Symposium Organizers
Christian Abromeit Hahn-Meitner Institute
Pascal Bellon University of Illinois, Urbana-Champaign
Jean-Louis Bocquet Centre d’Etudes Nucleaires de Saclay-CEA
David N. Seidman Northwestern University
HH4: Grain boundaries and Interfaces
Session Chairs
Tuesday AM, November 28, 2006
Back Bay A (Sheraton)
9:00 AM - **HH4.1
Grain Rotation Due to Coupling.
Jean Taylor 1
1 , Courant Institute, New York, New York, United States
Show AbstractGrowth of one crystal into another should usually be coupled to relative tangential motion of the grains. When applied to grain growth, the grains should rotate; for small misorientation, this rotation has been shown to be in the direction to increase, rather than decrease, the surface energy per unit area of the interface, while decreasing the total surface free energy. The necessary mass transport for shape accommodation is assumed to be by grain boundary diffusion. We give a variational formulation, involving anisotropy and possibly non-linear kinetics, to determine the laws of motion for a non-circular-cylindrical crystal enclosed within another crystal. The work is joint with John W. Cahn.
9:30 AM - **HH4.2
Grain Growth in 3-D: Generalization of the von Neumann Relation.
David Srolovitz 1 , Robert MacPherson 2
1 Department of Physics, Yeshiva University, New York, New York, United States, 2 School of Mathematics, Institute for Advanced Study, Princeton, New Jersey, United States
Show AbstractThe von Neumann - Mullins relation is the fundamental theoretical result upon which most theories of grain growth are based. It is an exact relation between the number of edges of a grain to its growth rate in two-dimensions. Although 50 years old, there has never been an exact extension of this result to three dimensions. In this talk, we present the exact extension of this relation to three and higher dimensions. The 2-d von Neumann - Mullins relation is shown to be a special case of a more general theory. After presenting the exact theory, we examine several important consequences of the new result. This theory will be the basis of a more rigorous foundation for statistical grain growth theories in three dimensions.
10:00 AM - **HH4.3
Fast Diffusion Paths in Ultrafine Grain Copper Alloys Produced by Equal Channel Angular Pressing.
Eugen Rabkin 1 , Sergiy Divinski 2 , Yuri Estrin 3
1 Department of Materials Engineering, Technion, Haifa Israel, 2 Institute of Materials Physics, University of Muenster, Muenster Germany, 3 , Technical University of Clausthal, Clausthal-Zellerfeld Germany
Show Abstract10:30 AM - **HH4.4
Segregation and Ordering in Nanocrystalline Ni-W.
Christopher Schuh 1 , Andrew Detor 1
1 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States
Show Abstract11:30 AM - **HH4.5
Phase Transformations at Interfaces in Metals and Compounds.
Pamela Williams 1 , Yuri Mishin 1
1 Department of Physics and Astronomy, George Mason University, Fairfax, Virginia, United States
Show AbstractInterfaces in materials can undergo a large variety of phase transformations. Some of the best known examples are order-disorder transitions at alloy surfaces, pre-wetting and pre-melting transformations, and transformations between stable and metastable structures at grain boundaries. While general features of interface transformations have been extensively studied by continuum models, atomistic mechanisms of such transformations in specific materials and their impact on bulk properties have received much less attention. We apply grand-canonical Monte Carlo simulations with embedded-atom potentials to examine two different types of interface transformations. In one, Ag segregation at Cu high-angle grain boundaries leads to the formation of a thin liquid-like layer with the composition close to the liquidus composition on the Cu-Ag phase diagram. By studying the evolution of the segregation profile as a function of temperature and bulk composition, we construct the grain boundary pre-wetting line on the phase diagram. To verify this transformation and assess possible consequences for mechanical behavior, the grain boundary response to appliedshear stresses and its abrupt change a cross the pre-wetting line have been studied. In the second example, the atomic disorder and chemical composition near anti-phase boundaries (APBs) in the gamma' phase of the Ni-Al system have been studied as functions of temperature and bulk composition. A "pre-wetting" transition has been found, in which the APB develops a layer of the disordered gamma-phase, whose thickness increases as we approach the gamma-gamma' miscibility gap. The APB "pre-wetting" line on the Ni-Al phase diagram has been constructed and the possible impact of this transition on the dislocation core structure in gamma' is analyzed. The results of the atomistic simulations are compared with predictions of continuum models.
12:00 PM - **HH4.6
Grain Growth Kinetics in Nanocrystalline Ni: An Atomistic Simulation.
Diana Farkas 1
1 Materials Science, Virginia Tech, Blacksburg, Virginia, United States
Show AbstractWe report fully three dimensional atomistic molecular dynamics studies of grain growth kinetics in nanocrystalline Ni of 4 nm average grain size. The grain size was monitored as a function of time for various temperatures, until the total number of grains in the sample decreased by a factor of two. The results show the grain size increasing linearly with time, contrary to the well known square root of time kinetics observed in coarse grained structures. Detailed analysis of the growth process shows that for these very small sizes the grain growth is accompanied by grain rotation and, as a result of grain rotation, the average grain boundary energy per unit area decreases simultaneously with the decrease in total grain boundary area associated with grain growth. Grain rotation is made possible because of the nano-scale nature of the grain size and results in the linear kinetics of grain growth. Despite this particular kinetics characteristic of the nanoscale sizes, the activation energy for the process coincides with that observed for grain boundary self diffusion in general boundaries.
12:30 PM - HH4.7
A Diffuse Interface Thermodynamic Model of Grain Boundary Transitions in Binary Alloys.
Ming Tang 1 , W. Craig Carter 1 , Rowland Cannon 2
1 Dept. of Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States, 2 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractGrain boundary transitions have been found in many systems and often produce abrupt changes in macroscopic material properties. For boundary transitions in multi-component systems, grain boundary disordering are usually accompanied by changes in equilibrium boundary segregation. Existent models accounting for this phenomenon are rare and system-specific. We present a generalized diffuse interface model for cooperative structural and chemical grain boundary transitions in binary alloys. The model incorporates field variables of composition, structural disorder and crystallographic orientation. A graphic analysis, similar to the approach used by Cahn in his seminal work of critical point wetting in liquid/liquid systems, was developed to illustrate the general possibility of a first-order coupled premelting/prewetting grain boundary transition that leads to discontinuous changes in the thickness, local crystallinity and composition of grain boundaries. Numerical calculations for model eutectic systems show that the transition can occur in both two and single phase regions, and the coexistence line may terminate at a critical point. The predictions by our model provide a thermodynamic explanation to the grain boundary behavior observed in various ceramic systems, known as intergranular glassy films, as well as in metallic systems (Cu-Bi, Ni-W, etc).
12:45 PM - HH4.8
Interface-Stabilized Nanoscale Quasi-Liquid Films and Interfacial Prewetting and Premelting Transitions.
Jian Luo 1 2 , Vivek Gupta 1 , Haijun Qian 1
1 School of Materials Science and Engineering, Clemson University, Clemson, South Carolina, United States, 2 Center for Optical Materials Science and Engineering Technologies, Clemson University, Clemson, South Carolina, United States
Show AbstractA unique class of equilibrium-thickness, intergranular "glassy" films (IGFs) has been observed in doped Si3N4 and other ceramics. For decades, it was has been widely accepted that such nanoscale disordered films could be stabilized only 1) at internal interfaces, 2) in ceramic materials, and 3) coexisting with a non-wetting bulk liquid. Recently, this theory has been revisited due to several intriguing discoveries. First, free-surface counterparts to these IGFs, known as surficial amorphous films or SAFs, have been observed (Acta Mater. 48, 4501 (2001); Langmuir 21, 7358 (2005); Mater. Sci. Eng. A422, 19, (2006)). Second, the existence of similar grain boundary films in metals has been revealed (Appl. Phys. Lett. 87, 231902 (2005)). Finally, a series of studies revealed the stabilization of quasi-liquid interfacial films well below the solidus or eutectic temperatures wherein the bulk liquid is no longer stable.This presentation critically compares several classes of interface-stabilized, nanometer-thick, quasi-liquid films, with a goal to explore a unifying theoretical framework. A focus is placed on recent observations of quasi-liquid grain boundary films in metals using W-Ni as a model system. High-resolution transmission electron microscopy and Auger electron spectroscopy have revealed the formation of 0.6 nm thick, Ni-enriched, disordered, grain boundary layers in Ni-doped W specimens at 95C below the bulk eutectic temperature. In general, the stability of nanoscale interfacial films should not follow bulk phase diagrams, and in principle, various interfacial phase transitions exist. Specifically, the stabilization of subeutectic quasi-liquid interfacial films in this model two-component metal alloy is analogous to premelting in one-component systems. These nanoscale films can also be considered as multilayer adsorbates at grain boundaries in a prewetting regime, bounded by complete wetting and drying transitions, wherein an analogy to Cahn's critical point wetting model can be made. We propose that a combined interfacial premelting and prewetting model applies well to these metallic IGFs, and serves as a base to understand more complex IGFs and SAFs in ceramics where additional interactions, e.g., dispersion forces and space-charges, should be added separately.The existence of such quasi-liquid interfacial films has important technological implications in grain boundary migration and diffusion kinetics, grain boundary embrittlement, and creep, corrosion and oxidation resistance. For example, short-circuit diffusion in quasi-liquid grain boundary films was found to be responsible for the solid-state activated sintering in W-Ni. Similar activated sintering mechanisms have previously been observed for ZnO-Bi2O3 and proposed for ice-impurity systems, showing analogous behaviors among metals, ceramics and molecular solids. (Acknowledgements: NSF CAREER award (DMR-0448879) and ORAU Ralph E. Powe Junior Faculty Enhancement award).
HH5: Plasticity I
Session Chairs
Tuesday PM, November 28, 2006
Back Bay A (Sheraton)
2:30 PM - **HH5.1
Excess Vacancies and Phase Transformations Under Strong Plastic Deformation.
Ferdinand Haider 1
1 Inst. f. Physics, Univ. Augsburg, Augsburg Germany
Show Abstract3:00 PM - HH5.2
Temporal Evolution of Microstructure and Mechanical Properties in Al Strengthened with Sc, Er and Yb.
David Dunand 1 , Marsha van Dalen 1 , Richard Karnesky 1 , David Seidman 1
1 Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
Show Abstract3:15 PM - HH5.3
Two-way Shape Memory Surfaces – Experimental Observations and Modeling.
Yijun Zhang 1 2 , Yang-Tse Cheng 2 , David Grummon 1
1 Department of Chemical Engineering & Materials Science, Michigan State University, East Lansing, Michigan, United States, 2 Materials & Processes Laboratory, General Motors Research & Development Center, Warren, Michigan, United States
Show AbstractTwo-way shape memory effect is realized in NiTi shape memory alloy from spherical indentation [1,2]. Both thermomechanical cycling and slip-plastic deformation under contact loading conditions are effective in inducing reversible indent depth changes: deeper indent at martensitic phase and shallower indent at austenitic phase. By planarization of these spherical indents to restore a flat surface, circular reversible surface protrusions appear by heating temperatures to austenitic phase and disappear by cooling to martensitic phase. Nano-protrusions are also realized in sputter deposited NiTi thin films on silicon substrates. Two-way reversible line protrusions are realized from planarizing scratch tracks on a NiTi shape memory alloy. A spherical cavity model is developed to understand two-way shape memory surfaces. The model is consistent with experimental observations and finite element calculations. Shape memory surfaces can be exploited for a wide range of potential applications, including information storage, optical devices, and smart tribological surfaces. [1] Yijun Zhang, Yang-Tse Cheng, and David S. Grummon, Appl. Phys. Lett. 88, 131904 (2006).[2] Yijun Zhang, Yang-Tse Cheng, and David S. Grummon, Appl. Phys. Lett. (in press).
3:30 PM - HH5: Plasticity1
BREAK
HH6: Irradiation Effects
Session Chairs
Tuesday PM, November 28, 2006
Back Bay A (Sheraton)
4:00 PM - **HH6.1
New Ideas in the Field of Kinetics in Metals and Alloys.
Colin Flynn 1
1 Physics, University of Illinois, Urbana, Illinois, United States
Show Abstract For most of his research career, George Martin's work has concerned thermal point defects and their interaction with fields of energetic radiation in metals and alloys. This is a fertile field that, to this day, remains the origin of interesting new ideas. Here I illustrate this point by discussing several recent contributions that each bring qualitatively new understanding. First, that the hopping of bulk, surface and edge defects are aspects of one process that is described by a single set of orthogonal relaxation modes[1]. These separate exactly into modes of differing dimensionality (eg surface or bulk modes) only in the limit that no hopping transitions connect the different types of sites. Second, that when precisely formulated, the equations for reacting thermal antidefects can be solved exactly[2] for the regime of linear response, to obtain two surfaces of relaxation modes spread through the Brillouin Zone. Only near the Zone center do these modes respectively describe recombination of antidefects, and diffusion of the antidefects to their sinks. In connection with sink action, one may further introduce the concept of 'pseudo-growth'. Michely and coworkers[3] report beautiful STM images showing formerly clean surface terraces newly decorated by 10s of adatoms per event following ion impacts of several keV energy. In the MD calculations of Averbach and coworkers[4] these adatoms are compensated by bulk vacancies. In recent LEEM work [5] on Pt(111,) we find that surface sinks lose atoms during steady state irradiation with Pt-, rather than gaining adatoms, no doubt due to recombination. Thus the excess of adatoms plays no part in real growth, and should instead be termed pseudogrowth. The excess is a property of a frozen configuration, not of the steady state.[1] C.P.Flynn, Phys Rev B73 155417 (2006); [2] C.P.Flynn, Phys Rev B71, 085422 (2005); [3] A.Petersen, C.Busse, C.Polop, U.Linke and T.Michely, Phys Rev B68, 3245410 (2003); [4] M.Ghaly, K.Nordlund and R.S.Averback, Phil Mag 79, 795-820 (1999); [5] C.P.Flynn, M.Rajappan, W.Swiech, M.Ondrejcek and C.P.Flynn, LEEM/PEEM 2006, Surface Science, to be published.
