Mechanical Behavior of Nanostructured Materials: Poster Session
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Mechanical Behavior of Materials Committee, TMS: Nanomechanical Materials Behavior Committee
Program Organizers: Xinghang Zhang, Purdue University; Yuntian Zhu, North Carolina State University; Joseph Poon, University of Virginia; Suryanarayana Challapalli, University of Central Florida; Enrique Lavernia, University of California, Irvine; Haiyan Wang, Texas A&M University
Tuesday 6:00 PM
February 28, 2017
Room: Hall B1
Location: San Diego Convention Ctr
Funding support provided by: AJA International; Hysitron Inc.
Session Chair: Joseph Poon, University of Virginia; Yuntian Zhu, North Carolina State University; Deliang Zhang, Shanghai Jiaotong University; Zhe Fan, Texas A&M University
L-121: Cyclic Response of Friction-stir Processed Ultra-fine Grained Copper: Salar Salahi1; G. Guven Yapici1; 1Ozyegin University
Friction processing has become a viable method of refinement down to ultra-fine and nanostructured regime, especially in the stir zone. It is also possible to obtain sound joints of similar and dis-similar materials with this technique. Reliable utilization of friction stir welded joints with ultra-fine grained microstructure requires attention on the fatigue behavior as well. In this work, cyclic response of pure copper at different joint zones was investigated. Fatigue properties were demonstrated with the S-N curves developed under positive mean stress. Fatigue properties were specified at a strain ratio of 0.1 with total strain amplitudes up to 0.2%. The results demonstrated cyclic hardening at high strain amplitudes, while softening was observed at low strain amplitude of 0.01%. The hysteresis loops indicated the concavity along with the small portion of linear behavior after the reversal point. Fatigue properties at various conditions were discussed in light of the respective failure mechanisms.
L-122: Projectile Induced Deformation Twinning in Nanocrystalline Aluminum: Sichuang Xue1; Zhe Fan1; Olawale Lawal2; Thevamaran Ramathasan2; Yue Liu3; Kaiyuan Yu4; Edwin Thomas2; Xinghang Zhang5; 1Texas A&M University; 2Rice University; 3Los Alamos National Laboratory; 4China University of Petroleum; 5Purdue University
It has been shown both experimentally and computationally that deformation twinning and stacking faults form in nanocrystalline Al with high stacking fault energy. The response of nanocrystalline Al under shock loading remains less well understood. Here by using a micro-bullet enabled ballistic technique, we performed extensive microscopy studies on perforated nc Al films. Under the high-strain-rate deformation, deformation twins have been identified. Furthermore, broad incoherent twin boundaries were identified in perforated nanocrystalline Al. High-density dislocation networks have been observed in large grain (with a diameter exceeding 100 nm). Grain fragmentation and coarsening have also been identified.
L-123: Aluminum with High Modulus and Superior Strength by Self-Dispersed TiC Nanoparticles: Chezheng Cao1; Abdolreza Javadi1; Weiqing Liu2; Xiaochun Li1; 1University of California, Los Angeles; 2Harbin Institute of Technology
Light metals (e.g. Al) matrix nanocomposites have tremendous potentials for automotive, aerospace, and military applications as they could offer low density, high specific strength, good stiffness and excellent thermal stability. It is also of fundamental interest to study mechanical behavior of such nanostructure material. However, the incorporation and dispersion nanoelement below 10 nm into metal matrix is a long-standing challenge. Here we report a way to synthesis TiC nanoparticles less than 10 nm in motel salt and then incorporated the nanoparticles into molten aluminum. A uniform distribution and dispersion of high loading TiC through a self-dispersion mechanism is achieved. Mechanical properties tests show the nanocomposites offer high Young’s modulus and superior strength. This scalable approach paves a way to mass produce high performance metal matrix nanocomposite with nanoelements (particles, plates and tubes) below 10 nm for a wide range of applications.
L-124: Multiscale Modeling of Deformation Behavior in Metal/Ceramic Mmultilayer Nanocomposites: Mohsen Damadam1; Iman Salehinia2; Georges Ayoub3; Hussein Zbib1; 1Washington State University; 2Northern Illinois University; 3University of Michigan-Dearborn
Metal/ceramic multilayer (MCM) nanocomposites exhibit promising mechanical properties, i.e. high strength and high ductility, which vary with the individual layer thicknesses. Studying the mechanical behavior of MCM’s when the structure is composed of a great number of nano layers requires the implementation of some relations that can predict the material behavior correctly. Hence, molecular dynamics simulations results on MCM’s systems were used to develop a continuum model within the framework of viscoplasticity theory. The mechanical behavior of MCM nanocomposites is studied for different layer thicknesses depending on the controlling deformation mechanisms including Hall-Petch, confined layer slip, and dislocation nucleation mechanisms.
L-125: Competition between Slip and Martensitic Transformation of Retained Austenite in Carbon-steel/Copper Nanolaminates: Yadong Ru1; Yang Ren2; Lishan Cui1; Kaiyuan Yu1; 1China University Of Petroleum Beijing; 2X-ray Science Division, Argonne National Laboratory
The ductility of steels with TRIP effects relies on the coupling between slip and transformation of retained austenite. Understanding the coupling mechanism is of great significance for the ductility enhancement of nanostructured steels. In this study, nanolamellar high-carbon-steel/copper composites are fabricated by hot pressing, rolling and wire drawing. Copper suppresses the growth of prior austenite (average size ~100nm) at elevated temperatures, and subsequent quenching and partitioning treatments result in a large amount of nanosized retained austenite phases, which in return enhance the plasticity of the materials to a maximum elongation of 60%. In situ tensile tests under synchrotron X-ray reveal that the transformation rate of retained austenite is much higher during the stress-induced regime than the strain-induced regime and the deformation mechanism of the composites is a result of the competition between transformation and slip of the retained austenite phases.
L-126: The Influence of Glassy Phase on the Crack Healing Efficiency of Silicon Carbide/Spinel Ceramic: Fariborz Tavangarian1; Guoqiang Li2; 1Penn State Harrisburg; 2Louisiana State University
Crack self-healing behavior of SiC/MgAl2O4 nanocomposite was evaluated as a function of time, temperature and atmosphere. In the presence of oxygen at high temperatures, SiC reacts with oxygen to form SiO2 which is accompanied with about 80% volume expansion. On the other hand, the formed silica reacts with the matrix and produces some transition compounds which can rebond crack walls together. The results showed that complete healing can be obtained in the specimens sintered at 1550 °C for 1 min. Detailed investigation revealed that the formation of aluminosilicate glassy phase is responsible for the complete recovery of mechanical properties. At around 1550 °C, enstatite dissociated into forsterite and silica rich liquid which reacted with spinel and produced a glassy phase which can flow into the cracks and heal the structure. This glassy phase flows to the location of the cracks and acts as a glue. With decreasing the temperature this glassy phase provides a strong physical and chemical bonds between the crack walls and hence enhance the self-healing efficiency of the composite.
