Ludovic Thilly University of Poitiers
Neville R. Moody Sandia National Laboratories
Amit Misra Los Alamos National Laboratory
Peter M. Anderson Ohio State University
Mukul Kumar Lawrence Livermore National Laboratory
FF1: Deformation Processing of Metal Phase Composites
Monday AM, November 27, 2006
Back Bay C (Sheraton)
9:30 AM - FF1.1
Elastic Properties of Bi-Ta composites Fabricated by Uniaxial Pressing at Room Temperature.
Louis Martin 1 , Andrea Hodge 2 , Geoffrey Campbell 2 Show Abstract
1 Mechanical Engineering, Lawrence Livermore National Laboratory, Livermore, California, United States, 2 Chemistry and Materials Science, Lawrence Livermore National Laboratory, Livermore, California, United States
Powder compacts of Bi and Ta-reinforced Bi were fabricated by uniaxial pressing at room temperature. Density, microstructure, elastic moduli, and strength were evaluated for different particle sizes and processing pressures. For micron-sized powders, apparent densities exceeding 95% of theoretical were achieved at pressures >300MPa. Compaction of unreinforced Bi powder yielded hardness of ~ 25 Hv, sound wave velocities, and elastic moduli consistent with published values for polycrystalline Bi. Incorporation of 25% (by volume) of Ta significantly increased the density, hardness, moduli, and sound wave velocities. Additionally, particle size was reduced by mechanical milling prior to compaction. The effect of milling time, temperature and powder-to- ball ratio on the mechanical properties will be discussed in detail. Work performed under the auspices of the U.S. DOE by the University of California, Lawrence Livermore National Laboratory under contract W-7405-ENG-48.
9:45 AM - FF1.2
Fabrication and Characterization of Cold Rolling Al/Ni Multilayer Foils.
Xiaotun Qiu 1 , Jesse Graeter 1 , Laszlo Kecskes 2 , Jiaping Wang 1 Show Abstract
1 ME, Louisiana State University, Baton Rouge, Louisiana, United States, 2 , Army Research Laboratory, Aberdeen Proving Ground, Maryland, United States
Self-propagating exothermic formation reactions have been intensively studied in Al/Ni multilayer foils made by physical vapor deposition (PVD) method and these reactive foils have been used as local heat sources to melt solders or brazes and thus bond components in a variety of applications, such as joining stainless steel, Al, Cu, and bulk metallic glass. In this paper, a series of Ni/Al multilayer foils were fabricated by cold rolling method and the self-propagating exothermic reactions in these foils were characterized. Thin sheets of Al and Ni were used to fabricate Al/Ni multilayer samples by cold rolling method. The initial Al and Ni layer thicknesses were chosen at a 3 to 2 ratio to obtain foils with a 1 to 1 atomic ratio. The Al and Ni sheets were stacked alternatively and then cold rolled using a laboratory rolling mill to reduce the total thickness. After several cold rolling cycles, the rolled strip were folded again for the next rolling process. The rolling-folding cycles were repeated several times to obtain Al/Ni multilayer foils with a range of bilayer thicknesses and total thicknesses. Compared with physical vapor deposition, such as magnetron sputtering, which is expensive to operate and time consuming, the simplicity and the low-cost nature of this cold rolling process will dramatically reduce the expense of reactive multilayers fabrication and thus lower the cost of reactive joining method.Self-propagating reactions in these Al/Ni multilayer foils can be initiated by heating the foils with flame and are driven by a reduction in atomic bond energy. As atoms mix normal to the layers, heat is released and conducted parallel to the layers. If atomic mixing and energy release are sufficiently fast, then the reactions are self-sustaining. Exothermic reactions in these foils are two-step reactions. The first step of the reaction involves limited amount of reaction at interfaces between Al and Ni layers, while the second step of the reaction releases much larger amount of heat very rapidly. The energy released from these foils was characterized using differential scanning calorimetry (DSC) and the reaction velocities were measured using a high speed camera. The phases in reacted multilayer foils were characterized using X-ray diffraction (XRD). The microstructure, heat, velocity, and products of reaction in the cold rolled multilayer foils are compared with the foils made by PVD method. Joining applications are explored using the cold rolled foils as local heat sources.
10:00 AM - **FF1.3
Generation of Nanocomposites by Severe Plastic Deformation.
Reinhard Pippan 1 , Darren Edwards 2 , Ilchat Sabirov 3 Show Abstract
1 Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Leoben Austria, 2 Defence Science and Technology Organization, Maritime Platforms Division, Melbourne, Victoria, Australia, 3 Deakin University, School of Engineering and Technology, Waurn Ponds, Victoria, Australia
10:30 AM - **FF1.4
Properties of Nanoscaled Multiphase Structures and Non-Equilibrium Solid Solutions Obtained by Severe Plastic Deformation.
Xavier Sauvage 1 , Xavier Quelennec 1 , Peter Jessner 1 2 , Florian Wetscher 2 , Reinhard Pippan 2 Show Abstract
1 Groupe de Physique des Matériaux - UMR 6634, CNRS - Université de Rouen, Saint-Etienne du Rouvray France, 2 CD-Laboratory for Local Analysis of Deformation and Fracture, Erich Schmid Institute of Material Sciences, Leoben Austria
12:00 PM - **FF1.6
On the Mechanism of Mechanical Mixing and Deformation-induced Amorphization in Heavily Drawn Cu-Nb-Ag in situ Composite Wires.
S. Ohsaki 1 , Dierk Raabe 2 , K. Hono 1 Show Abstract
1 Metallic Nanostructure Group, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047 Japan, 2 , Max-Planck-Institut, Duesseldorf Germany
12:30 PM - **FF1.7
Load Transfer between the Fe Matrix and Fe3C Reinforcement in an Ultra-High Carbon Steel.
David Dunand 1 Show Abstract
1 Department of Materials Science & Eng., Northwestern University, Evanston, Illinois, United States
Ultrahigh-carbon steels (UHCS) consist of a ferritic matrix with high volume fractions (>15 vol%) of cementite Fe3C particles. They are one of the oldest metal matrix composites (MMC), since they have been in use for many centuries (e.g., Damascus blades). As for all MMCs, the load transfer occurring between reinforcement and matrix controls their mechanical properties.In this study, a UHCS sample consisting of a fine-grained ferritic matrix with 27 vol % submicron spheroidized cementite particles is loaded in tension up to 1 GPa. At regular stress intervals, synchrotron X-ray diffraction is used to measured volume-averaged lattice strains in the matrix and reinforcement. Unlike most MMCs, UHCS exhibit no load transfer between matrix and reinforcement in the elastic range of deformation, as expected given that both phases have nearly equivalent Young’s moduli. However, in the plastic region up to fracture, strong load shedding occurs from the plastic matrix to the elastic cementite particles, as previously observed in other MMCs. This measured load transfer is compared with finite-element model predictions.Acknowledgments - The steel was supplied by Prof. O.D. Sherby (Stanford U.). The following co-workers are gratefully acknowledged: M.L. Young (Northwestern U.), Drs. J.D. Almer, U. Lienert and D.R. Haeffner (Argonne National Laboratory), Dr. M. Daymond (Queen’s U.)
FF2: Novel Metal Phase Composites
Monday PM, November 27, 2006
Back Bay C (Sheraton)
2:30 PM - **FF2.1
Composites for High Field Magnets.
Ke Han 1 Show Abstract
1 , National High Magnetic Field Laboratory, Tallahassee, Florida, United States
3:00 PM - FF2.2
Multiscale Mechanics of TRIP- and TWIP-aided Steels.
Pascal Jacques 1 , Arnaud Petein 1 , Thomas Pardoen 1 , Francis Delannay 1 Show Abstract
1 IMAP, Université catholique de Louvain, Louvain-la-Neuve Belgium
3:15 PM - FF2.3
Ultra-High Damping Metal Matrix Composites Based on Powders of Shape Memory Alloys.
Jose San Juan 1 3 , Gabriel López 2 , Mariano Barrado 1 , Eduardo Bocanegra 2 , Maria Nó 2 Show Abstract
1 Fisica Materia Condensada, Universidad del Pais Vasco, Bilbao Spain, 3 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Fisica Aplicada II, Universidad del Pais Vasco, Bilbao Spain
FF3: Deformation in Metal/Ceramic Composites
Monday PM, November 27, 2006
Back Bay C (Sheraton)
4:30 PM - **FF3.1
Deformation of Highly Loaded Alumina Reinforced Aluminium Composites: Internal Damage and the Size Effect.
Randoald Mueller 1 , Andreas Mortensen 1 Show Abstract
1 Laboratory for Mechanical Metallurgy, Institute of Materials, Ecole Polytechnique Fédérale de Lausanne, Lausanne Switzerland
The pressure infiltration of densely packed alumina particle preforms with molten aluminium produces defect-free composites containing roughly equal proportions of metal and ceramic. The process affords considerable latitude in microstructural design of the resulting composites. In particular, the matrix can be kept microstructurally simple, and the size of the reinforcement can be varied roughly between 3 and 100 µm. Despite their high ceramic loadings, these composites display appreciable plasticity, often deforming in tension to elongations of several percent before breaking. Beyond yield, their flow stress is largely governed by that of the matrix; this matrix, in turn, is a metal deforming between hard inclusions only a few micrometres apart. As is well-known from the composite literature, the high constraint imposed by the reinforcement on matrix deformation is manifest in a “size-effect”, whereby the matrix, and hence the composite, flow stress can depend on the microstructural scale of the composite.We present recent results from a recent investigation of this phenomenon on pressure-infiltrated alumina reinforced aluminium composites. We describe a methodology of analysis of the effect that takes into account both the complexity of the underlying mechanical problem and the influence of internal damage, which often develops extensively in these materials. We then present back–calculated in-situ flow curves of the matrix within such composites, showing that there is a strong and systematic size effect with pure aluminium, but not in solutionized binary Al-Cu alloys.
5:00 PM - FF3.2
Deformation Behavior of Nanolayered Metal-Ceramic Laminated Composites.
Nik Chawla 1 , Yu-Lin Shen 2 Show Abstract
1 School of Materials, Arizona State University, Tempe, Arizona, United States, 2 Department of Mechanical Engineering, University of New Mexico, Albuquerque, New Mexico, United States
5:15 PM - FF3.3
Controlling Residual Stress in Metal Matrix Ceramic Fiber Composite.
Marwan Al-Haik 1 , Hamid Garmestani 2 , Yousef Haik Show Abstract
1 Mechanical Engineering, University of New Mexico, Albuquerque, New Mexico, United States, 2 Materials Science and Engineering, Georgia Institute of Technology, Atlant, Georgia, United States
5:30 PM - FF3.4
Correlative Mechanisms in Deformation and Fracture Behavior of Composite Systems with Ductile Interphases.
Nasim Alem 1 , Vinayak Dravid 1 Show Abstract
1 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
5:45 PM -
Overview: Poster Session I
FF4: Poster Session I: Metal and Ceramic Composites
Monday PM, November 27, 2006
Exhibition Hall D (Hynes)
9:00 PM - FF4.10
Fatigue Crack Growth Mechanisms in High Pressure Die Cast Magnesium Based Alloys.
Haitham El Kadiri 1 Show Abstract
1 CAVS, MSU, Starkville, Mississippi, United States
9:00 PM - FF4.11
Microstructure – Resistivity Correlations in Solution Treated and Aged Waspaloy Microstructures.
V.Siva Kumar G. Kelekanjeri 1 , Rosario Gerhardt 1 Show Abstract
1 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Nickel-base superalloys are an important class of metallic ‘nanocomposite’ structural materials known for their good strength retention abilities at high homologous temperatures for long service times. The high temperature strength of superalloys may be ascribed to the presence of the nanometer size precipitation-hardening γ' phase that reinforces the austenitic matrix (γ) phase. The current work is focused on developing microstructure-electrical property correlations in Waspaloy microstructures produced via suitably designed heat-treatments. The initial heat-treatment step consisted of solutionizing the specimens at 1145°C, that was common to all the specimens. The first set of specimens (denoted by ‘A’) was subsequently vacancy-stabilized at 1045°C (above the γ' solvus), aimed at lowering the quenched-in vacancy concentration after the solution-treatment. The second set (denoted by ‘B’) was not subjected to the vacancy-stabilization treatment. After the initial treatments, ‘A’ was subjected to aging at nominal temperatures of 700°C, 800°C and 875°C for times ranging from 0.5 to 100 hours, with the objective of studying the coarsening kinetics of this alloy. The same aging scheme was followed for ‘B’, with the exception that the lowest aging temperature was 725°C.Microscopic examination of the specimens in an SEM revealed progressive growth of γ' precipitates with continued aging at all the aging temperatures. Electrical characterization of the specimens was conducted via DC four-probe resistivity measurements. The experimentally measured resistance of each specimen was multiplied by appropriate geometric correction factor to obtain the overall resistivity of the specimen. In general, the resistivity followed a decreasing trend as a function of increasing aging time for both sets of aged specimens. The drop in resistivity with continued aging is an expected result, since the size of the precipitates increases in comparison to the electron mean-free path due to progressive γ’ coarsening. Any deviations from this behavior are expected to be related to specific changes in the microstructure of the alloy.The microstructures of as-solution-treated and as-stabilized specimens show the presence of etch facets that are oriented along specific crystallographic directions within a single grain. During subsequent aging treatments, the facets undergo a gradual evolution from sharp edges to corner-rounded features to more irregular shapes until they finally dissolve into the matrix. This phenomenon is more noticeable at the lowest aging temperatures, presumably due to slower kinetics. It is speculated that the transformation of etch facets is related to progressive annihilation of quenched-in vacancies present after the initial heat treatments. We propose to conduct localized electrical measurements using an AFM to detect regions of higher resistivity than the surrounding matrix in order to verify the above hypothesis.
