bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of Electrodeposited Iridium as a Buffer Layer for YBCO Superconductors
Authors: Spagnol Priscila , Chaudhuri Tapas , Bhattacharya Raghu , Phok Sovannary
Published: June 2019

Electrodeposition (ED) is a potentially low-cost, non-vacuum, high-rate deposition process that can easily deposit uniform film on large non-planar substrates. In this paper, we report on successful biaxial textured electrodeposition of Ir on Ni-W substrates. Ir metal is well known for its excellent oxidation and corrosion resistance among platinumgroup elements; also, the lattice mismatch of cubic Ir is very close to that of CeO2 and Ni. The films were deposited in a vertical cell in which the electrodes (both working and counter) were suspended vertically from the top of the cell. The ED experiments were performed at 65°C without stirring the solution. The ED precursors were prepared at about -1.2 V from 2 to 15 minutes on Ni-W, where the Pt counter and Pt pseudo-reference electrodes were shorted together. To qualify the electrodeposited Ir buffer layer, a CeO2/YSZ/CeO2 and YSZ/CeO2 buffer structure was later deposited on ED Ir-coated Ni-W substrates by pulsed-laser deposition. The ED Ir/metal substrates were first heated at 800°C in 0.5 mTorr of forming gas, and then a CeO2 seed layer was deposited in 180 mTorr of forming gas. Subsequently, YSZ and CeO2 layers were deposited sequentially in 0.1 mTorr of oxygen.
Superconducting YBCO Films Prepared by Electrodeposition and Spray Pyrolysis
Authors: Phok S. , Spagnol P.D. , Chaudhuri T. , Bhattacharya R.N.
Published: June 2019

Biaxially textured YBa2Cu307-δ films were fabricated by non-vacuum electrodeposition and spray pyrolysis techniques. Electrodeposited YBCO was prepared on sputtered copper/single-crystal substrates. Electrodeposition was carried out at constant voltage and the deposition was completed in only few minutes. The thickness of the as-deposited films was in the range of 0.6 to 2 μm. The optimized sputtered copper layer thickness was about 200 Å on SrTiO3. In the spray pyrolysis method, the solution is sprayed directly onto SrTiO3 substrates. The substrate temperature is about 100°C. The thickness of the as-deposited films was in the range of 1.2 to 2μm. The electrodeposited and spray-deposited films were annealed at temperatures ranging from 800° to 920°C under various flowing gas mixtures. X-ray diffraction analysis revealed that processed electrodeposited and spray-deposited films were biaxially textured, where YBCO grains were well oriented along the c-axis and in the (a,b) plane. Δω, deduced from the rocking curve on the (005) reflection, was as low as 0.46°. Δφ, deduced from the phi-scan on the (103) reflection, was as low as 0.54°. The critical current density for these types of films is about 0.5 MA/cm2at 77 K and 0 T.
High-Performance Low Voltage Organic Thin-Film Transistors
Authors: Vusser Stijn De , Steudel Soeren , Myny Kris , Genoe Jan , Heremans Paul
Published: June 2019

In this work, we report on high-performance low voltage pentacene Organic Thin-Film Transistors (OTFT's) and circuits. Inverters and ring oscillators have been designed and fabricated. At 15 V supply voltage, we have observed invertors showing a voltage gain of 9 and an output swing of more than 13 V. As for the ring oscillators, oscillations started at supply voltages as low as 8.5 V. At a supply voltage of only 15 V, a stage delay time of 3.3 νs is calculated from experimental results.

We believe that these results show for the first time a high speed ring oscillator at relatively low supply voltages. The required supply voltages can be obtained by rectification using an organic (pentacene) diode. These results may have an important impact on the realization of RF-ID tags: by integrating our circuits with an organic diode, the fabrication of organic RF-ID tags comes closer.
Electrical Characterization of Transmission Lines on Nonwoven Textile Substrates
Authors: Merritt Carey R. , Karaguze Burcak , Kang Tae-Ho , Wilson John M. , Franzon Paul D. , Nagle H. Troy , Pourdeyhimi Behnam , Grant Edward
Published: June 2019

The focus of this paper is the electrical characterization of coplanar waveguide (CPW) transmission lines that are printed onto nonwoven textile substrates using conductive inks, to determine their suitability for wide-band applications, e.g. digital signaling. The conductive ink line characterization tests included the defining of DC and Time-Domain Reflectometry metrics. The transmission line test samples were screen printed onto two different types of nonwoven textile substrates using two different conductive inks, i.e. inks with different viscosities. Tests showed that the variations in the continuity of the transmission lines varied, giving rise to geometrical variations in the CPW structure; and in the characterization of the same.
Nanoindentation and Finite Element Analysis of Resin-Embedded Bone Samples as a Three-Phase Composite Material
Authors: L. Oyen Michelle , Ko Ching-Chang , K.Bembey Amanpreet , Bushby Andrew J. , Boyde Alan
Published: June 2019

