bluuebunny/crossref_metadata_2025_split huggingface dataset:
An Investigation of Non-linear Stress-strain Behavior of Thin Metal Films
Authors: Huber N. , Dietz T. , Tyulyukovskiy E. 
Published: April 2011

ABSTACTNon-linear stress-strain curves of various films with thickness of one to four microns were determined from nanoindentation experiments with a Berkovich indenter. The measured load-depth data are analysed using a method based on neural networks. An inverse mapping of depth-dependent dimensionless hardness and stiffness data yields the material parameters describing a non-linear elastic-plastic stress-strain curve of the Armstrong-Frederick type. Suppositions for the application of this method are a sufficiently different hardness between film and substrate, and hardness and stiffness data available in a depth range of 10 to 200% of the film thickness. For all films considered a significant thickness dependence in strength has been observed. In addition, a remarkable influence of the substrate material on the strength of the film material was found and has been confirmed by focussed ion beam microscopy.
Nanoindentation of multilayer PZT/Pt/SiO2 thin film systems on silicon wafers for MEMS applications.
Authors: Chima-Okereke C. , Reece M. J. , Bushby A. J. , Whatmore R. W. , Zhang Q. 
Published: April 2011

ABSTRACTNanoindentation is a promising tool for obtaining the elastic properties of thin films. However, no means exists to predict or extrapolate the elastic modulus of the top layer in multilayer systems from experimental data. The mechanical properties of PZT multilayer systems have become increasingly important in applications for MEMS devices. The indentation modulus vs. a/t behaviour of PZT on Pt/SiO2/Si wafer substrate was investigated and compared with a new analytical solution for Herztian indentation of multilayers. Five different PZT film thicknesses were indented (70, 140, 400, 700, 1500 nm), using a 10 μm radius indenter. Good agreement was found between analytical equations and experimental data. However the behaviour of the multilayer system was complex. This makes the deconvolution of film properties difficult for thicknesses less than about 1000 nm.
Effect of Fluoride on Mechanical Properties of Teeth Demineralized by Use of Orthodontic Appliances
Authors: Centeno Claudia , Ruiz Ulises , Contreras Oscar , Samano Enrique C. 
Published: April 2011

ABSTRACTThe risk of dental caries increases with the use of orthodontic appliances, and it does not only depend on a patient's oral hygiene. Caries cause teeth enamel demineralization close to the orthodontic bracket. The hardness of the teeth consequently decreases, and they become brittle and loose. The type of adhesive used to fix brackets may or may not reduce enamel demineralization. Previous studies have shown that a resin-modified glass ionomer (RMGI) inhibits demineralization. The purpose of this work is to evaluate the effect of a fluoride-releasing bracket on mechanical properties of dentin and enamel on regions adjacent to orthodontic brackets bonded with RMGI and composite resin cements. The remineralization effect due to fluoride on teeth was assessed by measuring hardness and reduced elastic modulus on dentin, enamel and dentin-enamel junction (DEJ) around the bracket area by nanoindentation methods. Nanoindentation was performed using a TriboScope from Hysitron. For this purpose two sets of polished samples were prepared: one sample was a cut along a longitudinal section and the other one along a cross-section of a tooth with orthodontic treatment using RMGI. Anisotropy in the mechanical properties of the teeth is observed along each direction.
Displacement Modulation Based Dynamic Nanoindentation for Viscoelastic Material Characterization
Authors: Singh Sehaj P. , Singh Raman P. , Smith James F. 
Published: April 2011

ABSTRACTThis paper demonstrates a new displacement modulation technique for using a depth sensing nanoindentation instrument to measure the dynamic mechanical properties of viscoelastic materials. For testing low modulus, high damping polymeric materials, dynamic nanoindentation offers several advantages over quasi-static testing. In this research, a model for the dynamic response of the system is proposed and shown to match well with experimental observations. A new calibration procedure, which involves the use of a variable cantilever spring, is employed to determine the damping characteristics of the testing frame as a function of excitation frequency. Using the proposed procedure dynamic nanoindentation tests are carried out on a viscoelastic material to determine the storage and loss moduli as functions of excitation frequency. Finally, a comparison with results from conventional testing (DMA) is provided.
On factors affecting the extraction of elastic modulus by nanoindentation of organic polymer films
Authors: Iacopi F. , Laknin M. , Mulloy A. , den Toonder J.M.J. , Vanhaeren D. , Brongersma S. H. 
Published: April 2011