4:30 PM - **HH6.2
Some Basic Questions Arising from Materials Applications in High Power Accelerators, with Comparisons to Fission and Fusion Reactors.
Louis Mansur 1
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractApplications of materials in high power accelerators, particularly for beam targets and nearby areas, present many challenging issues. In particular, spallation neutron sources impinge a proton beam of GeV energy onto a high atomic mass target. Research and development on materials for spallation neutron sources has increased substantially over the last decade. The purpose of much of this work has been to ensure that maximum scientific and technical information is made available for the designs of major high power accelerators throughout the world. In the course of this work a number of fundamental questions naturally have arisen related to mechanisms of radiation effects and to other aspects of these aggressive environments. While some are unique to high power accelerators, other basic questions are similar to those arising in materials applications in fission and fusion reactors. For example, the high displacement doses in the target structures, produced by the impinging proton beam and by spallation neutrons, are similar to those in high flux reactor cores and fusion reactor first walls.Performance limiting phenomena, such as embrittlement and dimensional instability, are the same in these three technologies. These phenomena depend upon the same physical mechanisms in an irradiation environment. Further, primary structural materials are selected from the same alloy classes and in some cases the same alloys. There are numerous other similar requirements such as operation at elevated temperatures under significant time-varying loads, and compatibility with special purpose fluids for heat transfer, neutron production or isotope breeding. In addition to radiation effects in metallic structural alloys, materials scientists must address radiation effects in polymers and ceramics, which may be employed as seals, sensors, or insulators. Some key areas of progress are reviewed and materials questions in need of basic research are described.
5:00 PM - HH6.3
Irradiation-induced Patterning in Cu-Co, Cu-Ag and Ag-Co Alloys.
Pavel Krasnochtchekov 1 , SeeWee Chee 1 , Matt Enloe 1 , Robert Averback 1 , Pascal Bellon 1
1 Materials Science and Engineering, University of Illinois, Urbana, Illinois, United States
Show AbstractThe effective temperature model introduced by Martin in 1984 has been widely used to explain the phase stability of irradiated materials. In this model, an irradiated alloy system is described by the equilibrium phase but at an effective temperature given by Teff = T(1 + g), where g is the ratio of atomic jumps from ballistic (i.e. random) events, such as energetic recoil collisions, and thermally activated events. Enrique and Bellon have shown that added to this picture is the possibility of an alloy undergoing mesoscopic patterning if g and the displacement distance of recoiling atoms, R, are sufficiently large. These concepts give rise to constructions of dynamic steady-state phase diagrams. The present work tests whether these models are sufficiently robust to predict the behavior in real alloys. Here we report on phase evolution in a series of irradiated immiscible alloys, CuAg, CuCo, and AgCo, which have increasingly more positive heats of solution. We employ a combination of x-ray diffraction, magnetization, and field-ion atom probe measurements as well as molecular dynamics and kinetic Monte Carlo calculations.For the Cu-15at% Ag and Cu-15at% Co systems, steady state microstructures were well described by the calculated dynamic phase diagram. At low temperatures, these systems were driven to complete solid solutions, patterning was observed at intermediate temperatures, and macroscopic phase separation occurred at high temperatures. The temperature interval in which patterning was observed was shifted to higher temperatures for the Cu-15at% Co alloy. This could be explained by the higher mobility of Ag than Co in the irradiated alloys, as determined independently by radiation-enhanced diffusion measurements, and molecular dynamics simulations.The Ag-15%atCo alloy also could be interpreted within the effective temperature model, however, the two regimes of solid solutions and patterning were not observed . This could be understood on the basis that diffusion in the thermal spikes of a cascade is not ballistic. Quantitative analysis of the growth rate in this alloy, however, suggests that the mechanism of growth does not, in fact, involve atomic diffusion, but rather precipitate coarsening by coalescence.
5:15 PM - HH6.4
Irradiation-Induced Amorphization of Titanate Pyrochlore—Insights from in situ Experiments and Atomistic Simulations.
Ram Devanathan 1 , William Weber 1
1 Fundamental Science Directorate, Pacific Northwest National Laboratory, Richland, Washington, United States
Show Abstract5:30 PM - HH6.5
The Influence of Electronic Stopping Interactions on the Microstructural Modification Observed in High Energy Ion Irradiated NiTi Thin Films.
Thomas LaGrange 1 , Rolf Gotthardt 2 , Christian Abromeit 3 , Siegfried Klaumünzer 3 , Gerhard Schumacher 3
1 Materials Science and Technology Division, Lawrence Livermore National Laboratory, Livermore, California, United States, 2 Institute of Physics of Complex Matter, Swiss Institute of Technology (EPFL), Lausanne Switzerland, 3 , Hahn Meitner Institute, Berlin Germany
Show Abstract5:45 PM - HH6.6
Identification of Nanoscale Patterning of Chemical Order in Alloys Driven by Ion Irradiation by Scaling Analysis of Order Fluctuations.
Jia Ye 1 , Yaofeng Chen 1 , Pascal Bellon 1
1 Materials Science and Engineering, university of Illinois, Urbana, Illinois, United States
Show AbstractRecent analytical modeling and atomistic computer simulations suggest that external forcing, for instance through ion irradiation, can lead to the spontaneous patterning of the degree of chemical order in alloys that form ordered phases at equilibrium. One fundamental question that needs to be addressed, however, is how to distinguish the disordered solid solution state from the state of patterning of order. This question is not trivial since kinetic Monte Carlo simulations for L12 and L10 ordered structures indicate that the dynamical transition between the two steady states, which both lack long range order, is continuous. We propose here to use a scaling approach of the fluctuations of order, both in space and time domain, to uncover key differences that make it possible to distinguish these steady states. For irradiation conditions that produce small cascade sizes, no patterning of order can be stabilized and the structure of the fluctuations obeys a scaling that is well described by the effective temperature introduced by G. Martin in 1984. However, for irradiation conditions producing dense and large cascades, typically above 2 nm in diameter, scaling of the fluctuations of order requires the introduction of a new parameter. We show that this new parameter can be used to define the transition between the disordered steady state and the patterning of order steady state. The possible application of this approach to experiments is discussed.
Symposium Organizers
Christian Abromeit Hahn-Meitner Institute
Pascal Bellon University of Illinois, Urbana-Champaign
Jean-Louis Bocquet Centre d’Etudes Nucleaires de Saclay-CEA
David N. Seidman Northwestern University
HH7: Microstructural Evolutions I
Session Chairs
Wednesday AM, November 29, 2006
Back Bay A (Sheraton)
9:00 AM - **HH7.1
Theoretical Characterization of Structural Evolution in Phase Transformations.
Armen Khachaturyan 1
1 Materials Science and Engineering, Rutgers University, Piscataway, New Jersey, United States
Show AbstractThe structural transformations in solids are constrained by elastic coupling of new phase particles, which greatly affects their thermodynamics, kinetics and morphology. There is a great variety of possible configurational sequences in the evolution leading to the equilibrium, and a model of such an evolution may be misleading if it postulates in advance the structures of transient states. The so-called Phase Field theory (Landau-Lifshitz-Khalatnikov type approach) is free from these shortcomings. This theory describes the spontaneous spatial and temporal evolution of the composition, displacive modes, the long-range order parameters, and etc. by non-linear kinetic equations for spontaneously evolving densities of these characteristics. The approach based on the density function evolution can be extended to the atomic scale. The corresponding Atomic Density Function method is also reduced to a solution of the non-linear kinetic equation. This method can be more suitable for modeling of “slow” processes such as diffusional phase transformations than the straightforward MD modeling. The examples of a nano-scale modeling of a heterogeneous nucleation of martensitic phase on dislocation loops and atomic scale modeling of the growth of a coherent particle with significantly different crystal lattice structure are presented. It is shown that martensitic embryos are not a single domain coherent particle as is usually thought but rather a complex assemblage of twin-related domains. A disappearance of the nucleation barrier reduced by the dislocation triggers an athermal martensitic transformation. The atomic-scale modeling illustrates an atomic mechanism of the phase transformation with a strong crystal lattice misfit. It is shown that a spontaneous atomic rearrangement results in the formation of a transient single-domain phase with complex atomic structures in the beginning of the phase transformation to reduce the transformation stress. These two examples illustrate that the approaches allowing a system to “select” its own evolution path may yield unexpected results. Some of them may motivate us even to rethink some established notions of the phase transformation theory.
9:30 AM - **HH7.2
Quantitative Phase Field Modelling Of Precipitation.
Quentin Bronchart 1 , Yann Le Bouar 1 , Alphonse Finel 1
1 LEM, ONERA / CNRS, Chatillon France
Show Abstract10:00 AM - HH7.3
Topological Modelling of Martensitic Transformations in Ferrous Systems.
Xiao Ma 1 , R. Pond 1
1 Materials Science and Engineering, The University of Liverpool, Liverpool United Kingdom
Show AbstractFor many years the cornerstone of our understanding of martensitic transformations has been based on the hypothesis that the habit plane is an invariant plane of the shape transformation, as developed by Wechsler, Lieberman and Read, and Bowles and MacKenzie. Experimental observations of the crystallography of a range of transformations are consistent with this notion, but several instances, including some ferrous alloys, are not. Recently, a topological model of martensitic transformations has been presented wherein the habit plane is a semi-coherent structure, as is observed using transmission electron microscopy. This approach not only describes the interface structure, but also demonstrates explicitly that the proposed transformation mechanism is diffusionless. According to the topological model, the parent-martensite interface comprises planar terrace segments reticulated by an array of defects, namely crystal slip or twinning dislocations and mobile disconnections, which accommodate coherency strains. Lateral motion of the disconnections also effects the transformation.The transformation crystallography predicted using the topological approach differs systematically from the classical approach, reflecting the differing compatibility criteria at interfaces between atomic solids, as represented in the former, and continua, as in the latter. Experimental observations of transformations in ZrO2 and Ti alloys are in excellent agreement with the topological model, and the objective of the present work is to consider ferrous alloys. The topological procedure to establish the habit plane, orientation relation of the parent and martensite crystals, and transformation displacement will be described for chosen ferrous alloys and compared with the phenomenological predictions. It is shown that the predictions of the topological model show good agreement with experimental observations obtained using transmission electron microscopy of parent-martensite interfaces.
10:15 AM - HH7.4
Multiscale Phase Field Modeling of Phase Transformation and Plastic Deformation
Chen Shen 1 , Ju Li 1 , Yunzhi Wang 1
1 Materials Science and Engineering, The Ohio State University, Columbus, Ohio, United States
Show AbstractThe phase field method has received much attention lately as a quantitative technique to model complex morphological patterns formed during many materials processes including phase transformation, grain growth, sintering, interdiffusion, and plastic deformation. It accounts self-consistently for high volume fraction of precipitates, multiple anti-phase domains and orientation variants, dislocation substructures, shape anisotropy and spatial alignment induced by long-range elastic interactions, and topological changes such as coalescence and splitting. In this presentation, we introduce a new microscopic phase field (MPF) model developed by using arbitrary inelastic strain fields, generalized stacking fault (GSF) energy, and continuum or lattice Green's function solution of long-range elastic interactions. In particular, we discuss the MPF formulation in contrast to the conventional mesoscopic phase field method. In combination with the nudged elastic band (NEB) method, we apply MPF to compute the minimum energy path, activation energy and critical nucleus configuration during phase transformations and plastic deformation. The effects of preexisting defects on nucleation processes are addressed.
10:30 AM - HH7.5
Modeling of Local Order Phase Transformations in Binary Alloys
Nikolay Lazarev 1 , Christian Abromeit 2 , Syo Matsumura 3 , Rolf Gotthardt 4 , Robin Schäublin 5
1 Theoretical Physics, NSC Kharkov Institute of Physics and Technology, Kharkov Ukraine, 2 Materials, Hahn-Meitner-Institut Berlin, Berlin Germany, 3 Applied Quantum Physics and Nuclear Engineering, Kyushu University , Fukuoka Japan, 4 Institute de Physique de la Materiere Complexe, EPFL , Lausanne Switzerland, 5 FT - Materials, CRPP - EPFL , Villigen Switzerland
Show AbstractPhase transformations in binary alloys are generally connected with local changes of the chemical and structural order. An analytical description of such coupled processes is usually based on a self-consistent field approach like Ginzburg-Landau theory where only global order parameter can be considered. However, using numerical simulation treatments such as Monte-Carlo (MC) or Molecular Dynamics (MD) simulations for the transformation, an atomistic local analysis is possible. The local environment around each alloy atom is checked with respect to the chemical and structural symmetry. The chemical order is based on an locally defined compositional order (LCO) parameter, whereas the local structural order (LSO) parameter definition uses the combined method of Voronoy tessellation with common-neighbor analysis. With these parameters the phase transformation can be followed on an atomistic scale showing how the nucleation process and the volume fraction of the new phase evolve with time.The procedure is illustrated through several examples: LCO-disorder without structural order changes by MC calculations in Ni3Al and Ni4Mo, displacive martensitic-austenitic transformations by MD simulation in Ni-Al and the irradiation-induced cascade or track formation in Ni-Al systems where both kinds of order changes are observed simultaneously.