The effective elastic modulus of composite materials results from a combination of elastic moduli of the component phases. Recent efforts to understand the mechanical behavior of calcified tissues in bones and teeth require estimates of the component phase properties, which are difficult to establish independently. A three-phase system, based on naturally occurring bone, is therefore examined by a combined nanoindentation and finite element modelling approach to better understand the proportions and properties of the component phases. Bone samples were prepared in four two- or three-phase composite configurations as follows: (1) as a dehydrated mineral-protein composite (with some void space); (2) similarly dehydrated mineral-protein composite but with polymethylmethacrylate (PMMA) resin filling the voids resulting in three solid phases; (3) as a PMMA-mineral composite following protein removal and replacement with PMMA, and (4) as a PMMA-protein composite following mineral removal and replacement with PMMA. Effective component volume fractions and elastic moduli for each phase in each system were computed based on the composite nanoindentation results. Finite element models of the two- and three-phase systems were constructed to explore the structural anisotropy of the composite systems, as demonstrated in the nanoindentation tests, and to examine the sensitivity of the composite results to changes in the assumed component properties.
AFM Imaging of Water, Cells and Tissues
Authors: Li Xiaodong
Published: June 2019

This paper presents the results of several AFM case studies of water, tumor cells, pit cells, and type-I collagen samples. The AFM imaging procedures, surface structural characterization capabilities such as contact mode, tapping mode, and friction mode are discussed. The difference in surface morphology between the pit cell submerged in liquid and the cell in air was observed. The AFM tapping mode phase imaging technique was used to study the crosslinks in the type-I collagen. The calibration method for accurately measuring the AFM cantilever spring constant with the help of a nanoindenter is also presented.
Viscoelastic Models Describing Stress Relaxation and Creep in Soft Tissues
Authors: Kobelev Alexa V. , Kobeleva Rimma M. , Protsenko Yuri L. , Berman Irina V. , Kobelev Oleg A.
Published: June 2019

The review of our approach to the specific rheological properties modeling of myocardium has been given. We are working on the level of ‘fascicule’ as a tissue element, which consists of several cardiomyocytes surrounded by a connective tissue shell. Actually, these properties are characteristic of large majority of living soft tissues. In order to describe essentially nonlinear static ‘force-deformation’ curves and quasi-static hysteresis loops together with non-exponential stress relaxation and creep time courses we suggest a set of 2D graphs with different topology composed of classical linear Hook's springs and Newtonian damps. Each spring and dashpot represents a group of 3D tissue structural elements. The stress response functions of these models are found for the uniaxial step-wise, or pulse (column-like) external stretching. The inverse response functions of the longitudinal displacement for the external stress loading of the pulse shape time dependencies were also found. The values of elastic modules and viscous coefficients are estimated by comparison theoretical curves of relaxation, creep and recovery with the experimental data. The latter are obtained on rather different objects, passive muscle preparations (the stress relaxation response) and endothelium cells (the creep response). It has been stated that the proposed 2D models appear to be quite general to describe nonlinear relaxation and creep properties, which are lacking in the traditionally used uniaxial 1D models.
Structural Distinctions Between Biogenic and Geological Aragonite
Authors: Pokroy Boaz , Quintana John P. , Zolotoyabko Emil
Published: June 2019

Energy-variable synchrotron x-ray diffraction was applied to probe local structure in different kinds of aragonitic seashells with spatial resolution. All investigated specimens revealed lattice distortions of biogenic aragonite with respect to the geological mineral. The obtained data are analyzed in terms of residual strains induced by intercalating organic macromolecules.
First Principles Study of Size Effect in BaTiO3 Ultrathin Films
Authors: Lai Bo-Kuai , Kornev Igor , Bellaiche Laurent , Salamo Greg
Published: June 2019

Properties and phase transition behaviors of ferroelectric thin films that are different from that of their bulk form is usually referred to as size effect. A first-principles-based scheme is used to investigate the effects of four important factors contributing to the size effects in epitaxial (001) BaTiO3 ultrathin films: misfit strain, existence of surface, film thickness, and electrical boundary conditions.
Effective Direct Piezoelectric Constants in Epitaxial Ferroelectric Films as MEMS Sensors
Authors: Ouyang Jun , Ramesh R. , Roytburd A. L.
Published: June 2019

Following our previous work on the converse piezoelectric constant- in epitaxial ferroelectric films for MEMS actuator applications, the orientation dependence of the direct piezoelectric constants , and are generally formulated, which can help to predict and optimize the performance of piezoelectric MEMS sensor devices based on ferroelectric thin films. Numerical results are obtained and discussed for Pb(ZrxTi1-x)O3 thin films grow on Si substrates with various compositions and structures.
Domain Structures and Phase Diagram in 2D Ferroelectrics Under Applied Biaxial Strains - Phase Field Simulations and Thermodynamic Calculations
Authors: Wang Jie , Li Yulan , Chen Long-Qing , Zhang Tong-Yi
Published: June 2019

Absract:The microscopic domain structures in 2D ferroelectrics under applied biaxial strains are investigated using a phase field model based on the time-dependent Ginzburg-Landau equation that takes both long-range electric and -elastic interactions into account. The stable polarization patterns are simulated at different temperatures and applied inequiaxial strains. The results show that the ferroelectrics transfer from multi-domain state to single-domain state when temperature surpasses a critical value. On the other hand, the macroscopic equilibrium polarization states are also studied through a nonlinear thermodynamic theory. The corresponding transition from a1, a2 state (p1 ≠ 0, P2 ≠ 0) to a1 state (p1 ≠0, P2 = 0) or a2 state (p2 ≠ 0, P2 = 0) is also found from the “strain-straintemperature” phase diagram, which is constructed by minimizing Helmholtz free energy.
Magnetoelectric Laminate Composites – Enhanced Magnetic Field Sensitivity, and High Voltage Gain
Authors: Dong Shuxiang , Zhai Junyi , Xing Zhengping , Li Jie-Fang , Viehland D.
Published: June 2019