ABSTRACTA detailed study of nanoindentation in Continuous Stiffness Mode (CSM) on a family of aromatic thermosetting polymers is carried out to identify the causes for the large variability in the extracted values of the elastic modulus of organic polymer films.It is shown that the variation of parameters determining the dynamics of the force application such as the CSM frequency, the actual strain or load rate, and the duration of the waiting time segments can lead up to 20% difference in the estimated elastic modulus. The reason for this is related to creep, more specifically to viscoelastic behaviour, typical of organic films. On the other hand, pile-up is shown to have a negligible effect on the extraction of the elastic modulus from indentation depths below 50% of the film thickness, even for films with hardness as low as 0.13GPa. It is also concluded that neither pile-up nor creep phenomena can account for the overestimation of the elastic modulus with nanoindentation as compared to the values extracted with the surface acoustic waves technique.
Some Issues of Rough Surface Contact Plasticity at Micro- and Nano-Scales
Authors: Gao Y. F. , Bower A. F. , Kim K.-S. 
Published: April 2011

ABSTRACTRough surface contact plasticity at microscale and nanoscale is of crucial importance in many new applications and technologies, such as nano-imprinting and nano-welding. This paper summarizes our recent progress in understanding contact plasticity from a multiscale point of view, and also presents our perspectives. We first discuss a contact model based on fractal roughness and continuum plasticity theory. Interestingly, our simple, elastic-plastic contact model of the Weierstrass-Archard type gives rise to many practical scaling relations of contact pressure, contact compliance etc. The usefulness of those predictions is discussed for experimental measurements of the thermal/electrical contact resistance. A material length scale can be introduced by a nonlocal plasticity theory, or implicitly by dislocation mechanics modeling. The recent work on micro-plasticity of surface steps gives a variety of surface yielding and hardening behaviors, depending on interface adhesion, roughness features and slip systems. As a consequence, a rough surface contact at mesoscale can lead to the formation of a boundary layer with sub-layer dislocation structures, which cannot be predicted by existing strain gradient plasticity theories. The micromechanical analysis of surface plasticity could serve as the connection between microscale bulk dislocation plasticity and nanoscale atomistic simulations.
Effect of Heat Treatments on Microstructure of Rapidly Solidified TiCo Ribbons
Authors: Yoshimi Kyosuke , Yamauchi Akira , Nakamura Ryusuke , Tsurekawa Sadahiro , Hanada Shuji 
Published: April 2011

ABSTRACTThe effect of heat treatments (aging or annealing) on microstructure was investigated for rapidly solidified ribbons of near-stoichiometric TiCo. In as-spun ribbons, it was observed by TEM that an equiaxed grain structure was developed and its crystal structure had been already B2-ordered, while a small amount of a second phase, Ti2Co, finely disperses in grains and along grain boundaries. Some grains were dislocation-free but others contained curved or helical dislocations and prismatic loops having a Burgers vector parallel to <100> directions. By annealing the as-spun ribbons at 700°C for 24h, the dislocation density was obviously increased compared with that of the as-spun ribbons, while grain growth appears to occur slightly. The increase of the dislocation density in the annealed ribbons is believed to result from the condensation and/or absorption of supersaturated vacancies. Therefore, the TEM observation results indicate that a large amount of supersaturated thermal vacancies were retained in the TiCo ribbons by the rapid solidification.
Pseudoelasticity of D03 Ordered Monocrystalline Fe3Al
Authors: Kabra S. , Bei H. , Brown D. W. , Bourke M.A.M. , George E. P. 
Published: April 2011