L-128: The Thermal Stability of Cryomilled 5083 Aluminum Containing Diamantane Nanoparticles: Walid Hanna1; Khinlay Maung2; Mohammed Enayati3; James Earthman4; Farghalli Mohamed4; 1Military Technical College; 2Precision Castparts Corp.; 3Department of Materials Engineering, Isfahan University of Technology, ; 4Department of Chemical Engineering and Materials Science, University of California, Irvine
Cryomilling of Al alloys results in a grain sizes ranging from 20 to 50 nm. However, the nanoscale grain size cannot be retained upon annealing making consolidation of the powders impractical. A novel approach to enhance the thermal stability of cryomilled Al alloy powders is to disperse nanoscale molecular additions onto the grain boundaries and grains via the cryomilling process. The validity of this approach was examined by adding diamantane nanoscale diamond molecules to 5083 Al during cryomilling. The experimental results showed that the average grain size for all powders containing 0.5 % diamantane remained in the nanocrystalline range for all exposures temperatures ranging from 473K to 773K for various time intervals. The observed grain sizes were also consistently less than those for cryomilled 5083 Al without diamantane annealed under the same conditions. The thermal stability due to the presence of diamantane is qualitatively explained in terms of Zener’s concept.
L-129: Dynamic Behavior of Ultra High Molecular Weight Polyethylene Reinforced with Ceramics Nanoparticles at High Strain Rates: Édio Lima Júnior1; Sergio Monteiro1; Ricardo Weber1; Alaelson Vieira1; 1Military Institute of Engineering
The dynamic behavior is an important characteristic when a material the specimen is subjected to high strain rates. Ultra high molecular weight polyethylene (UHMWPE) is a material that can be used for ballistic protection. In order to improve the UHMWPE response, a composite was fabricated with ceramic nanoparticles dispersed in UHMWPE matrix. In the present work, thermal, mechanical, XRD and SEM techniques were employed to evaluate the composite characterization. Additionally, dynamic behavior under high strain rates conditions were evaluated with split Hopkinson bar tests. The results were compared with uncharged UHMWPE similarly processed. The results showed that the composite has better response than the uncharged polymer and the mechanism responsible for improving performance.
L-130: Molecular Dynamics Study of the Creep Behavior of Metallic Glasses and Glass-composites: Constanze Kalcher1; Tobias Brink1; Jochen Rohrer1; Alexander Stukowski1; Karsten Albe1; 1Technische Universität Darmstadt
In contrast to crystals, where one can clearly distinguish between three different creep stages, the mechanism behind the high-temperature creep behavior of amorphous alloys is still unclear. In this work we present Molecular Dynamics simulations on the creep behavior of Cu64Zr36 metallic glass which is a prototypical binary glass former that is well described by EAM potentials. We analyze how the creep rate is altered in the presence of secondary crystalline CuZr-B2 phases, which are known to enhance the mechanical properties at room temperature. As opposed to the pristine glass, creep resistance is decreased in the composites. Moreover, it can be observed that not only the size of the interface, but also the topology of the secondary phase plays a strong role in the creep behavior of the composites. We propose an explanation in terms of different mean Schmid factors of the interfaces.
L-131: Dislocation Engineering in Novel Nanowire Structures: Chris Chow1; Sam Reeve1; Alejandro Strachan1; 1Purdue University
Leveraging defects is a cornerstone of materials science, and has become increasingly important from bulk to nanostructured materials. We use molecular dynamics simulations to explore the limits of defect engineering by harnessing individual dislocations in nanoscale metallic specimens and utilizing their intrinsic behavior for application in mechanical dampening. We study arrow-shaped, single crystal copper nanowires designed to trap and control the dynamics of dislocations under uniaxial loading. We characterize how nanowire cross-section and stacking-fault energy of the material affects the ability to trap partial or full dislocations. Cyclic loading simulations show that the periodic motion of the dislocations leads to mechanical dissipation even at frequencies up to 2x10^10 Hz, orders of magnitude higher than the current state of the art.
L-132: An Experimental Investigation of Deformation Mechanisms in FCC Thin Films: Marissa Linne1; Samantha Daly2; 1University of Michigan; 2University of California, Santa Barbara
This presentation will discuss an on-going investigation into the mechanical behavior of, and the interactions between slip and grain boundary sliding, in oligocrystalline Al thin films under uniaxial tensile loading. The hypothesis under examination is that slip at/near grain boundaries and grain boundary sliding are coupled, synergistic processes. Due to their nanoscale thickness and columnar grain structure, oligocrystalline Al films can be approximated as two-dimensional specimens, enabling characterization of dislocation glide and GBS mechanisms without sub-surface ambiguity. In this investigation, Al films with thicknesses of hundreds of nanometers were tested in-SEM under uniaxial tension through use of a custom MEMS actuator, and full-field surface displacements were measured using a high-resolution combination of scanning electron microscopy and distortion-corrected digital image correlation. Analysis of the resulting full-field data linking deformation behavior and underlying texture is used to inform crystal plasticity models provided insight into the interaction between GBS and dislocation-based deformation mechanisms.
L-133: Impact of Heat Treatments at Varying Temperature on the Strength and Ductility of Nanotwinned Inconel: Nathan Heckman1; Andrea Hodge1; 1University of Southern California
There has been much interest recently in nanotwinned metals due to their potential for simultaneous high strength and ductility. In this study, fully nanotwinned columnar Inconel has been synthesized by magnetron sputtering with an average twin thickness on the order of nanometers and grain width on the order of hundreds of nanometers. While the as sputtered film shows tensile strengths up to 2.5 GPa, there is very limited ductility. Heat treatments up to 800° C were performed on the sputtered films in order to tune the mechanical behavior. Microstructural characterization of the heat treated films were performed at each temperature and tensile tests were performed on each film in order to determine the impact heat treatment temperature has on strength and ductility and to understand how the observed microstructures contribute to the mechanical behavior.