9:00 PM - FF4.12
Mechanical Properties of Ni-P/Diamond Composite Films Processed by Electro-less Plating Method.
Jin Ki Cho 1 2 , Mi Sun Yoo 1 , Moon Tae Kim 1 , Seun Ryong Baek 1 3 , Chan Hyoung Kang 1 , Sung Goon Kang 2 Show Abstract
1 Department of Advanced Materials Engineering, Korea Polytechnic university, Kyonggi-Do Korea (the Republic of), 2 Division of Materials Science and Engineering , Hanyang university, Seoul Korea (the Republic of), 3 , Young In Plachem, Kyonggi-Do Korea (the Republic of)
Recent advancements in various industries have necessitated the development of new engineering materials exhibiting superior properties of different character. For example, composite electroplating renders excellent corrosion- and wear-resistant materials with good lubrication behavior and chemical stability. Nanometer-sized diamond particles are expected to be good dispersion materials in electro-less composite plating. However, the processing conditions and characteristics of metal/diamond composites are not well understood so far. In this investigation, we developed new processes for co-deposition of Ni-P/diamond composite films on steel plates using the commercial electrolyte composed of nickel sulfate and sodium hypophosphite. No additives were applied in this process as in the conventional methods for the efficient dispersion of diamond particles. The diamond particles of a few hundred nanometer size were dispersed in an ultrasonic bath of de-ionized water. The zeta potential of the diamond solution was measured prior to the incorporation into the electrolyte. The morphology of the prepared films was characterized by FESEM. Based on the FESEM images, the size distribution of the diamond particles was determined using an image analyzer program. The micro-hardness, the coefficient of friction, and the corrosion potential were measured by Vickers hardness tester, tribometer and potentiometer, respectively. The present experimental results revealed remarkable differences in the values of the micro-hardness, the coefficient of friction, and the corrosion potential, compared to those of conventional diamond-free electro-less Ni-P plates. Process conditions were optimized in terms of the concentration of diamond particles, ultrasonic dispersion time, and pH of the electrolyte. As the concentration of diamond particles increased from 0.5to 3g/l, the zeta potential was decreasing with more particles aggregated. The higher the diamond concentration, the higher the volume fraction of diamond particles co-deposited in the nickel matrix. In turn, the coefficient of friction and corrosion potential increasd with the increasing diamond concentration. The particle size distribution was the most uniform in the samples prepared at the concentration of 1.0g/l. The best mechanical properties were obtained when the dispersion time was 30min. and the pH 5.
9:00 PM - FF4.13
Effect of Seed Layer and Deposition Sequence on Strength of A/B Metallic Multilayer Thin Films.
John Carpenter 1 , Peter Anderson 1 Show Abstract
1 , Ohio State University, Columbus, Ohio, United States
9:00 PM - FF4.14
Evaluation of Elastic Moduli of Multi-layered Thin Films on Polymer Substrates Using Wrinkling Analysis.
Jun-Hyun Han 1 , Myoung-Woon Moon 1 , Jae-Hyun Kim 1 , Joost Vlassak 1 Show Abstract
1 Div. of Engineering and Applied Sciecnces, Harvard University, Cambridge, Massachusetts, United States
Multi-layered thin films on soft substrates are increasingly used in device applications such as flexible electronics. Since it is well known that the mechanical properties of thin films can be quite different from those of bulk materials, research engineers in the N/MEMS industry need to know the mechanical properties of thin films used in their devices for the purpose of reliability and performance estimation. The mechanical properties of a single-layer thin film on a substrate are readily measured using nanoindentation if film and substrate have similar properties. The technique has severe problems, however, when applied to stiff films on compliant substrates, a situation often encountered when dealing with flexible electronics. Moreover, the technique is not capable of measuring the mechanical response of the individual layers in a multi-layered thin-film system because the indentation response of a multi-layered system is not a simple sum of the responses of the individual layers. Clearly, there exists a need for a technique capable of measuring the mechanical properties of thin films on compliant substrates and of individual layers in multilayered systems.One such technique relies on an analysis of the wrinkling patterns that develop in thin films on polymer substrates. When a stiff film on a compliant substrate is subjected to a compressive stress, the large elastic modulus difference between film and substrate allows the film to relieve the compressive stress by wrinkling. The period of the wrinkles is directly related to the stiffness mismatch between film and substrate.Ti, Cu and Cu/Ti film stacks have been deposited onto uni-axially pre-strained polydimethylsiloxane (PDMS) substrates by means of DC magnetron sputtering. When the PDMS substrates are allowed to recover their original shape, straight wrinkles develop as a result of the uni-axial compressive stress in the film stacks. The wrinkling pattern of the film stacks is analyzed and the elastic moduli of the individual films are extracted with knowledge of the wrinkling wavelengths and film thicknesses only; there is no need to determine the stress in the films.
9:00 PM - FF4.15
Processing-Microstructure-Property Relations in Anisotropy Thermal Sprayed Composites
Weiguang Chi 1 , Vasudevan Srinivasan 1 , Atin Sharma 1 , Sanjay Sampath 1 , Richard Gambino 1 Show Abstract
1 Center for Thermal Spray Research, Materials Science and Engineering Department, State University of New York at Stony Brook, Stony Brook, New York, United States
Thermal spray is a significantly advanced but inherently complex deposition process that involves successive impingement of melted droplets on substrate to form coating with a brick-wall layered structure. The anisotropic microstructure of coatings is very sensitive to processing and has significant influence on the property. This study aims to understand the processing-microstructure-thermal property correlation of thermal sprayed coatings. Thermal transport properties of three coating systems forming composites with pores (YSZ-Air), a second phase (Mo-Mo2C) and a graded material (YSZ-NiCrAlY) are interpreted from the point of view of microstructure and chemical composition. In the case of YSZ-Air composite, results indicate that porosity contribution from 10-30% decreases the thermal conductivity by 20-50% of bulk value. For the intrinsic composite of Mo and Mo2C, which coexist as stable phase, thermal conductivity increases significantly with 1.75wt% carbon addition since reducing formation of MoO2 but decreases with 3.5wt% due to more retaining of carbon. As for the discrete layered and graded composites of YSZ-NiCrAlY, which are made up of varying fraction of these two constituents, thermal conductivity decreases sharply up to 40wt% YSZ and then more gradually with increasing YSZ content. This paper examines these experimental findings by treating the coatings as composites.
9:00 PM - FF4.16
Structure Optimization of Strained Si/Si1-yGey Dual-Channel Heterostructures on Relaxed Si1-xGex (x≤y) Virtual Substrate for High Performance MOSFETs.
Sang Hoon Kim 1 , Hyun Cheol Bae 1 , Sang Heung Lee 1 Show Abstract
1 , SiGe Circuit Team, RF Circuit Group, Electronics and Telecommunications Research Institute, Daejeon Korea (the Republic of)
9:00 PM - FF4.17
Effect of Operating Conditions on Growth rate, Particulates, Non-stoichiometric transfer, Uniformity and Crystallinity of the Si1-xGex Thin Films Grown by PLD.
Mohammed Khan 1 3 , Clinton Lee 1 3 , D. Kumar 2 3 , Jagannath Sankar 2 3 Show Abstract
1 Electrical and Computer Engineering, North Carolina A&T State University, Greensboro, North Carolina, United States, 3 Center for Advanced Materials and Smart Structures (CAMSS), North Carolina A&T State University, Greensboro, North Carolina, United States, 2 Mechanical and Chemical Engineering Department, North Carolina A&T State University, Greensboro, North Carolina, United States
9:00 PM - FF4.18
Residual Stress Distribution, Intermolecular Force, And Frictional Coefficient Maps In Diamond Films: Processing-Structure-Mechanical Property Relationship.
Sanju Gupta 1 , Paul May 2 , Oliver Williams 3 , Klaus Haenen 3 , Eric Bohannan 4 Show Abstract
1 Physics and Materials Science, Missouri State University, Springfield, Missouri, United States, 2 School of Chemistry, Bristol University, Bristol United Kingdom, 3 Institute of Materials Research, Universiteit Hasselt, Hasselt Belgium, 4 Materials Science, University of Missouri, Rolla, Missouri, United States
Carbon in its various forms, specifically diamond, may become a key material for the manufacturing of micro-electromechanical and nano-electromechanical (M/NEMS) devices in the 21st Century [1, 2]. The novel nanocrystalline diamond films may provide a basis for this revolution . In order to effectively utilizing these materials for these applications, understanding of their structural and physical (mechanical properties, in particular) become indispensable. The nanocrystalline diamond films were grown using hot-filament and microwave chemical vapor deposition techniques involving novel CH4/doping [H2S, TMB and N2 for sulfur, boron and nitrogen, respectively] in high hydrogen dilution and CH4/Ar chemistry. Such physico-chemical processes induce synthesis-specific nanostructuring (grain size: 10-30 nm and sp3 versus sp2 bonded C configurations) and offer unique physical properties (extremely smooth surfaces, high electrical conductivity especially when doped with n- and p-type impurities) enabling several applications. In order to investigate residual stress and to measure intermolecular forces, the films were characterized extensively using Raman spectroscopy and atomic force microscopy in terms of topography and force curves where the latter measuring elasticity maps. Traditional force curve measures the force felt by the tip as it approaches and retracts from a point on the sample surface, while force volume is an array of force curves over an extended range of sample area. Moreover, by using atomic force microscopy for nanoscale force constant measurements and surface spectrosopy techniques for detailed chemical and structural studies, we are able to demonstrate that the carbon bonding configuration (sp2 versus sp3 hybridization) and surface chemical termination in both the undoped and doped nanocrystalline diamond surfaces has a strong effect on nanoscale intermolecular forces. The preliminary information in the force volume measurement was decoupled from topographic data to offer new insight into the materials and surface properties. These measurements are also complemented with X-ray diffraction to reveal their lattice structure and lateral force microscopy for friction behavior. We discuss these results for their potential impact on N/MEMS applications. *Supported by internal funds. A. Krauss, et. al. Diam. and Relat. Mater. 10, 1952 (2001); A.V. Sumant, Adv. Mat. 14, (2004).
9:00 PM - FF4.19
Mechanical Properties of Textured Alumina Prepared by Colloidal Processing in a Strong Magnetic Field.
Tohru Suzuki 1 , Tetsuo Uchikoshi 1 , Koji Morita 1 , Keijiro Hiraga 1 , Yoshio Sakka 1 Show Abstract
1 Nano Ceramics Center, National Institute for Materials Science, Tsukuba, Ibaraki, Japan
9:00 PM - FF4.2
Texture and Microstructure Evolution During Severe Plastic Deformation of a Copper Matrix Reinforced by Niobium Nanotubes: Correlation with Macroscopic Mechanical Properties.