ABSTRACTPseudoelasticity in monocrystalline Fe3Al (23 at.% Al) was investigated by room-temperature mechanical testing along the <418> tensile and compressive axes. In tension, up to ∼10% strain is recoverable whereas only ∼5% strain is recoverable in compression. Straight, parallel, surface step lines were seen to appear/disappear as the specimens were pseudoelastically loaded/unloaded. In contrast, in the plastic region (ε >10%), wavy slip lines appeared on the specimen surfaces which did not disappear upon unloading. In-situ neutron diffraction was performed during compressive straining and the intensities of several diffraction peaks increase/decrease reversibly during loading/unloading. These changes are consistent with a deformation twin which produces large crystal rotations. They could also be indicative of a phase transformation. Unfortunately, we were able to sample only a limited range of 2θ in the present investigation and, within this range, none of the new peaks that appeared during the pseudoelastic deformation were disallowed peaks for the D03 crystal structure. Therefore we are unable at this time to distinguish between the two possible mechanisms, twinning and phase transformation.
Dislocation Structure, Phase Stability and Yield Stress Behavior of Ultra-High Temperature L12 Intermetallics: Combined First Principles-Peierls-Nabarro Approach
Authors: Kontsevoi Oleg Y. , Gornostyrev Yuri N. , Freeman Arthur J. 
Published: April 2011

ABSTRACTWe present results of comparative studies of the dislocation properties and the mechanical behavior for a class of intermetallic alloys based on platinum group metals (PGM) which are being developed for ultra-high temperature applications: Ir3X and Rh3X (where X = Ti, Zr, Hf, V, Nb, Ta). For the analysis of dislocation structure and mobility, we employ a combined approach based on accurate first-principles calculations of the shear energetics and the modified semi-discrete 2D Peierls-Nabarro model with an ab-initio parametrization of the restoring forces. Based on our analysis of dislocation structure and mobility, we provide predictions of temperature yield stress behavior of PGM-based intermetallics, show that their dislocation properties are closely connected with features of the electronic structure and the L12 → D019 structural stability, and demonstrate the dramatic difference in dislocation structure and the mechanical behavior between PGM alloys with IVA and VA group elements.
Role of Microstructure in Promoting Fracture and Fatigue Resistance in Mo-Si-B Alloys
Authors: Kruzic J. J. , Schneibel J. H. , Ritchie R. O. 
Published: April 2011

ABSTRACTAn investigation of how microstructural features affect the fracture and fatigue properties of a promising class of high temperature Mo-Si-B based alloys is presented. Fracture toughness and fatigue-crack growth properties are measured at 25° and 1300°C for five Mo-Mo3Si-Mo5SiB2 containing alloys produced by powder metallurgy with α-Mo matrices. Results are compared with previous studies on intermetallic-matrix microstructures in alloys with similar compositions. It is found that increasing the α-Mo phase volume fraction (17 – 49%) or ductility (by increasing the temperature) benefits the fracture resistance; in addition, α-Mo matrix materials show significant improvements over intermetallic-matrix alloys. Fatigue thresholds were also increased with increasing α-Mo phase content, until a transition to more ductile fatigue behavior occurred with large amounts of α-Mo phase (49%) and ductility (i.e., at 1300°C). The beneficial role of such microstructural variables are attributed to the promotion of the observed toughening mechanisms of crack trapping and bridging by the relatively ductile α-Mo phase.
Comparison of temperature driven ordering in bulk foil and thin film of L10ordered FePd
Authors: Issro Chaisak , Püschl Wolfgang , Pfeiler Wolfgang , Sepiol Bogdan , Rogl Peter F. , Soffa William A. , Acosta Manuel , Pierron-Bohnes Véronique 
Published: April 2011

ABSTRACTChanges in the degree of long-range order of 10 μm thick FePd foil are presented and compared with results on 50 nm thick FePd films. The films were produced by dc and rf magnetron co-sputtering on Si as well as by molecular beam epitaxy co-deposition on MgO substrates. Long-range order was studied by electrical resistivity measurement, X-ray diffraction and Möβbauer spectroscopy.
Shape Memory Effect through L10-fcc Order-Disorder Transition
Authors: Tanaka K. 
Published: April 2011

ABSTRACTShape memory effect not associated with martensitic transformation but with order-disorder phase transformation is examined in the compounds of AuCu, CoPt and FePd. These exhibit the L10-fcc transition at 680K, 1060K and 950K, respectively, which is relatively high temperature. Under a uniaxial compressive stress, a reversible shape change (reduction and elongation in edge length) is observed by cooling and heating the specimen temperature. The elongation of the specimen associated with the disordering occurs at their equilibrium transition temperatures, and the reduction along the direction of a compressive stress associated with the ordering occurs at a certain supercooled temperature. A trial actuator constructed with FePd polycrystalline wire and a conventional inconel wire properly works by heating up and cooling down the temperature.
Directional Thermoelectric Performance of Ru2Si3
Authors: Simkin Benjamin A. , Hayashi Yoshinori , Inui Haruyuki 
Published: April 2011