L-134: Mechanical Characterization of fcc and bcc Metals by Extraction of Nanoindentation Stress-strain Curves: Alexander Leitner1; Verena Maier-Kiener1; Reinhard Fritz1; Daniel Kiener1; 1Montanuniversität Leoben
The extraction of stress-strain curves from nanoindentation measurements has been widely investigated and would be a beneficial tool, especially when material is limited. Various approaches, such as the use of different shaped indenter tips as well as finite element simulations have shown promising results. However, a direct comparison of those methods on a broad range of materials and microstructures has not yet been examined. This study will provide new insights into the feasibility of these techniques by investigating a comprehensive set of materials including face-centered cubic and body-centered cubic metals with microstructures spanning from a single crystalline to a nanocrystalline length scale. We will demonstrate that once the ratio of yield strength to modulus and exact tip shape are considered in the analysis, nanoindentation is a unique and convenient tool to extract true stress-strain curves of metals at a small-scale, and that the mentioned approaches deliver comparable results.
L-135: Multi-stages Spiral Twist Extrusion: A Novel Severe Plastic Deformation Technique for Bulk Nanostructured Materials: Waleed El-Garaihy1; Dina Fouad2; Hanadi Salem2; 1Qassim University; 2American University in Cairo
In this study, an innovative technique of severe plastic deformation named Multi-stages Spiral Twist Extrusion (MSTE) was designed to produce bulk nanostructured materials (BNM). The principle of MSTE was adopted to guarantee shear strain accumulation within a square cross-section workpiece without undergoing dimensional or shape change. The induced total effective strain via MSTE is a function of the length of the twist extrusion zone, the die slop angle, the angle of the outlet zone relative to the twist angle and the number of passes. Accordingly, MSTE is capable of producing ultrafine nanoscale structure with variable texture. In an attempt to evaluate the cumulative strain associated with MSTE for different alloy rods with variable cross-sectional areas are processed at different deformation temperatures and strain rates. Evaluation and validation of the novel process is conducted via series of investigation of the mechanical behavior and structural evolution before and after processing.
L-136: Superelasticity, Micaceous Plasticity and Size Effects of
Novel Intermetallic Compound CaFe2As2 At Small Length Scales: John Sypek1; Christopher Weinberger2; Paul Canfield3; Sergey Bud'ko3; Seok-Woo Lee1; 1University of Connecticut; 2Drexel University; 3Iowa State University
Shape memory materials (SMMs) have the capability to recover their original shape after plastic deformation when they are subjected to certain stimulus. Here, we report the first discovery of SMM behavior in a novel intermetallic compound CaFe2As2. We fabricated micropillars out of single crystals of CaFe2As2, and conducted in-situ micropillar compression test. CaFe2As2 exhibits unprecedented superelasticity: over 13% recoverable strain without any residual fatigue damage, yield strengths over 3.5 GPa at room temperature, and has potential to show cryogenic linear shape memory effects at low temperatures by the reversible phase transformation between tetragonal/orthorhombic to collapsed tetragonal phase. Also, this material exhibits strong anisotropy in plasticity. Superelasticity and micaceous plasticity as a function of micropillar diameter was investigated. This represents a new class of smart materials with a set of properties that includes the highest actuation work per volume reported and has potential for space applications.
L-138: Manipulating the Grain Boundary Structure of an Ultrafine Grained Cu-Zr Alloy to Enhance Strain Hardening Capability and Strength: Dengshan Zhou1; Deliang Zhang1; 1Northeastern University
The nanocrystalline and ultrafine grained metallic materials normally lack strain hardening ability due to rapid dynamic recovery of dislocations at boundaries of nanometer and submicron grains. Due to this effect, these materials just show a uniform strain of 2-3% before reaching their ultimate tensile strength during tensile tests. We found that the strain hardening capability of an ultrafine grained Cu-Zr alloy, produced by a combination of spark plasma sintering and hot rolling, can be substantially improved via the formation of a unique grain boundary structure. The plastic strain of the uniform deformation stage (6-8%) of the sample with the unique grain boundary structure during tensile testing was two times that of the as-rolled sample, making the former achieve a clearly higher tensile strength.
L-139: Enhanced Mechanical and Electrical Properties of Nanocrystalline Cu Matrix Nanocomposite with In-situ Formed NbC Nanoparticles: Wei Zeng1; Dengshan Zhou1; Deliang Zhang1; 1Shanghai Jiaotong University
Nanocrystalline Cu-6.4vol.%NbC nanocomposite with grain size of about 96 nm containing in-situ formed NbC particles of about 6.1 nm was successfully fabricated through high energy mechanical milling, cold pressing, vacuum sintering and hot extrusion. The mechanical and electrical properties of the nanocomposite are outstanding, reflected by a tensile strength of 868 MPa, an elongation to failure of 5.3%, and an electrical conductivity of about 56% international annealed copper standard (IACS). The material exhibited ultrahigh thermal stability, with limited grain growth from 96 to 165 nm after annealing the sample at 1000 ˚C for 50 h, though the average size of the NbC nanoparticles increased dramatically from 6 to 29 nm. The high strength of the nanocomposite is ascribed to the concurrent effects of both grain boundary strengthening and nanoparticles strengthening, the good tensile ductility maybe due to the resistance to deformation instability through the interactions between NbC nanoparticles and dislocations.
L-140: Effects of the Angle between Micro-crack and Loading Direction on Crack Propagation of Single Crystal γ-TiAl Alloy: Ruicheng Feng1; Jiantao Lu1; Haiyan Li1; Hui Cao1; Zhiyuan Rui1; 1Lanzhou University of Technology
Molecular dynamics simulation is employed to make the model of crack propagation for single crystal γ-TiAl alloy. The effects of the angle between micro-crack and loading direction on crack propagation are studied. When the angle is 0°, the first dislocation is emitted at t=86ps. As for 45° and 90°, the first dislocation is emitted at t=66ps and at t=63ps respectively. When the dislocations slip, there are intrinsic stacking faults, Hirth locks and Lomer-Cottrell locks formed and with the increasing angle, the number of them decreases. Stacking fault tetrahedral appears only in the model with 0°. As the crack extends, fracture firstly occurs when the angle is 90° and as for 0°, fracture finally occurs. Comparing the stress–strain curves for three angles of 0°, 45° and 90° shows that as the angle increases, the critical stress decreases from 9.36GPa to 7.91GPa. The corresponding strain also reduces from 9.4% to 6.93%.