Vanessa Vidal 1 2 , Ludovic Thilly 2 , Pierre-Olivier Renault 2 , Florence Lecouturier 1 Show Abstract
1 , Laboratoire National des Champs Magnétiques Pulsés - CNRS, Toulouse France, 2 , Laboratoire de Métallurgie Physique - Université de Poitiers, Poitiers France
The development of reinforced conductors, with high electrical conductivity and high strength, is essential to provide non-destructive high pulsed magnetic fields over 80 Teslas: a compromise is obtained with Cu-based continuous nanofilamentary wires (2 GPa ultimate tensile strength and 0,6 µohm.cm electrical resistivity at 77K).The elaboration process of these nanocomposite wires is based on severe plastic deformation applied by repeated drawing and bundling stages and leads to a multi-scale copper matrix containing up to N=85^4 (52.2 10^6) continuous and parallel bcc filaments (niobium or tantalum) with diameter as low as 25 nm.The mechanical study of the Cu/Nb system showed that the strength of Nb fibers, considered as nanowhiskers, is inversely proportional to their diameter and approaches, for smaller diameters, the theoretical strength for perfect crystals G/2π. Moreover, nanoindentation and in-situ Transmission Electron Microscopy (TEM) tensile tests showed that the Cu/Nb interfaces are barriers to the dislocation motion. Thus, a geometric optimization was developed through a Cu/Nb/Cu “co-cylindrical” structure composed of a Cu matrix embedding Nb nanotubes filled with Cu. In this structure, the nanometer scale is more rapidly achieved and the contribution of the Cu/Nb interfaces is increased. TEM as well as X-rays diffraction experiments (theta/2theta scans, pole figures and psi scans) have been carried out on Cu/Nb/Cu samples taken throughout the fabrication process to study the formation of microstructure, i.e. grain size and grain type distribution in Cu and Nb phases. Nb nanotubes exhibit a rather homogeneous microstructure with unique <110> axial texture and grains in the 100nm range. However, a complex microstructure was pointed out in the Cu matrix with different size and type of grains in the different Cu channels. The large Cu channels exhibit a microstructure similar to ultra fine grain Cu produced by other SPD techniques, with a majority of grains in the 200-400 nm range and remaining grains in the µm range, while the finest Cu channels (inter-tube and inner-tube Cu) are composed of only one or two grains between Cu/Nb interfaces. The formation of texture in Cu is analyzed with respect to the SPD steps and the occurrence of heat treatments and reveals two different states: the “deformation” texture (major <111> fiber texture) and the “recrystallization” texture (major <200> fiber texture). The texture of the final product is therefore the result of the interplay between these texture states and the grain size distribution. On the basis of these microstructural features, a correlation with macroscopic mechanical propertie is proposed.
9:00 PM - FF4.20
Surface Properties of Transparent Conductive Oxide Films on Flexible Substrates Treated by Linear Ion Source.
Shih Hsiu Hsiao 1 , Yoshikazu Tanaka 1 , Ari Ide-Ektessabi 1 Show Abstract
1 Mechanical Engineering and Science, Kyoto University, Kyoto Japan
Transparent conductive oxide films are extensively used in display industry and they can be utilized for flexible display. The polymer and the plastic materials used as the flexible substrates in display are more bendable and lighter weight compared to glass substrates. However, their mechanical and surface properties differed from glass substrates affect the quality of transparent conductive oxide film deposited on it. It is one of the reasons for the cracks and the failures of flexible display. In this study, Polyethylene Terephthalate (PET) and the silicone were used as the flexible substrate. The linear ion source was developed to treat the surface before the transparent conductive oxide film deposited by sputtering method. ITO (Indium Tin Oxide), MZO (Magnesium Zinc Oxide) and AZO (Aluminum Zinc Oxide) were the sputter targets used for transparent conductive oxide films deposited. Surface crystal grain, light transmission rate and surface resistance were measured in the different thickness of transparent conductive oxide films deposited. X-ray photoelectron spectra (XPS) and Atomic Force Microscope (AFM) were used to analyze the transformation of chemical composition on surface and surface topography after the irradiation of argon and oxygen ion. Moreover, the linear ion source provides the good uniformity of surface treatment and it is suitable for production-scale.
9:00 PM - FF4.21
Deposition of Dense Al2O3-40wt% ZrO2 Composite Coating by Solution Precursor Plasma Spraying
Dianying Chen 1 , Eric Jordan 2 1 , Maurice Gell 1 , Xinqing Ma 3 Show Abstract
1 Materials Science Program, University of Connecticut, Storrs, Connecticut, United States, 2 Department of Mechanical Engineering, University of Connecticut, Storrs, Connecticut, United States, 3 , Inframat Corporation, Farmington, Connecticut, United States
Dense Al2O3-40wt%ZrO2 coating was deposited by solution precursor plasma spraying process (SPPS). In SPPS, an aqueous solution precursor feedstock, instead of conventional powder, is injected into the plasma jet. The solution droplets undergo a series of physical and chemical reactions prior to deposition on the substrate as Al2O3-ZrO2 coating. SEM microstructure shows the as-sprayed coating is very dense with ~2% porosity. The coating hardness is ~12GPa. Phase stability of the as-sprayed composite coating at high temperature was also investigated.
9:00 PM - FF4.22
Preparation of Thick films of Mesoporous Materials by Electrophoretic Deposition
Akira Endo 1 , Hideyuki Negishi 1 , Keiji Sakaki 1 , Masaru Nakaiwa 1 Show Abstract
1 , National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Japan
Ordered mesoporous inorganic materials templated by surfactant molecular assemblies have attracted a great deal of attention because of their potential applications as catalysts, adsorbents, molecular sieves, sensors, etc. From the practical point of view, the fixation of the mesoporous powder onto substrates with a cetain thickness is very important. In this work, the electrophoretic deposition (EPD) technique was investigated for the fabrication of thick films of mesoporous silicate. A mesoporous powder was prepared by spray-drying and deposited by EPD onto a tublar metal substrate and more than 200μm thick uniform coating was obtained. The desposition rate was about 1μm/sec. After the thermal treatment at 573K, the obtained thick film of mesoporous silicate can be fixed on the substrate without the addition of binders. The films possessed the same porous structure and adsorption properties as the original mesoporous silicate powder.
9:00 PM - FF4.23
Measurement of Stress-strain Curves of PECVD Silicon Oxide Thin Films by Means of Nanoindentation.
Zhiqiang Cao 1 , Xin Zhang 1 Show Abstract
1 Manufacturing Engineering, Boston University, Brookline, Massachusetts, United States
9:00 PM - FF4.24
Fabrication of CaTiO3 Thin Film on Ti-Zr-Nb Alloy by Using Hydrothermal-electrochemical Technique.
Naota Sugiyama 1 , Tomoaki Watanabe 1 , Nobuhiro Matsushita 1 , Xinmin Wang 2 , Akihisa Inoue 2 , Masahiro Tsukamoto 3 , Nobuyuki Abe 3 , Yuichi Komizo 3 , Takamasa Onoki 1 , Yasuhiro Tanabe 1 , Masahiro Yoshimura 1 Show Abstract
1 Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama Japan, 2 Institute of Materials Rsearch, Tohoku University, Sendai Japan, 3 Joining and Welding Research Institute, Osaka University, Osaka Japan
Titanium and its alloys are used as load bearing dental and orthopedic implants due to their well mechanical properties and biocompatibility. To enhance the bone bonding ability of Ti based implant, various bioactive coating such as plasma spray process, CVD, and micro-arc oxidation have been developed. However these synthetic techniques using high temperature and/ or high vacuum cause cracks in the fabricated films during cooling process.We proposed low temperature and crack free titanate coating on Ti metal and Ti alloy by hydrothermal or hydrothermal-electrochemical treatments. These treatments are appropriate for bioactive coating on Ti alloys without using toxic solutions and high temperature processes. We succeeded in depositing thin metal oxide films, such as BaTiO3, SrTiO3, and CaTiO3, at temperatures of 473 K or blow. In the present study, we tried to fabricate bioactive CaTiO3 films on Ti-Zr-Nb alloys, which have excellent mechanical properties to improve biocompatibility such as appetite-inducing ability. In the all experiments, Ti-Zr-Nb specimen surfaces were polished with cleanser to remove some contaminations. Subsequently surfaces were washed with acetone in the ultrasonic bath. Ca-containing titania films were prepared on these specimens by hydrothermal treatment and hydrothermal-electrochemical treatment at 473 K for 2-48 h in mixed aqueous solutions of 0.4M-NaOH and excess Ca(OH)2 under saturated water vapor of 2.0 MPa. During the hydrothermal–electrochemical treatment, a constant electrical current of 0.1-20 mA/cm2 was applied between Ti-Zr-Nb alloy plate (anode) and Pt (cathode). After hydrothermal or hydrothermal–electrochemical treatments, the specimens were removed from aqueous solutions, washed with distilled water, and then dried. The phase of the obtained specimens were determined by X-ray diffraction and Raman spectroscopy. The surface morphology of the fabricated films was observed using scanning electron microscopy. Theses evaluations revealed that CaTiO3 thin films were fabricated on Ti-Zr-Nb alloy plate surface in this study.
9:00 PM - FF4.25
Optical Coating Properties for Enhanced Blown-Sand Abrasion Resistance
Christopher Drew 1 , Suzanne Bosselman 1 , David Ziegler 1 Show Abstract
1 , US Army, Natick Soldier Center, Natick, Massachusetts, United States
Lenses and other transparent optical materials suffer rapid damage when subjected to blowing abrasive particulates. Polymeric lens materials like polycarbonate are often treated with a scratch-resistant coating, which is typically silica-based. The coating provides some protection, yet is generally not sufficiently effective at resisting abrasion from blown sand in most commercial products. We demonstrate that silicone rubber coatings are superior to polycarbonate and silica glass at resisting damage by blown sand particles. Sand abrasion tests were conducted using a custom-built test apparatus that exposes the samples to 400 micron diameter quartz silica moving at 17 m/s (40 mph). Scanning electron microscopy showed the presence of small cracks and pits in polycarbonate, coated polycarbonate, and silica glass after exposure. No such damage was observed in the silicone coated samples after an identical exposure.Three different silicone formulations were studied, with molecular weights between crosslinks of 700, 1700, and 2300 Daltons, in an effort to identify critical mechanical properties that correlated to particle abrasion resistance. Polycarbonate and glass each have much higher elastic modulus and greater resilience in both tension and compression, relative to the silicones. The silicones have greater energy to break per volume in compression, yet is still far lower than that of glass or polycarbonate. These data suggest that the mechanical properties that govern rubbing type abrasion resistance play a lesser role in particle abrasion resistance. Specifically, reversible compressive deformation along with storage and loss moduli may be potentially better predictors than material toughness or elastic modulus.
9:00 PM - FF4.26
Damage of Multilayer Coatings on Glass: Scratch Resistance, Adhesion and Friction.
Xuan Geng 1 , Davy Dalmas 1 , Etienne Barthel 1 Show Abstract
1 , Laboratoire "Surface du verre et interfaces (SVI)" - Unité mixte CNRS/Saint-Gobain - UMR 125, Aubervilliers France
Optical coatings deposited on glass are widely used for numerous applications: solar control, thermal isolation and anti-reflection. These coatings are usually thin (<300 nm) multilayer stacks with respective layer thickness of tens of nanometres. For most of them, surfaces are very sensitive to damage due to scratch loading or other in-service contact, which will undermine the product’s performance. In general, coating damage is controlled by mechanical properties of the coating system, such as elastic modulus, hardness, friction, adhesion… However, a quantitative analysis of the damage becomes very difficult due to the complexity of multilayered structures and also due to the difficulties in characterization of extremely thin layers. Owing to the importance of surface and interface properties, especially for multilayer coatings, we focus on friction and adhesion as key parameters for understanding scratch damage mechanisms. In order to study these two key parameters and to propose a model which can predict scratch morphologies, several model multilayer coatings have been developed. We used different top layers in order to modify superficial friction coefficient and also different types of base layers in order to modify the adhesion of the weakest interface. Then, we have reproduced the morphology of scratches which are observed in industrial context (flat groove, straight edges, no damaged in substrate…) by using a scratch test performed on a sphere/plane tribometer. Superficial friction coefficients before damage were measured with the tribometer. Adhesion measurements were performed by using a cleavage test which has been specially developed in our laboratory for thin multilayer coatings on glass substrate. As expected, multilayer coatings with low friction coefficients have a much better scratch resistance than those with high friction coefficients. The determination of rupture surfaces by XPS analysis and the measurement of scratch morphologies with a profilometer show a good correlation between the position of the weakest interface and the scratch depth. The consistency of those results with currently available models has been checked and further parameters such as film thickness and residual stresses will now be investigated.
9:00 PM - FF4.27
Improvement of the Scratch Resistance of Glass by Means of a Silica Nanoparticle-based Coating Synthesized by a Reverse Microemulsion Method.
Ronan Tartivel 1 , Emmanuelle Reynaud 1 , Fabien Grasset 2 , Jean-Christophe Sangleboeuf 1 , Tanguy Rouxel 1 Show Abstract
1 LARMAUR, University of Rennes 1, Rennes France, 2 Sciences Chimiques de Rennes, University of Rennes 1, Rennes France
Used throughout human history, glass has recently been reconsidered as a major structural material as shown by the large window surfaces in use nowadays in vehicles and buildings. Its transparency hides a significant mechanical drawback, however: Brittleness, which arises from surface flaws. In times where reducing the weight and increasing the lifetime of structures is a growing concern, any strategy to increase the toughness of glass is of interest. Our study aims at coating glass surfaces with a hard, thin, transparent protective layer in order to minimize the density of surface flaws. A reverse micro-emulsion synthesis was used to produce a dispersion of colloidal silica nanoparticles (~30 nm in diameter) which were then deposited on a glass substrate by dip-coating. Thermal treatment was then used to remove any organic components, leading to the production of mono- and bilayer structures as observed via atomic force microscopy (AFM). Microindentation experiments revealed a lower elastic modulus in the coating versus the substrate, in spite of its fully inorganic nature. Scratch tests were then performed at increasing applied load using a custom-built sclerometer. The coating was found to delay the appearance of visually apparent scratches by reducing the degree of chipping observed during scratch development. Instead, such coatings exhibit a transition from ductile behavior directly to the abrasive regime classically observed in glass at high loads, avoiding the production of extended sub-surface cracks that normally give rise to visual damage.