In this paper, the magnetoelectric (ME) coupling and working modes are defined and discussed. Several types of ME laminate composites based on Terfenol-D, Fe-Ga magnetostrictive layers and piezoelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 crystal, Pb(Zr,Ti)O3 ceramic layers have been developed. Our experiments confirm that these ME composites have giant magnetoelectric voltage coefficients of ∼0.43×103 mV/Oe in the frequency range of 10-2<f<104 Hz under low magnetic bias. When operated under resonant conditions, the ME voltage coefficient is dramatically enhanced to maximum values as high as ∼20×103 mV/Oe. At resonance, our ME laminates have (i) a strong voltage gain effect; and (ii) an ultrahigh magnetic field sensitivity of near 10-12 Tesla.
Beyond Weight Percent - The Influence of Material Characteristics on Hydrogen Storage System Performance
Authors: Mosher Daniel A. , Anton Donald L.
Published: June 2019

The attribute of solid state hydrogen storage materials that is most commonly the focus of evaluations is reversible hydrogen weight percent. Other material characteristics, including density, charging pressure, enthalpy and conductivity can influence the weight of storage system components and hence the overall hydrogen weight percent that is ultimately of interest. However, accounting for these effects involves some level of storage system representation that typically is not undertaken when making material assessments and comparisons.

The current paper will present a simple model that represents system elements and trade-offs on a high level so that overall system performance can be estimated without the burden of detailed design studies. The model should be useful to evaluate novel materials in a more complete manner for a better assessment of their potential when implemented in a storage system. While the model has been derived based on the design of a particular NaAlH4 system, the key attributes are sufficiently general to be applicable to a range of system designs. Using this approach, the properties of materials can be related more precisely to goals for overall system performance with modest additional effort.
Effect of Carbon Addition on Hydrogen Storage Performances of Magnesium-based Alloys: from Bulk Powders to Thin Films
Authors: Rougier A. , Darok X. , Bhat V.V. , Aymard L. , Nazri G.A. , Tarascon J.-M.
Published: June 2019

Mg-based thin films were successfully grown by Pulsed Laser Deposition. Dramatic optical changes were observed depending on the conditions of deposition. Films grown in vacuum were shiny metallic whereas the ones grown in a Ar/H2 gas mixture were highly transparent. Ex situ hydrogenation, by annealing the films at 200 °C in 15 bars of hydrogen, led to similar metallictransparent transformation. Mg-Cx (x ≤ 20 %) films show a faster hydrogenation associated with a significant decrease in oxygen content by carbon addition.
Development of Hydrogen Absorbing Alloy with High Dissociation Pressure
Authors: Kojima Yoshitsugu , Kawai Yasuaki , Towata Shin-Ichi , Matsunaga Tomoya , Shinozawa Tamio , Kimbara Masahiko
Published: June 2019

The effective hydrogen capacity of TixCr2-yMny [≫X λ1.1 (1.08≤0x≤1.16), y λ1.0 (0.96≤y≤1.08)rsqb; exhibited the maximum value of 1.8 wt% in the pressure range of 33 MPa and 0.1 MPa at 296K (dissociation pressure: 5-11 MPa), and the alloy provided over 10% more capacity than conventional Ti-Cr-Mn (Ti1.2CrMn: 1.6 wt%, Ti1.2Cr1.9Mn0.1: 1.3 wt%). At the low temperature of 233 K, the alloy absorbed 2.0 wt% of hydrogen and the hydrogen desorption capacity at 0.1 MPa was 1.6 wt%. The dissociation pressure decreased with the Ti and the Mn contents and was explained by the function of the bulk modulus and the cell volume. According to the van't Hoff plots, the standard enthalpy differences (heat of formation) of the Ti1.16Cr0.92Mn1.08 and Ti1.08Cr1.04Mn0.96 hydrides were -21 and -22 kJ/molH2, respectively. These absolute values were about 10 kJ/molH2 smaller than those of LaNi5 and Ti-Cr-V. The alloy had sufficient hydriding and dehydriding kinetics. In the pressure range of 33 MPa and 0.1 MPa at 296 K, the alloy absorbed and desorbed 1.8 wt% of hydrogen in 60 sec and 300 sec, respectively. The hydrogen capacity changed gradually over many cycles and that after 1000 cycles was 94 % of the initial capacity. Thus Ti1.1CrMn can be utilized for a high- pressure MH tank which contains a hydrogen absorbing alloy with high dissociation pressure and compressed hydrogen.
Multi-Scale Modeling of Human Cortical Bone: Aging and Failure Studies
Authors: Budyn Elisa , Hoc Thierry
Published: June 2019

