–Cr–Ta alloy. |
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NU @ m-krug @ ; NU @ c-booth @ |
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10296 |
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Zhou, Yang; Mao, Zugang; Booth-Morrison, Christopher; Seidman, David N. |
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The partitioning and site preference of rhenium or ruthenium in model nickel-based superalloys: An atom-probe tomographic and first-principles study |
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2008 |
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Applied Physics Letters |
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93 |
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171905 |
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The partitioning behavior and sublattice site preference of Re or Ru in the Ni3Al (L12) gamma[prime]- precipitates of model Ni-Al-Cr alloys are investigated by atom-probe tomography (APT) and first-principles calculations. Rhenium and Ru are experimentally observed to partition to the gamma(fcc)-phase, which is consistent with the smaller values of the gamma-matrix Re and Ru substitutional formation energies determined by first-principles calculations. APT measurements of the gamma[prime]-precipitate composition indicate that Re and Ru occupy the Al sublattice sites of the Ni3Al (L12) phase. The preferential site substitution of Re and Ru at Al sublattice sites is confirmed by first-principles calculations |
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NU @ c-booth @ |
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10532 |
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Booth-Morrison, Christopher; Zhou, Yang; Noebe, Ronald D.; Seidman, David N. |
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On the nanometer scale phase decompositon of a low-supersaturation Ni-Al-Cr alloy |
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2010 |
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Philosophical Magazine |
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90 |
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1-4 |
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219-235 |
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nickel-based superalloy; phase decomposition; atom probe tomography; temporal evolution; nanostructure |
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The phase separation of a Ni–6.5 Al–9.5 Cr at. % alloy aged at 873K was studied by atom-probe tomography and compared to the predictions of classical precipitation models. Phase separation in this alloy occurs in four distinct regimes: (i) quasi-stationary-state [gamma]'(L12)-precipitate nucleation; (ii) concomitant precipitate nucleation, growth and coagulation and coalescence; (iii) concurrent growth and coarsening, wherein coarsening occurs via both [gamma]'-precipitate coagulation and coalescence and by the classical evaporation–condensation mechanism; and (iv) quasi-stationary state coarsening of [gamma]'-precipitates, once the equilibrium volume fraction of precipitates is achieved. The predictions of classical nucleation and growth models are not validated experimentally, likely due to the complexity of the atomistic kinetic pathways involved in precipitation. During coarsening, the temporal evolution of the [gamma']-precipitate average radius, number density and the [gamma] (fcc)-matrix and [gamma]'-precipitate supersaturations follow the predictions of classical models. |
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NU @ c-booth @ |
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10575 |
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Booth-Morrison, Christopher; Zhou, Yang; Noebe, Ronald D.; Seidman, David N. |
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On the nanometer scale phase separation of a low-supersaturation Ni–Al–Cr alloy |
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Journal Article |
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2009 |
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Philosophical Magazine |
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Philosophical Magazine |
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90 |
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1-4 |
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219-235 |
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* nickel-based superalloy, * phase decomposition, * atom probe tomography, * temporal evolution, * nanostructure |
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The phase separation of a Ni?6.5 Al?9.5 Cr at. % alloy aged at 873 K was studied by atom-probe tomography and compared to the predictions of classical precipitation models. Phase separation in this alloy occurs in four distinct regimes: (i) quasi-stationary-state ??(L12)-precipitate nucleation; (ii) concomitant precipitate nucleation, growth and coagulation and coalescence; (iii) concurrent growth and coarsening, wherein coarsening occurs via both ??-precipitate coagulation and coalescence and by the classical evaporation?condensation mechanism; and (iv) quasi-stationary-state coarsening of ??-precipitates, once the equilibrium volume fraction of precipitates is achieved. The predictions of classical nucleation and growth models are not validated experimentally, likely due to the complexity of the atomistic kinetic pathways involved in precipitation. During coarsening, the temporal evolution of the ??-precipitate average radius, number density and the ?(fcc)-matrix and ??-precipitate supersaturations follow the predictions of classical models. |
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Taylor & Francis |
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1478-6435 |
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doi: 10.1080/14786430902806660 |
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NU @ karnesky @ |
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11158 |
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Mao, Zugang; Booth-Morrison, Christopher; Sudbrack, Chantal K.; Martin, Georges; Seidman, David N. |
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Kinetic pathways for phase separation: An atomic-scale study in Ni–Al–Cr alloys |
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Journal Article |
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2011 |
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Acta Materialia |
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60 |
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4 |
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1871-1888 |
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Nickel-based superalloys; Kinetic pathways; Atom probe tomography; Lattice kinetic Monte Carlo; Nanostructures |
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The kinetic pathways involved in the formation of [gamma]'(L12 structure)-precipitates during aging of concentrated Ni–Al–Cr alloys at 873 K, for three distinct alloy compositions, are studied experimentally by atom probe tomography, and computationally with lattice kinetic Monte Carlo (LKMC) simulations using parameters deduced from first-principles calculations of cohesive energies, and from experimental diffusion data. It is found that the compositional evolution of the [gamma]'-precipitate phase does not follow the predictions of a classical mean-field model for coarsening of precipitates in ternary alloys. LKMC simulations reveal that long-range vacancy–solute binding plays a key role during the early stages of [gamma]'-precipitation. With the aid of Monte Carlo techniques using the parameters employed in the LKMC simulations, we compute the diffusion matrix in the terminal solid-solutions and demonstrate that key features of the observed kinetic pathways are the result of kinetic couplings among the diffusional fluxes. The latter are controlled by the long-range vacancy–solute binding energies. It is concluded that, because it neglects flux couplings, the classical mean-field approach to phase separation for a ternary alloy, despite its many qualitatively correct predictions, fails to describe quantitatively the true kinetic pathways that lead to phase separation in concentrated metallic alloys. |