ABSTRACTThe orthorhombic compound Ru2Si3 is currently of interest as a high-temperature thermoelectric material. In order to clarify the effects of crystal orientation on the thermoelectric properties of Ru2Si3, we have examined the microstructure, Seebeck coefficient, electrical resistivity, and thermal conductivity of Ru2Si3 along the three principal axes, using these measured quantities to describe the relative thermoelectric performance as a property of crystal orientation. Ru2Si3 undergoes a high temperature (HT)→low temperature (LT) phase change and polycrystalline Si platelet precipitation during cooling, both of which are expected to effect the thermoelectric properties. The HT tetragonal→LT orthorhombic phase transformation results in a [010]//[010], [100]//[001] two-domain structure, while polycrystalline Si precipitation occurs on the (100)LT and (001)LT planes. The [010] orientation is found to posses superior thermoelectric properties (with the dimensionless figure of merit, ZT[010]/ZT[100]>4 at 650°C), due principally to the larger Seebeck coefficient along the [010] direction. The effect of the domain structure on the thermoelectric properties is discussed.
B2 Phases and their Defect Structures: Part I.I. Ab initio Vibrational and Electronic Free Energy in the Al-Ni-Pt-Ru System
Authors: Arroyave Raymundo , Prins Sara , Liu Zi-Kui 
Published: April 2011

ABSTRACTIn this work, we calculate the finite temperature thermodynamic properties of the binary B2 phases in the Al-Ni-Pt-Ru system, particularly the B2 RuAl phase in the Pt-Al-Ru ternary, through the incorporation of the vibrational and electronic contributions to the total free energy. The harmonic approximation is used to consider the atomic vibrations, with the quasi-harmonic correction to account for volume expansion effects on the vibrational entropy as the temperature increases. The vibrational entropy calculations are incorporated through the supercell approach. The calculated phonon dispersion curves show that the B2 PtRu structure is mechanically unstable at low temperatures, while B2 PtAl is marginally stable. The thermal electronic contribution is added to the total free energy. Finally, the formation enthalpies and entropies of B2 RuAl are calculated as a function of temperature.
Microstructure and Mechanical Properties of Fe-Ni-Mn-Al Alloys
Authors: Wittmann M. W. , Baker I. , Hanna J. A. 
Published: April 2011

ABSTRACTIn an attempt to produce a two-phase alloy consisting of a L21–structured (Fe, Ni)2MnAl-based phase in either a B2 or b.c.c. matrix, seven Fe-Ni-Mn-Al alloys were cast. Transmission electron microscopy (TEM) of the as-cast alloys revealed a range of microstructures including single phase L21, a f.c.c./B2 eutectic, and alternating, coherent 10–60 nm wide ordered and disordered b.c.c. rods aligned along <100>. A description of the phases, including chemical compositions and hardnesses is presented.
Crystal Structure, Phase Stability and Plastic Deformation Behavior of Ti-rich Ni3(Ti, Nb) Single Crystals with Various Long-Period Ordered Structures.
Authors: Hagihara Koji , Tanaka Tetsunori , Nakano Takayoshi , Umakoshi Yukichi 
Published: April 2011

ABSTRACTIn Ni-Ti-Nb ternary system, there are some geometrically close-packed (GCP) phases with long-period stacking sequences of a close-packed plane (CPP). Among them, our focus is on the Ni3(Ti0.90Nb0.10) crystals with Pb3Ba-type rhombohedral structure with nine-fold stacking sequence. Compression tests were conducted using the single crystals and the temperature and orientation dependences of plastic deformation behavior were investigated in comparison with those of D024-Ni3Ti crystals with the four-fold stacking sequence. The K-W locking of screw dislocation was found to occur not only in the compounds such as Ni3Al and Ni3Ti with a relatively small unit cell, but also even in complex compounds with longer-period stacking structures by slip on the common CPP in the GCP structures.
Compressive Creep Behavior in Coarse Grained Polycrystals of Ti3Al and its Dependence on Binary Alloy Compositions
Authors: Takahashi Tohru , Sakaino Yuki , Song Shunzi 
Published: April 2011