A multi-scale analysis for unit cells of human cortical bone is presented. Two studies are conducted: the first study concerns the effect of aging over the structural and mechanical properties of human cortical bone; the second study is devoted to the failure mechanism and the development of cracks in cortical bone under various loading conditions. Experiments are conducted on human specimen of different ages in order to measure relevant geometrical and mechanical parameters and obtain microscopic data that will be injected into finite element models. First a continuum FEM model will compute macroscopic information that will be validated through comparison with the experimental measurements. For the failure mechanism study, an XFEM model will be developed in order to allow the growth of multiple cracks until complete failure of the cell. An elastic-damage criterion will be used in order to place the initial cracks in maximum strain locations. To follow the global response of the cell, the stress intensity factors are computed at each crack tip and a load parameter is adjusted so that the stress intensity factors remain at the critical value. In the case of competitive crack tips, a stability analysis is performed by computing the second derivative of the potential energy for each crack. Fatigue loading will be also investigated. The discretization utilizes the eXtended Finite Element Method and requires no remeshing as the cracks grow. The crack geometries are arbitrary with respect to the mesh, and are described by a vector level set. Special boundary conditions and the algorithm for detecting crack bridging and crack entering Haversian canals which allows the cracks to grow until maximum failure and/or percolation is presented.
Directed Mineralization on Polyelectrolyte Multilayer Films
Authors: Advincula Maria C. , Patel Pritesh A. , Mather Patrick T. , Underhill Daniel , Huey Bryan D. , Goldberg A. Jon
Published: June 2019

Silica formation aided by polypeptides is being actively investigated for a wide range of applications including biomaterials synthesis, ceramics and controlled release systems. We envision that biocatalyzed mineralization could have application as a dental material where in situ formation of mineral layers could provide needed wear-resistance or sealing capability. The approach would be more clinically relevant, if a polymer host could be used to carry and specifically position the biocatalyst on a surface and additionally maintain the catalyst activity.

Accordingly, we studied the influence of simple catalytic polypeptides on silica formation from prehydrolyzed alkoxide precursor solutions onto a surface. The polypeptides were localized on to the surface as multilayered thin films using the layer-by-layer (LbL) assembly of polyelectrolytes. Polylysine (PLL) or another biocatalytic polycation, poly(ethyleneimine) (PEI), was adsorbed layer-by-layer up to 10 bilayers on silicon wafers in combination with a negatively charged polyelectrolyte polymer host, poly(sodium-4-styrene sulfonate) (PSS) to prepare PEI-(PLL/PSS)10, PEI-(PEI/PSS)10 and PEI-(PEI/PSS/PLL/PSS)10 multilayer films. Pre-hydrolyzed alkoxysilane solutions were placed dropwise on the catalytic films for silicification. Additionally, the effects of precursor concentration, solvent and drying were evaluated. The morphology, roughness and contact mechanical stiffness of the formed silica were investigated using optical microscopy (OM), scanning electron microscopy (SEM) and atomic force microscopy (AFM).

The resulting silica morphology was plate-like or spherical, and porous with average particle size depending on the catalyst and its positions on the surface. Without a catalyst the silica formed over longer times with a fine, gel-like appearance. The morphology of silica produced on the substrate was different from that of particles catalyzed in solution with the same polypeptide catalyst. Additionally, it was found that the homogeneity of PEI-(PLL/PSS)10 films increased with drying temperature, silica precursor concentration and the presence of ethanol. The contact mechanical stiffness of the silica particles (40 N/m) catalyzed from PEI-(PLL/PSS)10 films was lower than the non-silicified areas (48 N/m) suggesting that regions of the silica were amorphous and hydrated. These results show that a polypeptide applied to a surface as a multiple layer with an oppositely charged polymer host (PSS) maintains its activity for silicification. The generally coherent nature of the mineral coating suggests its potential for enhancing critical restorative dental interfaces; however properties like porosity, hydration and their effect on hardness and permeability will need further study.
Effects of Volume Fraction and Composition on the Rheological Properties of Polyacrylic Acid/Polyacrylamide Hydrogels
Authors: Baker Bryan , Murff Rebecca , Milam Valeria T.
Published: June 2019

Polyacrylamide-based hydrogels are popular materials that have been extensively studied for their applications in the field of biomaterials due to their permeability and biological compatibility. A major limitation of this polymeric material, however, in biological applications stems from their limited mechanical stiffness. The current study examines the mechanical properties of polyacrylamide-polyacrylic acid-based hydrogels at varying volume fractions and compositions using oscillatory rheology. For a fixed chemical cross-linker concentration, an increase in the volume fraction of hydrogel resulted in an increase in the shear elastic modulus of the hydrogel. Additionally, varying the relative ratio of polyacrylamide to polyacrylic acid resulted in modest changes in the shear elastic modulus.
Mechanical Properties Evolution of Polydimethylsiloxane During Crosslinking Process
Authors: Zhao Yi , Zhang Xin
Published: June 2019

This paper reports mechanical properties evolution of polydimethylsiloxane (PDMS) during the crosslinking process. In this work, PDMS crosslinking was induced by mixing base prepolymer and curing agent at certain ratios. The liquid prepolymer was spun coated on a silicon wafer, and the curvature change of the wafer was measured continuously using a curvature measurement system. The relationship between the curvature change and typical mechanical properties was investigated using a bilayer model; and the evolution of the properties was derived, as a function of operational parameters. This work is expected to help better understanding of the crosslinking process and provide practical strategies for controlling the mechanical behavior of the resulting polymer structures, especially those for mechanical sensing applications.
Structural Evolution and Mechanical Behavior of Bio-inspired Oxide Films on Self-Assembled Organic Layers
Authors: Zhang Guangneng , Cho Junghyun
Published: June 2019