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1359-6454 |
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NU @ karnesky @ |
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11306 |
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Booth-Morrison, Christopher; Seidman, David N.; Dunand, David C. |
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Effect of Er additions on ambient and high-temperature strength of precipitation-strengthened Al-Zr-Sc-Si alloys |
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Journal Article |
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2012 |
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Acta Materialia |
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60 |
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8 |
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3643-3654 |
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Aluminum alloys; Precipitation; Scandium; Zirconium; Erbium |
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The effect of substituting 0.01 at.% Er for Sc in an Al-0.06Zr-0.06Sc-0.04Si (at.%) alloy subjected to a two-stage aging treatment (4 h/300 °C and 8 h/425 °C) is assessed to determine the viability of dilute Al-Si-Zr-Sc-Er alloys for creep applications. Upon aging, coherent, 2-3 nm radius, L12-ordered, trialuminide precipitates are created, consisting of an Er- and Sc-enriched core and a Zr-enriched shell; Si partitions to the precipitates without preference for the core or the shell. The Er substitution significantly improves the resistance of the alloy to dislocation creep at 400 °C, increasing the threshold stress from 7 to 10 MPa. Upon further aging under an applied stress for 1045 h at 400 °C, the precipitates grow modestly to a radius of 5-10 nm, and the threshold stress increases further to 14 MPa. These chemical and size effects on the threshold stress are in qualitative agreement with the predictions of a recent model, which considers the attractive interaction force between mismatching, coherent precipitates and dislocations that climb over them. Micron-size, intra- and intergranular, blocky Al3Er precipitates are also present, indicating that the solid solubility of Er in Al is exceeded, leading to a finer-grained microstructure, which results in diffusional creep at low stresses. |
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1359-6454 |
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NU @ karnesky @ |
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11342 |
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C. Booth-Morrison, Z. Mao, M. Diaz, D. C. Dunand, C. Wolverton, D. N. Seidman. |
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Role of Silicon in Accelerating the Nucleation of Al3(Sc,Zr) Precipitates in Dilute Al-Zr-Sc alloys |
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Journal Article |
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2012 |
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Acta Materialia |
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60 |
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60 |
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4740-52 |
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NU @ michaeljsrawlings @ |
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11447 |
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Booth-Morrison, Christopher; Dunand, David C.; Seidman, David N. |
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Coarsening resistance at 400 °C of precipitation-strengthened Al–Zr–Sc–Er alloys |
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Journal Article |
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2011 |
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Acta Materialia |
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59 |
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18 |
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7029-7042 |
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Aluminum alloys; Precipitation; Scandium; Zirconium; Erbium |
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The effect of substituting 0.01 or 0.02 at.% Er for Sc in an Al–0.06 Zr–0.06 Sc at.% alloy was studied to develop cost-effective high-temperature aluminum alloys for aerospace and automotive applications. Spheroidal, coherent, L12-ordered Al3(Sc, Zr, Er) precipitates with a structure consisting of an Er-enriched core surrounded by a Sc-enriched inner shell and a Zr-enriched outer shell (core/double-shell structure) were formed after aging at 400 °C. This core/double-shell structure strengthens the alloy, and renders it coarsening resistant for at least 64 days at 400 °C. This structure is formed due to sequential precipitation of solute elements according to their diffusivities, D, where DEr > DSc > DZr at 400 °C. Zr and Er are effective replacements for Sc, accounting for 33 ± 1% of the total precipitate solute content in an Al–0.06 Zr–0.04 Sc–0.02 Er at.% alloy aged at 400 °C for 64 days. Er accelerates precipitation kinetics at 400 °C, resulting in: (i) strengthening due to the elimination of lobed-cuboidal precipitates in favor of spheroidal precipitates; and (ii) a decrease in the incubation time for nucleation because DEr > DSc. Finally, a two-stage aging treatment (24 h at 300 °C + 8 h at 400 °C) provides peak microhardness due to optimization of the nanostructure. |
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1359-6454 |
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NU @ karnesky @ |
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11265 |
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Booth-Morrison, Christopher; Noebe, Ronald D.; Seidman, David N. |
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Effects of tantalum on the temporal evolution of a model Ni-Al-Cr superalloy during phase decomposition |
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Journal Article |
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2009 |
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Acta Materialia |
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Acta Mater. |
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57 |
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909-920 |
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Nickel-based superalloys; Tantalum; Atom-probe tomography; Nanostructures |
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The effects of a 2.0 at.% addition of Ta to a model Ni–10.0Al–8.5Cr (at.%) superalloy aged at 1073 K are assessed using scanning electron microscopy and atom-probe tomography. The γ′(L12)-precipitate morphology that develops as a result of γ-(fcc)matrix phase decomposition is found to evolve from a bimodal distribution of spheroidal precipitates, to {0 0 1}-faceted cuboids and parallelepipeds aligned along the elastically soft left angle bracket0 0 1right-pointing angle bracket-type directions. The phase compositions and the widths of the γ′-precipitate/γ-matrix heterophase interfaces evolve temporally as the Ni–Al–Cr–Ta alloy undergoes quasi-stationary state coarsening after 1 h of aging. Tantalum is observed to partition preferentially to the γ′-precipitate phase, and suppresses the mobility of Ni in the γ-matrix sufficiently to cause an accumulation of Ni on the γ-matrix side of the γ′/γ interface. Additionally, computational modeling, employing Thermo-Calc, Dictra and PrecipiCalc, is employed to elucidate the kinetic pathways that lead to phase decomposition in this concentrated Ni–Al–Cr–Ta alloy. |
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NU @ c-booth @ |
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10537 |
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