9:00 PM - FF4.28
Residual Stresses and Deformation around Indentations in Alumina/SiC Nanocomposites.
Apichart Limpichaipanit 1 , Richard Todd 1 Show Abstract
1 Department of Materials, University of Oxford, Oxford United Kingdom
Alumina/SiC nanocomposites are more wear resistant and have better surface finish than pure alumina of a similar grain size. Grain pullouts caused by intergranular fracture are observed on worn surfaces of alumina whereas only a few pullouts resulting from transgranular fracture and scratches caused by plastic deformation are the main features of a worn surface of nanocomposites. Surface mechanical properties were investigated under idealised conditions using indentations. The stress around the indentations was investigated by Cr3+ fluorescence microscopy. The experiments were carried out using a variety of microstructures and varied indentation loads. In addition, the surface damage below indentations and worn surfaces was examined by Transmission Electron Microscopy (TEM). TEM samples were prepared by Focused Ion Beam (FIB) milling directly from the surface.
9:00 PM - FF4.29
Development of Evaluation Method for Delamination StrengthBetween Micro-Sized Materials in MEMS Devices.
Chiemi Ishiyama 1 , Junichi Hata 1 , Satoru Koyama 1 , Masato Sone 1 , Yakichi Higo 1 Show Abstract
1 , Precision & Intelligence Laboratory, Tokyo Institute of Technology, Yokohama Japan
9:00 PM - FF4.30
An Integrated AFM/RAMAN Tool For Local Stess Measurements of MEMS Devices
Aaron Lewis 2 1 , Rimma Dekhter 1 , Artium Khatchatouriants 1 , Noel Axelrod 2 Show Abstract
2 Applied Physics, Hebrew University of Jerusalem, Jerusalem Israel, 1 , Nanonics Imaging, Jerusalem Israel
Microelectromechanical (MEMs) devices are composed of silicon structures of various geometries and forms. These forms could extend from floating structures to bridges and membranes. Raman microspectral analysis has been recognized for many years as a tool that could monitor local stress in silicon. The local silicon stress that has been monitored in the past by Raman spectroscopy has in general been a result of thermal oxidation, wafer thinning, and chip bonding. Atomic force microscopy (AFM) has also been used for many years for characterizing MEMs structures. Although numerous papers have been published with each of these tools on these devices the world of AFM and Raman have been separate and apart. In this presentation we will describe the first tool that combines the uniqueness of AFM for mechanical characterization with the capability of Raman to measure the chemical characteristics associated with local and highly defined silicon stress. For this application of the integration of the worlds of defined and local AFM stress with Raman analysis of such stress we have developed a singular atomic force microscope (Nanonics Imaging Ltd. MultiView 1000 SPM System). This is the first such microscope that can be combined with any upright optical microscope for the analysis of opaque structures with AFM and Raman simultaneously. An essential aspect of this combined system is the AFM probe that is used in these measurements. AFM cantilevers have a significant silicon background Raman signal that would prevent the measurements described in this presentation. Nanonics has developed glass AFM cantilevers that not only are the first AFM cantilevers to permit a clear view of the tip of the probe by the on-line optical microscope but also do not have any Raman background.With such a combination of an AFM platform fully integrated into a conventional upright microscope complexed to a state of the art Renishaw PLC InVia Raman spectrometer defined measurements of local strain in silicon MEMs devices can be monitored. This presentation will demonstrate such AFM defined Raman spectral analysis. The results indicate a variety of interesting phenomena such as hysteresis, wear etc.
9:00 PM - FF4.5
Precessing of 2024 Al /W Composites Prepared by Powder Metallurgy.
Zhimin Yang 1 , Jian Yang 1 , Youyun Lian 1 Show Abstract
1 , General Research Institute for Non-ferrous Metals, Beijing China
9:00 PM - FF4.7
The Effect of Molybdenum on the Microstructure, Tensile and Creep Behavior of Orthorhombic-Based Ti-24Al-17Nb-xMo Alloys and SCS/Ti-24Al-17Nb-xMo Composites.
Jeff Quast 1 , Carl Boehlert 1 Show Abstract
1 Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan, United States
9:00 PM - FF4.9
Strain Effects on the Magnetic Properties of Cu-Nb Nanofilamentary Composites.
Maria R. J. Sandim 1 , Dimosthenis Stamopoulos 2 , Hugo R. Z. Sandim 1 , Luis Ghivelder 3 , Ludovic Thilly 4 , Vanessa Vidal 5 4 , Florence Lecouturier 5 , Dierk Raabe 6 Show Abstract
1 USP Lorena, University of São Paulo, Lorena, SP, Brazil, 2 Institute of Materials Science, NCSC “Demokritos”, Athens Greece, 3 Instituto de Física, UFRJ, Rio de Janeiro, RJ, Brazil, 4 Lab. Metallurgie Physique, University of Poitiers, Futuroscope France, 5 Laboratoire National des Champs Magnétiques Pulsés, UPS-INSA-CNRS, Toulouse France, 6 , Max-Planck-Institut für Eisenforschung, Düsseldorf Germany
We report on the dependence of the ac and dc magnetic properties on the strain effects for three Cu-3.5%Nb nanocomposite wires. These wires were elaborated using a process based on severe plastic deformation (with a logarithmic true strain η > 30) applied via repeated hot extrusion, cold drawing and restacking procedures. The final average thickness of the niobium filaments as well as the interfilamentary spacing in the investigated samples is estimated to be below 10nm. The microstructure of the Cu-Nb nanocomposites was investigated using high-resolution scanning electron microscopy. Microtexture data was determined by high-resolution EBSD measurements. The dc magnetization measurements as a function of magnetic field, M(H), were performed at several temperatures in the range 3K ≤ T ≤ 7K and at magnetic fields up to 2T. The temperature dependence of the real part of the ac-susceptibility, χ’(T), was determined in the temperature range from 3K up to 12K. In all magnetization measurements the external magnetic field was applied parallel to the wire axis. The comparison between the dc/ac magnetization data and microstructural characterization reveals that the characteristics of the Cu-Nb interfaces influence strongly the superconducting behavior of the system. Noticeable differences among samples of the Cu-3.5%Nb nanocomposites deformed at distinct strains were observed from the isothermal dc magnetization curves. These curves display a double-peak structure: the first peak, which occurs at low magnetic fields, is attributed to superconductivity that is induced in the interfilamentary Cu matrix due to its proximity with Nb nanofilaments; we argue that the second peak is related to the phase of the niobium nanofilaments, since this peak decreases with increasing strain.
Ludovic Thilly University of Poitiers
Neville R. Moody Sandia National Laboratories
Amit Misra Los Alamos National Laboratory
Peter M. Anderson Ohio State University
Mukul Kumar Lawrence Livermore National Laboratory
FF5: Composites Based on Amorphous Phases
Tuesday AM, November 28, 2006
Back Bay C (Sheraton)
9:30 AM - FF5.1
Synthesis and Mechanical Properties of Amorphous Steel Composites.
Xiaojun Gu 1 , Hsiang-Jen Wang 2 , S. Joseph Poon 1 , Gary J. Shiflet 2 Show Abstract
1 Department of Physics, University of Virginia, Charlottesville, Virginia, United States, 2 Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia, United States
The use of hard particulate phases to impede run-away shear bands and to promote multiple-shear band formation has been demonstrated in several bulk metallic glasses (BMGs). We report the synthesis, microstructure, and mechanical properties of bulk-solidified nonmagnetic amorphous steel composites that contain refractory carbides such as TiC and NbC particulates and having the formula (Fe48Cr15Mo14C15B6Er2)100-x(MC)x, where M=Ti or Nb, and x ranges from 0.1 to 10. Compared with the monolithic amorphous steel, the bulk amorphous steel composites are found to exhibit enhanced fracture strengths and elastic moduli. The fracture surfaces of composite samples show multiple deflected tear lines, which are different from the conchoidal fracture features observed for the monolithic amorphous samples. For some compositions, the Poisson’s ratios have exceeded the critical value of ~0.32 for the onset of plasticity. However, plasticity is not detected prior to fracture in compression tests. The basic differences between the present amorphous-steel composites and other BMG composites will be discussed.Supported by DARPA and ONR
9:45 AM - FF5.2
Tailoring the Tribological Properties of Graphite-Reinforced BMG Composites.
Esther Amstad 1 , Marco Siegrist 1 , Jorg Loffler 1 Show Abstract
1 Laboratory of Metal Physics and Technology, ETH Zurich, Zurich Switzerland
10:00 AM - **FF5.3
Gerhard Wilde 1 2 Show Abstract
1 Institute of Nanotechnology, Forschungszentrum Karlsruhe, Karlsruhe Germany, 2 Institute of Materials Physics, University of Münster, Münster Germany
Composite approaches, e.g. with mutually immiscible constituents or including at least one refractory phase, present a viable and maybe even necessary route for stabilizing massive nanostructured materials against detrimental coarsening under thermal and/or mechanical loading conditions. A different way for nanoscaled composite formation is presented by the nanocrystallization of marginally glass-forming amorphous alloys, such as Al-rich alloys with rare earth and transition metal additions. Such composite systems that are stabilized at nanometer-scaled structure sizes due to diffusion limitations have conventionally been processed by supplying thermal energy for initiating the nanocrystal formation. New opportunities for fabricating massive nanocrystalline composites in bulk quantities and with improved microstructures from such alloys might be based on the plastic deformation of the amorphous quenching products, as indicated by the observation of nanocrystallization in shear bands. Here, different deformation methods with largely different strain and pressure levels have been applied on rapidly quenched Al-rich metallic glasses in order to investigate the strain-induced nanocrystal formation. The results indicate e.g. that shear straining under a high pressure and to large strain values can produce uniform nanocrystalline structures in bulk samples, which is essential to their functional performance. Moreover, detailed structure analyses indicate that the amorphous structure of the entire sample volume, and not only the shear band regions, might be affected by the plastic deformation. In addition to the significance concerning the understanding of the deformation of glasses, the results also indicate the applicability of the new processing routes for synthesizing massive, porosity-free nanocrystalline materials.
10:30 AM - **FF5.4
Miromechanics of Macroelectronics.
Zhigang Suo 1 Show Abstract
1 , Harvard University, Cambridge, Massachusetts, United States
For half a century, the technology of integrated circuits has been advancing by miniaturization. While the trend to miniaturize features will continue in the field of microelectronics, a new trend to enlarge systems is gaining momentum in the nascent field known as macroelectronics. Macroelectronics will be a platform for many technologies, such as paper-like displays, medical imaging systems, and thin-film solar cells, technologies that aim to address the essential societal needs for accessible information, renewable energy, affordable healthcare, and sustainable environment. The widespread use of the macroelectronic products will depend on their low costs and ruggedness, attributes that will come from new material choices and new manufacturing processes. For example, thin-film devices on thin polymer substrates lend themselves to roll-to-roll fabrication, and impart flexibility to the products. These large structures will have diverse architectures, hybrid materials, and small features; their mechanical behavior during manufacturing and use poses significant challenges to their development. This talk describes our ongoing work in the emerging field of research – the mechanics of macroelectronics, with emphasis on hybrid organic/inorganic structures of nanoscale features. This talk will be based on work done in collaboration with Teng Li, Sigurd Wagner, Stephanie Lacour, Helena Glascova, Joost Vlassak, and Yong Xiang. Pdf file of a review article is available: Publication # 176 http://www.deas.harvard.edu/suo/publications.html
11:30 AM - **FF5.5
Processing, Structure, and Mechanical Properties of Mg Composites based on Amorphous or Nanostructured Alloys.
Evan Ma 1 , Jian Xu 2 Show Abstract
1 Materials Sci & Eng, Johns Hopkins University, Baltimore, Maryland, United States, 2 , Institute of Metal Research, Chinese Academy of Sciences, Shenyang China
Magnesium alloys are of interest because of their low density, but their low strength is a major drawback. By getting rid of dislocations, in an amorphous structure, we have elevated the strength of Mg alloys to over 1 GPa. Such Mg-based bulk metallic glasses can also be produced in relatively large sizes, e.g., over 1 inch in diameter. However, the ductility of monolithic Mg metallic glasses is very low. To restore some plasticity, crystalline metal or ceramic second phases can be added in situ during processing. In addition, a microstructure based on ultrafine eutectic structures can be formed directly via chill casting, leading to a good combination of strength and plasticity. Such attempts have been made in the light-weight Mg-Al-Ca system.
12:00 PM - FF5.6
Mechanical Properties of Combinatorially Prepared Aluminum-Silicon Thin Film Nanocomposites.