A bio-inspired approach is employed to deposit the oxide films on the substrates coated with self-assembled organic layers. Particularly, titania and zirconia films are grown in aqueous precursor solutions at near room temperatures. This process, directed by the nanoscale organic template, mimics the controlled nucleation and growth of the biominerals such as bones and teeth. Multiscale structural evolution resulting from initial bulk nucleation, nanoparticle aggregation, and ultimate film formation are systematically studied by adjusting the precursor solution conditions. Dynamic light scattering (DLS) is utilized to characterize initial nanoparticles and their associated aggregates/clusters formed in situ in solution. Corresponding nano- and microstructure developments of the oxide films are investigated through high-resolution transmission electron microscope (TEM) and scanning electron microscope (SEM). In addition, mechanical performance is evaluated with the aid of a dynamic nanoindentation testing to establish the structure-property relationships of the bio-inspired oxide films. The goal of this study is to have a capability to tailor microstructures and mechanical behaviors by identifying the controlling mechanisms responsible for nucleation and growth of such oxide films.
Strength of Calcium Phosphate Cements
Authors: Veresov Alexander , Stepuk Alexander , Kuznetsov Alexander , Putlayev Valery , Kuznetsov Vladimir
Published: June 2019

Calcium phosphates materials are widely used to treat the bones defects. HA bioceramics traditionally used in medicine has some serious disadvantage – week resorbility properties. Calcium phosphate cements seems to be promising compounds to replace conventional ceramics. High macroporosity of hardened materials leads to low mechanical strength. The main objective of present work was a development of new chemically bonded materials based on α-tricalcium phosphate (α-TCP) and hydroxylapatite phase. The main idea was to combine the benefit of ceramics technology (compacting of powders to reduce the starting macroporosity) to improve the materials strength with advantages of cement product (small resorbable calcium phosphate particles). α-Ca3(PO4)2-based biocements were synthesized with initial composition of HA, α- and β-TCP containing 80% wt. of TCP phase. The rate of α-TCP transformation to apatite phase during setting reaction was about 20% wt. in case of cylindrical samples (8mm × 8 mm) at 60°C for 50 hours. The fabricated TCP – bio-composites demonstrated high mechanical strength and stiffness characteristic. Most efficient results were achieved with chitosan biopolymer containing samples (σc = 120 MPa).
What is Behind the Inverse Hall-Petch Behavior in Nanocrystalline Materials?
Authors: Carlton Christopher , Ferreira P. J.
Published: June 2019

An inverse Hall-Petch effect has been observed for nanocrystalline materials by a large number of researchers. This result implies that nanocrystalline materials get softer as grain size is reduced below a critical value. Postulated explanations for this behavior include dislocation based mechanisms and diffusion based mechanisms. In this paper, we report an explanation for the inverse Hall-Petch effect based on the statistical absorption of dislocations by grain boundaries, showing that the yield strength is both dependent on strain rate and temperature, and that it deviates from the Hall-Petch relationship at a critical grain size.
Atomic Events at the Onset of Plasticity in the Au(001) Surface
Authors: Carrasco Esther , Rodríguez de la Fuente Oscar , Rojo Juan Manuel
Published: June 2019

Atomic defects, in the form of dislocation configurations, are identified following nanoindentation of Au(001) surfaces. Combined STM, dislocation theory and atomistic simulations fully characterise these defects and describe their motion. By comparing with AFM data the emission of those defects are correlated with the incipient stages of plasticity, the latter recognised from force vs penetration curves. The size distribution, the spatial pattern and the motion of these dislocations under stress have also been investigated and explained in terms of the theory of dislocations in a continuum.
Thermo-Mechanical and Size-Dependent Behavior of Freestanding AuAg and Nanoporous-Au Beams
Authors: Seker Erkin , Zhu Jianzhong , Bart-Smith Hilary , Begley Matthew , Kelly Robert , Zangari Giovanni , Reed Michael L.
Published: June 2019

Nanoporous gold (np-Au), produced by selectively removing silver from an AuAg alloy, has recently gained considerable attention from the scientific community. Biocompatibility, chemical inertness, increased surface area, relatively low elastic modulus, and ease of synthesis make np-Au an important candidate for biomedical, catalytic, and MEMS applications. Np-Au films also offer substantial ground for theoretical and empirical research, including mechanical characterization, fracture mechanics, and porosity evolution. Even though a significant effort has been directed towards exploring blanket np-Au films (i.e., foils, strips), to our knowledge no work has been done on fabricating or investigating freestanding np-Au structures (i.e., micro-beams, cantilevers). Recently we have developed techniques to create freestanding clamped np-Au beams with widths from 5 to 40 microns and lengths from 20 to 500 microns. The percentage yield was more than 97% for 2880 beams on a 2-inch wafer. A critical step in the fabrication process, necessary to prevent tensile failure of the beams during dealloying, is a thermal heat treatment prior to dealloying. The study of thermal treatment of beams at temperatures between 100°C and 600°C prior to dealloying revealed three distinct beam behavior regimes, namely quasi-elastic buckling, plastic buckling, and material interdiffusion. This paper will present the preliminary results from thermal treatment experiments particularly focusing on how beam dimensions affect percentage yield and beam fracture.
Investigation of the Bi-linear Behavior of the Indentation Size Effects in Single and Polycrystalline Ni Thin Films/MEMS Thin Films
Authors: Elmustafa Abdelmageed A. , Lou J. , Zong Z. , Soboyejo W. O.
Published: June 2019