L-141: Tensile Properties of Perovskite in Flexible Solar Cells: Seung-min Ahn1; Eui Dae Jung1; Myoung Hoon Song1; Ju-Young Kim1; 1UNIST
Photovoltaic energy is currently drawing attention as an upcoming alternative energy source, and perovskite solar cells hold promise for next-generation photovoltaic devices due to their remarkable optical properties, high light-absorption coefficient and good cost-effectiveness. However, these materials are still afflicted with long-term stability and reliability issues. To commercialize this device, understanding of its mechanical behavior is of high priority. Many researchers have attempted to solve its stability issues, but information on its mechanical properties is still insufficient. For this reason, we fabricate free-standing component thin films of perovskite solar cells and evaluated their elastic properties using in-situ nanoindentation tests on hole-substrates. We confirmed that the perovskite layer is most fragile layer among all components. Therefore, we evaluated and analyzed the intrinsic tensile properties of perovskite layer by in-situ tensile testing using push-to-pull devices. We believe that this study sheds light on the durability and fundamental mechanisms of the material.
L-142: Fabrication and Characterization of Aluminum-carbon Nanotubes (Al-CNT) Functionally Graded Cylindrical Composites: Amal Esawi1; Ehab Salama1; Sherry Morad2; 1American University in Cairo; 2American University in Cairo
The current investigation focuses on functionally-graded (FG) Aluminum-Carbon Nanotube composites (Al-CNT) with the goal of obtaining a desirable trade-off between the material strength and its ductility at the lowest possible reinforcement concentrations to reduce overall cost. In this study we developed a new simple manufacturing route to fabricate coaxial multilayered FG composite structures using powder metallurgy methods. Different FG layer configurations were investigated. Preliminary mechanical tests showed around 50% increase in the material’s strain at failure and 30% increase in the compressive strength for FG structures with 1% wt. and 2% wt. of overall CNT contents, respectively, as compared to Al-CNT composites with uniformly dispersed CNTs having the same reinforcement concentrations. The novel structure and geometry of the produced FG cylindrical composites could be of interest to applications which require high surface strength combined with high overall ductility while keeping the cost of the composite as low as possible.
L-143: High Strength and High Conductivity Wires Made from Cu-Ag Alloys Designed for the Construction of High Magnetic Fields Generators: Eliza Sieja-Smaga1; Artur Kawecki1; Tadeusz Knych1; Andrzej Mamala1; Krystian Franczak1; Kinga Korzeń1; Grzegorz Kiesiewicz1; Paweł Kwaśniewski1; 1AGH University of Science and Technology
This paper presents the results of experimental research on the evolution of the set of high strength and electrical properties of Cu-Ag (3-15 wt.%) alloys. Continuous melting and casting process of rods and the drawing process of wires using pre- and inter-operation of multi-stage heat treatment in order to improve the mechanical (UTS=900-1600 MPa) and electrical (63-90 % in IACS scale) properties of circular and profiled cross-section wires has been presented. Metallographic analysis for casts, drawn wires and wires after heat treatment was performed with the use of SEM and TEM microscopy presented in the paper. Effect of different kind of microstructure and the value of deformation on electrical conductivity of the wires during low temperature tests were presented. Model calculations and a construction of the electromagnet coils made of wires with Cu-Ag alloys and the results of the tests carried out at cryogenic temperature has been also shown.
L-144: Mechanical Characterization of Cold Sprayed Aluminum Alloy Using Micropillar Compression: Tyler Flanagan1; Benjamin Bedard1; Sumit Suresh1; Mark Aindow1; Avinash Dongare1; Harold Brody1; Xuemei Wang2; Victor Champagne3; Seok-Woo Lee1; 1University of Connecticut; 2United Technologies Research Center; 3U.S. Army Research Laboratory
The mechanical characterization of shocked materials is of great interest since the severe deformation process creates unusual microstructure, resulting in unique mechanical properties. Here, we will present the mechanical properties of single-pass cold spray trials of Al-6061 microparticles onto substrates of the same alloy with a velocity of ~1 km/s. The mechanical properties of these splats have been studied by utilizing in-situ micro-pillar compression in scanning electron microscope. We found a strong size effect in the submicron diameter range, but negligible size effect in pillars above 1 um in diameter. We explain these two distinct size effect regimes in terms of microstructural length scales such as grain/dendrite size, precipitation, and dislocation densities. We compared these findings with the micro-mechanical properties of undeformed single Al alloy particles. This study will give an insight in fundamental understanding in high strain rate deformation mechanisms in aluminum alloys.
L-145: Development and Characterization of Sputter Deposited Nickel-molybdenum-tungsten Thin Films for High Temperature Metal MEMS Applications: Gianna Valentino1; Gidong Sim1; Jessica Krogstad2; Timothy Weihs1; Kevin Hemker1; 1Johns Hopkins University; 2University of Illinois at Urbana-Champaign
Micro-electro-mechanical systems (MEMS) are customarily fabricated from silicon, which lacks the density, conductivity and toughness that metal alloys possess. Metal MEMS offer exceptional strength and ductility, which would greatly expand the design space for MEMS devices. However, previous attempts to incorporate LIGA Ni into MEMS devices failed due to lack of dimensional stability associated with room temperature creep. Ni-base superalloys have exceptional creep resistance and can be sputter deposited as nanocrystalline thin films. Their thermal expansion is, however, much greater than silicon. In this study, we characterized a compositional spread of sputter deposited nickel-molybdenum-tungsten thin films, uncovering exceptional thermal-mechanical stability associated with the presence of nano-twins and stacking faults and reducing thermal expansion through compositional control. Experimentally capturing the effects of chemical composition on the microstructure, CTE and the mechanical and electrical properties is needed to enable future integration with MEMS sensors and micro-switches.
L-146: Mechanical Behavior of Sub-micron-sized Nanocrystalline Pillars under Monotonic and Cyclic Loading: Jung-A Lee1; Brandon B. Seo2; Moo-Young Seok1; Yakai Zhao1; Upadrasta Ramamurty3; Ting Y. Tsui2; Jae-il Jang1; 1Hanyang University; 2University of Waterloo; 3Indian Institute of Science
Size effect on deformation behavior of sub-micron-sized nanocrystalline pillars was systematically explored by applying monotonic and cyclic compressive stress. Pillars were prepared by e-beam lithography and electroplating which can produce several hundreds of uniform pillars simultaneously. Then, micro-compression tests were performed under various conditions. This presentation will cover two topics. First, the size effects on the rate-sensitive deformation were statistically investigated under three different strain rates. The obtained results revealed that smaller pillars show more pronounced rate-sensitive deformation, which is explained by Weibull modulus, strain-rate sensitivity, and activation volume. Second, the influences of cyclic loading on yielding behavior and plastic flow were examined by low-amplitude cyclic compression followed by compression tests. It was observed that yield strength and flow stress were non-negligibly influenced by cyclic stress even in elastic regime. This phenomenon was analyzed in terms of various parameters including number of cycles and pillar size.