Daad Haddad 1 , Charles Olk 1 , Michael Lukitsch 1 Show Abstract
1 Materials & Processes Lab, General Motors Research Development & Planning, Warren, Michigan, United States
We have undertaken the exploration of the AlxSi(1-x) systems to discover new alloys with enhanced properties. In this report we describe the mechanical properties of thin film AlxSi(1-x) alloys determined through indentation experiments. Combinatorial methods were used to systematically control thin film microstructure through variations in composition and growth temperature. Discrete libraries of compositionally graded films have been sputter deposited onto silicon substrates to produce two structural phase regions: amorphous Al-Si and amorphous Si plus crystalline Al. The mechanical properties of the thin films were determined by analyzing the load-displacement traces based on the Oliver-Pharr method. X-ray diffraction was used to investigate the microstructures and determine the crystallite sizes.
12:15 PM - FF5.7
Molecular Dynamics Simulations of the Mechanical Response of Metallic glass/BCC Nanocomposite Materials.
Yunfeng Shi 1 , Michael Falk 1 Show Abstract
1 , Univ. of Michigan, Ann Arbor, Michigan, United States
Bulk metallic glass (BMG) has been of intense interest recently because of its unique combination of excellent mechanical properties including high strength. One of the major drawbacks of monolithic BMG materials is the limited ductility due to strain localization. Except a few recent reports on monolithic ductile BMG, the most popular method to enhance the ductility of the BMG samples is to introduce a crystalline or quasicrystalline phase by precipitation or mixing. The composite material usually exhibits some degree of strain hardening along with significantly higher impact resistance and fracture toughness. However, the mechanism of this strain hardening is not well understood. We present simulated uniaxial compression tests on a monatomic model amorphous system embedded with body-center cubic (BCC) nanocrystals. The advantage of this model system is that intimate amorphous-crystal interfaces can be obtained. We observe that when comparing to monolithic glassy samples where a single shear band normally dominates, multiple shear bands appear in the BCC-amorphous composite samples. The plastic deformation initiates at the interfaces between nanocrystals and the glassy phase due to stress concentration. Furthermore, we demonstrate that shear along the bands results in growth of the nanocrystals.
12:30 PM - **FF5.8
Amorphous-Crystalline Metallic Multilayers
Frans Spaepen 1 Show Abstract
1 Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
At high stress and low temperature, plastic deformation of amorphous metals occurs by the formation of shear bands. The formation, number and extent of these bands are governed by the geometry of the deformation. An interesting question about the formation of these bands arises when the thickness of the amorphous metal becomes similar to that of the shear band. This can be accomplished in a several ways: in multilayers of alternating crystalline and amorphous metals; in ultra-thin films of amorphous metal supported on a polymer backing; and in microfabricated small pillars. Experiments on these samples indicate that shear band formation becomes less pronounced at smaller size scales. Furthermore, the amorphous-crystalline interfaces provides an interesting boundary condition for the texture changes in the crystalline parts of the multilayers.
FF6/DD5: Joint Session: Biomaterials and Biocomposites
Tuesday PM, November 28, 2006
Back Bay C (Sheraton)
2:30 PM - **FF6.1/DD5.1
Structural Hierarchy and Mechanics of the Skeleton in a Glass Sponge.
Joanna Aizenberg 1 , Peter Fratzl 3 , James Weaver 2 , Daniel Morse 2 Show Abstract
1 , Lucent Technologies/Bell Laboratories, Murray Hill, New Jersey, United States, 3 , Max-Planck-Institute of Colloids and Interfaces, Potsdam Germany, 2 , University of California, Santa Barbara, California, United States
3:00 PM - FF6.2/DD5.2
Self-Assembled Peptide Fibrils-based Nanocomposite: Using Peptides as both the Matrix and Reinforcement.
Rohan Hule 1 , Darrin Pochan 1 Show Abstract
1 Materials Science and Engineering and Delaware Biotechnology Institute, University of Delaware, Newark, Delaware, United States
Nanocomposites were formed using self-assembled, peptidic β-sheet fibrils as the reinforcement phase and polypeptide as the matrix. The fibrils, self-assembled from short (16-30 amino acids) peptide sequences were characterized using TEM and exhibit either a non-twisting, laminated or a highly twisted fibril morphology. Each of the fibrils, both non-twisting and twisting, exhibits lengths exceeding several microns. The secondary conformation of the peptides, investigated using Circular Dichroism (CD) spectroscopy and FTIR, is predominantly β-sheet. SANS studies globally quantify the local morphology of these fibrils as rod-like structures, as indicated by a good agreement between experimental data and cylinder form fits. Atomic Force Microscopy (AFM) reveals the height of each fibril to be consistent with an interdigitated peptide assembly. Modeling a single fibril using an interdigitated peptide assembly as a constitutive unit was carried out to determine the elastic modulus. The modulus values from modeling agree well with those from Indentation Force Microscopy, a technique for nanoscale mechanical characterization. The nanocomposites so formed are biodegradable and exhibit mechanical properties comparable to traditional engineering polymers.
3:15 PM - FF6.3/DD5.3
Physical Properties and Shear Sensing Potential of a SWNT/Copolypeptide Bionanocomposite.
Conrad Lovell 1 , Kristopher Wise 2 , Cheol Park 2 , Joycelyn Harrison 3 Show Abstract
1 Materials Science and Engineering, University of Virginia, Charlottesville, Virginia, United States, 2 , National Institute of Aerospace, Hampton, Virginia, United States, 3 Advanced Materials and Processing Branch, NASA Langley Research Center, Hampton, Virginia, United States
With the existence of twenty natural amino acids, numerous combinations of copolypeptides may be developed, each with their own unique properties. In addition, polypeptides have been shown to exhibit shear piezoelectricity. One of these combinations, a high molecular weight copolypeptide of the amino acids Leucine and Phenylalanine, was combined with single wall carbon nanotubes (SWNTs) in an attempt to create a stronger and more conductive bionanocomposite for potential shear sensing applications. The dispersion state of the carbon nanotubes will be shown through scanning electron micrographs, and the mechanical and dielectric property enhancement of the nanocomposites will be discussed. Our investigation into the shear sensing capabilities of this copolypeptide will also be detailed.
3:30 PM - FF6.4/DD5.4
Effect of Crystallinity on the Protein Adsorption and Friction Behavior of Ultra-high-molecular-weight-polyethylene.
Kanaga Karuppiah Kanaga Subramanian 1 , Angela Bruck 1 , Sriram Sundararajan 1 , Zhiqun Lin 2 , Zhi-Hui Xu 3 , Xiaodong Li 3 Show Abstract
1 Mechanical Engineering, Iowa State University, Ames, Iowa, United States, 2 Materials Science and Engineering, Iowa State University, Ames, Iowa, United States, 3 Mechanical Engineering, University of South Carolina, Columbia, South Carolina, United States
3:45 PM - FF6.5/DD5.5
Novel, High Strength Nanostructured Composites Prepared with Layer-by-Layer Assembly Technique.
Paul Podsiadlo 1 , Bong Sup Shim 1 , Zhongqiang Liu 2 , Zhiyong Tang 1 , Messersmith Phillip 2 , Nicholas Kotov 1 Show Abstract
1 Chemical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Biomedical Engineering, Northwestern University, Evanston, Illinois, United States
Nature has evolved highly complex and elegant mechanisms for materials design and synthesis with physical properties that still surpass those of analogous synthetic materials with similar phase compositions, e.g. nacre, or bones. Finding a synthetic pathway to artificial analogs of such materials represents a fundamental milestone in the development of composites. Recently we have reported preparation of a thin film nanostructured composite from montmorillonite clay nanosheets and (poly(diallylmethyl ammonium chloride (PDDA) (Nature Materials, 2003, 2, 413) using the layer-by-layer assembly technique (LBL). The structure, deformation mechanism, and mechanical properties (tensile strength ~100 MPa and Young’s modulus ~11 GPa) of the material are very similar to those of natural nacre and lamellar bones. These results are encouraging for generation of new class of biomimmetic materials.We present here our results from exploration of different routes towards further improvement of the mechanical properties of the material. New composites were prepared from different polyelectrolytes: chitosan, a custom-designed 4-armed poly(ethylene glycol) with L-3,4-dihydroxyphenylalanine (DOPA), an amino acid that is responsible for both unusual adhesion and crosslinking characteristics of mussel adhesive proteins, and poly-L-lysine molecules grafted at the four ends, and poly(vinyl alcohol). LBL assembly of chitosan and clay resulted in a completely natural composite with high uniformity and stability under aqueous environment. High rigidity of the polymer chains, despite high macroscopic properties (tensile strength ~60-67 MPa), resulted in lower overall mechanical properties when compared to PDDA-clay system, tensile strength ~66 MPa and Young’s modulus ~7 GPa. LBL assembly of the (DOPA-Lys-PEG)4 system (22% of overall DOPA content) resulted in a composite with tensile strength approaching that of our previously reported values, σ ≈ 78 MPa and Y ≈ 4 GPa. Further cross-linking with Fe3+, implicated to be the natural cross-linking agent, resulted in dramatic increase in the tensile strength to σ ≈ 220 MPa and Y ≈ 6 GPa. Finally, LBL assembly with poly(vinyl alcohol) and further chemical cross-linking with glutaraldehyde or Al3+ ions, resulted in an increase of the tensile strength, from ~80 MPa to ~330 MPa (as high as 430 MPa) and to ~250 MPa (as high as 330 MPa), respectively. Young’s modulus for plain and cross-linked PVA composites was ~10 GPa. Results from dynamic nanoindentation studies showed Young’s modulus ranging from 10-20 GPa for the PVA composites and hardness of ~0.7 GPa.
4:30 PM - **FF6.6/DD5.6
Flaw Tolerant Hierarchical Structures in Biocomposites.
Huajian Gao 1 Show Abstract
1 Engineering, Brown University, Providence, Rhode Island, United States
This talk is focused on making use of the principle of flaw tolerance to explain the hierarchical structures of biological systems including bone and gecko. Bone-like biological materials have achieved superior mechanical properties through hierarchical composite structures of mineral and protein. Gecko and many insects have evolved hierarchical surface structures to achieve robust and releasable adhesion on random rough surfaces. We show that the hierarchical structures of these biological systems from nanoscale and up may have played a key role in allowing these materials to achieve their superior properties. We suggest that the principle of flaw tolerance may have had an overarching influence on the evolution of biological materials. We discuss that the bottom-up hierarchical designs allow mechanical properties of biological nanostructures to be optimized from nanometer to macroscopic length scales.
5:00 PM - FF6.7/DD5.7
Formation of Porous Hydroxyapatite
Deepa Khushalani 1 Show Abstract
1 Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai India
5:15 PM - FF6.8/DD5.8
Characterization of Electrospun Polymer Biocomposite
Smita Gadre 1 , Perena Gouma 1 Show Abstract
1 Materials Science and Engineering, SUNY at Stony Brook, Stony Brook, New York, United States
Polymer biocomposite fibers find applications in biosensing, tissue engineering, and as smart fibers in textile industry. Polymer biocomposites fibers consisting of one or more polymers such as hydroxypropyl cellulose, chitosan, cellulose acetate and a biological component such as enzymes, cell growth factor were synthesized using the electrospinning process. The processing parameters such as applied voltage, needle tip to collector distance, flow rate of polymer solution affect the microstructure of biocomposite fibers. The diameter of polymer biocomposite fibers was found to vary with these parameters. Concentration of polymer solution also affects the diameter of electrospun biocomposite fibers. Results will include mechanical properties of such biocomposite fibers and their dependence on processing and microstructure
5:30 PM - FF6.9/DD5.9
The Influence of Sterilization Pprocesses on the Micromechanical Properties of Carbon Fiber Reinforced PEEK Composites for Bone-implant Applications.
Ajay Godara 1 , Dierk Raabe 1 , Stuart Green 2 Show Abstract
1 Department of Microstructure Physics and Metal Forming, Max-Planck Institute for Iron Research, Duesseldorf Germany, 2 Research and Development, Invibio Ltd, Cleveleys Lancashire United Kingdom
The effect of sterilization on the structural integrity of the thermoplastic matrix composite PEEK (polyetheretherketone) reinforced with carbon fibers (CF) is investigated by nanoindentation and nanoscratch tests. The use of the material as a medical grade implant requires extensive understanding of its micromechanical properties which primarily define the in-vitro performance. Sterilization is a mandatory process for materials that are used in medical applications such as bone-implants. The steam and gamma radiation sterilization processes employed in this study are at sufficient levels to affect the micromechanical properties of some polymer materials, particularly in the interphase region between the polymer matrix and the reinforcing fibers.Nanoindentation and nanoscratch tests are a powerful method to reveal local gradients in the hardness and the elastic properties of such interphase regions. In this work both techniques are used to explore microscopic changes in the hardness, reduced stiffness and scratch resistance properties of the interphase region and bulk polymer matrix due to the different sterilization processes employed. The results reveal that sterilization by steam and gamma induces no significant change in the reduced elastic modulus, hardness or coefficient of friction in the bulk polymer matrix, and only a minimal modification of the PEEK matrix at almost negligible levels in the micron-scale interphase region. Of the two sterilization methods used, steam sterilization is shown to have the greatest influence on the small changes in properties in this region and it appears to slightly increase the thickness of the interphase zone.