This paper presents the results of an experimental study of the indentation size effects at the nano, sub-micron, and micron-scales. The size dependence of the indentation hardness in these regimes is shown to exhibit a bi-linear behavior when the data are fitted to Taylor Dislocation Hardening (TDH) model. The deformation in indent sizes corresponding to the onset of the transition from micro and deep nano indents to shallow nano indents represent dislocation substructures at the sub-micron and micron scales whereas the deformation at the nano-scale represents dislocation source-limited behavior.
Size Effects in LiF Micron-Scale Single Crystals of Low Dislocation Density
Authors: Nadgorny Edward M. , Dimiduk Dennis M. , Uchic Michael D.
Published: June 2019

This study examines the deformation response of 20, 5, and 1 micron diameter samples fabricated by FIB-milling from bulk ultrapure LiF single crystals. The bulk crystals have a very low initial dislocation density as revealed by an etch-pit technique. Two types of <001> microsamples were deformed preferentially by single slip when compressed inside a nanoindentation system. Similar to previously studied FCC-derivative metals, LiF microsamples demonstrate dramatic strengthening achieving the engineering flow stress σ ≈ 650 MPa in 1-μm samples. The stress-diameter dependence obeys a power law, σ ∼ D−m, where m ≈ 0.8. Stochastic variation of flow stress, fast intermittent deformation events (“avalanches”) and highly localized slip bands after avalanches - all characteristic of size effects in metals, are also observed in LiF. Possible dislocation mechanisms of the observed size effects are discussed.
Size Effects on Yield Instabilities in Nickel
Authors: Cordill Megan J , Moody Neville R , Gerberich William W
Published: June 2019

Dislocation events are seen as excursions, or pop-in events, in the load-displacement trace of nanoindentation experiments. When indenting single crystal metals these events occur frequently during quasi-static and dynamic loading. A single crystal of Ni (111) has been indented quasi-statically using three different loading rates (10, 100, and 1000 μN/s) as well as with three different radii diamond indenter tips (1000 nm cone, 300 nm Berkovich, and 50 nm cube corner) to examine the occurrences of excursions. As expected, excursions at higher loads have larger displacements, and that initial loading follows Hertzian behavior up to the point of yield. Also, as the tip size is reduced the excursion loads are reduced. The excursion events depend mostly on the statistical distribution of surface sources and substructure dislocation arrangements.
Mechanical Behavior of Nanocrystalline Cu Alloy Thin Film on Elastomer Substrates Under Constant Uniaxial Tensile Strain
Authors: Inoue Junya , Fujii Yousuke , Koseki Toshihiko
Published: June 2019

In this study, mechanical behavior of nanocrystalline Cu alloy thin films under constant tensile strain is studied, by taking advantage of the enhanced resistance to strain localization of a thin metal film on a thick elastomer with appropriate Young's modulus. Cu and Cu alloy thin films with a thickness of 100nm were deposited on heat-resistant polyimide substrates. On the top of the Cu alloy layer, Ta thin film was further deposited to suppress the surface diffusion of Cu alloy. A uniform uniaxial tensile strain was induced to the films by applying a constant radius of curvature to the polyimide substrate. Isothermal deformation and rupture modes of the films were studied by keeping the samples at various elevated temperatures. Microstructural observation was carried out using SEM, TEM, STEM, and confocal violet laser microscope at several stages of deformation. From the observation, the evolution of damage in the sub-critical strain level and the effect of alloying elements are discussed.
Phase Transformations Induced by Grinding: What is Revealed by Molecular Materials
Authors: Descamps Marc , Willart Jean François , DUDOGNON Emeline , LEFORT Ronan , DESPREZ Sylvain , CARON Vincent
Published: June 2019

The purpose of this paper is to show some examples of phase transformations induced by grinding molecular materials. These materials are considered because they are extremely sensitive to external disturbances and are generally very good glass formers. This allows investigating more easily a broad range of the parameters which are open to influence the nature of the end product namely the temperature and intensity of grinding. Such an investigation has also a practical interest in pharmaceutical science. It is shown that the position of the grinding temperature with regard to the glass transition temperature of the compound is a key parameter. Comparison of the effects of temperature and intensity of grinding demonstrates that the driven material concept offers a framework to rationalize all the observed transformations.
Precipitation Sequence in Mg-Zn-Sn Based Alloys
Authors: Gorny Anton , Katsman Alexander , Shepelev Dmitry , Bamberger Menahem
Published: June 2019

Extensive experimental research work has been carried out in order to develop an Mg-Zn-Sn based creep resistant alloy. It was found that the addition of Y improves the structural stability of this alloy. The main goal of this work was to investigate precipitation sequence in Mg-Zn-Sn-Y alloys during aging at different temperatures. In order to elucidate the sequence of phase formation, XRD, TEM, SEM and EDS analyses were applied. It was found that, firstly, an hcp-MgZn2 phase nucleates homogeneously, and grows in the form of needles having coherent interphase boundaries with Mg-matrix. High-resolution TEM images in combination with Fourier transformed images reveal a topotaxial orientation relationship which is given by {110}MgZn2 <100>MgZn2∥(002)α-Mg<110>α-Mg. The cubic fcc Mg2Sn-phase nucleates heterogeneously, mainly at the tips of MgZn2-needles when the needle's width reaches a certain critical value. The orientation of Mg2Sn-precipitates is usually perpendicular to the one of MgZn2-needles. Two-phase T-like particles are very typical of alloys aged for 1-16 days at 175-225C. The width/length ratio of MgZn2-needles inside T-like particles differs substantially from the one found in single needles. The elastic/surface energy balance of needles and its influence on the morphology and coarsening behaviour has been analyzed.
Texture Evolution of Lithium Fluoride Thin Films by Nucleation
Authors: Kim Hakkwan , King Alexander H.
Published: June 2019