10:45 AM - HH7.6
Transformations by Design.
Greg Olson 1
1 MSE, Northwestern University, Evanston, Illinois, United States
Show AbstractPredictive theory of first-order phase transformations plays a central role in the modern discipline of materials design. Thermodynamic and kinetic theory support parametric materials design while explicit simulation of microstructural evolution supports process optimization at the component level. Martensite kinetic theory enables control of retained austenite in cryogenically processed martensitic steels, and the PrecipiCalc precipitation simulator has demonstrated both component process optimization and prediction of manufacturing variation in aeroturbine superalloys. The combination of precipitation and martensitic transformation theory enables application of dispersed-phase transformation toughening in high-performance steels. Molecular associate thermodynamics based models of Trg in Fe-based bulk metallic glasses have provided critical cooling rates down to 100K/s enabling twin roll casting of mm thick glass sheet, and transformation toughening models predict the feasibility of transformation toughening in partially devitrified glasses.
11:00 AM - HH7: Micro 1
BREAK
HH8: Amorphous Materials
Session Chairs
Wednesday PM, November 29, 2006
Back Bay A (Sheraton)
11:30 AM - **HH8.1
Glass Transition and Shear Modulus in Amorphous Metallic Systems.
Konrad Samwer 1 , William Johnson 2 , Stefan Mayr 1 , Mareike Zink 1 , Marios Demetriou 2 , Annelen Kahl 1
1 I.Physik. Institut, Univ. Gottingen, Goettingen Germany, 2 , Caltech, Pasadena, California, United States
Show AbstractThe dynamics of the undercooled liquid and the mechanical properties of the glassy state is a long ongoing problem. Recently we presented a new concept for metallic glasses on the basis of the potential energy landscape using the Frenkel concept and the Wales criterion to discuss the yield stress of all known systems [1]. Here we present MD simulations and shear sound velocity measurements on PdNiP which give further evidence for the concept of cooperatively shear flow zones (STZ) as predicted in the model [2]. Further details concerning the glass transition and the relaxation behaviour will be discussed.[1] W.L. Johnson and K.Samwer, PRL 95 (2005) 195501[2] M.Zink,K.Samwer,W.L. Johnson and S.Mayr Phys.Rev.B 73 (2006) 172203
12:00 PM - **HH8.2
Microstructural Stability of Amorphous Al Alloys during Intense Deformation and Annealing.
John Perepezko 1 , Rainer Hebert 1 , Joseph Hamann 1
1 Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractMaterials for structural applications should offer both, high strength and useful ductility. The development of amorphous alloys, for example, has pushed the specific strength levels of metallic materials into the domain of ceramic materials. At ambient temperatures, however, the formation of shear bands during deformation often limits the ductility of monolithic amorphous alloys and therefore precludes their use for engineering applications. This limitation can be addressed with the dispersion of nanocrystals in amorphous matrices with specific size distributions and particle number densities. For Al-based amorphous alloys, for example, nanocrystal particle number densities of the order of 1022 m-3 and nanocrystal sizes of the order of the width of the shear bands (10-20 nm) improve the mechanical properties. The nanocrystal size and number density dependence of the mechanical properties accentuates the need for refining the microstructure control options. Besides thermally induced crystallization of nanocrystals, intense deformation of amorphous alloys at room-temperature represents a novel approach that is related to a driven system response for tailoring microstructures of metallic nanocrystal/glass composites. Intense deformation offers the opportunity, for example, to reduce the size of existing cluster dispersions during dislocation-based disintegration reactions of the nanocrystals. At the same time, intense deformation can not only disintegrate nanocrystals, but also induce them inside shear bands. Combined annealing, deformation, and electron microscopy studies demonstrate that the deformation is not only limited to shear bands as previously assumed and indicated by the development of nanocrystals during deformation, but induces atomic rearrangements in the amorphous matrix outside the shear bands. The thermally and deformation-induced primary crystallization reactions that provide the basis for the nanocrystal dispersions appear to develop from quench-retained structural heterogeneities in the amorphous phase. These heterogeneous atomic arrangements therefore represent the key characteristic to control nanoscale microstructures and thus to advance the mechanical properties of nanocrystal/glass composites.
12:30 PM - HH8.3
Amorphous Structures and Polymorphic Transitions in Metallic Glasses.
Evan Ma 1 , Howard Sheng 1
1 Materials Sci & Eng, Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractUnlike the well-defined long-range order that characterizes crystalline metals, the details of atomic arrangements in amorphous alloys remain mysterious (although short-range order is considered ubiquitous and medium-range order likely). Solving the atomic packing structure and short-to-medium range order is an important and challenging problem for the materials science of (metallic) glasses. A comprehensive knowledge of the glass structure has broad implications for understanding the properties of amorphous metals, including how they deform in absence of dislocations.In this work, we use a combination of experimental and computational techniques to elucidate how the atoms pack in 3D, in several model metallic glasses with different chemistry and atomic size ratios [1]. Very recent progress, employing large systems using potentials derived from inverse Monte Carlo simulations, will also be discussed. In particular, we will add information regarding bond angle distributions and comparison with other structural analysis instruments (such as bond orientation parameter analysis) to further confirm the medium-range order uncovered. The tuning of the local structure of a metallic glass using pressure [2] will be briefly described. Finally, we will discuss the polyamorphism, i.e., the observation of amorphous-to-amorphous transformation in metallic glass [3]. [1] H.W. Sheng et al., Nature Vol. 439(2006) pp. 419-425.[2] H.W. Sheng et al., Appl. Phys. Lett. 88 (2006) article No. 171906.[3] H.W. Sheng et al., to be published.
12:45 PM - HH8.4
Characterizing Shear Ttransformation Zones - a Key for Understanding Plasticity of Glasses.
Stefan Mayr 1
1 I. Physikalisches Institut, Universitaet Goettingen , Goettingen Germany
Show AbstractHH9: Microstructural Evolutions II
Session Chairs
Wednesday PM, November 29, 2006
Back Bay A (Sheraton)
2:30 PM - **HH9.1
Properties of Alloy Crystal-Melt Interfaces from Atomistic Simulations.
Chandler Becker 1 , Mark Asta 2 , Jeffrey Hoyt 3 , Stephen Foiles 3
1 Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States, 2 Department of Chemical Engineering and Materials Science, University of California at Davis, Davis, California, United States, 3 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show Abstract3:00 PM - **HH9.2
The Evolution of Bicontinuous Interfaces During Coarsening.
Yongwoo Kwon 1 , Katsuyo Thornton 2 , Peter Voorhees 1
1 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States, 2 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show Abstract3:30 PM - HH9: Micro 2
BREAK
HH10: Plasticity II
Session Chairs
Wednesday PM, November 29, 2006
Back Bay A (Sheraton)
4:00 PM - **HH10.1
Phase Transformations during Plastic Deformation.
Michael Atzmon 1
1 NERS & MSE, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractIn an externally-driven alloy, e.g., by irradiation or plastic deformation, the phases present may differ from those required by thermodynamic equilibrium. The external action leads to two simultaneous processes: a) introduction of excess disorder and b) increase in atomic diffusivity due to the production of nonequilibrium defects. If the initial state corresponds to thermodynamic equilibrium, effect (a) will move the alloy away from equilibrium. On the other hand, (b) may increase the rate of back-diffusion toward equilibrium. If a balance is reached between the two, a nonequilibrium steady state is expected. Martin* has shown that the steady state of some externally-driven alloy models can be described in terms of an effective temperature that is greater than the true temperature. Research results on alloy phase formation during mechanical alloying have led to renewed interest in the concepts analyzed by Martin. In the present paper, examples of alloys driven by ball milling will be presented. The examples include supersaturated solutions of Cu and Fe, as well as a metallic glass that crystallizes as a result of plastic deformation. In addition, controlled deformation by nanoindentation is used to gain insight into mechanically assisted crystallization of a metallic glass. ____* G. Martin, Phys. Rev. B30, 1424 (1984).This work was funded by the NSF Division of Materials Research.
4:30 PM - **HH10.2
Phase Transformation Induced by Grinding: What is Revealed by Molecular Materials?
Descamps Marc 1 , Willart Jean Francois 1
1 Physique, University Lille1, Villeneuve d' Ascq France
Show Abstract5:00 PM - **HH10.3
Dislocation Length Scales in f.c.c. Crystals.
Ladislas Kubin 1 , Benoit Devincre 1 , Thierry Hoc 2
1 CNRS-ONERA, LEM, Chatillon Cedex France, 2 Laboratoire MSSMat, Ecole Centrale Paris, Chatenay-Malabry France
Show AbstractThere are three dislocation length scales in dislocation theory: the average distance between dislocations, the dislocation mean-free path and the wavelength of self-organized dislocation patterns. These quantities are involved in the modeling of strain hardening and patterning phenomena but, unfortunately, only the role of the first one is understood. The average distance between dislocations governs the local stress for the unpinning of a dislocation segment blocked by interactions with other segments. In average over the microstructure, it is approximately proportional to the inverse of the critical stress for the onset of plastic flow on the slip system of the considered segments.The mean-free path of dislocations in a given slip system governs the rate at which dislocations of this system are stored during plastic flow. Within an expanded storage-recovery framework, this quantity is modeled for the first time in terms of the short-range interactions between dislocations in multislip conditions. It is shown that it depends on three quantities, the density of obstacles piercing the considered slip planes, the probability for making a junction, which is a material constant for all f.c.c. crystals, and the average strengths of the dislocation interactions between slip systems which are also material constant for all f.c.c. crystals. The values of these constants are determined using dislocation dynamics simulations. The combination of the first two length scales allows establishing a model for strain-hardening of f.c.c. crystals in monotonic deformation, which is based on known parameter values. The predictions of this model and its limits are discussed with respect to experimental data on single crystals. At present, there is no dislocation-based model that is able to simultaneously deal with both hardening and patterning phenomena. As a consequence, it seems that the dislocation properties governing the wavelength of dislocation patterns are presently treated in a too simple manner to be totally realistic. This question is discussed in the light of recent simulations of dislocation dynamics.
5:30 PM - HH10.4
Nucleation and Kinetics of Shock-induced Plastic Deformations.for group-IV nanoparticles from first-principles molecular dynamics
Matteo Cococcioni 1 , Gerbrand Ceder 1 , Nicola Marzari 1
1 DMSE and ISN, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show Abstract5:45 PM - HH10.5
Effects of Temperature and Structural Defects on the Strength and Structural Response of Cubic Inorganic Crystals under Mechanical Loading
Hadrian Djohari 1 , Frederick Milstein 2 , Dimitrios Maroudas 1
1 Department of Chemical Engineering, University of Massachusetts at Amherst, Amherst, Massachusetts, United States, 2 Departments of Mechanical Engineering and Materials, University of California, Santa Barbara, California, United States
Show AbstractPredicting the limit of strength of crystalline solids under specified mechanical loading requires systematic analyses of the crystals’ elastic stability, taking all the relevant parameters into account. At given temperature, the structural response of a crystal to a specified mode of applied mechanical loading becomes unstable beyond a critical stress level. This large-strain mechanical deformation may lead to phase transformation or fracture of the crystal. Determining the onset of elastic instability and analyzing the structural response of the crystalline solid beyond the instability onset is a topic of major interest in the mechanics of crystalline inorganic materials. In this presentation, we report systematic elastic stability analyses for cubic metallic crystals subjected to mechanical loading using isostress-isothermal, as well as canonical, molecular-dynamics (MD) simulations. We examine in detail geometric, mechanical, energetic, and kinetic characteristics of elastic instabilities that are triggered as the applied stress on the crystals is varied.
Results are presented for the structural response to hydrostatic and uniaxial loading of several model crystals that have cubic lattice structure at equilibrium. Under hydrostatic loading, we find that the computed pressure-volume relations over the entire loading range at different temperatures are described satisfactorily by the Birch-Murnaghan equation of state. In all cases, it is demonstrated that the observed instabilities are thermally activated and associated with a vanishing or diminishing elastic modulus or combination of elastic moduli and that the instability causes phase transformation or failure of the crystal. In addition, the temperature dependence is calculated of the critical stress that marks the instability onset and of the associated thermal activation enthalpy barrier. We find that the critical stress and the activation enthalpy are monotonically decreasing and monotonically increasing functions of temperature, respectively, and that the enthalpy barrier vanishes completely as the temperature is lowered to absolute zero. The MD simulation results at low temperature are in excellent agreement with the predictions of stability criteria according to “static” elastic stability theory. Introduction of structural defects, such as nanovoids, into the crystal affects the instability onset significantly. For example, the critical hydrostatic tension required to cause the fracture of the imperfect (defective) crystal is lowered at each temperature. Furthermore, it is demonstrated that in the imperfect crystal, fracture or phase transformation is initiated at the defects of the lattice structure (heterogeneous nucleation) and proceeds in either case through a subsequent growth stage. In the case of phase transformation, the new phase nucleates at the defect site and grows outwards to cause the structural transition of the crystalline lattice.