5:45 PM - FF6.10/DD5.10
Mechanical Properties of an in-vivo Modified Biological Nano-composite Material.
Christoph Sachs 1 , Helge Fabritius 1 , Dierk Raabe 1 Show Abstract
1 Microstructure Physics and Metal Forming, Max-Planck-Institut fuer Eisenforschung, Duesseldorf Germany
The cuticle of the American lobster Homarus americanus has to meet a wide range of mechanical properties according to its various biological functions. In our study we examined the deformation behavior and the microstructure of cuticle as a function of the grade of mineralization. Two distinct locations of the exoskeleton were selected, namely, the flexible articular membranes and the rigid parts of the claws. By performing tensile tests the elastic-plastic deformation behavior was examined. The combination of tensile tests with a detailed strain analysis via digital image correlation allows to measure at a global scale with high precision the stress-strain behavior of the bulk cuticle and to reveal strain heterogeneity and strain localization phenomena at a microscopic scale. In the cuticle three structurally different layers can be distinguished: an outermost epicuticle and an inner procuticle consisting of the exocuticle and the endocuticle. The epicuticle is a thin waxy layer which provides a permeability barrier to the environment. Both exocuticle and endocuticle are made up of mineralized chitin-protein fibers forming lamellae. The endocuticle makes up around 90 vol.% of the cuticle. Local variations in composition and structure of the material provide a wide range of mechanical properties. Particularly, the grade of mineralization and the stacking density of the twisted plywood layers affect the mechanical properties of the cuticle. The test specimens originate from the claws of the lobster and are tested both in dry and in wet state to evaluate the effect of moisture on the deformation behavior. For estimating variations in the grade of mineralization, cross-sections of the cuticle were analyzed by the use of EDX mapping. The microstructure and the fracture surfaces of the test specimens were investigated using scanning electron microscopy.
Ludovic Thilly University of Poitiers
Neville R. Moody Sandia National Laboratories
Amit Misra Los Alamos National Laboratory
Peter M. Anderson Ohio State University
Mukul Kumar Lawrence Livermore National Laboratory
FF7/EE7: Joint Session: Size Effects in Composites
Wednesday AM, November 29, 2006
Back Bay C (Sheraton)
9:30 AM - FF7.1/EE7.1
Experimental Study of Size-effects on the Mechanical Elastic Properties of Nanometric W/Cu Multilayers.
Pascale Villain 1 , Baptiste Girault 1 , Pierre-Olivier Renault 1 , Eric Le Bourhis 1 , Philippe Goudeau 1 , Frederic Badawi 1 Show Abstract
1 Laboratory of Physical Metallurgy, University of Poitiers, Futuroscope Chasseneuil France
9:45 AM - FF7.2/EE7.2
Tensile Behavior of Cu/Nb Nanoscale Multilayers.
Nathan Mara 1 , Yun-Che Wang 1 , Alla Sergueeva 2 , Richard Hoagland 1 , Amit Misra 1 , Amiya Mukherjee 2 Show Abstract
1 Center for Integrated Nanotechnology, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 Chemical Engineering and Materials Science, University of California, Davis, Davis, California, United States
Most earlier work on mechanical behavior of nanoscale multilayers has utilized room temperature nanoindentation, giving some valuable insight to the properties of these materials, but little direct experimental data pertaining to yield stress, ductility to failure, or fracture characteristics. In this work, the microstructure and tensile properties of free-standing textured, polycrystalline Cu-Nb nanolayered composites prepared by magnetron sputtering were evaluated. Samples of various layer thickness ranging from 75 to 5 nm were tested at temperatures varying from 20° to 700°C. At all temperatures tested, mechanical behavior is dominated by the large number of Cu-Nb interfaces in the composite. Maximum strength at room temperature is seen to be approximately 1.5 GPa, which far exceeds the strength dictated by rule-of-mixtures calculations. Effects of decreasing layer thickness on high temperature properties show a dependence of strength and ductility on layer thickness and test temperature. Increasing test temperatures results in greater ductility of up to 0.30 true strain at decreased flow stresses (~200 MPa for 60 nm layer thickness). Elevated temperature strain rate jump tests reveal strain rate sensitivities ranging from m= 0.35 to 0.8 over a range of strain rates, indicating that several mechanisms may be occurring during deformation. These dependencies are associated with microstructural changes observed during tensile testing. The role of elevated-temperature deformation mechanisms such as interlayer and grain boundary sliding, as well as interface-related strengthening at room temperature is discussed.
10:00 AM - **FF7.3/EE7.3
Fabrication and Mechanical Behavior of Nanocomposite Thin Films
Robert Cammarata 1 2 Show Abstract
1 Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 2 Mechanical Engineering , Johns Hopkins University, Baltimore, Maryland, United States
Nanocomposites are multiphase materials where the characteristic microstructural length scale is of order 100 nm or less. Examples of such nanocomposites are multilayered materials where the characteristic length scale is the layer thickness, and nanoparticulate composites where the characteristic length scale is the particle diameter. Thin film deposition methods have proven to be particularly useful with regard to producing these types of nanostructured materials with very precise microstructural control. Nanocomposites have displayed novel and in many cases enhanced properties compared to bulk materials. This has often been shown to be the case for mechanical properties such as hardness, tensile strength, and fracture. Nanoprobe techniques such as nanoindentation have been shown to be extremely effective in the investigation of these properties of nanostructured thin films. In addition, there has been evidence that other properties such as damping capacity and fatigue can be significantly changed as the characteristic length scale is reduced below 100 nm.Examples of physical vapor deposition and electrochemical deposition methods used to produce nanocomposite materials will be discussed. This will be followed by the presentation of a selection of results from the study of mechanical behavior of nanoscale multiayered and nanocomposite thin films. A variety of mechanical properties will be discussed in both crystalline and amorphous systems. It is noted that the deposition of a completely amorphous multilayered thin film, for example, allows for the introduction of a microstructural length scale, the layer thickness in an otherwise amorphous material. The observed mechanical properties will then be considered in terms of micromechanisms used to model bulk materials in order to determine if such mechanisms are still valid when the microstructural length scale approaches nanoscale dimensions.
10:30 AM - FF7.4/EE7.4
Strength of Coherently Strained Nanolayers Under High Temperature Nanoindentation.
Ken P'ng 1 , A. Bushby 1 , D. Dunstan 1 Show Abstract
1 Centre of Materials Research, Queen Mary, University of London, London United Kingdom
Semiconductor strained layer superlattices are an ideal model material to study the effects of coherency strain in plasticity, due to the fine control of nanolayer thickness and internal strain afforded by MBE deposition. Previously, nanoindentation of bulk InGaAs at 300K gave a yield pressure of 6GPa (Jayawera et al Proc. Roy Soc, A459, 2049, 2003) while bending at 500°C gave a yield value of 30MPa (P’ng et al Phil. Mag. 85, 4429, 2005). In contrast, coherently strained InGaAs superlattices gave nanoindentation values of 3GPa at room temperature and bending at 500°C gave a yield value also around 3GPa. It appears that the coherency strain can impart an athermal strengthening to the superlattice. It is clearly necessary to do mechanical testing over the range 300-800K that will be able to link the room temperature nanoindentation with the results from the high temperature bending experiment and to determine the relationship between strength, coherency strain and temperature. Preliminary experiments on these samples at elevated temperatures using a hot stage and the UMIS nanoindentation system is difficult but feasible with the help of AFM to verify the contact area. Consideration is given to the uncertainty in measurement due to thermal instability in the system and suitable reference materials for calibration in high temperature nanoindentation.
10:45 AM - FF7.5/EE7.5
Internal and Effective Stress in Nanocrystalline Metals.
Steven Van Petegem 1 , Stefan Brandstetter 1 , Helena Van Swygenhoven 1 Show Abstract
1 ASQ/NUM - Materials Science & Simulation, Paul Scherrer Institute, PSI-Villigen Switzerland
11:30 AM - **FF7.6/EE7.6
Microstructure and Mechanical Strength Evolution With Scale Refinement in Metallic Multilayers.
Marc Verdier 1 , Muriel Veron 1 Show Abstract
1 , LTPCM-CNRS, St Martin d'Heres France
12:00 PM - FF7.7/EE7.7
Size Effect in the Plasticity of Multiscale Nanofilamentary Cu/Nb Composite Wires During in-situ Tensile Tests Under Neutron Beam.
Vanessa Vidal 1 2 , Ludovic Thilly 2 , Steven Van Petegem 3 , Uwe Stuhr 3 , Florence Lecouturier 1 , Pierre-Olivier Renault 2 , Helena Van Swygenhoven 3 Show Abstract
1 , Laboratoire National des Champs Magnétiques Pulsés - CNRS, Toulouse France, 2 , Laboratoire de Métallurgie Physique - University of Poitiers, Poitiers France, 3 , Paul Scherrer Institute, Villigen Switzerland
Copper-based high strength nanofilamentary wires reinforced by bcc nanofilaments (niobium or tantalum) are prepared by severe plastic deformation (repeated hot-extrusion, cold-drawing and bundling steps) for the windings of high pulsed magnets. The fabrication process leads to a multi-scale Cu matrix containing up to N=85^4 (52.2 10^6) continuous parallel bcc filaments, ribbons or tubes with diameter down to few tens nm.The magnet application requires a complete characterization of the microstructure, the strength and their relationship for further optimization: after heavy strain, the multi-scale Cu matrix is nanostructured and the bcc reinforcing phase is strongly refined. The resulting macroscopic strength is in excess from rule of mixture predictions calculated from bulk coarse-grained counterparts: an Ultimate Tensile Strength up to 2 GPa is reached at 77K. Using TEM in-situ tensile tests, it was shown that the observed strengthening is related to dislocation starvation in the nanostructured phases (single dislocation regime) added to the barrier role of fcc/bcc interfaces.In-situ tensile tests under neutron beam were performed on Cu/Nb nanocomposite wires composed of Nb nanofilaments with a diameter of 267 nm and spacing of 45 nm. The evolution of elastic strains and peak profiles versus applied stress evidenced the co-deformation behavior with different elastic-plastic regimes: the Cu matrix exhibit size effect in the finest channels while the Nb nanowhiskers remain elastic up to the macroscopic failure, with a strong load transfer from the Cu matrix onto the Nb filaments. The measured yield stress in the finest Cu channels is in agreement with calculations based on a single dislocation regime.
12:15 PM - FF7.8/EE7.8
Effects of Interfacial Topography on Fracture at the Nanoscale
Neville Moody 1 , Marian Kennedy 2 , Alec Talin 1 , David Bahr 2 , E. David Reedy 3 Show Abstract
1 , Sandia National Laboratories, Livermore, California, United States, 2 , Washington State University, Pullman, Washington, United States, 3 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Interfaces play a critical role in determining thin film component performance and reliability. They are defined by composition, structure and the nature of bonding at the atomic scale, and by the variations in surface topology at larger scales. These variations are used to great advantage in improving reliability of thin film devices at the micron and sub-micron scales. However, limitations in test capabilities have prevented a direct measure of surface topology contributions to adhesion of thin films at the nanoscale. We have therefore begun a program integrating nanomechanics tests and finite element-based simulations to develop an understanding of how patterns of small-scale interfacial heterogeneities affect interfacial crack nucleation and crack propagation. For this work, tungsten films were deposited onto smooth silicon substrates for reference and onto nanopatterned silicon substrates to determine the effects of surface topography. The tests showed that adhesion increased significantly for films on the nanopatterned substrate. Detailed finite element analyses were conducted in parallel with these tests to define the effects of nanopatterned surfaces on fracture resistance. In this presentation, we will use the test results and finite element simulations to show how creation of an energy-absorbing crack trajectory at the nanoscale increases resistance to fracture while providing a means to tailor nanoscale film device performance and reliability. This work was supported by Sandia National Laboratories under USDOE grant DE-AC04-94AL85000. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under Contract DE-AC04 94AL85000.
12:30 PM - FF7.9/EE7.9
Fracture in Thin Film Metal Sandwich Structures.
Audrey Chng 2 , William Curtin 1 , Michael O'day 3 Show Abstract
2 , National University of Singapore, Singapore Singapore, 1 , Brown University, Providence, Rhode Island, United States, 3 , Intel Corporation, Chandler, Arizona, United States
12:45 PM - FF7.10/EE7.10
Repeated Stress Relaxation Experiments in Probing Mechanical Behavior of Nanostructured Materials.
