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Mao, Zugang; Sudbrack, Chantal K.; Yoon, Kevin E.; Martin, Georges; Seidman, David N. |
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The mechanism of morphogenesis in a phase separating concentrated multi-component alloy |
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Journal Article |
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2007 |
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Abstract |
Nature Materials |
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6 |
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3 |
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Summary Language |
210-216 |
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Abbreviated Series Title |
What determines the morphology of a decomposing alloy? Besides the well
established effect of the nucleation barrier, we demonstrate that, in a concentrated
multi-component Ni(Al,Cr) alloy, the details of the diffusion mechanism affect
strongly the kinetic pathway of precipitation. Our argument is based on the
combined use of atomic-scale observations, employing 3-dimensional atom-probe
tomography (3-D APT), lattice kinetic Monte Carlo simulations, and the theory of
diffusion. By an optimized choice of thermodynamic and kinetic parameters we first
reproduce the 3-D APT observations, in particular the early stage transient
occurrence of coagulated precipitates. We then modify the kinetic correlations
among the atomic fluxes in the simulation, without altering the thermodynamic
driving force for phase separation, by changing the vacancy-solute interactions,
resulting in a suppression of coagulation. Such changes can only be quantitatively
accounted for with nonzero values for the off-diagonal terms of the Onsager matrix,
at variance with classical models. |
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NU @ karnesky @ |
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1885 |
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Tang, Fengzai; Gault, Baptiste; Ringer, Simon P.; Martin, Phil; Bendavid, Avi; Cairney, Julie M. |
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Microstructural investigation of Ti-Si-N hard coatings |
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Journal Article |
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2010 |
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Scripta Materialia |
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63 |
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2 |
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192-195 |
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Titanium silicon nitride; Pulsed laser atom probe (PLAP); Nanostructure; Nanocomposite |
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The microstructures of nanostructured Ti-Si-N hard coatings were investigated by transmission electron microscopy and pulsed laser atom probe. C and O impurities were detected. No evidence of increased Si levels at the grain boundaries was found, suggesting that Si is either in the form of a layer too thin to be detected using the techniques employed or in the form of a solid solution of SiN clusters. |
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1359-6462 |
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NU @ karnesky @ |
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10856 |
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Antepara, I.; Villarreal, I.; Rodriguez-Martinez, L.M.; Lecanda, N.; Castro, U.; Laresgoiti, A |
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Evaluation of ferritic steels for use as interconnects and porous metal supports in IT-SOFCs |
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Journal Article |
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2005 |
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Journal of Power Sources |
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151 |
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103-107 |
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SOFC; ferritic stainless steel; oxidation; ASR |
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As a way of reducing the production costs of stacks by replacing ceramic components with metal components with a similar thermal expansion coefficient (TEC), today, much of the research work has focused on SOFCs operating at temperatures of under 800 degrees C. Some semi-commercial ferritic stainless steels (FSS) satisfy this TEC. Ikerlan has evaluated samples of two of these. Also, AMETEK stainless steel powders were tested in sintered disks until they were completely densified in order to compare results from dense and porous materials. The first tests performed by Ikerlan were conducted with dense samples and included the oxidation test in air at 800 degrees C and measurements of contact surface electrical resistance (area specific resistance, ASR), to compare electrochemical techniques (electrochemical impedance spectroscopy, EIS) with the traditional four-wire method and indirect measuring of the resistance through current and voltage measurements. An alloy from the last melt manufactured by the company ThyssenKrupp VDM GmbH performed best. These results did not differ greatly from the previous laboratory results attained during alloy development. Only AMETEK powder metallurgy materials were tested as porous bodies, to compare these with these dense materials. and were found to provide much higher oxidation levels, as might be expected. While dense materials can operate under the working conditions of the SOFC, porous materials still need new alloys. |
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NU @ karnesky @ |
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497 |
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Blavette, D.; Soisson, F.; Martin, G.; Pareige, C. |
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Ordering and Phase Separation in Model Superalloys: 3D Atom Probe versus Monte Carlo simulation |
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Book Chapter |
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1999 |
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Proceedings of the International Conference on Solid-Solid Phase Transformations |
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65-72 |
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ordering, phase separation, Ni-Al-Cr, 3D atom-probe, monte carlo simulation; 3D Atom Probe, Superalloys |
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The kinetics of ordering and unmixing in model superalloys (NiCrAl) at 600C were
effects in the ' investigated at the atomic scale using 3D atom probe and by transmission electron
it ion here that microscopy. Very fine precipitates (lnm) with a well ordered structure (Ni3 Al) were
observed in the early stages of growth At this stage, their composition was found very close
to the equilibrium composition of the y' phase. Coarsening of y' precipitates was observed in
the early stages, for particle radius under 2 nm Monte Carlo simulations of kinetics based on
a atom-vacancy exchanges mechanism and using a residence time algorithm were also
conducted. Experiments and simulations have shown a good agreement. Monte carlo
simulations indicate that short range ordering of both Al and Cr precedes the nucleation and
Ni3AI ordered phase. The Cr content in nuclei was foun: to be close to that of