HH11: Poster Session
Session Chairs
Christian Abromeit
Pascal Bellon
David Seidman
Thursday AM, November 30, 2006
Exhibition Hall D (Hynes)
9:00 PM - HH11.1
Real-time X-ray Observation of Solidification from Undercooled Si Melt.
Kosuke Nagashio 1 , Masayoshi Adachi 2 , Kensuke Higuchi 2 , Akitoshi Mizuno 2 , Masahito Watanabe 2 , Kazuhiko Kuribayashi 1 , Yoshinori Katayama 3
1 , Japan Aerospace Exploration Agency, Sagamihara, Kanagawa, Japan, 2 , Gakushuin University, Toshima, Tokyo, Japan, 3 , Japan Atomic Energy Agency, Sayo, Hyogo, Japan
Show Abstract Grain refined microstructure is often obtained spontaneously in the solidification of metals and semiconductors from the undercooled melt without any external forces. Although it has been reported that the grain refinement is mainly caused by the fragmentation of the dendrites, the dynamic process of the fragmentation of dendrites has not been fully understood because only the microstructure after the solidification has been analyzed. Recently, the third generation synchrotron facilities enable us to observe solidification process even in the metallic system in situ. If the time-resolved 2-dimensional X-ray detector is combined with an electromagnetic levitator (EML) and the transition of the diffraction pattern from spots to rings is detected, the dynamic process of the fragmentation dendrites can be discussed. Here, we present a time-resolved 2- dimensional X-ray diffraction experiment on the solidification of Si from the undercooled melt. The B-doped Si was levitated and melted in EML. The molten sample was cooled by the He gas flow. The data of the 2D diffraction pattern was acquired using a CCD camera with X-ray image intensifier at a sampling rate of 5.7 Hz during cooling. The number of diffraction spots observed at low undercoolings (ΔT < 100 K) did not increase at the plateau stage, while the diffraction pattern at medium undercoolings (100 K < ΔT < 200 K) changed from the spots with the tail to rings with the lapse of time. Both this result and high speed video imaging suggested that the high-order arms of the dendrites mostly detached from the main stems because nucleation could not be expected at the melting point after recalescence. The several spots observed at low undercoolings drastically changed to rings at high undercoolings (ΔT > 200 K), which indicated the complete fragmentation of dendrite main stem as well as high-order arms. This complete fragmentation resulted in the grain refined microstructure.
9:00 PM - HH11.10
Giant (~cm size) Au and AuAg(111) Grains with Large, Nearly Atomically Flat Terraces
Anant Mathur 1 , Jonah Erlebacher 1
1 Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractWe report a very simple, inexpensive method to make ~cm size (111)-oriented grains of Au and AuAg alloy in free-standing foils 10 – 80 micron thick. Large, defect-free grains are produced by recrystallization and surface-energy driven abnormal grain growth (AGG) in the foils after successive cold-rolling and high-temperature annealing operations. The surfaces of the grains possess large, nearly atomically flat terraces as evidenced by STM/AFM, which makes them useful as STM substrates for biological samples or catalysis, as well as in many other research applications.
9:00 PM - HH11.11
Interplay Between Diffusive and Displacive Phase Transformations: Effect on Microstructures and Mechanical Response
Mathieu Bouville 1 , Rajeev Ahluwalia 1
1 , Institute of Materials Research and Engineering, Singapore Singapore
Show AbstractSome materials systems can undergo extremely fast displacive transformations as well as very slow diffusive transformations. These two types of phase transformations may interact and compete with each other. In the case of pearlite and martensite in eutectoid steel for example, there is a competition between thermodynamics and kinetics: thermodynamically pearlite is the ground-state but for kinetic reasons martensite may form instead. Interplay between diffusive and displacive transformations is also relevant to shape-memory alloys: the formation of precipitates by a diffusive phase transformation can influence the mechanical response and the stress-induced martensitic transformations. The phase-field method has been extensively used to study the two types of phase transformations; however they have been studied "in isolation". We propose a phase-field model which includes both martensitic transformation and the (diffusive) formation of the ground-state phase. In some materials systems there can exist intrinsic volume changes associated with these transformations. We show how this can affect microstructures and TTT (temperature-time-transformation) diagrams, in particular volume changes can lead to the formation of mixed microstructures by competitive or cooperative mechanisms. The interplay of diffusive and displacive transformations also plays a role in the aging of shape-memory alloys: the formation of precipitates may alter or destroy the shape-memory and pseudoelasticity properties. Using our phase-field model we study the effect of precipitates on the stress-strain curves.
9:00 PM - HH11.12
Temperature and Concentration Dependence of the Effective Pair Interaction Parameters in Ni-Pd from High-energy X-ray Diffuse Scattering.
Markus Mezger 1 , Harald Reichert 1 , Ingo Ramsteiner 1 , Alexander Udyansky 1 , Oleg Shchyglo 1 , Vladimir Bugaev 1 , Helmut Dosch 1 2 , Veijo Honkimäki 3
1 , Max Planck Institute for Metals Research, Stuttgart Germany, 2 Institute for Theoretical and Applied Physics, University of Stuttgart, Stuttgart Germany, 3 , European Synchrotron Radiation Facility, Grenoble France
Show AbstractEffective interaction potentials are most important quantities in order to predict the structure and properties of multicomponent systems. They determine phase stability as well as the macroscopic properties of alloys, such as the elastic constants or Debye temperature. Experimental access to the effective pair interaction potential of a given system is possible by the detailed study of the fluctuation spectrum in its high temperature (disordered) phase. These local fluctuations give rise to a characteristic diffuse scattering distribution which is known as short range order diffuse scattering. By using high-energy Synchrotron x-rays (100keV) in transmission geometry in combination with two-dimensional area detectors we gain orders of magnitude in data quality and time resolution when recording 3D diffuse scattering maps in reciprocal space. We combine this experimental approach with a new reciprocal-space description based on the socalled spherical model and the Kanzaki force concept. We performed in situ measurements of the x-ray diffuse scattering on macroscopic Ni55Pd45 and Ni25Pd75 single crystals in the temperature range from 20 °C up to 920 °C. One single measurement is sufficient to retrieve the short-range chemical pair interaction parameters, the long-range strain-induced interaction as well as thermal and elastic properties (Debye temperature, elastic constants) of the Ni-Pd system quantitatively on time scales as short as 100 seconds. We demonstrate that only seven (!) independent and physically motivated parameters are sufficient to describe short-range order correlations, lattice distortions, and thermal parameters in the entire temperature and concentration range. Our results open up ways for the investigation of entire phase diagrams as a function of concentration and temperature as well as investigations of alloy interactions in nanoconfinement and at interfaces. Furthermore, time-resolved measurements become possible in the future.Reference:[1] M. Mezger et al., Phys. Rev. B 73, 184206 (2006).
9:00 PM - HH11.14
The Nucleation of Widmanstatten Ferrite in Iron-Nickel Meteorites.
Patrick Ray 1 , Takayuki Honda 1 , Zi-Kui Liu 1 , Paul Howell 1
1 Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractThe start-temperature for the Widmanstatten reaction in iron meteorites is of critical importance for determining the cooling rate of the parent body. For many years, it was assumed that the nucleation of Widmanstatten ferrite plates could be described by classical diffusional nucleation theory. More recently, Yang and Goldstein have argued that, for low P iron meteorites, ferrite must nucleate via shear at or below the martensite start temperature.In the present paper, we examine the possibility that Widmanstatten ferrite in meteorites nucleates via shear, however at a temperature above the martensite start. We have calculated the driving force for the nucleation of Widmanstatten ferrite, via a shear reaction in iron-nickel alloys We have also estimated the undercooling required, assuming that the Widmanstatten start temperature is determined by the activation energy for interface motion, and/or by the strain energy associated with back-to-back nucleation. Experimental data from e.g., the Gibeon, Cape York and Odessa meteorites will be presented: experimental techniques employed include light microscopy, scanning electron microscopy, orientation imaging microscopy, and the electron microprobe. We shall also compare our results with the ground-breaking work of Goldstein, Williams and colleagues.
9:00 PM - HH11.15
Effects of Defects, Surfaces and Interfaces on the Melting of Zircon.
Jincheng Du 1 , Ram Devanathan 1 , Rene Corrales 1 , William Weber 1
1 Fundamental Science Directorate, Pacific Northwest National Lab, Richland, Washington, United States
Show Abstract9:00 PM - HH11.16
Variant Selection of h-Al2Ti Superstructure in TiAl Single Crystals with Gradient Compositions.
Satoshi Hata 1 , Itto Sugimoto 1 , Koujirou Shiraishi 1 , Noriyuki Kuwano 2 , Masaru Itakura 1 , Takayoshi Nakano 3 , Yukichi Umakoshi 3
1 Department of Applied Science for Electronics and Materials, Kyushu University, Kasuga, Fukuoka Japan, 2 Art, Science and Technology Center for Cooperative Research, Kyushu University, Kasuga, Fukuoka Japan, 3 Course of Materials Science & Engineering, Division of Materials & Manufacturing Science, Graduate School of Engineering, Osaka University, Suita, Osaka Japan
Show Abstract9:00 PM - HH11.17
Swift-ion Induced Amorphization by Tracks in a Quasicrystalline Zr-Ti-Cu-Ni Alloy
Stefan Mechler 1 , Gerhard Schumacher 1 , Siegfried Klaumuenzer 1 , Nelia Wanderka 1 , Christian Abromeit 1 , Michael Macht 1
1 Structural Research, Hahn-Meitner-Institut berlin, Berlin Germany
Show AbstractAmorphous specimens of composition Zr64.5Ti11.4Cu10.3Ni13.8 were produced by rapid quench-ing from the melt using a splat quench device. Quasicrystalline specimens of the same com-position were obtained by approriate thermal treatment of the amorphous splats. The quasi-crystalline specimens were irradiated with 593 MeV Au ions at 80 K, 293 K and at 455 K. The irradiation experiments were performed at the Ionenstrahllabor (ISL) of the Hahn-Meitner-Institute. An analysis of the structure prior to irradiation and after various fluence steps was performed at room temperature by means of transmission electron microscopy (TEM), high resolution electron microscopy (HRTEM) and X-ray diffraction (XRD). The TEM analysis showed that each swift ion produces an amorphous track along its tra-jectory. For the quantification of the degree of amorphization as a function of fluence the three peaks of highest intensity in the XRD diagram of the quasicrystalline phase were used. For all three irradiation temperatures a decrease in peak intensity with increasing fluence was observed. Within the experimental uncertainty, the results obtained at room temperature and at 455 K coincide. In these both cases the track diameters of 5.8 and 6.0 nm are observed, re-spectively. Irradiation at 80 K yielded an appreciably smaller track diameter of 4.5 nm reflect-ing the slower decrease in peak intensity with increasing ion fluence. The value of the track diameter obtained by XRD for room temperature irradiation agrees within the experimental uncertainty with the value determined by means of HRTEM. The present results are in apparent contrast to the temperature dependence of plastic flow in amorphous alloys under irradiation where an opposite temperature dependence has been measured, i.e., plastic flow at 80 K was about one order of magnitude larger than at room temperature [1]. The microstructural development during irradition are discussed according to the thermal spike model.[1]S. Klaumuenzer and G. Schumacher, Phys. Rev. Lett. 51 (1983) 1987.
9:00 PM - HH11.18
Precipitation Sequence in Mg-Zn-Sn based Alloys
Anton Gorny 1 , Alexander Katsman 1 , Dmitry Shepelev 1 , Menahem Bamberger 1
1 Materials Engineering, Technion - Israel Institute of Technology, Haifa Israel
Show AbstractExtensive experimental research work was carried out in order to develop an Mg-Zn-Sn based creep resistant alloy. It was found that addition of Y improves the structural stability of this alloy. The main goal of this work was to investigate precipitation sequence in Mg-Zn-Sn-Y alloys during ageing at different temperatures. In order to elucidate the sequence of phase formation, XRD, TEM, SEM and EDS analyses were applied. It was found that, firstly, hcp-MgZn2 phase nucleates homogeneously, and grows in the form of needles having coherent interphase boundaries with α-Mg-matrix. High-resolution TEM images in combination with Fourier transformed images reveal a topotaxial orientation relationship which is given by <100>MgZn2 {110}MgZn2//<110>α-Mg (002)α-Mg. The cubic Mg2Sn-phase nucleates heterogeneously, mainly at the tops of MgZn2-needles when the needle’s width reaches a certain critical value. Orientation of Mg2Sn-precipitates is usually perpendicular to the one of MgZn2-needles. Two-phase T-like particles are very typical for the alloys aged for 1-16 days at 175-225C. The width/length ratio of the MgZn2-needles inside the T-like particles differs substantially from one in the single needles. Elastic/surface energy balance of needles and its influence on the morphology and coarsening behaviour are analyzed.