Yinmin (Morris) Wang 1 , Alex Hamza 1 Show Abstract
1 Chemistry and Materials Science Directorate, Lawrence Livermore National Laboratory, Livermore, California, United States
FF8: Ceramic Phase Composites
Wednesday PM, November 29, 2006
Back Bay C (Sheraton)
2:30 PM - **FF8.1
Microstructure-property Relationships in Wear Resistant Alumina/SiC ``nanocomposites" the Importance of Plastic Deformation in Ceramics.
Richard Todd 1 , Apichart Limpichaipanit 1 , Jose Ortiz Merino 1 Show Abstract
1 Department of Materials, University of Oxford, Oxford United Kingdom
Alumina/SiC “nanocomposites” consist of a dispersion of submicron SiC particles in an alumina matrix. The resistance to severe wear of the nanocomposites and the surface finish produced by a given grinding treatment are strikingly superior to those of pure alumina with the same grain size. We have explored the reasons for this by correlating a wide range of variations in the basic microstructure with the wear behaviour observed, including both the wear rate, and quantitative surface fractography of the worn surfaces. These improved properties of the nanocomposites are shown to be a consequence of a reduction in surface grain pullout by brittle fracture. In “dilute” nanocomposites (<10% SiC), this is due largely to a reduction in size of the individual pullouts. With 10% SiC nanoparticles, however, there is also evidence that the SiC directly suppresses the nucleation of cracking by plastic deformation of the surface. The origin of these effects will be discussed.
3:00 PM - FF8.2
Toughened Nanoreinforced Ceramic Composites.
Abhishek Kothari 1 , Brian Sheldon 1 , Kengqing Jian 1 , Zhenhai Xia 1 , Xingcheng Xiao 1 , Robert Hurt 1 , Janet Rankin 1 , William Curtin 1 , Erkan Konca 2 , Yang Cheng 2 Show Abstract
1 Engineering, Brown university, providence, Rhode Island, United States, 2 Research and Development, General Motors, Warren, Michigan, United States
3:30 PM - FF8.4
Superhardening and Deformability in Epitaxially Grown W/NbN Nanolayers Under Shallow and Deep Nanoindentations.
Scott Mao 1 , Brain Ennis 1 Show Abstract
1 Mechanical Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
3:45 PM - FF8.5
Measurement of Residual Stress Gradients in Hard Nanocrystalline Films by X-ray Microdiffraction.
Gang Chen 1 , Dileep Singh 1 , Jules Routbort 1 , Wenjun Liu 2 , Bennett Larson 3 Show Abstract
1 Energy System Division, Argonne National Laboratory, Argonne , Illinois, United States, 2 Advanced Photon Source, Argonne National Laboratory, Argonne , Illinois, United States, 3 Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
4:30 PM - **FF8.6
Processing and Characterization of Nanoceramic Compositeswith Interesting Mechanical Properties
Amiya Mukherjee 1 Show Abstract
1 Chemical Engineering & Materials Science , University of California, Davis, California, United States
Processing and characterization of ceramic nanocomposites that produce nanostructures with attractive mechanical properties have been emphasized. A three-phase alumina based nanoceramic composite demonstrated superplasticity at a lower temperature and at a higher strain rate. An alumina-carbon nanotube-niobium nanocomposite produced fracture toughness values that are five times higher than that of pure nanocrystalline alumina. A silicon nitride/silicon carbide nanocomposite, produced by pyrolysis of liquid polymer precursor, demonstrated one of the lowest creep rates reported so far in ceramics at the comparison temperature of 1400 degrees C. These improvements in mechanical properties will be discussed in the context of microstructural investigations. This research is supported by research grants from ONR and ARO.
5:00 PM - FF8.7
One Step Synthesis and Consolidation of Nanocrystalline TiC-Al2O3 Composites: Study of the Relationships Between their Processing, Structure, and Mechanical Properties.
Veronique Gauthier 1 , A. Khitev 2 , Vladimir Shcherbakov 2 , Sylvain Dubois 1 Show Abstract
1 , Laboratoire de Metallurgie Physique, Chasseneuil du Poitou France, 2 , Institute of Structural Macrokinetics and Materials Science, Chernogolovka Russian Federation
5:15 PM - FF8.8
Mechanical Characterization of Thin-Film Composites using the Load-Deflection Response of Multilayer Membranes – Elastic and Fracture Properties.
Joao Gaspar 1 , Patrick Ruther 1 , Oliver Paul 1 Show Abstract
1 Dept. Microsystems Engineering, Microsystems Materials Laboratory, University of Freiburg - IMTEK, Freiburg, BW, Germany
The characterization and understanding of the mechanical properties of thin-film composites is of great importance for their use as structural layers in MEMS or ICs since device functionality and reliability depend strongly on mechanical parameters.This paper reports on a novel mechanical model for the load-deflection of multilayer membranes under uniform differential pressure. Its application to the experimental extraction of material parameters is demonstrated. Going beyond previous results, the mechanics of multilayers and elastic supports covering all cases between rigidly clamped to simply supported structures are taken into account. The plate equation is solved analytically, thus enabling an efficient extraction of reliable mechanical parameters and a straightforward assessment of stress profiles.To validate the model, an extensive set of membranes made of multilayers of silicon nitride (SiNx) and silicon oxide (SiOx) films, deposited using different techniques, are fabricated and characterized. Depositions include LPCVD at several temperatures, PEVCD at several reactor frequencies and thermal oxidation. Sub-μm-thick films are deposited on one side of a Si wafer, while the other side is patterned by bulk micromachining resulting in rectangular membranes (aspect ratios of 1:10 and 1:20) with shorter side lengths ranging from 300 to 800 μm. A pressure is applied to the membranes and the resulting out-of-plane deflection profile is monitored by means of a laser profilometer. The pressure is stepped until fracture occurs. This bulge setup has been fully automated for the measurement of 100 membranes on a wafer and, for the first time, a high throughput-acquisition of bulge data with good statistical control has been achieved. As a consequence, the bulge test is extended to the determination of fracture properties of thin-films used in multilayer membranes.As preliminary results obtained from more than 500 samples of LPCVD-SiNx, a plane-strain modulus of 278 GPa and pre-stress value of 1255 MPa are extracted. The brittle material strength data are analyzed using Weibull distributions from the stress profiles in the membrane at the fracture load, from which a Weibull modulus of 40.8 and mean fracture strength of 7.3 GPa are obtained. For PECVD-SiNx films in multilayer membranes, the plane-strain modulus decreases from 183 to 146 GPa as the plasma deposition frequency is switched from 187 kHz to 13.56 MHz. The opposite trend is observed for the pre-stress, which increases from -1104 MPa to 432 MPa. In the case of PECVD-SiOx films measured in multilayer structures, the plane-strain moduli are 92 and 63 GPa and pre-stresses are -430 and -152 MPa for low and high frequency depositions, respectively.A comprehensive list of dielectric materials in multilayer membranes, their extracted mechanical properties, correlation between mechanical properties and deposition parameters, and a study of the fracture mechanisms will be presented.
5:45 PM - FF8.10
Computational Modeling and Design of Adaptive Thin-Film Composite Coatings
James Pearson 1 , Mohammed Zikry 1 , Omid Rezvanian 1 Show Abstract
1 Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, North Carolina, United States
The tailoring of thin film coatings comprised of high strength constituents, such as diamond like carbon and partially stabilized zirconia and ductile constituents, such as gold and molybdenum is investigated by new microstructurally-based finite-element techniques for applications related to the wear, durability, and performance of these coatings over a broad range of temperatures and loading conditions. The effects of contact transfer films, grain-shape sizes and distributions, grain-boundary structure and sliding, texture, and strength are used to determine the optimal thin film coating compositions. Comparisons are made with experimental measurements and observations for validation and for the development of design guidelines for thin film composite coatings.
Ludovic Thilly University of Poitiers
Neville R. Moody Sandia National Laboratories
Amit Misra Los Alamos National Laboratory
Peter M. Anderson Ohio State University
Mukul Kumar Lawrence Livermore National Laboratory
FF9/GG14: Joint Session: Modeling Composite Materials
Thursday AM, November 30, 2006
Back Bay C (Sheraton)
9:30 AM - FF9.1/GG14.1
Atomistic Study of Structure and Failure of fcc/bcc Heterophase Boundaries
Adham Hashibon 1 2 , Peter Gumbsch 1 2 , Yuri Mishin 3 , Christian Elsässer 1 Show Abstract
1 , Fraunhofer IWM
, Freiburg Germany, 2 , IZBS, University of Karlsruhe, Karlsruhe Germany, 3 , George Mason University, Fairfax, Virginia, United States
Heterophase interfaces between fcc and bcc metals are present in microelectronic devices and composite materials. The functional properties of these systems hinges strongly on the micro and nano-mechanics of the interfaces. The Copper-Tantalum system is a technologically important fcc/bcc interface system, since Ta may be used as a diffusion barrier to keep the Cu from interacting with the Si-chip. The structure and mechanical properties of the Copper-Tantalum interfaces are investigated by atomistic methods employing a specifically developed Cu-Ta interatomic potential which is based on a generalization of the embedded atom method by the addition of angular-dependent interactions. These angular forces are believed to be important in correctly describing the structure of dislocation cores and of interfaces. Interfaces considered include those with the two well known low energy orientation relationships for fcc/bcc interfaces, namely the Kurdjumov-Sachs (KS) and Nishiyama-Wasserman (NW) orientations, for which the closed packed planes and directions are parallel to each other. In addition, interfaces are formed by depositing liquid Cu on Ta free surfaces. It is found that for the equilibrium interface structure, the first layer of Cu has a distinct structure from the rest of the fcc Cu lattice. This layer facilitates the transition from the bcc to the fcc crystal structures across the interface. Results for the properties of this specific layer, its role in interface adhesion, the vacancy formation energy profile, pore nucleation and for dislocations at the interface will be presented.
9:45 AM - FF9.2/GG14.2
Plasticity mechanisms of Cu/Nb nanofilaments: a Molecular Dynamics study
Ludovic Thilly 1 , Peter Derlet 2 , Helena Van Swygenhoven 2 Show Abstract
1 Lab. Metallurgie Physique, University of Poitiers, Futuroscope France, 2 NUM ASQ, Paul Scherrer Institut, Villigen Switzerland
Ultra high strength Cu/Nb nanofilamentary conductors are processed by severe plastic deformation for the windings of coils producing non-destructive high magnetic fields with long pulse duration. They are composed of a <111> textured Cu matrix embedding <110> oriented Nb nanofilaments. Plasticity of these structures is characterized by a single dislocation regime in the nanometer scaled Cu and whisker-like behavior in the Nb nanofibers. Because of the severe plastic deformation process, the Cu/Nb interfaces are semi-coherent with misfit dislocations every 8 or 9 atomic planes in the Cu phase. These interfaces are assumed to act as dislocation barriers.To study the role of the interfaces in the plasticity mechanisms of the Cu/Nb nanocomposites with respect to dislocation nucleation, propagation and absorption/transmission, molecular dynamics simulations using embedded atom method were conducted at 300K. A Cu/Nb nanostructure composed of a single crystalline Nb <110> nanofiber embedded in single crystalline <111> Cu matrix (fiber size: 25nm, fiber spacing: 8nm) is simulated. The role of interface structure and interfacial misfit dislocations on dislocation nucleation and propagation is studied during tensile loading of the Cu/Nb nanostructure along the Nb nanofilament axis at constant strain rate. The stress distribution is computed in both phases, accounting for the different elastic-plastic regimes. The results are discussed in terms of the atomic level structure of the interfaces.
10:00 AM - **FF9.3/GG14.3
On the Role of Interfaces in Providing Strength and Radiation Damage Resistance in Nanolayered Composites.
Richard Hoagland 1 , M. Demkowicz 1 , A. Misra 1 Show Abstract
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
The theoretical strength is nearly achieved in layered metallic composites when the layer thicknesses are reduced to about 5 nm or less. In cases where the constituents have the same phase and are coherent or even semicoherent, high strengths are attributable to coherency stresses. However, coherency stresses cannot be important in incoherent systems when the phases of the components are dissimilar. Nevertheless, composites with constituents separated by incoherent interfaces also achieve very high strength levels. We describe the results of experiments and atomistic simulations that reveal some of the features of fcc/bcc composite materials that are important to strength. Another important discovery is that composite nanolayered systems with incoherent interfaces, such as Cu/Nb, possess an unusual resistance to radiation damage. TEM studies of He implanted samples with nanometer layer thicknesses reveal delayed onset of bubble formation and a greatly reduced population of defect clusters. This behavior is attributed to accelerated annihilation of Frankel pairs at or in the near vicinity of the interfaces. This research supported by OBES of the U. S. Dept. of Energy.