ABSTRACTCompressive creep behavior has been investigated on coarse grained Ti3Al alloys with aluminum contents ranging from 15mol%Al to 42mol%Al, in order to obtain basic information concerning the chemical composition effect on creep of Ti3Al. Pure aluminum and titanium of 99.99% purity were arc-melted into small ingots weighing about 10grams under an argon atmosphere. The resulting microstructures after the hot deformation and vacuum annealing contained equiaxed grains whose average diameter ranged from 125 to 192 micrometers except alloys containing 40 and 42 mol% aluminum.Compressive creep tests were performed in vacuum on parallelepiped specimens with dimensions of 2mm×2mm×3mm. The applied compressive stress was 159MPa, and the test temperature was around 1200K.A very small primary transient and the minimum creep rate region followed by a gradual creep acceleration were observed in the materials containing aluminum up to 25mol%. In contrast to this, the materials containing more aluminum than 25mol% showed greater primary transient where creep deceleration continued up to about 0.1 true strain. Dual phase materials containing the γ phase showed small primary transient probably due to the constraint from the γ phase.
Formation of Defect Structures during Annealing of Cold-deformed L10-ordered equiatomic FePd Intermetallics
Authors: Deshpande Anirudha R. , Wiezorek Jörg M.K. 
Published: April 2011

ABSTRACTPlanar defects produced in L10-ordered FePd during annealing after cold-deformation in the disordered cubic state have been characterized by transmission electron microscopy (TEM). The defects evolving during annealing include arrays of overlapping stacking faults (SF's), {111}-conjugated microtwins (μT's) and thermal antiphase boundaries (APB's). The defect formation mechanisms proposed here are similar to twinning mechanism reported for FCC-metals during annealing. Thus, SF arrays and faulted μT's in the L10-ordered FePd appear to form during the early stages of annealing by atomic attachment faulting on {111}-facets of the transformation interfaces. During later stages of annealing the reduced amount and the change in nature of the driving forces for the microstructural rearrangement result in changes in the predominant defect formation mechanism. The features of the defect genesis in L10-FePd are discussed with respect to solid-state transformations during processing of these ferromagnetic intermetallics.
On the Effects of Interstitial Elements on Microstructure and Properties of Ternary and Quaternary TiAl based alloys
Authors: Chevalier Jean-Pierre , Lamirand Mélanie , Bonnentien Jean-Louis 
Published: April 2011

ABSTRACTTi-Al-Cr ternary and Ti-Al-Cr-Nb quaternary alloys have been studied as a function of initial purity and added interstitial content. Using strict clean processing together with either ultra high purity or commercial purity alloys, the effects of interstitial elements (essentially O, but also C and N) on microstructure and hardness, yield stress and fracture strain have been studied for both fully lamellar microstructures and duplex microstructures. The results are clear and similar trends are observed : as long as they do not precipitate, these stabilise the lamellar microstructure and affect the kinetics of the α-γ phase tranformation, leading to a higher than equilibrium value for the α2phase for continuous cooling. Both the lamellar spacing and the α2phase fraction correlate with increased hardness and yield stress, and also with decreasing fracture strain. The effects are significant.
Effect of B Addition on Thermal Stability of Lamellar Structure in Ti-47Al-2Cr-2Nb Alloys
Authors: Yamamoto Y. , Evans N. D. , Maziasz P. J. , Liu C. T. 
Published: April 2011

ABSTRACTThermal stability of fully lamellar microstructures in Ti-47Al-2Cr-2Nb (at.%) alloys with and without B additions has been evaluated in the temperature range of 800 to 1200°C. The alloy with 0.15B exhibits an α2 + γ fully lamellar microstructure containing ribbon-like structures (TiB2+β) inside the lamellar colonies. During aging at 800 and 1000°C, β particles surrounded by γ grains form adjacent to the ribbon-like structures. The formation of these grains is attributed to the precipitation of thin plate-like β phase along {1100} within the TiB2 ribbon particles, resulting in the loss of α2 plates around the ribbon-like structure by scavenging Ti. This allows coarsening γ lamellar plates to form new γ grains, and then the ribbon-like structure completely dissolves to leave only β particles. At 1200°C, discontinuous coarsening (DC) of the lamellae becomes the dominant mode of microstructural change for all the alloys. However, the ribbon-like structures in the alloy with B additions play a role in pinning the DC cells, which leads to higher thermal stability of the lamellar microstructure in that alloy.