9:00 PM - HH11.19
Texture Evolution of Lithium Fluoride Thin Films by Nucleation
Hakkwan Kim 1 , Alexander King 1
1 School of Materials Engineering, Purdue University, West Lafayette, Indiana, United States
Show AbstractWe have developed a TEM-based method to extract the texture information from the (111) surface normal grain sizes in lithium fluoride (LiF) thin films, and applied this to measure textures as a function of substrate temperature and annealing time. We measured the grain size distributions of (111)(200) and (220) diffracting grains separately using dark field (DF) images taken by transmission electron microscope (TEM) and deduced the distribution of (111) surface normal grain sizes based on the assumption that only 3 main direction textures (100), (110) and (111) exist in films. The grain size data can be matched to lognormal distributions within an acceptable error, which is determined for each bin of the data. The {111} texture formation and surface morphology was observed by x-ray diffraction (XRD) and atomic force microscope (AFM). The atomic structure at the junction of grain boundaries with the free surface was also studied using focused ion bean (FIB) and high resolution TEM. Contrary to the previous researches, {111} texture component strengthens with annealing and substrate temperature. Moreover, it developed through the nucleation of new grains rather than the growth of existing ones. This work is supported by the National Science Foundation, grant number 0504813.
9:00 PM - HH11.2
Theoretical Predictions of the Thermodynamics of InGaN alloys: Reducing the Critical Temperature.
Chee Gan 1 , David Srolovitz 2
1 , Institute of High Performance Computing Singapore, Singapore Singapore, 2 Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey, United States
Show AbstractWe present the most rigorous theoretical study to date of thethermodynamics of InGaN alloy at the level of accuratefirst-principles density-functional theory. Because of its potential forhigh-power, high-frequency, and high-temperature optoelectronicapplications, the InGaN alloy system has attracted considerable theoretical attention;including many predictions of the pseudo-binary phase diagram. Thedifficulties inherent in such calculations include an accurate descriptionof the interactions between the constituent atoms, the faithfulrepresentation of a random alloy, the effect of temperature on latticevibrations, and the configurational entropy. Different approachesand approximations have led to vastly varying results,e.g., the predicted critical temperature (below which phase separationoccurs) ranges from 1500 K to 2000 K. We have used accuratedensity-functional theory to calculate the heat of formation of thealloy, as well as the phonon spectra for the lattice vibrationalcontribution to the free energy. The alloy has been faithfullyrepresented via special quasi-random structures. Both wurtzite andzinc-blende pseudo-binary InGaN alloys have been considered. Ourresults reveal that the commonly used valence force field for thethermodynamics calculation of InGaN underestimates the heat offormation. The wurtzite structure is always morestable than the zinc-blende structure for all temperatures andcompositions investigated, in agreement with experiment. We find thatthe lattice vibrations lead to a reduction of the criticaltemperature by more than 20%, leading to a temperature of 1654 K and1771 K for the wurtzite and zinc-blende structures, respectively. Thelattice vibrations also change the shape of the binodal and spinodal curves.This resultsuggests that quaternary alloy additions may increase thevibrational contribution to the stability of the disordered phase.Our predicted phase diagrams are used to interpret several key experimentmeasurements on MOCVD InGaN films.
9:00 PM - HH11.20
Influence of Processing Parameters on Microstructure of Pulsed Laser Deposited Au Thin Films.
Andreas Kulovits 1 , John Leonard 1 , Jorg Wiezorek 1
1 MSE, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Show AbstractPulsed laser deposition (PLD) is an attractive process offering high deposition rates and excellent fidelity of composition for preparation of elemental, alloy and compound thin films. PLD Au thin films were prepared on an amorphous SiO2 and a single crystalline (200) NaCl substrate. The film topography, morphology, texture, average grain size and grain size distribution have been determined for a range of deposition conditions by AFM, XRD, SEM and TEM. For each deposition condition the average kinetic energy of the Au particles upon arrival on the substrate has been estimated and is used to discuss carefully the observed differences in the thin film microstructure. Our results are compared to deposition results achieved using other deposition techniques available from the literature. Using the process parameter of kinetic energy enables comparison of the different deposition techniques regarding the thin film microstructure for a given substrate. Strong correlation between the process kinetic energy and the thin film microstructure observed here for PLD Au is also found for other deposition techniques. Charts correlating film microstructure with the kinetic energy have been derived, which
9:00 PM - HH11.21
Ab Initio Study of Chemical and Structural Trends of Ti-based Binary Alloys.
Martin Friak 1 , Jörg Neugebauer 1 , Benedikt Sander 1 , Dierk Raabe 1
1 , Max-Planck-Institut für Eisenforschung, GmbH, Duesseldorf Germany
Show AbstractTitanium alloys represent an important class of materials with a wide range of applications in both industry and medical science (e.g. human implants). To systematically enhance their mechanical properties we performed an ab initio study to identify constitution trends in Ti-alloys with respect to their structural and elastic properties. We present a comprehensive quantum-mechanical study of selected Ti-binaries containing 3d (V, Cr), 4d (Nb, Mo), and 5d (Ta) elements. Our results provide a guide when choosing suitable thermodynamic systems on demand for a specific purpose. Using density functional theory (DFT) and generalized gradient approximation (GGA) implemented in the Vienna Ab initio Simulation Package (VASP), we simulated a large variety of binary solid solutions in both hexagonal and cubic 16-atom supercells. To find the ground-state structure, we first optimized the volume for a dense mesh of concentration and configurations. Then, we selected the states minimizing the energy for each concentration and performed a full relaxation of both the cell-shape and internal degrees of freedom. The formation energies, lattice-constant behavior, and the bulk moduli as functions of composition were thus determined and analyzed. Based on the calculated ground state energies and adding entropy contributions temperature dependent phase diagrams have been derived which allow to extract information regarding the energetically stable crystal structure and miscibility. Guided by the calculated phase diagrams, selected binaries were actually melted, cast, heat treated to a homogeneous state. The samples have been experimentally characterized by x-ray methods, electron microscopy including crystallographic (EBSD) and chemical analysis (EDX), and mechanical testing. These data have then be used to check the accuracy of the theoretical predicted materials parameters such as crystal structure, lattice constant, and bulk modulus.
9:00 PM - HH11.22
Nucleation-Initiated Solidification of Thin Si Films.
Sharona Hazair 1 , Paul van der Wilt 1 , Yikang Deng 1 , Alexander Limanov 1 , Ui-Jin Chung 1 , James Im 1
1 Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York, United States
Show Abstract9:00 PM - HH11.24
Interactions Between Recrystallisation and Phase Transformations in Cold Rolled Low Alloy Steels and Ti Alloys
Pascal Jacques 1 , Cedric Georges 1 , Astrid Lenain 1 , Nicolas Clement 1 , Victor Andrade-Carozzo 2
1 IMAP, Université catholique de Louvain, Louvain-la-Neuve Belgium, 2 ICP, Pontificia Universidad Católica del Perú, Lima Peru
Show Abstract9:00 PM - HH11.25
Formation of Stable Cu2O from Reduction of CuO Anoparticles and Calculation of CuO-Cu2O Interfacial Energy.
Jenna Pike 1 , Siu-Wai Chan 1 , Jonathan Hanson 2
1 Applied Physics and Applied Mathematics, Columia University, New York, New York, United States, 2 Chemistry, Brookhaven National Laboratory, Upton, New York, United States
Show Abstract9:00 PM - HH11.26
High Energy X-Ray Study of Structural Transformations in Ti-V
Ingo Ramsteiner 2 1 , Harald Reichert 1 , Helmut Dosch 1 , Veijo Honkimäki 3
2 Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 1 , Max-Planck-Institute for Metals Research, Stuttgart Germany, 3 , European Synchrotron Radiation Facility, Grenoble France
Show AbstractPhase transformations in alloys and especially precipitation processes are very important phenomena in materials science. We present a synchrotron in situ study of a metastable Ti60-V40 beta-alloy, using monochromatic high-energy x-ray scattering. Single crystals of Ti-V were probed in transmission geometry with 60-100 keV x-rays. Due to the large Ewald sphere the scattered intensity recorded by a 2D detector represents an almost flat section of reciprocal space. In addition to the diffuse scattering of TiV which is mainly caused by static (atomic size mismatch) and dynamic lattice distortions we observed time-resolved the formation of Bragg reflections betraying the growth of precipitates within the bulk during aging at elevated temperatures. The presentation will focus on these precipitation phenomena. Depending on the aging temperature, we observe two different precipitation processes: the formation of alpha-Ti according to the binary phase diagram and the formation of TiC particles from a very small C content of the sample. Time-resolved measurements show that both phenomena are reversible: the corresponding Bragg reflections vanish upon annealing. Complementary HRTEM measurements support our findings and shed new light on the long standing issue of transient ordering in Ti-V.The synchrotron experiments have been performed at the beamline ID15A of the European Synchrotron Radiation Facility in Grenoble.
9:00 PM - HH11.27
Formation of Metastable Phases in the quasi-binary Lu2O3-Fe2O3 System by Containerless Solidification Method.
Kenji Niwata 1 , Kosuke Nagashio 2 , Taketoshi Hibiya 1 , Kazuhiko Kuribayashi 2
1 , Tokyo Metropolitan University, Hino, Tokyo, Japan, 2 , Inst Space & Astronautical Sci, Sagamihara, Kanagawa, Japan
Show Abstract9:00 PM - HH11.28
Ex-situ and In-situ TEM Studies on the Crystallization Process of Zr70Cu27.5Rh2.5 Metallic Glass.
Chunfei Li 1 , David Cushman 1 , Junji Saida 2
1 Physics, Portland State University, Portland, Oregon, United States, 2 Center for Interdisciplinary Research, Tohoku University, Sendai, Miyagi, Japan
Show AbstractIt has been known that addition of some selected metal to the Zr-based metallic glass with high glass forming ability stimulates the precipitation of icosahedral quasicrystalline (IQC) particles as metastable phase in the initial crystallization stage, followed by precipitation of stable crystalline phases. It is believed that the precipitation of IQC is related to the original structure of the metallic glass. It has also been reported that controlled precipitation of IQC leads to the improved mechanical property of the metallic glass. While most of previous studies aimed to clarify the condition for the appearance of the IQC phase, we designed the present work to focus on the precipitation process of the stable crystalline phase, which is expected to bring in in-depth knowledge for the high glass-forming ability of the selected Zr-based alloys and the stability of the metastable IQC particles. Zr70Cu27.5Rh2.5 amorphous alloy was chosen because the precipitation of IQC has been reported and the stable crystalline phase is expected to be simple from composition. Since the spatial locations of different phases are of the interest for the present experiment, Transmission Electron Microscopy (TEM) is the main tool used. For ex-situ experiment, thin ribbon with a cross section of approximately 0.1×3 mm2 prepared by single roller melt spinning was annealed in the cell of Differential Scanning Calorimeter (DSC). It is concluded that the alloy consists of IQC particles distributed in amorphous matrix prior to the precipitation of Zr2Cu stable crystalline phase. Zr2Cu nucleates from the amorphous matrix, not from the boundary of two IQC particles or the interface between IQC and amorphous matrix as speculated before the experiment. The encounter of Zr2Cu and IQC phases transform the later to the former so quickly that no interface between them was found in the present experiment. Elemental analysis revealed that Cu is depleted and Zr is enriched in the IQC particles as compared to the amorphous matrix. In-situ TEM heating experiment did not observe the precipitation of IQC particles. Instead, the direct appearance of Zr2Cu stable crystalline phase from the amorphous matrix was suggested. These results lead to the conclusion that the difficulty for the nucleation of Zr2Cu phase from the amorphous matrix retards its precipitation, which, in turn, allows the precipitation of IQC particles in the initial stage due to its ease of nucleation. These understandings provide the basis to discuss the stability of amorphous alloys and the IQC particles required for different purposes.
9:00 PM - HH11.29
Kinetics and Thermodynamics of Phase Changes to Hitherto-Unknown Phases in the Most Important Solid State Materials – Si: TiO2; BaTiO3; Ferrites; All Caused by Magnetic Fields at 2.45 GHz.
Rustum Roy 1 2 , D. Dube 1 , C. Fang 1 , F. Ming 1 , D. Agrawal 1
1 Materials Research Institute, Penn State, University Park, Pennsylvania, United States, 2 Chemical and Materials Engineering, Arizona State University, Tempe, Arizona, United States
Show Abstract9:00 PM - HH11.31
Kinetic Interactions In The Formation of Iron Aluminide Coating by Fluidized-Bed Chemical Vapor Deposition.
Sophia Tsipas 1 , Francisco Bolívar 1 , Laura Sánchez 1 , Maria Hierro 1 , Juan Trilleros 2 , Francisco Pérez 1
1 Grupo de Investigación de Ingeniería de Superficies y Materiales Nanoestructurados, Universidad complutense de Madrid, Madrid Spain, 2 Grupo de Investigación en Ingeniería Metalúrgica, Universidad complutense de Madrid, Madrid Spain
Show Abstract9:00 PM - HH11.32
Phase Transformations in Non-stoichiometric GaAs with Sb and P Doping.
Vladimir Chaldyshev 1 , Nikolai Bert 1 , Anton Boitsov 1 , Yuri Musikhin 1 , Maria Yagovkina 1 , Valerii Preobrazhenskii 2 , Michail Putyato 2 , Boris Semyagin 2
1 , Ioffe Institute, St. Petersburg Russian Federation, 2 , Institute of Semiconductor Physics, Novosibirsk Russian Federation
Show Abstract9:00 PM - HH11.33
Observation of Epitaxy of Body Centered Cubic TiB2 on Si(001) by Pulsed Laser Ablation.