We have used a transmission electron microscope (TEM)-based method to extract grain size information for 〈111〉 surface normal grains in lithium fluoride (LiF) thin films, and applied this to analyze textures as a function of substrate temperature and annealing time. The size distributions of grains diffracting into the (111)+(200) and (220) rings were measured separately using dark field (DF) TEM images. From these data, we deduce the distribution of 〈111〉 surface normal grain sizes based on the assumption that only 3 principal textures (100), (110) and (111) exist in films. The (111) texture formation was also observed by x-ray diffraction (XRD). For all deposition and annealing conditions, the grain size data can be matched to lognormal distributions within an acceptable error, but at longer annealing times the distribution becomes bimodal. A novel feature of the LiF films is that the (111) texture component strengthens with annealing and substrate temperature, through the nucleation of new grains rather than the growth of existing ones.
Precipitation of Zr2Cu Stable Crystalline Phase from Zr70Cu27.5Rh2.5 Amorphous Alloy
Authors: Cushman David , Saida Junji , Li Chunfei
Published: June 2019

The crystallization process of Zr70Cu27.5Rh2.5 metallic glass was studied with Transmission Electron Microscopy (TEM). In contrast to previous studies where the precipitation of metastable icosahedral quasicrystalline (IQC) particles is of the interest, we designed the present work to focus on the nucleation process of the stable Zr2Cu crystalline phase. It has been found that the alloy consists of IQC particles distributed in amorphous matrix prior to the precipitation of the Zr2Cu stable crystalline phase and Zr2Cu nucleates from the amorphous matrix. The encounter of the IQC phase with Zr2Cu transforms the former into the latter so quickly that no interface between them was found in the present experiment. These insights provide the basis for a discussion of the stability of metallic glasses and the IQC particles.
Strengthening Mechanisms for Fe-Al-based Alloys with Increased Creep Resistance at High Temperatures
Authors: Palm Martin , Krein Ronny , Milenkovic Srdjan , Sauthoff Gerhard , Risanti Doty , Stallybrass Charles , Schneider André
Published: June 2019

Lack of strength, in particular creep resistance, has been considered as the principal shortcoming of Fe-Al-based alloys for long which prevented their use for structural applications at high temperatures. Only recently it has been realized that various strengthening mechanisms are available by which Fe-Al-based alloys can be sufficiently strengthened for applications at high temperatures. From the recent studies at the Max-Planck-Institut für Eisenforschung GmbH (MPIE) examples of applying different strengthening mechanisms are presented by which Fe-Al-based alloys with considerable creep resistance have been obtained.
Strengthening at High Temperatures in an Iron-Aluminium Alloy by the Precipitation of Stable and Coherent Intermetallic Particles
Authors: Morris David G. , Muñoz-Morris Maria A. , Requejo Luis M.
Published: June 2019

Despite decades of intensive research iron aluminides remain characterised by relatively poor ductility at room temperature and low strength at high temperatures, especially under slow strain rate or creep conditions. A variety of strengthening particles has been tested for improving high temperature strength, but each has serious limitations: typical carbide precipitates are unable to resist dissolution or coarsening at high temperatures; as-solidified iron aluminides with sufficient amounts of transition elements such as Nb or Mo show heavy solidification segregation and are embrittled by a network of Laves phase; mechanical milling with stable oxides appears an excessively expensive processing route. A new iron-aluminium alloy has been developed with Zr and Cr additions that forms fine coherent precipitates even after extended annealing at temperatures as high as 900ºC. These precipitates have a complex Fe3Zr structure and form in a cube-on-cube orientation relationship in the bcc matrix. The low solubility and diffusivity of the solute, as well as the low energy, near-coherent interface ensures excellent stability of these intermetallic precipitates. Interesting strengthening is possible for this material under the relevant high temperature creep conditions.
Texture Memory Effect During Heat Treatment in the Heavily Cold Rolled Ni3Al Foils
Authors: Demura Masahiko , Xu Ya , Kishida Kyosuke , Hirano Toshiyuki
Published: June 2019

Texture evolution during grain growth was examined in the 84% cold-rolled Ni3Al with a Goss texture, {110}<001>, using the electron backscatter diffraction method. By recrystallization at 873K/0.5h, the texture was disintegrated and composed of several orientations, most of which had a 40° rotation relationship about <111> to the Goss orientation. Also, a small number of the Goss grains existed. With grain growth, the Goss grains grew faster than the 40°<111> rotated grains, leading to the texture reversion to the original, Goss texture. This phenomenon can be referred to Texture memory effect. In the early stage of the grain growth, the preferential growth occurred on the Goss grains surrounded by the 40°<111> rotated grains. It can be thus ascribed to the high mobility of 40°<111> grain boundary. In the late stage, the Goss grains were adjacent to each other and the preferential growth was accelerated. It is considered that the adjacent Goss grains survived in the grain coalescence process since the boundary between them are low angle boundary having a low energy.
COMPRESSION CREEP BEHAVIOR OF B2 AL-NI-RU TERNARY ALLOYS
Authors: Cao Fang , Pollock Tresa M.
Published: June 2019