L-147: Nanoindentation Response of Fe-10%Cr Structures with Voids: An Atomistic Study: Mohammad Abu-Shams1; Ishraq Shabib1; 1Central Michigan University
Molecular Dynamics (MD) simulations are performed to investigate the nanoindentation response of single crystal Fe-10%Cr structures containing voids of various sizes distributed over various spatial locations. For structures with smaller void clusters (e.g. radius r≤1.5Å), the load response with indentation depth shifts to a lower magnitude when the number of voids is increased and the voids are located closer to the indenter surface. For structures with larger single void (e.g. r≥3Å), the nature of the load-depth curve depends on the location of the void from the indenter surface. When the void is located closer to the indenter the load-displacement response deviates significantly from the response obtained in defect-free model. However, after a sufficiently large indentation depth the void collapses and the curve follows the defect-free response. The results reveal the nucleation of 1/2 <111> and <001> types of dislocations in various active slip planes.
L-148: Preparation and High Temperature Deformation of Nanocrystalline MgO: Darren Dewitt1; Yasuhiro Kodera1; Harry Green2; Javier Garay1; 1University of California, San Diego; 2University of California, Riverside
Very little is known about deformation of nanocrystalline material at large strain-rates. Here, we present initial findings on bulk nanocrystalline magnesia (MgO) that is both densified and deformed using the current-activated, pressure-assisted densification (CAPAD) apparatus – a process that allows for very high heating-rates and limited exposure to higher temperatures, reducing the amount of time for grain growth. Nanocrystalline MgO powder is synthesized by reaction of brucite (Mg(OH)2), followed by densification in CAPAD at low homologous temperatures and relatively low pressures – yielding fully-dense, equiaxed, nanocrystalline bulk samples with an average grain size less than 50 nm. These samples are then deformed in CAPAD at varying pressures, temperatures, and strain rates. Initial results display strain-rates and microstructures that have not been seen previously in deformation experiments.
L-149: Solute Atoms Enhance Tensile Ductility in a Nanostructured Al-Mg Alloy: Yaojun Lin1; Shulei Li2; Zhigang Yan2; Haiming Wen3; Enrique Lavernia4; 1Wuhan University of Technology; 2Yanshan University; 3Idaho State University; 4University of California, Irvine
Nanostructured materials exhibit ultra-high strength but low ductility. In order to solve this problem, various approaches have been developed, which have their own advantages and disadvantages. In this talk we propose a new approach: using solute atoms to pin and entrap dislocations and thus to enhance work hardening ability and ductility. In the present work, nanostructured Al-Mg alloy 5083 was prepared via accumulative-rolling bonding followed by well-controlled annealing. During room-temperature uniaxial tensile testing, the nanostructured 5083 Al achieves a uniform elongation as high as approximately 13% and simultaneously a yield strength of approximately 350 MPa. Microstructural observation reveals the absence of intragranular second-phase particles, and 3.8 wt.% of Mg solute is estimated based on the X-ray diffraction pattern, indicating that the high ductility is attributed to the presence of solute Mg atoms. The effect of solute atoms combined with preexisting dislocations and grain size on ductility is discussed.
L-150: Strong, Ductile, Thermally Stable Cu-based Metal-intermetallic Nanostructured Alloys: Keith Dusoe1; Sriram Vijayan1; Thomas Bissell1; Mark Aindow1; Seok-Woo Lee1; 1University of Connecticut
Bulk metallic glasses (BMGs) and nanocrystalline metals (NMs) have been investigated extensively due to their superior mechanical properties. However, their practical application has been limited by their low ductility at room temperature and poor microstructural stability at elevated temperatures. Thus, there is a clear need for a metallic system which can overcome the performance shortcomings of BMGs and NMs. Recently, we discovered novel Cu-based and Ni-based metal-intermetallic nanostructured composites (MINCs), which exhibit high yield strengths (over 1.7 GPa), high compressive ductility (over 18%) and superior microstructural stability at an elevated temperature higher than the glass transition temperature of their counterpart metallic glasses. In this presentation, we will discuss the important roles of intermetallic compound phases to explain the exceptional mechanical properties and superior thermal stability of our MINCs. We will also discuss how the cooling rate affects their strength and ductility in terms of their unique phase boundary sliding mechanisms.
L-151: Synthesis of Bulk Single-crystalline Quasicrystal Approximant YCd6 and Its Small-scale Mechanical Properties: Gyuho Song1; Tai Kong2; Paul Canfield2; Seok-Woo Lee1; 1University of Connecticut; 2Iowa State University
Novel complex intermetallic compounds possess unique chemical, physical, electronic, and magnetic properties but their extreme brittleness at room temperature significantly limits their practical applications. However, the recent small-scale mechanics revealed that a brittle material could become ductile via size reduction. Here, we investigated the mechanical properties of Y-Cd quasicrystals and their approximants. A single crystal of YCd6 quasicrystal and its approximant were synthesized by a solution growth in the binary Y-Cd melt, and conducted in-situ micropillar compression test. We found the preferential slip system in YCd6 quasicrystal approximant, which can be explained by the translational symmetry and large interplanar spacings, and the size-dependence of yield strength, which would be related to the weakest link statistics. Furthermore, transmission electron microscopy was used to visualize the intrinsic defect structure. The fundamental mechanisms of unusual plastic deformation will be discussed in terms of two possible viewpoints: dislocation slip vs. rigid translational slip.
L-152: Flexibility of Perovskite LED Based on Mechanical Properties of Component Materials: Si Hoon Kim1; Jae Choul Yu1; Young-Cheon Kim1; Yun-Seok Nam1; Myoung Hoon Song1; Ju-Young Kim1; 1UNIST
Perovskite has been used in light-emitting diode (LED) due to its high luminous efficiency. As the demand for stretchable and flexible electronics increases, research has progressed to applying perovskite in deformable electronics. The component materials of LED are deformed in the iso-strain condition, because they are stacked to form a thin film in a multilayer structure. It is important to measure the stress concentration point in device during bending and analyze the critical bending radius, because it is at this point that fracture will occur. This study evaluates the flexibility of perovskite LEDs based on the mechanical properties of the component materials. We conducted hole indentation in component materials to investigate elastic properties and performed tensile test in SEM for perovskite samples, the weakest component in perovskite LEDs to accuracy tensile properties. A critical bending radius was analyzed by FEM simulation using the mechanical properties of component materials.
