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Martin, Georges |
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Solute Transfer at Interfaces |
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2003 |
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NU @ karnesky @ |
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103 |
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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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163 |
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Clouet, Emmanuel; Nastar, Maylise; Barbu, Alain; Sigli, Cristophe; Martin, Geroges |
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Precipitation in Al-Zr-Sc alloys:a comparison between kinetic Monte Carlo, cluster dynamics and classical nucleation theory |
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Book Chapter |
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2005 |
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Solid-Solid Phase Transformations in Inorganic Materials |
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2 |
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683-703 |
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Zr and Sc precipitate in aluminum alloys to form the Al3ZrxSc1−x compound which, for low
supersaturations of the solid solution, exhibits the L12 structure. The aim of the present
study is to model at an atomic scale the kinetics of precipitation and to build mesoscopic
models so as to extend the range of supersaturations and annealing times that can be simulated
up to values of practical interest. In this purpose, we use some ab initio calculations
and experimental data to fit an Ising type model describing thermodynamics of the Al-Zr-Sc
system. Kinetics of precipitation are studied with a kinetic Monte Carlo algorithm based on
an atom-vacancy exchange mechanism. Cluster dynamics is then used to model at a mesoscopic
scale all the different stages of homogeneous precipitation in the two binary Al-Zr and
Al-Sc alloys. This technique correctly manages to reproduce both the kinetics of precipitation
simulated with kinetic Monte Carlo as well as experimental observations. Focusing
on the nucleation stage, it is shown that classical theory well applies as long as the short
range order tendency of the system is considered. This allows us to propose an extension of
classical nucleation theory for the ternary Al-Zr-Sc alloy. |
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TMS |
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Howe, J. M.; Laughlin, D. E.; Lee, J. K.; Dahmen, U.; Soffa, W. A. |
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NU @ karnesky @ |
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166 |
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Clouet, Emmanuel; Barbu, Alain; La, Ludovic; Martin, Georges |
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Precipitation kinetics of Al3Zr and Al3Sc in aluminum alloys modeled with cluster dynamics |
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Journal Article |
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2005 |
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Acta Materialia |
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Acta Mater. |
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53 |
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8 |
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2313-2325 |
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Precipitation; Kinetics; Aluminum alloys; Cluster dynamics |
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Precipitation kinetics of Al3Zr and Al3Sc in aluminum supersaturated solid solutions is studied using cluster dynamics, a mesoscopic modeling technique which describes the various stages of homogeneous precipitation by a single set of rate equations. The only parameters needed are the interface free energy and the diffusion coefficient which are deduced from an atomic model previously developed to study the same alloys. A comparison with kinetic Monte-Carlo simulations based on the vacancy diffusion mechanism shows that cluster dynamics correctly predicts the precipitation kinetics provided a size dependent interface free energy is used. It also manages to reproduce reasonably well existing experimental data. |
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NU @ karnesky @ |
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211 |
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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 |
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Soisson, F.; Martin, G. |
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Kinetics of Decomposition of Metastable Solid Solutions: Comparison between Monte Carlo Simulations and Classical Theories |
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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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757-760 |
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precipitation, nucleation, incubation time, Monte Carlo simulations |
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We present a study on the kinetics of coherent precipitation in metallic binary alloys by . ~ Monte ~ & l osim ulations, based on a simple atomistic model with diffusion by vacancy jumps~ .
The whole precipitation process (from early stages to late stage coarsening) is followed for
various surpersaturations and temperatures, and typical behaviours observed in the simulations
are compared to those predicted by the classical theories. Special emphasis is placed on the first
stages of the decomposition (incubation and nucleation). |
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NU @ karnesky @ |
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276 |
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Athenes, M.; Soisson, F.; Bellon, P.; Martin, G. |
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Solid State Diffusion and Configurational Kinetics |
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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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433-440 |
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precipitation, ordering, nucleation, growth, coarsening, diffusion, vacancy, atomic scale, Monte Carlo simulation, kinetics |
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NU @ karnesky @ |
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277 |
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Ladwig, Peter F.; Olson, Jesse D.; Bunton, Joseph H.; Larson, David J.; Ulfig, Robert M.; Martens, Richard L.; Gribb, Tye T.; Kelly, Thomas F.; Bonsager, Martin C.; Schultz, Allan E.; Pant, Bharat B.; Chang, Y. Austin |
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Intermixing and phase separation at the atomic scale in Co-rich (Co,Fe) and Cu multilayered nanostructures |
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Journal Article |
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2005 |
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Applied Physics Letters |
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Appl. Phys. Lett. |
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87 |
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121912:1-3 |
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LEAP |
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Despite the fact that Co-rich (Co,Fe) alloys and Cu are immiscible materials in bulk form, evidence of thermally induced mixing at the atomic scale has been observed in thin-film multilayers of (Co,Fe) and Cu. However, long term anneals at lower temperatures produced a breakup of the multilayers into a two-phase mixture of (Co,Fe) and Cu particles. The observations were made with the use of the three-dimensional atom probe technique, with supporting evidence from differential scanning calorimetry and x-ray diffraction. Besides their scientific importance, these results are of interest where these (Co,Fe) and Cu thin films are used to produce the giant magnetoresistive effect. |
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NU @ karnesky @ |
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420 |
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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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Habibi-Bajguirani, H. R.; Martin, J. W.; Cantor, B. |
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TEM Studies of the Precipitation in High {Zr} Spray Formed {Al-Li-Zr} |
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Book Chapter |
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1996 |
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Aluminium Alloys: Their Physical and Mechanical Properties, Pts 1-3 |
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871-876 |
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Materials Science Forum |
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refbase @ user |
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1166 |
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