Lydia Longstreth-Spoor 1 2 , P. Gibbons 1 2 , K. Kelton 1 2 , Ramki Kalyanaraman 1 2
1 Physics, Washington University in St. Louis, St. Louis, Missouri, United States, 2 Center for Materials Innovation, Washington University in St. Louis, St. Louis, Missouri, United States
Show Abstract9:00 PM - HH11.34
On the Stability of Grain Boundary Discontinuous Precipitation in Dilute Cu-Co Alloys.
Ana Rocha 1 , Guillermo Solorzano 1
1 , PUC-Rio, Rio de Janeiro Brazil
Show Abstract9:00 PM - HH11.35
Predicting Benefits of Sc in Aluminum Alloys: Interaction of Sc with other Alloying Elements.
Darko Simonovic 1 , Marcel Sluiter 1
1 Material Science and Engineering, Delft University of Technology, Delft Netherlands
Show Abstract9:00 PM - HH11.36
Formation and Thermodynamic Stability of Cu2O Nano-islands and Cu(001) Reconstructions.
Paul Fuoss 1 , Dillon Fong 1 , Jeffrey Eastman 1 , Peter Baldo 1 , Guangwen Zhou 1 , Lynn Rehn 1 , Loren Thompson 1
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractWe will present results from an in-situ x-ray scattering study of interactions of equilibrium structures of Cu (001) surfaces in controlled partial pressures of oxygen (pO2) and of Cu2O nano-islands formed from those surfaces. Near room temperature the common(√2×2√2)R45° phase is stable while above ∼200°C a c(2×2) phase is present. Fully reversible transitions between the two phases demonstrate that these are stable rather than metastable structures. Furthermore, based both on diffraction peak intensity measurements and observations of crystal truncation rod intensity under variable pO2, we find that the concentration of oxygen in the surface is also reversible, meaning that an oxygen-free metal surface is recovered when temperature is increased sufficiently and/or pO2 is reduced below an equilibrium phase boundary. We also find that, as pO2 is increased to the point at which Cu2O islands nucleate, these oxide islands co-exist and interact with the c(2×2)-structured surface regions. For example, Cu2O islands will temporarily stabilize the c(2×2) structure even under reducing conditions; the c(2×2) structure disappears only after complete reduction of the oxide islands. These results unify apparently conflicting studies of oxygen induced structures on Cu(001) surfaces1 and clarify long postulated intermediate mechanisms for the oxidation of Cu (001) surfaces.2
1M. Sotto, Surf. Sci., 260, 235(1992) and references therein.
2K. Heinemann, D. Bhogeswara Rao, and D. L. Douglass, Oxidation of Metals, 9, 379 (1975).
9:00 PM - HH11.37
Statistical and Elasticity Analysis of Split Patterns in γ-γ’ Ni Alloys.
Hector Calderon 1 , Christian Kisielowski 2 , Tsutomu Mori 3
1 Ciencia de Materiales, ESFM-IPN, Mexico, DF, Mexico, 2 NCEM, LBNL , Berkeley, California, United States, 3 Materials Science Centre, University of Manchester, Manchester United Kingdom
Show Abstract9:00 PM - HH11.38
Investigation of Disorder and Transformation Under Shock in Boron Carbide B4C.
Giovanni Fanchini 1 , Paola Jaramillo 1 , Varun Gupta 1 , James Mc Cauley 2 , Manish Chhowalla 1
1 , Rutgers University, Piscataway, New Jersey, United States, 2 , ARL, Aberdeen, Maryland, United States
Show Abstract9:00 PM - HH11.39
Quasi One-dimensional State of Ultra-thin Ag Films Prepared on One-dimensional Surface Superstructure.
Naoka Nagamura 1 , Iwao Matsuda 1 , Takashi Uchihashi 2 , Nobuhiro Miyata 1 , Toru Hirahara 1 , Shuji Hasegawa 1
1 Department of Physics, School of Science, University of Tokyo, Tokyo Japan, 2 , National Institute for Materials Science , Tsukuba Japan
Show Abstract Reduction of epitaxial metal film thickness down to electron wavelength induces energy quantization by quantum size effect, resulting in formation of quantum-well states(QWS's). Well-known examples are the QWS's in semiconductor/semiconductor and metal/metal-layered systems, which are relevant to modern optoelectronic and data storage devices. Recently, there has been a growing interest in such QWS's(resonances) of quantum films on solid surfaces, and intriguing physical properties are reported such as anomalous in-plane dispersion[1] and oscillation of superconducting transition temperature with thickness[2]. Now we will suggest new one, changing the Fermi surface topology by an atomic interface layer(Electronic Topological Phase Transition)[3]. We prepared quantum Ag(111) films on two different substrates. One is clean Si(111)7x7 and the other is Si(111)4x1-In, typical one-dimensional metallic superstructure. They are prepared by depositing 0.71-7.1 nm-thick of Ag below 150K, then post-annealing at 300-400K. The band structures and Fermi surfaces are mapped by photoemission spectroscopy. For Ag films on 7x7, discrete levels at Gamma point and each subbands show isotropic in-plane dispersions, making isotropic two-dimensional Fermi surfaces. On the other hand, for Ag films on 4x1-In, those show highly anisotropic in-plane dispersions which are parabolic along the In-chain direction but almost flat in the perpendicular direction and making open Fermi surfaces of 1D lines parallel to In-chains. These quasi-1D quantum-wire-states-like properties are suggested by STM observation of this Ag/Si(111)4x1-In system[4], showing that Ag film has 1D stripe structure parallel to In-chains of the interface caused by periodic stacking faults corresponding to the spatial interval between In-chains. Furthermore, comparing the normal spectra at the same thickness, binding energy levels of quantized states of Ag/Si(111)4x1-In shift to higher than that of Ag/Si(111)7x7. To estimate this experimental results by calculation, we must consider the confinement from periodic potential modulations due to stacking faults in the direction perpendicular to In-chains, in addition to the reflection phase shift of the interface. In conclusion, we have found the quasi-1D states in a Ag quantum film prepared on Si(111)4x1-In[5]. Such Fermi surface topological regulation induces various effects of geometry on the physical properties of electrons, such as transport properties which can be measured by our 4-tip STM instrument, attracting interests in low-dimensional physics and technology. In the session, we will discuss in detail with the results of ARPES, STM, calculations with a simple model and possible applications.References[1]I.Matsuda et al. Phys.Rev.B 65 085327(2002)[2]Y.Guo et al. Science 306 5703(2004)[3]A.E.Meyerovich et al. Phys.Rev.B 66 235306(2006)[4]T.Uchihashi et al. Phys.Lev.Lett 96,136104(2006)[5]N.Nagamura et al. Phys.Lev.Lett 96,256801(2006)
9:00 PM - HH11.4
Modelling of Precipitation Kinetics with Simultanous Stress Relaxation.
Franz Fischer 1 , Jiri Svoboda 2 , Ernst Gamsjager 1 , Ernst Kozeschnik 3 , Bernhard Sonderegger 3
1 Institute of Mechanics, Montanuniversität Leoben, Leoben Austria, 2 Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno Czech Republic, 3 Institute for Materials Science, Welding and Forming, University of Technology, Graz Austria
Show Abstract9:00 PM - HH11.40
Unusual Alloying Effect on the Melting Temperature of Metal Nanoclusters.
Francesca Baletto 1 , Christine Mottet 3 , Riccardo Ferrando 2 , Giulia Rossi 2
1 DMSE, MIT, Cambridge, Massachusetts, United States, 3 , CMRCN/CRNS, Campus de Luminy-Marseille France, 2 Dept. of Physics, Univ. di Genova, Genova Italy
Show Abstract9:00 PM - HH11.41
Effects of Oxygen on the β-α Phase Transformation and Microstructure in Tantalum Thin Films.
Max Aubain 1 , Robert Knepper 1 , Shefford Baker 1
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States
Show AbstractA very unusual microstructure has been found in tantalum thin films after transformation from the metastable tetragonal β phase to the stable bcc α phase. Films deposited in the β phase transform to the stable α phase when heated to sufficiently high temperatures, dependent on the amount of oxygen in the film. The microstructure of the phase-transformed films has been studied using electron backscatter diffraction (EBSD). In these films, large gradients in crystal orientation are often seen within individual grains leading to a grain boundary structure that is discontinuous. Both the nucleation and growth of the α phase are dramatically slowed by the addition of oxygen beyond a critical amount, leading to larger grain sizes and changes in boundary character with increasing oxygen content. The mechanism of the phase transformation is discussed based on thermomechanical data and the microstructures of as-deposited and phase-transformed films.
9:00 PM - HH11.42
Effect of Relative Humidity on the Crystallization Characteristics of Sol-gel Processed Lanthanum Zirconium Oxide Thin Films.
Srivatsan Sathyamurthy 1 2 , Mariappan Paranthaman 2
1 , University of Tennessee/ ORNL, Oak Ridge, Tennessee, United States, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show Abstract9:00 PM - HH11.43
Composition Effects on the Nucleation and Growth of Cu2O Islands During Early-stage Oxidation of Cu-Au Alloys.
Guangwen Zhou 1 , Liang Wang 2 , Pete Baldo 1 , John Pearson 1 , Loren Thompson 1 , Judith Yang 2 , Jeffery Eastman 1
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Materials Science and Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Show Abstract9:00 PM - HH11.46
The Role of Interstitials in Phase Segregation of Binary Alloys Under Ion Irradiation Conditions from KMC Simulations.
Pavel Krasnochtchekov 1 , Pascal Bellon 1 , Robert Averback 1
1 , University of Illinois at UC, Urbana, Illinois, United States
Show Abstract9:00 PM - HH11.48
Structure of GP Zones in Al-Ag Alloys.
Emmanuelle Marquis 1 , Francois Leonard 1 , Norman Bartelt 1
1 , Sandia National Laboratory, Livermore, California, United States
Show Abstract9:00 PM - HH11.49
In Situ TEM Study of the Super-elastic Effect in Cu Based Shape Memory Alloys.
María Nó 2 , Alfonso Ibarra 2 3 , Daniel Caillard 3 , Jose San Juan 1 4
2 Fisica Aplicada II, Universidad del Pais Vasco, Bilbao Spain, 3 CEMES, CNRS, Toulouse France, 1 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 4 Fisica Materia Condensada, Universidad del Pais Vasco, Bilbao Spain
Show Abstract9:00 PM - HH11.5
Controlling the Morphology of TiO2 Nanoparticles.
Jennifer Synowczynski 1 , Bonnie Gersten 2 , Samuel Hirsch 1
1 Weapons and Materials Research Directorate, Army Research Laboratory, Aberdeen Proving Grounds, Maryland, United States, 2 Department of Chemistry and Biochemistry, Queens College of CUNY, Flushing, New York, United States
Show AbstractABSTRACT The morphology and distribution of phases in sintered ceramic nanocomposite materials is highly dependent on the morphology of the starting powders including their size, monodispersity, and shape. Powders with asymmetrical (rod) morphologies act as seeds to induce grain growth along a preferred direction. Previous research has shown that polycrystalline ferroelectrics textured using this method can achieve tunabilities approaching that of single crystals. Here, we present the results of a study that looked at the effect of solvent conditions and additives on the morphology, particle size, phase and chemical purity of TiO2 nanoparticles produced during hydrothermal reactions. The reactions were performed at 160oC for 6 hours on suspensions containing amorphous titania (TiO2*nH2O, concentration = 0.1 M). Spherical, cubic, and rod morphologies were created by manipulating the chemistry of the additive and the pH of the solution. The nanoparticle size, morphology, phase, and purity was confirmed using TEM, XRD, and SLS (Static Light Scattering). In general, as the pH increased, the aspect ratio of the titania powders increased. These results will be presented along with results using ammonium phosphate, butributylamine, cyclohexylamine, and di-isopropylamine as additives.
9:00 PM - HH11.50
The Implication of (111)-Textured Grains Obtained via Nucleation and Growth of Solids in Pulsed-Laser-Quenched Al Films on SiO2.
Jae Beom Choi 1 2 , MinHwan Choi 1 , Ui-Jin Chung 1 , Alex Limanov 1 , James Im 1
1 Program in Materials Science, Applied Physics & Applied Mathematics, Columbia University, New York, New York, United States, 2 LCD Business, Samsung Electronics Co., Ltd., Yongin, Gyeonggi, Korea (the Republic of)
Show AbstractPulsed-laser induced melting and quenching of thin films can lead to subsequent solidification of the films via nucleation and growth. The combination of the small thermal mass of the films and the spatially localized heating possible with short-pulse-duration irradiation leads to very high quench rates that kinetically constrain a nucleation-initiated transformation to take place under deeply supercooled conditions. Overall, the situation is unusually well suited for systematically examining the nature of nucleation phenomenon, particularly the heterogeneous nucleation mechanism.This paper will begin by presenting experimental findings from investigating excimer laser irradiation (308 nm, 30-ns pulse duration) of 100-nm-thick Al films that were sputter-deposited onto oxidized Si wafers. Microstructural analysis of the irradiated films conducted with AFM and EBSD methods reveals that there exists a wide energy density over which large equiaxed grains with a strong (111) surface texture are obtained. Consideration of (1) the geometrical details of the polycrystalline microstructure, (2) the energy density regime within which the grains are obtained, and (3) the thermal evolution of the film makes it possible to conclude that these oriented grains are obtained via spontaneous and random nucleation of crystalline nuclei and subsequent epitaxial growth of the nuclei. Given that such textured grains can only be obtained if the grains are nucleated heterogeneously, and further that the nuclei must be crystallographically oriented, we conclude (as it is the only conceptually possible option) that oriented heterogeneous nucleation has taken place. We will discuss how the present experimental observation unequivocally substantiates—likely for the first time—the thermodynamic effect associated with the orientation of crystalline nuclei relative to a planar catalytic interface in heterogeneous nucleation involving condensed systems.