L-153: The Influence of Severe Plastic Deformation on the Fatigue Crack Growth Behavior of Pure Metals and Alloys: Thomas Leitner1; Anton Hohenwarter1; Reinhard Pippan2; 1Montanuniversität Leoben; 2Austrian Academy of Sciences
Ultrafine-grained (UFG) and nanocrystalline (NC) metals exhibit exceptional strength under monotonic and cyclic loading and are therefore interesting materials for many engineering applications. However, beside strength also damage tolerance has to be considered in order to guarantee the safety of components made of UFG metals. Therefore fatigue crack growth (FCG) experiments were performed on pure nickel, ARMCO iron, austenitic steel, fully pearlitic steel and a NiTi alloy, which were severely plastically deformed to obtain UFG microstructures. In general, deteriorated FCG resistance is observed in the near-threshold region for nanostructured metals, compared to their coarser-grained counterparts. However, at higher stress intensity factor ranges UFG and NC samples can exhibit comparable or even slower crack propagation. The results are discussed with focus on the microscopic FCG mechanisms and the contributions from extrinsic and intrinsic toughening.
L-154: The Precipitation and Strengthening Behavior of Ultrafine Structured Al-7wt%Si-0.3wt%Mg Alloy: Jiamiao Liang1; Zhen Zhang1; Xun Yao1; Yifeng Zheng1; Deliang Zhang1; 1Shanghai Jiao Tong University
The precipitation and strengthening behavior of ultrafine structuredAl-7Si-0.3Mg (wt%) alloy were investigated. The needle shaped precipitates with length of 5-20 nm were detected in T5 and T6 heat treated samples. The slight grain coarsening in ultrafine grained Al-7Si-0.3Mg alloy after T6 heat treatment shows a good microstructure stability which is mainly attributed to the pinning of silicon particles and Al3FeSi particles to grain boundaries. Following T6 heat treatment, the ultrafine grained Al-7Si-0.3Mg alloy shows improved ductility due to the decrease of dislocation density and the increase of grain size caused by T6 heat treatment. With the same T6 heat treatment process, ultrafine grain Al-7Si-0.3Mg alloy exhibit better YS and UTS than coarse grained counterpart due to its fine grain size which produces more grain boundary strengthening. Significant precipitation strengthening behavior is observed in ultrafine grained Al-7Si-0.3Mg alloy after T5 heat treatment, and the strengthening mechanism is correlated to its microstructure.
L-155: Towards an Understanding of Shear Band Formation in Nanocrystalline and Ultrafine-grained Single Phase Materials: Oliver Renk1; Pradipta Ghosh1; Reinhard Pippan1; 1Erich Schmid Institute of Materials Science
The limited strain hardening capacity of nanocrystalline (nc) or ultrafine-grained (UFG) materials reduces their ductility compared to the coarse grained counterparts. This reduction in ductility is often caused by strain localization along shear bands. Interestingly, shear band formation can even be observed during compression or cold rolling where no geometric softening occurs. Although frequently observed, detailed understanding of the formation conditions is still incomplete.A variety of nc and UFG materials, synthesized by high pressure torsion and further deformed by cold rolling, was studied to understand the conditions for shear band formation. The samples were rolled along two different orientations with respect to the rolling coordinate system. It will be shown, that only materials with a specific starting texture with respect to the rolling coordinate frame exhibit shear band formation. Therefore it is possible to overcome shear band formation in UFG materials by an appropriate choice of the sample orientation.
L-156: Effect of Annealing Temperature on Texture Transformation in FCC Thin Films: Nathaniel Rogers1; Rekha King1; Margaret Kirkland2; Laurel Vincett2; Brandon Hoffman2; Shefford Baker1; 1Cornell University; 2Houghton College
FCC metal thin films are often deposited with a strong (111) texture, but under relatively mild annealing conditions, the texture may transform into the much more compliant (100) orientation. This transformation dramatically changes film properties and can therefore be problematic for potential applications. Although the texture transformation is well known to depend on thickness, the few studies in which temperature dependence have been examined suggest that there is little or no effect of increasing annealing temperature up to agglomeration. To investigate this, Ag films were annealed at temperatures from 100 to 500˚C and the texture transformation was monitored with x-ray diffraction. Surprisingly, films annealed at low temperatures or under slowly increasing temperature ramps, transformed more than identical films annealed at higher temperatures. A variety of phenomena, including grain boundary grooving, are discussed as possible explanations for this behavior, with the eventual goal of being able to stabilize a desired microstructure.
L-157: Anisotropy of Solute Effect on Dislocation Slip in an HCP Metal: A Molecular Simulation Study of Mg Alloys: Peng Yi1; Michael Falk1; 1Johns Hopkins University
Magnesium has great potential as a lightweight material in transportation and aerospace industries. However, its broad application is limited by poor ductility, originated from its low symmetry HCP structure. Fundamental understanding of the anisotropy of the dislocation slip mechanisms and the associated solute effects is crucial to property prediction and materials design. We studied the mobility of dislocations on the basal, prismatic, and pyramidal planes in Mg/Al and Mg/Y alloys using molecular simulations. Both solute hardening and solute softening were observed and compared favorably with experiments. Solute hardening for in-plane basal slip follows Labusch statistics and Kocks thermo-mechanical model. Solute softening was observed for prismatic slip and pyramidal slip, and it is due to out-of-plane dislocation motions like cross-slip or climb. A 2D energy landscape can be constructed to couple the in-plane and out-of-plane dislocation motions. Lastly, double cross-slip and super-jog formation were observed as potential Frank-Read dislocation multiplication sources.
L-158: A Study on Growth Nanotwins for CuZn Synthesized by Electrodeposition and Magnetron Sputtering: Chelsea Appleget1; Andrea Hodge1; 1University of Southern California
Metals containing nanoscale growth twins have shown great potential as an alternative to nanocrystalline metals. Nanotwinned (nt) metals have been shown to produce similar strengths to nanocrystalline metals while retaining desirable properties such as ductility, thermal stability, and mechanical stability. To date, most experimental work has focused on single elements, mainly copper, with limited studies on binary alloys. The microstructures and mechanical properties of the nt-CuZn synthesized by electrodeposition and magnetron sputtering are compared and discussed. Exploring nanoscale growth twin formation in alloys provides important insight into the future synthesis of nanomaterials and the successful development of highly twinned complex alloys is essential for the future application of nanometals.