The compression creep behavior of five Al- Ni-Ru ternary alloys with compositions across the NiAl-RuAl B2 phase field has been investigated within the temperature range of 950 °C to 1050 °C. A continuous increase of the melting temperature and creep resistance with increasing Ru/Ni ratio in these alloys was observed. Post-creep dislocation analyses identified the presence of <100> and <110> edge dislocations in the Al-deficient alloys. Conversely, jogged <100> screw dislocations predominated in the Ru-rich ternary alloys. Dislocation substructures and transient experiments suggest a transition of the creep mechanism from viscous glide controlled to jogged screw motion in these alloys.
Structural transformations and improved ductility in ordered FeCo and ZrCo intermetallics
Authors: Krcmar Maja , Fu Chong Long , Morris James R.
Published: June 2019

Using the first-principles calculations, we find that Fe-Co has a tendency for a structural transformation to a lower symmetry sheared L10 phase under the applied shear stresses. This tendency for structural transformation can have a significant influence on the mechanical properties of FeCo, as it might be closely connected with the intrinsic brittleness of Fe-rich and stoichiometric FeCo alloys and with the improved ductility of Co-rich FeCo alloys. We suggest that improved ductility in Co-rich FeCo alloys may originate from transformation toughening due to the B2→L10 structural transformation near the regions of high stress concentration, as the stress energy is fully dissipated by the decrease in the electronic energy due to the structural phase transformation into a lower energy structure. Similarly, in ZrCo, our first-principles calculations find that a B2→B33 martensitic phase transformation can occur under the applied shear stress, which may contribute to the good ductility of this alloy, despite the fact that ZrCo is a strongly ordered line compound.
The Effect of Constraints on Plastic Deformation
Authors: Paidar Vaclav
Published: June 2019

The effect of the deformation constraints is examined for the lamellar structure of TiAl where the unconstrained plastic deformation occurs parallel to the lamellae. The constraints generally redistribute the stresses in such a way that the resolved shear stresses are decreased on the most stressed systems and increased on other systems. This behaviour leads to the material strengthening and may enhance the ductility when more deformation modes are activated.
Cold-Deformation and Annealing of equiaxed L1o-ordered FePd Intermetallics
Authors: Desphande Anirudha , Wiezorek Jorg
Published: June 2019

The L10 ordering equiatomic intermetallic FePd has been used as a model system for the investigation of the evolution of microstructure and properties during annealing at temperatures below the ordering temperature after deformation in the L10 state. The two different routes for the preparation of equiaxed L10 FePd polycrystals, annealing after cold deformation in the disordered FCC state or after cold deformation in the ordered state, produce similar grain size distributions, differ in the transformation kinetics and importantly in the sequence of texture evolution during the post-cold-deformation annealing. Cold deformed L10 FePd progresses through the classic stages of annealing known from studies of disordered elemental metals and alloys based on them. The reduced L10 SLRO of the ‘mechanically disordered’ FePd is recovered in the early stages of annealing and both the recrystallization and the grain growth stages are quite sluggish, presumably because of the slow diffusion processes in the L10 lattice.
Thermoelectric properties of Ba-Ge based Type-III Clathrate Compounds
Authors: Kim Jung-Hwan , Okamoto Norihiko L. , Kishida Kyosuke , Tanaka Katsushi , Inui Haruyuki
Published: June 2019

The crystal structures and thermoelectric properties of Ba-Ge based type-III clathrate compounds in Ba-Al-Ge and Ba-In-Ge systems have been investigated as a function of Al and In content. The absolute values of electrical resistivity and Seebeck coefficient increase, while that of lattice thermal conductivity decreases with increasing Al and In content. The increase in electrical resistivity and Seebeck coefficient is discussed in terms of the number of the excess electrons deduced from the Zintl concept, on the other hand, the decrease in lattice thermal conductivity is discussed in terms of an anisotropic deformation of the open-dodecahedron cage encapsulating Ba atom. High ZT values of 0.74 and 0.87 are obtained at 780 and 580 °C for Ba24Al12Ge88 and Ba24In16Ge84, respectively.
Classification and Characterization of the Shape Memory Binary Alloys
Authors: Notomi Mitsuo , Van Vliet Krystyn J , Yip Sidney
Published: June 2019

All shape memory binary alloys (SMBA) that exhibit not only perfect shape recovery but also partial shape recovery were reviewed and classified into three groups, B2, A2 and A1 type, according to the parent phases. There are the thirteen, six and eleven alloys belonging to B2, A2 and A1 type, respectively. In the group of B2 type SMBA the alloys are divided into two categories due to the combination of the elements. Over A1 and A2 type SMBA the atomic composition of one element is larger than the other so the larger one is called a major element. The major elements, Ti, U, Fe, and Cu, of A2 type SMBA do not belong to the group 5 and 6 in which the elements have a typical BCC (A2) crystal structure. In the A1 type SMBA there are four major elements, Mn, Fe, Co, and In and the SMBA except for In-based SMBA have ferromagnetic or antiferromagnetic natures. The shape memory effect (SME) for A1 (FCC) type SMBA might need the magnetic properties.