9:00 PM - HH11.51
Influence of Axial Heat Processing on Microporosity Formation in Ni-Mo-Ta-Al Alloy.
Joo Ro Kim 1 , Hangjoon Im 3 , Reza Abbaschian 2 1
1 Material Science and Engineering, University of Florida, Gainesville, Florida, United States, 3 Material Science and Engineering, Korea Polytechnic University, Shihung, Kyonggi-Do, Korea (the Republic of), 2 Mechenical Engineering, University of California, Riverside, California, United States
Show Abstract9:00 PM - HH11.52
An Experimental Investigation of Solute-Driven Melting Kinetics in the Sn-Bi System.
David Yasensky 1 , Reza Abbaschian 2 1
1 Materials Science and Engineering, University of Florida, Gainesville, Florida, United States, 2 Mechanical Engineering, University of California Riverside, Riverside, California, United States
Show AbstractThe Goal of the present study was to gain insight into the mechanisms and behavior of solute driven melting processes. The migration of the solid/liquid interface is and important feature of many manufacturing processes. The topic of solidification has received far more attention than the reverse process of melting because during solidification of an alloy the microstructure of an alloy that determines many of its properties is produced. However, solute-driven melting has recently been the focus of several recent studies after it was identified as an important mechanism of dendrite fragmentation in the casting of alloys. Simulations have shown that while convection currents are usually only capable of bending dendrites, solute rich liquid that has been rejected into the interdendritic region may dissolve the dendrite base thus detaching it from the rest of the solid. Solute driven melting in this way can lead to casting defects associated with dendrite fragmentation such as freckling. This has reportedly occurred in superalloys.An experimental apparatus was designed and experiments were carried out on Sn-Bi alloys. The apparatus involved diffusing Bi into solid Sn cast inside a glass capillary to cause it to melt. The confinement of melting within a capillary was intended to suppress convection in the melting region. The Bi source was an enriched liquid Sn-Bi alloy contained in a reservoir. The system was held at a constant temperature below the melting point of the pure solid so that the melting was caused only by the increasing Bi content. The progression of the interface was monitored by quenching the process at various times for the same conditions and measuring the size of the melted region.The apparatus was successful in delivering data for the displacement of the interface against time. It was found that interface position was approximately proportional to the square root of time, and so the process may be diffusion controlled as conjectured in previous literature. The velocities may be able to be predicted with a solution to Fick’s 2nd law available for dissolution processes. An equation is derived that relates the temperature and liquid solute content to the displacement coefficient A in the equation z = At0.5 where z is displacement and t is time. Kinetic constants are calculated that can be compared to those of other systems and used to identify melting mechanisms. An activation energy of 60,000J/mol is calculated. Suggestions for modification of the apparatus to include in-situ interface monitoring are made.
9:00 PM - HH11.53
Formation of Domain Structures in Ordering Processes of B2 or D03, L12 and L10 Types.
Ryuichiro Oguma 1 , Syo Matsumura 2 , Tetsuo Eguchi 1 , Sung-Kyu Son 3
1 Applied Physics, Fukuoka University , Fukuoka, Fukuoka, Japan, 2 Applied Quantum Physics and Nuclear Engineering, Kyushu University, Fukuoka, Fukuoka, Japan, 3 HVEM Laboratory, Kyushu University, Fukuoka, Fukuoka, Japan
Show Abstract9:00 PM - HH11.54
Atomistic Simulation of Pressure-induced Solidification in Molten Ta: From Nucleation to Coalescence.
James Glosli 1 , Mehul Patel 2 , Frederick Streitz 1
1 H-Division, Lawrence Livermore National Lab, Livermore, California, United States, 2 AX-Division, Lawrence Livermore National Lab, Livermore, California, United States
Show Abstract9:00 PM - HH11.55
Laser Ignition of Self-propagating Exothermic Reactions in Multilayer Metal Films.
Yoosuf Picard 1 , Michael Grosskopf 2 , R. Drake 2 , David Adams 3 , Steven Yalisove 1
1 Materials Science & Engineering, Univ. of Michigan--Ann Arbor, Ann Arbor, Michigan, United States, 2 Space Physics Research Lab, Univ. of Michigan--Ann Arbor, Ann Arbor, Michigan, United States, 3 , Sandia National Labs, Albuquerque, New Mexico, United States
Show Abstract9:00 PM - HH11.56
Crystal Growth Behavior and Phase Transformation in Non- equilibrium Oxygen-doped Titanium Nitride Thin Films Prepared by Pulsed Laser Deposition.
Sei Otaka 1 , Wakana Hara 1 , Kota Akiyama 1 , Takahiro Watanabe 1 , Wataru Tsuji 1 , Mamoru Yoshimoto 1
1 Innovative and Engineered Materials, Tokyo inst. of Tech., Yokohama, Kanagawa, Japan
Show Abstract9:00 PM - HH11.57
Synthesis of Nano-sized Sialons by Carbothermal and Gas Reduction Nitridation of a Zeolite.
Toru Wakihara 1 , FenJin Li 1 , Junichi Tatami 1 , Katsutoshi Komeya 1 , Takeshi Meguro 1
1 Department of Environmental and Information Sciences, Yokohama National University, Yokohama Japan
Show Abstract9:00 PM - HH11.6
The Calculated Interfacial Entropies Between theta prime Al2Cu and fcc Al.
Yi Wang 1 2 , Zi-Kui Liu 1 , Long-Qing Chen 1 , Christopher Wolverton 2
1 Materials Science & Engineering, Penn State, State College , Pennsylvania, United States, 2 , Ford Research and Advanced Engineering, MD3083/SRL, Dearborn, Michigan, United States
Show Abstract9:00 PM - HH11.8
Influence of Layer Microstructure on the Asymmetric Nucleation and Growth Process of CuMg2 in Cu/Mg Multilayers.
Marta Gonzalez-Silveira 1 , Javier Rodriguez-Viejo 1 , Gemma Garcia 1 , Francesc Pi 1 , János L. Lábár 2 , Francisco J. Ager 3 , Árpád Barna 2 , Miklós Menyhárd 2 , László Kótis 2
1 Dept. of Physics, Universitat Autonoma de Barcelona, Bellaterra, Barcelona, Spain, 2 , Research Institute for Technical Physics and Materials Science, Budapest Hungary, 3 , Centro Nacional de Aceleradores, Sevilla, Sevilla, Spain
Show Abstract9:00 PM - HH11.9
Effect of Ion Irradiation on α- and β-Phase Evolution of Sputtered Tantalum Thin Films
Hua Ren 1 , Marek Sosnowski 1 2
1 Materials Science and Engineering, New Jersey Institute of Technology, Newark, New Jersey, United States, 2 ECE, New Jersey Institute of Technology, Newark, New Jersey, United States
Show AbstractTantalum has two distinct crystallographic phases with different physical properties. A stable body centered cubic α-phase, characteristic of the bulk metal, and a metastable tetragonal β-phase, often found in thin films. The tough and ductile α-phase is desired in most thin film applications but the presence of hard and brittle β-phase often degrades the film performance. The conditions of growth of the two phases are still not well understood. In this work, we investigated the α- and β-phase evolution in tantalum thin film deposited by RF (13.56 MHz) magnetron sputtering with ion irradiation of the substrate (~ 0.3 mA/cm^2) controlled by applying different negative DC bias voltages (0-400 V) to the substrate. Silicon and aluminum were chosen as substrates because of interest in Ta as a barrier layer in Si devices and in Ta coating of Al for bipolar plates of fuel cells.Film thickness, measured by Rutherford Backscattering Spectrometry, ranged from tens to hundreds of nm. The crystallographic phases of Ta in the films were identified using X-ray diffraction by the presence of prominent peaks: at 2θ = 38.47 deg. for (110) α-phase and at 2θ = of 33.57 deg. for (002) β-phase. At zero bias voltage (ion energy ~10 eV), only the tetragonal β-phase is formed. Increasing the ion energy to 100 eV results in the presence of both phases in thin Ta films, while further increasing the ion irradiation energy to 150 eV results in only α-phase Ta on both Si <100> and Al substrates. At the ion energy of 250 eV, or higher, β-phase Ta dominates the film structure on Si <100> substrate but not on Al substrate. The films were deposited in compressive stress with the lowest stress measured for α-phase Ta films deposited with ion energy of 150 eV. These results are different than those published earlier on the effect of ion irradiation on the crystallographic phase of sputter-deposited Ta films. The ion energy required for the growth of the α-phase Ta was reported to be below 100 eV [1] and even below 20 eV, although with a very high ion to atom flux ratio (>26) [2]. In our case the ratio was close to one. Both papers report formation of only β-phase Ta at ion energies higher than those quoted above. We thus found a new set of deposition parameters for the growth bcc α-phase Ta films at ambient temperature by sputtering process with substrate ion irradiation. One advantage of the new findings is relative simplicity of the equipment, which consists of a standard RF magnetron deposition system with a provision of substrate biasing. The new process for deposition of α-phase Ta films can be much easier scaled-up to industrial applications than the processes based on the earlier reported deposition parameters, which require complex systems.[1] P. Catania, Ronnen A. Roy, and J. J. Cuomo, Journal of Applied Physics, 74(2), 1993, p1008[2] K. Ino, T. Shinohara, T. Ushiki et al., Journal of Vacuum Science and Technoligy A, 15(5), 1997, p2627
9:00 PM - HH11: Posters
HH11.13 Transferred to HH5.3
Show Abstract
Symposium Organizers
Christian Abromeit Hahn-Meitner Institute
Pascal Bellon University of Illinois, Urbana-Champaign
Jean-Louis Bocquet Centre d’Etudes Nucleaires de Saclay-CEA
David N. Seidman Northwestern University
HH12: Order-Disorder Transformations
Session Chairs
Thursday AM, November 30, 2006
Back Bay A (Sheraton)
9:30 AM - **HH12.1
Ab Initio Study of Oxygen Ordering in the Superconductor YBCO.
Didier deFontaine 1
1 MSME, UC Berkeley, Berkeley, California, United States
Show AbstractThe discovery in the late 1980s of cuprate superconductors caused the so-called "Woodstock of Physics" at the New York APS meeting which followed soon after the announcement of the 90 K YBa2Cu3Ox Hi-Tc superconductor (YBCO) by Paul Chu at the University of Houston. YBCO, and other compounds, has not ceased to mystify researchers, and will no doubt continue to do so at least until a valid mechanism for its superconducting properties has been elucidated. One feature of this fascinating material, which is sometimes overlooked, is the tendency of oxygen ions to order in the Cu-O plane (the chain plane). In the early 90s, our group at UC Berkeley investigated the ordering mechanisms in some detail, but did not attempt to relate it to the phenomenon of superconductivity per se. It may be time to do so. In this presentation, an attempt will be made to relate O-ordering to dynamical spin fluctuations in the Cu-O2 plane (the "superconducting" plane), following a recent ab initio study of oxygen ordering in this material. It will be shown that diffuse x-ray scattering spectra can be explained as resulting directly from atomic displacements caused by the ordering of O-Cu-O- chains in the CuO planes. Remarkable agreement is illustrated in the case of underdoped YBCO between experimental diffraction patterns and satellite intensity derived from "first principles" electronic structure calculations.
10:00 AM - **HH12.2
Time-Evolution of Short-Range and Long-Range Ordering in Ni4Mo Alloys Studied by Advanced Transmission Electron Microscopy and Monte Carlo Simulation.
Syo Matsumura 1 , Satoshi Hata 2 , Kousuke Kimura 1 , Tatsurou Takahashi 1 , Christian Abromeit 3
1 Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, Fukuoka Japan, 2 Department of Applied Science for Electronics and Materials, Kyushu University, Fukuoka Japan, 3 , Hahn-Meitner-Institut, SF3, Berlin Germany
Show Abstract10:30 AM - HH12.3
High-Temperature Order-Disorder Transformations in Rare Earth-Transition Metal Systems.