L-159: Atomistic Simulation of Creep Deformation in Metallic Nanoglasses: Omar Adjaoud1; Karsten Albe2; 1Technische Universität Darmstadt ; 2Technische Universität Darmstadt
Metallic nanoglasses (MNGs) are amorphous materials with an inhomogeneous microstructure which consists of glassy grains connected by glass-glass interfaces. The MNGs can be produced by cold-compaction of glassy nanospheres which are prepared by inert-gas condensation. The glass-glass interfaces are interphases of different composition and short-range order. When MNGs are under mechanical load, their interfaces promote shear band nucleation and prevent strain localization. Therefore the MNGs show enhanced plasticity as compared to metallic glasses of the same chemical composition. In this contribution, we present a detailed analysis of the creep deformation in MNGs by means of molecular dynamics computer simulations at temperatures close to the glass transition temperature (Tg) under a constant load. We address the effect of temperature and stress on the creep strain rate. Moreover, we discuss the role of the glass-glass interfaces in the plastic deformation.
L-160: Effects of the Processing Variables on Microstructural Homogeneity Manufactured by High Pressure Double Torsion: Mohammad Jahedi1; Irene Beyerlein2; Marko Knezevic1; 1Department of Mechanical Engineering, University of New Hampshire; 2Department of Mechanical Engineering, Materials Department, University of California at Santa Barbara
Electron backscatter diffraction and transmission electron microscopy were utilized to study the grain refinement and the uniformity in the evolution of microstructure in commercial purity Cu samples during high-pressure double torsion (HPDT). For both processes, grain sizes decrease with the number of turns and applied pressure. It is found that HPDT provided a more homogeneous grain structure than HPT. In addition, more homogeneous grain structure is achieved by a larger number of turns. However, the rate of grain refinement substantially increases with increasing pressure. As a result, the HPDT process, compared to HPT, takes better advantage of the role that high pressure plays in shear strain induced grain refinement and homogenizing the microstructure. Estimating the applied work finds that the least amount of work required for achieving fine and homogeneous microstructure when the applied pressure is maximized and number of turns is minimized.
L-161: Grain Growth in Nanostructured Materials during Cyclic Loading: Is the Description Complete?: Marlene Kapp1; Oliver Renk1; Thomas Leitner2; Bo Yang1; Reinhard Pippan1; 1Erich Schmid Institute of Materials Science; 2Montanuniversität Leoben
Grain coarsening during cyclic loading of ultrafine-grained or nanocrystalline structures has been identified to deteriorate the fatigue performance, especially when tested with high plastic strain amplitudes. Not only the understanding of basic mechanisms of the coarsening process but also the impact of the crystallographic orientation and grain boundary type is still at its infancy. We will present results obtained from a new experimental approach to solve these questions. Using cyclic high pressure torsion enables to study the coarsening process at different temperatures up to infinite lifetime, thus the coarsening process can be captured without failure of the sample. We will show, that grain coarsening stops when a certain equilibrium grain size, depending on the applied strain amplitude, is reached. Texture analyses clearly show similarities with cyclic torsion loading of coarse grained samples. The results indicate that the applied strain and not the stress are responsible for the growth process.
L-162: Microstructural Influences on the Transition to Drag Dominated Dislocation Motion at High Rates of Strain: Scott Turnage1; Kristopher Darling2; Kiran Solanki1; 1Arizona State University; 2Army Research Laboratory
Thermal activation dominates dislocation motion at low strain rates (< 10 s-1), but as strain rates increase, drag forces become dominant causing an upturn in flow stress and a subsequent decrease in ductility. The strain rate at which this shift in deformation mechanism takes place depends on the material and microstructure of the deformed sample, but the effects of individual microstructural components have not yet been identified. Here, strain rate data for characteristic samples are gathered from literature to analyze the effects of grain size, precipitates, twin boundaries, and deformation induced twin growth on the rise in flow stress. Results show that as defect density is increased, the upturn in flow stress occurs at higher strain rates. In the case of deformation induced twinning, dislocations move too slowly for the high rate of deformation; therefore, twinning becomes the dominant deformation mechanism resulting in decreased flow stress as strain rate increases.
L-163: Low Temperature Compositional Patterning in Plastically-deformed Immiscible Alloys: Nirab Pant1; Yinon Ashkenazy2; Pascal Bellon1; Robert Averback1; 1University of Illinois at Urbana-Champaign; 2The Hebrew University of Jerusalem
Microstructure homogenization in engineering alloys can be achieved via deformation processing at low temperatures. Recent modeling and experimental works suggest, however, that highly immiscible alloy systems often do not homogenize when subjected to severe plastic deformation, but rather undergo phase separation, even at ambient temperature regimes where thermal diffusion is suppressed. We employ molecular dynamics simulations to systematically investigate this surprising behavior using model FCC binary and ternary alloys. Utilizing Cleri-Rosato potential functionals, we can independently vary the heat of mixing between the alloy constituents while holding constant the elastic moduli of the different phases. We show that inter-species thermodynamical interactions alone can induce the self-organization of the microstructure into a stable distribution of nanoscale precipitates and that this self-organization originates from a dynamical competition between dislocation glide-induced mixing and shear-assisted clustering.
L-164: Effect of High Temperature Annealing Time and Temperature on Microcrack, Micro-nanostructures and Mechanical Properties of a 14YWT Nanostructured Ferritic Alloy: Md Ershadul Alam1; Soupitak Pal1; Yuan Wu1; G. R. Odette1; 1University of California, Santa Barbara
FCRD NFA-1 is a 14YWT nanostructured ferritic alloy (NFA) in the form of a hot extruded and cross-rolled plate containing pancake-shaped grains along with a population of microcracks. NFA-1 is strengthened and imbued with irradiation tolerance by an ultrahigh density of nm scale oxides. The microcracks form extensive delaminations during deformation and fracture tests. Annealing at 1300ºC for 1 and 5 h results in equiaxed grains and heals the microcracks. Room temperature tensile ductility is increased and the delaminations are suppressed. However, microhardness, yield stress and fracture toughness decrease. The results of annealing for 1 and 5 h at 1100 and 1200°C are described in an effort to optimize both the NFA microstructures and mechanical properties. The micro/nanostructural changes associated with these heat treatments are described.