10:30 AM - FF9.4/GG14.4
Brittle-Ductile Transition in Heterogeneous Metallic Materials
Silvester Noronha 1 , Nasr Ghoniem 1 Show Abstract
1 Mechanical & Aerospace Engineering, University of California Los Angeles, Los Angeles, California, United States
Low temperature fracture behavior of multiphase metallic materials is controlled by the microcracks originated in brittle precipitates embedded metallic matrix. Fracture in these materials propagates by the extension of 'critical microcrack' situated in the plastic zone of macrocrack ahead of it. The crack-tip plasticity of both microcrack and macrocrack are simulated as dislocation arrays using as discrete dislocation simulation. The analysis reveals the factors that contribute to the exponential increase in fracture toughness with temperature at the brittle - ductile temperature (BDT). They are found to be: (a) the marginal increase in microscopic fracture stress, (b) the increase in crack-tip blunting with increase in plastic-flow with temperature, and (c) the increase in dislocation mobility with temperature. On applying the model to a set of microcrack distributions it has been found that (1) always it is one of the largest microcracks that lead to the fracture (2) the scatter in fracture toughness measurements is due the scatter in the size of the microcracks not their relative position to the macrocrack.
10:45 AM - FF9.5/GG14.5
Influence of Mineral -polymer Interactions on Molecular Mechanics of Polymer in Composite Bone Biomaterials.
Rahul Bhowmik 1 , Kalpana Katti 1 , Dinesh Katti 1 Show Abstract
1 Civil Engineering, North Dakota State University, Fargo, North Dakota, United States
FF10: Plasticity and Fracture At Interfaces
Thursday AM, November 30, 2006
Back Bay C (Sheraton)
11:30 AM - FF10.1
Interfacial Plasticity in Nanostructured Metals.
Ting Zhu 1 , Ju Li 2 , Amit Samanta 2 , Hyoung Gyu Kim 2 , Subra Suresh 3 Show Abstract
1 Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Department of Materials Science and Engineering, Ohio State University, Columbus, Ohio, United States, 3 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
11:45 AM - FF10.2
Role of Interfacial Phases on the Mechanical Behavior of Ta-Au Multilayers.
Andrea Hodge 2 1 , Mukul Kumar 1 , Geoffrey Campbell 1 Show Abstract
2 Nanoscale Synthesis and Characterization Lab, LLNL, Livermore, California, United States, 1 Chemistry and Materials Science, LLNL, Livermore, California, United States
12:00 PM - FF10.3
A Strained Cu Monolayer Mediates Misfit at Cu-Nb Kurdjumov-Sachs Interfaces
Michael Demkowicz 1 , Richard Hoagland 1 , Amit Misra 2 , Yun-Che Wang 2 Show Abstract
1 MST-SPR: Structure-Property Relations, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 MST-CIN: Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Misfit strains at incommensurate interfaces have traditionally been thought to be mediated by arrays of interface dislocations or ledges. In the case of some grain boundaries in covalently bonded materials, thin amorphous layers have also been viewed as possible structures for mediating interface misfit. A third possibility is indicated in the case of the Kurdjumov-Sachs interface between Cu and Nb, namely that the interface misfit can be mediated by a single ordered monolayer of Cu atoms. This monolayer is a Cu (111) layer that has been strained and rotated with respect to the neighboring Cu crystal. EAM potential simulations show that this interface structure is at least metastable for a broad range of potential parameterizations. The unique structural and mechanical properties of the interfacial monolayer can play a significant role in the overall behavior of layered composites, e.g. Cu-Nb multilayer composites with layer thicknesses of a few nanometers. The behavior of point defects, particularly with respect the to the defect core size, is shown to depend dramatically on the structure of the interfacial monolayer. This feature may be related to the experimentally observed radiation damage resistance of CuNb multilayer composites. Based on insight gained from studying the Kurdjumov-Sachs interface between Cu and Nb, interfaces between other pairs of materials that may also exhibit similar interfacial monolayer structures are identified.This work was supported by the U.S. Department of Energy Office of Basic Energy Sciences, Division of Materials Sciences and the Los Alamos National Laboratory Directed Research and Development Program.
12:15 PM - FF10.4
Confinement of Plasticity During Interfacial Fracture
Marian Kennedy 1 , Neville Moody 2 , David Bahr 1 Show Abstract
1 School of Mechanical and Materials Engineering, Washington State University, Pullman, Washington, United States, 2 , Sandia National Laboratories, Livermore, California, United States
A broad range of devices, from microelectronics to MEMS, use thin films to form composite structures. In recent years, the length scales of films being deposited have decreased and many new devices are employing films on the nm length scale. The mechanical properties of these films, such as strength and hardness, have been shown to be a function of the film thickness. These alterations are due to mechanisms including dislocation pile-up, interface strengthening and changes in chemical bonding due to short range diffusion. Another property that can be affected by control of plasticity is the practical adhesion energy or interfacial fracture energy, which is impacted by both chemical bonding and plasticity. This study examines the effects of plasticity and alterations in chemical bonding on interfacial fracture energy. Composites of Pt and Ti have been tested using indentation and four point bending to see the effect of thickness of the Ti system on adhesion. Varying the thickness of the Ti film from 2 to 17nm in a Pt/Ti/SiO2 system should alter the amount of deformation via plasticity within the Ti layer. The mixed mode toughness of the Pt/SiO2 system increased from 10 to 62 N/m for the same 175 nm thick Pt film at a Ti thickness of 6 nm. Further increases in thickness to 17 nm led to a decrease in toughness to 40 N/m. This optimization of toughness with interlayer thickness suggests a method of improving strength in multilayer composite structures which will be subjected to mixed mode loading, as opposed to only uniaxial tension parallel to the layer thickness. The balance between improved bonding between layers and the plastic deformation which can be accommodated in these thin layers will be discussed in light of recent models. This work was supported by Sandia National Laboratories. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
12:30 PM - FF10.5
Experimental Investigation of Local Adhesion in a Composite Interface of a Thin Film Multilayer Coating.
Davy Dalmas 1 , Damien Vandembroucq 1 , Etienne Barthel 1 , Stéphane Roux 1 Show Abstract
1 , Laboratoire "Surface du verre et interfaces (SVI)" - Unité mixte CNRS/Saint-Gobain - UMR 125, Aubervilliers France
12:45 PM - FF10.6
Two-Plate Buckling of Thin Polymer Films for Polyelectrolyte Multilayer Modulus Measurements.
Adam Nolte 1 , Michael Rubner 1 , Robert Cohen 2 Show Abstract
1 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
We present a modified version of the “strain-induced elastic buckling instability for mechanical measurements” (SIEBIMM) technique and demonstrate its use in measuring the elastic modulus of polyelectrolyte multilayer (PEM) films. We have previously used SIEBIMM to analyze PEM films amenable to assembly directly onto poly(dimethylsiloxane) (PDMS) testing substrates. This work broadens the applicability of the SIEBIMM technique through construction of the PEM with unknown modulus on a thin film of polystyrene (PS) with known mechanical properties that has been previously transferred to the PDMS surface. The PS provides a deposition surface that can be treated to promote adhesion of PEMs that cannot be assembled on the normally hydrophobic PDMS substrate. The PEM and PS films form a composite laminate with two regions of different modulus. Two-plate mechanical analysis is used to mathematically de-convolute the mechanical contribution of the PS layer from the behavior of the composite film in order to arrive at a Young’s modulus value for the PEM part of the composite film. The two-plate method is evaluated and found to give measurements consistent with the conventional technique when used to test PEM systems that could be assembled onto both untreated PDMS and the PDMS-PS substrates. In addition to these results, we present modulus measurements of PEMs comprised of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) that can not be measured by the conventional SIEBIMM approach and thus require application of the two-plate technique. Measurements performed in a controlled humidity environment reveal a strong dependence of PEM stiffness on the ambient humidity. At low (20%) ambient humidity, PEM films comprised of PAH and PSS have moduli on the order of 5 GPa, and those comprised of PAH and PAA have moduli on the order of 10 GPa—high values for non-reinforced, crosslinked polymer networks. Our results suggest that the dry-state mechanical properties of PEM films are affected primarily by the choice of polyelectrolytes and the ambient humidity, with pH assembly conditions being of secondary consequence. Although we demonstrate application of the two-plate technique to thin films comprised of polyelectrolytes, this method is general and could be used to enable straightforward modulus measurements on other thin-film materials amenable to deposition or transfer onto the PS-coated PDMS substrate.
FF11: Polymer Based Composites I
Thursday PM, November 30, 2006
Back Bay C (Sheraton)
2:30 PM - **FF11.1
Toughening Mechanisms in Epoxy Matrix, Hybrid Composites
Raymond Pearson 1 2 , Yi-Ling Liang 2 Show Abstract
1 Materials Sci. & Eng., Lehigh University, Bethlehem, Pennsylvania, United States, 2 Center For Polymer Sci. & Eng., Lehigh University, Bethlehem, Pennsylvania, United States
Epoxy resins are inherently brittle and can be toughened using either hard glass spheres or soft rubber particles. Moreover, certain combinations of rubber particles and glass spheres can exhibit synergistic toughening. Such positive interactions have been observed when using either micron size fillers or nanosized fillers. In this paper, we will show how the toughening mechanism are effected by the changes in size of both the soft and hard fillers.
3:00 PM - FF11.2
Local Deformation Mechanisms in Polymer Nanocomposites
Ioannis Chasiotis 1 , Qi Chen 1 , Chenggang Chen 2 , Ajit Roy 3 Show Abstract
1 Aerospace Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 , University of Dayton Research Institute, Dayton, Ohio, United States, 3 Air Force Research Laboratory, Wright-Patterson AFB, Dayton, Ohio, United States
The mechanical property enhancement of polymer matrix nanocomposites reinforced with nanometer size silica nanospheres was investigated as a function of nanosphere size and volume fraction. A multi-scale experimental system was designed and implemented to measure full-field strains at scales larger than the Representative Volume Element (RVE) of the nanocomposites and at the scale of the nanoreinforcement. The multi-scale test system employed miniature tension specimens fabricated from nanocomposites with 15 nm and 100 nm silica nanospheres evenly distributed in cross-linked EPON 862 (diglycidylbisphenol-F) with curing agent W (diethyltoluenediamine). A custom-built tensile testing apparatus was integrated with a high-resolution optical microscope/CCD camera and an Atomic Force Microscope (AFM) to record in situ 400x600 μm2 (optical) and 3x3 μm2 images (AFM) of the specimen surface at different stress levels.The effective mechanical property enhancement was strong at small particle volume fractions (1% and 3%) but it did not increase monotonically at larger volume fractions (5%.) The elastic strains were relatively uniform at scales larger than the RVE contrary to the local strain fields at the scale of the inhomogeneity that maintained a high degree of deformation inhomogeneity in the entire elastic-plastic regime for the dilute and non-dilute cases. Furthermore, significant nanoparticle strain shielding was observed for large volume fractions (5%) that decreased the efficiency of load transfer to the hard nanophase.
3:15 PM - FF11.3
Split Singularities and the Competition Between Crack Penetration and Debond at a Bimaterial Interface.
Zhen Zhang 1 , Zhigang Suo 1 Show Abstract
1 Division of Eng. & Appl. Sci., Harvard University, Cambridge, Massachusetts, United States
3:30 PM - FF11.4
Optimization of Mechanical Properties and Electrical Conductivity in ABS Polymer Nanocomposites filled with Carbon Black and Carbon Nanotubes.
Shantanu Talapatra 1 , Rosario Gerhardt 1 Show Abstract
1 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Poly(acrylonitrile-co-butadiene-co-styrene) (ABS) is a thermoplastic polymer that is used in numerous structural applications as a result of its excellent mechanical properties. For those applications where good electrical conductivity is also desired, carbon black is often used as the filler of choice. Most reports in the literature indicate that at least 8 wt% carbon black filler is needed in order to achieve percolation. Our group recently reported that by manual mixing of ABS pellets and carbon black to create a segregated microstructure, percolation was achieved at an unprecedented low filler fraction of less than 0.01 wt% carbon black, a value which is comparable to or even better than that obtained using single wall carbon nanotubes as the filler. While the ABS/CB composites had excellent electrical performance, with a conductivity as high as 10-1 S/m, their mechanical strength was compromised.
In this paper we report on new experiments designed to maintain high electrical conductivity while improving on the mechanical behavior of percolating ABS/CB nanocomposites. The experiments were aimed at controlling the processing parameters such as temperature, pressure and time during hot pressing of the mechanically mixed precursor materials.
In order to prepare our nanocomposites, beads of ABS resin of approximately 5mm in diameter and 2mm in height were mechanically mixed with the filler particles and then compression molded. The ABS – carbon black/carbon nanotube mixtures were pressed using hot pressing temperatures between 120-200°C and pressures ranging from 20-40 kN. After measuring the geometric dimensions, the specimens were electroded with silver paint and the electrical properties were measured using impedance spectroscopy. The composites microstructures were observed using SEM and optical microscopy. Images from the as hot-pressed surface and cross-sectional fracture surfaces were obtained.