Yulia Kostogorova-Beller 1 , Jeffrey Shield 1 , Matthew Kramer 2
1 Mechanical Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska, United States, 2 Materials Science and Engineering, Iowa State University, Ames, Iowa, United States
Show Abstract10:45 AM - HH12.4
The A1 to L10 Phase Transformation in FePt and Related Ternary Alloy Thin Films for Ultra-high Density Magnetic Recording Media
David Berry 1 2 , Katayun Barmak 1 2
1 Dept. of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 2 Data Storage Systems Center, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show Abstract Further increases in the storage density of magnetic recording media towards 1 Tb/in2 require materials with magnetocrystalline anisotropy energy density (MCA) greater than those of current Co-alloy media materials. The most likely candidates to replace the current alloys include rare-earth alloys such as SmCo5 and L10 alloys such as CoPt and FePt, though the superior corrosion resistance of the L10 alloys makes these more viable candidates than the rare-earth based alloys. However, when deposited at room temperature, the L10 films form in the chemically-disordered, face-centered cubic A1 phase, requiring post-deposition annealing at temperatures and times that are incompatible with current manufacturing requirements. Previously, we have shown that the A1 to L10 transformation is kinetically faster in FePt than CoPt, and along with a slightly higher MCA, 6.6×107 vs. 4.9×107 erg/cm3, results in FePt as the most viable candidate for further study. The A1 to L10 transformation in FePt is first order in the Ehrenfest sense, occurring by nucleation and growth of the ordered L10 domains in the A1 matrix; therefore the transformation can be described by an appropriate Johnson-Mehl-Avrami-Kolmogorov (JMAK) formulation, enabling the calculation of time-temperature-transformation (TTT) diagrams. These TTT diagrams, which are contours of time and temperature for a given fraction transformed, should prove extremely useful for the selection of appropriate annealing cycles for media manufacturing. For this work, we provide an in-depth derivation of the JMAK model developed to describe the A1 to L10 transformation for a range of compositions in FePt and related ternary alloys from thermodynamic and kinetic data obtained using non-isothermal differential scanning calorimetry (DSC) of 1 μm-thick free-standing films. The results of this model are illustrated in the form of TTT diagrams. Additionally, experimental validation of the JMAK model is presented using isothermal DSC measurements of a partially transformed FeCuPt alloy. From this model, parameters including but not limited to the density of nuclei, the interfacial energy, and the growth velocity are calculated, along with their compositional dependence. TTT diagrams comparing FePt binary alloys show that at low temperatures, Fe-rich films transform significantly faster, ~300× at 300 °C, than Pt-rich films. Lastly, a correction factor is derived to extend the results from 1 μm-thick films to ultra-thin films on the order of 10 nm-thick for magnetic recording media. For all alloy compositions, transformation in ultra-thin films results in longer times at any given temperature. However, the departure from 1 μm-thick films is dependent upon alloy composition, with Pt-rich alloys showing very small deviations at low fraction transformed and Fe-rich alloys evidencing large deviations at all fractions transformed.
11:00 AM - HH12: Order
BREAK
HH13: Defect and Diffusion I
Session Chairs
Thursday PM, November 30, 2006
Back Bay A (Sheraton)
11:30 AM - **HH13.1
Impact of First Principles Calculations on the Simulation of the Kinetics of Defects in Metals under Irradiation.
Francois Willaime 1
1 SRMP, CEA/Saclay, Gif-sur-Yvette France
Show AbstractI will review some of the successes obtained recently using first principles techniques to predict not only the structure but also the migration barriers of defects in metals, including defect clusters and defect complexes.These properties are a prerequisite for atomistic simulations of the behaviour of defect population evolution under or after irradiation. The examples will be based on two classes of materials of particular importance for the nuclear industry, namely iron-based and zirconium-based materials.
12:00 PM - **HH13.2
Kinetics of Crystallization at Extreme Undercoolings:A Window into the Structure of Liquids.
Yinon Ashkenazy 1 , Robert Averback 2
1 Racah Institute of Physics, The Hebrew University of Jerusalem, jerusalem Israel, 2 Materials Science and Engineering, University of Illinois, Urbana, Illinois, United States
Show AbstractUnderstanding the solid-liquid phase transition, and more generally the structure and dynamics of liquids and glasses, have remained enduring challenges in condensed matter sciences. While no models describing the microscopic behavior of liquids are presently accepted, the small changes in volume and heat capacity across the melting transition have motivated various theories that treat liquids as perturbed solids. One possible realization of this idea is a solid with a high percentage of defects. Based on previous observations that inhomogeneities in simple metallic liquids have properties similar to those of interstitialcy defects, and indeed the interstitialcy model of liquids and glasses, we explore whether such defects bear on the mechanisms of crystallization. Since interstitials have migration energies below 0.3 eV, we examine crystallization at deep undercoolings, both above and below the glass temperature.We show first that crystallization in this regime is best described as a diffusion limited process, rather than by the previously assumed collision limited model. We also show that the activation energy for crystallization from the glass is identical to the migration energy of interstitialcy atoms in their respective crystalline states. Furthermore, using direct observations in Fe, we show that the rate limiting step for the crystal to advance into the liquid is the jump of a <110> dumbbell interstitial on the liquid side of the solid-liquid interface, to jump into a kink site on the solid side of the interface. The migration step, moreover, is same interstitial rotation-translation, migration mechanism observed in crystals. Lastly, we provide results for pressure and surface orientation effects, as well as vibrational density of states ahead of the crystallization front, to further quantify the crystallization process.
12:30 PM - HH13.3
Calculations of the Vacancy Formation Energy near GP Zones and a Possible Nucleation Mechanism of Precipitates in Al-Cu Alloys
Shenyang Hu 1 , Michael Baskes 1 , Srinivasan Srivilliputhur 1
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractAlthough the precipitation sequence during heat treatment of an Al-Cu alloy with a small amount of Cu: solid solution → GPI → GPII → → θ is well known, fundamental information such as the nucleation process is not available. In this work, we calculated the vacancy formation energy around GPI and GPII using both first principles and semi-empirical calculations. The results of both sets of calculations show that compared to the vacancy formation energy in pure Al: 1) the vacancy on the Al layer next to the GPI has a much higher formation energy; 2) the vacancy on the second nearest Al layer to the GPI has much lower formation energy; and 3) the vacancy on the middle Al layer in the GPII has the lowest formation energy. Multi-vacancy formation energies and configuration entropies are calculated and estimated. These results suggest that the vacancy concentration is enhanced around the GPI and GPII, and one possible nucleation process could be that Cu atoms on GPI and GPII jump to the second nearest Al layer, and then order to form nuclei.
12:45 PM - HH13.4
Ab initio-Based Thermokinetics of the Ni-Cr Binary.
Julie Tucker 1 , Dane Morgan 1 , Todd Allen 1
1 , University of Wisconsin - Madison, Madison, Wisconsin, United States
Show AbstractLow temperature diffusion is enhanced by the creation of point defects in irradiated materials. A fundamental understanding of the diffusion mechanisms in multi-component alloys is essential in predicting microstructural and microchemical changes such as void swelling and radiation induced segregation, which can degrade material properties, a major concern in the nuclear power industry. We combine ab initio, cluster expansion, Monte Carlo and kinetic Monte Carlo techniques to calculate concentration and temperature dependent diffusion coefficients where experimental data is unavailable. This methodology is being applied to the face-centered cubic Fe-Ni-Cr system with a current emphasis on the Ni-Cr binary. We will present ab initio based thermodynamics for the Ni rich region, with an emphasis on the phase boundaries of the Ni2Cr phase and the importance of the thermodynamic factor for kinetic properties. We will also present formation and migration energies of point defects for varying chemical environments in order to assess how local environment and overall composition impact these properties.
HH14: Defect and Diffusion II
Session Chairs
Thursday PM, November 30, 2006
Back Bay A (Sheraton)
2:30 PM - **HH14.1
A Self-consistent Mean Field Theory for Diffusion in Concentrated Alloys.
Maylise Nastar 1 , Vincent Barbe 1
1 DMN/SRMP, CEA , Gif-sur-Yvette France
Show AbstractStarting from a microscopic model of the atomic transport via vacancies and interstitials in alloys, a self-consistent mean field (SCMF) kinetic theory yields the complete Onsager matrix of the phenomenological coefficients. The alloy is represented by a set of atoms and point defects distributed on a rigid lattice. The jump frequencies depend on the local environment trough a ‘broken bond model’ such that the large range of frequencies involved in concentrated alloys is produced by a small number of thermodynamic and kinetic parameters. Kinetic correlations are accounted for through a set of time-dependent effective interactions within a non-equilibrium distribution function of the system. The introduction of a master equation describing the evolution with time of the distribution function and its moments leads to general self-consistent kinetic equations [1]. It provides with new expressions of the phenomenological coefficients of concentrated multi-component alloys which are usually in good agreement with Monte Carlo simulations based on the same atomic diffusion model [1,2,3,4,5]. The different levels of approximation of the SCMF theory allow to reproduce many results of the previous diffusion models, in particular the percolation phenomena predicted by the random lattice gas theories in alloys with high jump frequency ratios [3] and the exact results of the dilute alloy models [2]. Recent improvements of the theory were to extend the multi-frequency approach usually restricted to dilute alloys to diffusion in concentrated alloys with jump frequencies depending on local concentrations [2,4] and to generalize the formalism first developed for the vacancy diffusion mechanism to the more complex diffusion mechanism of the interstitial dumbbell configuration [5]. A first application is to study grain-boundary segregation induced by irradiation and its dependence on the phenomenological coefficients associated to both vacancies and dumbbells created by irradiation. An important result is that the correlation effects and the variation of the phenomenological coefficients with local concentration cannot be neglected. [1] M. Nastar, V. Yu Dobretsov and G. Martin, Phil. Mag A80 (2000), 155.[2] M. Nastar, Phil. Mag. 85 (2005), 3767.[3] V. Barbe and M. Nastar, Phil. Mag. 86 (2006), 1513.[4] M. Nastar and V. Barbe, Faraday Discuss., (2006), DOI:10.1039/B605834E.[5] V. Barbe and M. Nastar, Phil. Mag. 86 (2006), 3503.
3:00 PM - **HH14.2
Control of Thin Film Morphologies and Nanoparticle Arrays during Vapor Deposition: Predictions based on Kinetic Monte Carlo Simulations.
George Gilmer 1 , Vasily Bulatov 1 , Tomas Oppelstrup 1 , Malvin Kalos 1 , Babak Sadigh 1
1 , Lawrence Livermore National Laboratory, Livermore, California, United States
Show Abstract3:30 PM - HH14.3
Phase Stability in Carbides and Nitrides in Steel.
Marcel Sluiter 1
1 3ME-MSE, TU Delft, Delft Netherlands
Show Abstract3:45 PM - HH14.4
Lattice Monte Carlo Simulations of Y-Ti-O Nanoclusters in Ferritic Alloys.
Brian Wirth 1 , Matthew Alinger 2 , G. Robert Odette 3
1 Nuclear Engineering, University of California, Berkeley, Berkeley, California, United States, 2 , GE Global Research, Niskayuna, New York, United States, 3 , University of California, Santa Barbara, Santa Barbara, California, United States
Show Abstract4:00 PM - HH14: Defect 2
BREAK
HH15: Nucleation, Growth, and Coarsening II
Session Chairs
Thursday PM, November 30, 2006
Back Bay A (Sheraton)
4:30 PM - **HH15.1
The Early Stages of Precipitation in Metals at the Atomic Scale: Experiments Versus Simulations.
Blavette Didier 1 , Pareige Cristelle 1 , Martin Georges 2 , Soisson Frederic 2
1 Phys., University of Rouen, St Etienne du Rouvray, xxx, France, 2 , SRMP-CEA, Saclay France
Show AbstractAtom Probe Tomography (APT) provides an unique approach of solid state phase transformations kinetics (ordering, unmixing). Chemical species can be mapped out in the three dimensions of space with a spatial resolution at the specimen surface of a few tenth nanometer [1,2]. The depth resolution, of a single atomic layer makes it possible the sacking sequence of superstructure planes within an ordered phase to be exhibited. Both the composition field and in some extend (all components of the order vector in FCC system are not imaged), the order field can therefore be imaged on a scale close to the unit cell and combined with both composition and topological information. Atom Probe Tomography was applied to numerous problems, and notably to the study of irradiation induced precipitation in ferritic steels. This presentation will be focussed on the transformation paths in nickel base alloys (NiAlV and NiAlCr). One of the key adavantage of APT is that the dimension of the small volume that is analysed (10x10x100 nm3) is close to that of simulated volumes in Monte-Carlo Simulations (MCS). In addition, both approaches, APT and MCS work on the same scale – the atom. Precipitation kinetics of Ni3Al-type phase in model NiCrAl superalloys was studied using this dual approach. In this work, experimental kinetics were compared to MCS predictions. [1] - BLAVETTE (D.), BOSTEL (A.), SARRAU (J.M.), DECONIHOUT (B.) and MENAND (A.) Nature 363 (1993) 432-435[2] - D. BLAVETTE, B. DECONIHOUT, S. CHAMBRELAND, A. BOSTELUltramicroscopy 70 (1998) 115-124[3] L. MARTEAU, C. PAREIGE, D. BLAVETTEImaging the three orientation variants of the DO22 phase by 3DAP microscopyJ. OF MICROSCOPY, 204, PT3 (2001) 247-251[4] C. PAREIGE, F. SOISSON, G. MARTIN, and D. BLAVETTEOrdering and phase separation in NiCrAl alloys: Monte Carlo simulation and 3D atom probe study, Acta Met Mater. 47-6 (1999) 1889-99
5:00 PM - HH15.2
Effect of Temperature on the Kinetics of Nanocluster Nucleation and Growth in Polymeric Media
Oz Gazit 1 , Rina Tannenbaum 1 2 , Nily Dan 3
1 Chemical Engineering, Technion, Haifa Israel, 2 Chemical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 3 Chemical and Biological Engineering, Drexel University, Philadelphia, Pennsylvania, United States
Show AbstractPresentation Time & Paper Number changeThursday 11/30HH15.3 to HH15.2from 4:30 to 4:00 pmEffect of Temperature on the Kinetics of Nanocluster Nucleation and Growth in Polymeric Media. Oz Gazit