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Title (up) Booth-Morrison, Christopher; Mao, Zugang; Noebe, Ronald D.; Seidman, David N.
Year Chromium and tantalum site substitution patterns in Ni3Al (L1[sub:2]) [gamma]’-precipitates
Abbreviated Journal Journal Article
Issue 2008 Keywords Applied Physics Letters
Address App. Phys. Let.
Thesis 93
Place of Publication Language 033103
Original Title Nickel-based superalloys; Site substitution; Atom-probe tomography; Tantalum; Nanostructures, First-principles calculations
Series Title 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. Series Volume
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no NU @ m-krug @ ; NU @ c-booth @ 10296
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Booth-Morrison, Christopher; Dunand, David C.; Seidman, David N. Coarsening resistance at 400 °C of precipitation-strengthened Al–Zr–Sc–Er alloys Journal Article 2011 Acta Materialia 59 18 7029-7042 Aluminum alloys; Precipitation; Scandium; Zirconium; Erbium 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. 1359-6454 no NU @ karnesky @ 11265
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Booth-Morrison, Christopher; Seidman, David N.; Dunand, David C. Effect of Er additions on ambient and high-temperature strength of precipitation-strengthened Al-Zr-Sc-Si alloys Journal Article 2012 Acta Materialia 60 8 3643-3654 Aluminum alloys; Precipitation; Scandium; Zirconium; Erbium 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. 1359-6454 no NU @ karnesky @ 11342
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Booth-Morrison, Christopher; Noebe, Ronald D.; Seidman, David N. Effects of a tantalum addition on the morphological and compositional evolution of a model Ni-Al-Cr superalloy Journal Article 2008 Proceedings of the 11th International Symposium on Superalloys Proceedings of the 11th International Symposium on Su 73-79 The effects of a 2.0 at.% addition of Ta to a model Ni-Al-Cr superalloy aged at 1073 K are assessed using scanning electron microscopy and atom-probe tomography. The addition of Ta results in appreciable strengthening, and the morphology is found to evolve from a bimodal distribution of spheroidal precipitates, to cuboidal precipitates aligned along the elastically soft <001>-type directions. Tantalum is observed to partition preferentially to the &#947;’-precipitate phase and decreases the mobility of Ni in the &#947;-matrix sufficiently to cause an accumulation of Ni on the &#947;-matrix side of the &#947;’-precipitate/&#947;-matrix heterophase interface. The Minerals, Metals and Materials Society (TMS) Warrendale, PA Reed, R.C.; Green, K.A.; Caron, P.; Gabb, T.P.; Fahrmann, M.G.; Huron, E.S.; Woodard, S.A. no NU @ c-booth @ 10481
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Booth-Morrison, Christopher; Weninger, Jessica; Sudbrack, Chantal K.; Mao, Zugang; Noebe, Ronald D.; Seidman, David N. Effects of solute concentrations on kinetic pathways in Ni-Al-Cr alloys Journal Article 2008 Acta Materialia 56 14 3422-3438 Atom-probe tomography; Nanostructures; Nickel-based superalloys; Temporal evolution The kinetic pathways resulting from the formation of coherent &#947;'-precipitates from the &#947;-matrix are studied for two Ni-Al-Cr alloys with similar &#947;'-precipitate volume fractions at 873 K. The details of the phase decompositions of Ni-7.5Al-8.5Cr at.% and Ni-5.2Al-14.2Cr at.% for aging times from 1/6 to 1024 h are investigated by atom-probe tomography, and are found to differ significantly from a mean-field description of coarsening. The morphologies of the &#947;'-precipitates of the alloys are similar, though the degrees of &#947;'-precipitate coagulation and coalescence differ. Quantification within the framework of classical nucleation theory reveals that differences in the chemical driving forces for phase decomposition result in differences in the nucleation behavior of the two alloys. The temporal evolution of the &#947;'-precipitate average radii and the &#947;-matrix supersaturations follow the predictions of classical coarsening models. The compositional trajectories of the &#947;-matrix phases of the alloys are found to follow approximately the equilibrium tie-lines, while the trajectories of the &#947;'-precipitates do not, resulting in significant differences in the partitioning ratios of the solute elements. no NU @ karnesky @ 9627
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Booth-Morrison, Christopher; Noebe, Ronald D.; Seidman, David N. Effects of tantalum on the temporal evolution of a model Ni-Al-Cr superalloy during phase decomposition Journal Article 2009 Acta Materialia Acta Mater. 57 3 909-920 Nickel-based superalloys; Tantalum; Atom-probe tomography; Nanostructures 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 &#947;&#8242;(L12)-precipitate morphology that develops as a result of &#947;-(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 &#947;&#8242;-precipitate/&#947;-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 &#947;&#8242;-precipitate phase, and suppresses the mobility of Ni in the &#947;-matrix sufficiently to cause an accumulation of Ni on the &#947;-matrix side of the &#947;&#8242;/&#947; 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. no NU @ c-booth @ 10537
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Mao, Zugang; Booth-Morrison, Christopher; Sudbrack, Chantal K.; Martin, Georges; Seidman, David N. Kinetic pathways for phase separation: An atomic-scale study in Ni–Al–Cr alloys Journal Article 2011 Acta Materialia 60 4 1871-1888 Nickel-based superalloys; Kinetic pathways; Atom probe tomography; Lattice kinetic Monte Carlo; Nanostructures 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. 1359-6454 no NU @ karnesky @ 11306
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Booth-Morrison, Christopher Nanoscale Studies of the Early Stages of Phase Separation in Model Ni-Al-Cr Superalloys Journal Article 2009 Ph.D. Thesis 196 Ph.D. thesis no NU @ c-booth @ 10592
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Zhou, Yang; Booth-Morrison, Christopher; Seidman, David N. On the field-evaporation behavior of a model Ni-Al-Cr superalloy studied by picosecond pulsed-laser atom probe tomography Journal Article 2008 Microscopy and Microanalysis 14 06 571-580 The effects of varying the laser pulse-energy of a picosecond laser used in pulsed-laser atom- probe (PLAP) tomography of an as-quenched Ni-6.24 Al- 9.64 Cr at.% are assessed based on the quality of the mass spectra and the compositional accuracy of the technique. PLAP tomography improves mass resolution, increases the signal-to-noise (S/N) ratio, and improves compositional accuracy, compared to pulsed-voltage atom-probe tomography (APT). Experimental evidence suggests that Ni2+, Al2+ and Cr2+ ions are formed by post-ionization of singly charged ions, as well as by a thermally-activated evaporation process. An analysis of the detected noise levels reveals that there is no significant steady-state heating of the Ni-6.24 Al- 9.64 Cr at.% tips during PLAP tomography for properly chosen instrument parameters. no NU @ m-krug @ 10216
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Amouyal, Yaron; Mao, Zugang; Booth-Morrison, Christopher; Seidman, David N. On the interplay between tungsten and tantalum atoms in Ni-based superalloys: An atom-probe tomographic and first-principles study Journal Article 2009 Applied Physics Letters Appl. Phys. Lett. 94 041917 no NU @ c-booth @ 10551
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