solution in the very early stages of phase separation |
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NU @ karnesky @ |
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275 |
| Permanent link to this record |
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Sarrau, J. M.; Martin, C.; Bostel, A.; Gallot, J. C. R. |
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Atom probes: relationship between results of analysis and structure of a sample |
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Journal Article |
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1980 |
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C. R. Hebd. Seances Acad. Sci. B |
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290 |
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63-66 |
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atom probe field ion microscopy |
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7886 |
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Stone, D.S.; Gao, H.; Chantharangsi, C.; Paksunchai, C.; Bischof, M.; Jaeger, D.; Martini, A.; Scharf, T.W.; Aouadi, S.M. |
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Load-dependent high temperature tribological properties of silver tantalate coatings |
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Journal Article |
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2014 |
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Surface and Coatings Technology |
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244 |
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37-44 |
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Friction; Tribology; Silver tantalate; Molecular dynamics; Sputtering |
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Abstract Silver tantalate coatings were produced by reactive unbalanced magnetron sputtering from silver and tantalum sources as potential high temperature solid lubricants. The films were wear-tested at 750 °C under normal loads of 1, 2, 5, or 10 N against a Si3N4 counterface. These sliding tests revealed that the friction monotonically increased as the load was increased. A systematic investigation of the surface and sub-surface regions of the wear track, using techniques such as Scanning Auger Nanoprobe, Atom Probe Tomography, and cross-sectional transmission electron microscopy, revealed the following trends with increasing load: (1) a decrease in the amount of Ag on the surface of the wear track; (2) a decrease in the thickness of the mechanically mixed layer that forms as a result of the reconstruction of AgTaO3 to form Ta2O5 and Ag; and (3) the formation of a porous structure throughout the tribofilm as a result of the segregation and migration of Ag from the original AgTaO3 matrix. These results were complemented by molecular dynamics simulations, which confirmed the increase of friction with load. Further, the simulations support the hypothesis that this trend can be explained in terms of decreased presence of Ag clusters near the sliding surface and the associated decreased porosity. |
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0257-8972 |
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NU @ karnesky @ |
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11490 |
| Permanent link to this record |
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Mao, Zugang; Sudbrack, Chantal K.; Yoon, Kevin E.; Martin, Georges; Seidman, David N. |
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Impact of vacancy diffusion on the early decomposition stages of alloys |
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Journal Article |
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2005 |
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Nature |
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To be submitted |
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36 |
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The kinetic pathway for nucleation and growth is commonly thought to be
dictated by the initial supersaturation of solutes in the solid solution undergoing
phase separation. We demonstrate that the details of the diffusion mechanism, in
the solid solution affect deeply the early stage morphologies of precipitates. Our
argument is based on a combined use of atomic-scale observations, with atom-probe
tomography (APT) and lattice kinetic Monte Carlo simulation of a Ni(Al,Cr) alloy.
By an optimized choice of thermodynamic and kinetic parameters we first
reproduce the experimental APT observations. We then modify only the long-range
vacancy-solute binding energy, without altering the thermodynamic driving force
for phase separation, thereby demonstrating that the microstructural evolution
changes from a coagulation to an evaporation-condensation coalescence mechanism.
The changes can only be accounted for with nonzero values for the vacancychemical potential and off-diagonal terms of the Onsager matrix, at variance with
classical models. |
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NU @ karnesky @ |
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163 |
| Permanent link to this record |
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Soisson, F.; Pareige, C.; Athénes, M.; Martin, G.; Blavette, D. |
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Kinetics of phase transformations in metallic alloys: Monte-Carlo simulations versus experiments |
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Journal Article |
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1997 |
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Annales de Physique |
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Ann. Phys.-Paris |
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C2-22 |
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3-10 |
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3D Atom Probe, Phase transformation |
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2320 |
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Sarrau, J. M.; Martin, C.; Gallot, J. |
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An atom probe field ion microscope calibrated using tantalum a single isotope metal (French) |
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Journal Article |
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1975 |
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C. R. Hebd. Seances Acad. Sci. B |
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281 |
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calibration and charge state studies; atom probe field ion microscopy |
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6959 |
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Walls, J. M.; Martin, A. D.; Southworth, H. N. |
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Combined FIM AES and LEED study of the structure and composition of ion- bombarded W surfaces |
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Journal Article |
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1975 |
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Surface Science |
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Surf. Sci. |
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low energy ion bombardment; Field Ion Microscopy |
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6984 |
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