L-165: Microstructure and Mechanical Behavior of Nanostructured FeMn Bioresorbable Alloy: Anqi "Angel" Yu1; Michael Heiden2; Christian Roach1; Lia Stanciu2; Suveen Mathaudhu1; 1University of California Riverside; 2Purdue University
FeMn alloys have recently shown efficacy as bioresorpable bioimplant materials for fracture fixation in hard tissue. Prior work has shown that large-strain processing can be used to refine the microstructure and control the degradation rate, however novel processing approaches are necessary to tailor the necessary mechanical properties without negatively affecting the corrosion rate. In this study, we report on the refinement of Fe-33%Mn bioresorbable alloy via high pressure torsion (HPT). Important factors to the successful refinement include homogenization of the as-cast hard dendritic microstructure prior to HPT and the thermomechanical processing parameters for optimal HPT refinement. Resultant microstructures and mechanical properties will be reported, and compared with literature data on Fe-based bioresorbable implant materials.
L-166: Stress-driven Microstructural Evolution and Grain Boundary Doping in Nanocrystalline Alloys: A Direct Link Revealed by Quantitative In Situ Electron Microscopy: Mo-Rigen He1; Gyuseok Kim2; Saritha Samudrala3; Peter Felfer3; Andrew Breen3; Julie Cairney3; Daniel Gianola4; 1University of Wisconsin-Madison; 2University of Pennsylvania; 3University of Sydney; 4University of California-Santa Barbara
The large fraction of material residing at grain boundaries (GBs) in nanocrystalline (NC) metals and alloys is responsible for their ultrahigh strength, but also undesirable microstructural instability under thermal and mechanical loads. However, the underlying mechanism of stress-driven microstructural evolution in a real NC microstructure is still poorly understood and precludes rational alloy design. Here we combine quantitative in situ electron microscopy with three-dimensional atom probe tomography to directly link the mechanics and kinetics of GB migration in NC Al films with the GB excess of O atoms. Site-specific nanoindentation leads to grain growth that is retarded by impurities, and enables quantification of the critical stress for the onset of GB migration. Our results show that a critical excess of impurities is required to stabilize interfaces in NC materials against mechanical driving forces, providing a new avenue for controlling deformation mechanisms and tailoring mechanical properties apart from grain size alone.
L-168: Surface Rebound of Relativistic Dislocations Directly and Efficiently Initiates Deformation Twinning: Qingjie Li1; Ju Li2; Zhi-Wei Shan3; Evan Ma1; 1Johns Hopkins University; 2Massachusetts Institute of Technology; 3Xi'an Jiaotong University
Recent experiments on small-volume metals have shown that deformation twinning (DT) initiates at ultra-high stresses and on a very short timescale. This indicates strongly correlated dislocation dynamics which remain poorly understood. Using atomistic simulations, we demonstrate that under a wide range of laboratory experimental conditions DT can be accomplished by surface rebound of relativistic dislocations. A dislocation nucleated under high stresses can accelerate to near the sound speed within a distance of 10^1 nanometers. The resulting high-speed dislocation rebounds back when hitting a free surface. The ensuing rebounds, back and forth from opposing surfaces, lead to self-sustained breeding of twinning partial dislocations, directly initiating DT. Due to its stronger temporal correlation, surface rebound sustained (SRS) relay of twinning dislocations is shown to be dominant in initiating DT over thermally activated nucleation (TAN). This dislocation breeding mechanism may also play a role in other high-stress and high-strain-rate deformation processes.
L-169: Thermal Stability and Mechanical Behaviour of Electrodeposited Nanocrystalline Iron: Vijay Kumar D1; Prasad Mjnv1; 1Indian Institute of Technology Bombay
The exceptional mechanical properties of nanocrystalline materials are being limitedly explored for applications at elevated temperatures due to their poor microstructural stability. The present study is aimed at understanding microstructural stability and mechanical behaviour of pulsed electrodeposited nanocrystalline iron (nc Fe). Thermal stability of nc Fe foils having a grain size of ~25 nm was assessed using differential scanning calorimetry. The thermogram displayed four exothermic peaks in the temperature range of 373-773 K and a strong endothermic peak at ~853 K during heating. The samples heat treated to different temperatures were examined for evaluating the microstructural stability and mechanical behaviour. Upon heating, the nc Fe exhibited reasonably stable grain structure but undergoes stress relieving, sulphidation, oxidation and eutectoid transformation. The as-deposited sample exhibited a very high hardness of ~8 GPa and excellent wear resistance. Significant variation in hardness and wear resistance was noted in the heat treated samples.
L-170: Twinning-dominated Deformation in Body-centered Cubic Tungsten Nanowires: Jiangwei Wang1; 1Zhejiang University
Twinning and dislocation slip is two competing deformation modes in crystalline solids. In metallic nanostructures, plastic deformation requires higher stresses than those needed in their bulk counterparts, resulting in the "smaller is stronger" phenomenon. Such high stresses are thought to favour twinning over dislocation slip. Deformation twinning has been well documented in face-centred cubic (FCC) nanoscale crystals. However, it remains unexplored in body-centred cubic (BCC) nanoscale crystals. By using in situ high-resolution transmission electron microscopy and atomistic simulations, here we show that twinning is the dominant deformation mechanism in nanoscale crystals of BCC tungsten. We find that the competition between twinning and dislocation slip can be mediated by loading orientation,loading mode and crystal size. Based on the experimental observations, a full deformation map is established for the W nanowires.
L-171: UV Light, Temperature and Humidity Effects on the Mechanical Behavior of Nanocomposites: Claudia Luhrs1; Stephanie Rockford1; Sarath Menon1; Hugo Zea2; 1Naval Postgraduate School; 2Universidad Nacional de Colombia
UV light, temperature and humidity are suspected to cause changes in nanocomposites properties to a point that could represent a liability, not only reducing the useful lifetime of components but also compromising the systems that contain them and posing safety and health risks. Inclusion of diverse fillers is believed to enhance the thermal-mechanical-chemical stability of the nanocomposites; however, detailed analyses that substantiate and quantify its effects are very limited. To address this need, we fabricated epoxy based nanocomposites containing diverse fillers and exposed them to the weathering factors mentioned above. The study focused on epoxy composites fabricated with: CNT, silica, nickel and Ni/NiO nanoparticles. The first because they are commonly used, the latter to determine the effects of using materials with different polymer-filler interfaces and electrical conductivity. The corrosion effects in metal sheets/nanocomposite couples were studied using a salt fog and accelerated weather chambers and are included in the analysis.