bluuebunny/crossref_metadata_2025_split huggingface dataset:
Behavio of Supeaplastically Extruded Cu-26wt%Zn–3.5wt%Al Shape Memory Alloy
Authors: Zhengyt Zheng , Weijian Zhcng , Fuzeng Lin , Yingsheng Chew 
Published: March 2011

ABSTRACTThe influence of superplastic extrusion on the microstructures and the shape memory effect of the Cu-Zn-Al shape memory alloys has been investigated. The shape memory alloy Cu-26%wt%Zn-3.5wt%Al is superplastio with an index of strain rate sensitivity n = 0.48 at 600°C, at a strain of . After extrusion under the superplastio condition the miorostruotures are improved and no cavities are observed. The superplastically extruded specimens of this alloy were heat-treated to obtain the shape memory effect. These specimens indicate that no deterioration of shape memory effect of the alloy is induced by the superplastio extrusion and the shape memory effect of the alloy is somewhat improved.
Dissipative Structures and Superplasticity
Authors: Chen Hechun , Smith Reginald W. , Shi Jiwei , Zhengheng Yang 
Published: March 2011

ABSTRACTThe characteristics of superplasticity are discussed from the viewpoint of irreversible thermodynamics, in particular, system evolution and the formation of dissipative structures. A mathematical model combining determinism with indeterminism is used to analyze plastic deformation and superplasticity in metals. Since the plastic deformation of a metal is in essence a dissipative process occurring in a system far away from thermodynamic equilibrium, the instability of the system resulting from structure fluctuations (defects) and thermodynamic bifurcations (possible thermodynamic states) will result in many deformation mechanisms being available to provide the deformation observed in the system. Thus it is virtually impossible to describe all the possible models in conventional terms i.e. by the application of the method of determinism. A new model is proposed, and is shown to account for much of the experimental data reported.
Dynamic Grain Growth in Superplastic Y-TZP and Al2O3/YTZ
Authors: Nieh T. G. , Tomasello C. M. , Wadsworth J. 
Published: March 2011

ABSTRACTBoth static and dynamic grain growth have been studied during superplastic deformation of fine-grained yttria-stabilized tetragonal zirconia (Y-TZP) and alumina reinforced yttria-stabilized tetragonal zirconia (Al2O3/YTZ). Grain growth was observed in both materials at temperatures above 1350° C. In the case of Y-TZP, both static and dynamic grain growth were found to obey a similar equation of the form: where D is the instantaneous grain size, Do is the initial grain size, t is the time, and k is a kinetic constant which depends primarily on temperature and grain boundary energy. The activation energies for Y-TZP were approximately 580 and 520 kJ/mol, for static and dynamic grain growth, respectively. In the case of Al2O3/YTZ, it was found that the grain growth rate for the Al2O3 phase was slower than that for the ZrO2 phase. The growth rate of the ZrO2 phase in Al2O3/YTZ is, however, similar to that in monolithic ZrO2, i.e., Y-TZP.
Mechanical Behavior and Cavitation in Commercial and High Purity Zn-22% Al
Authors: Park Kyung-Tae , Earthman James C. , Mohamed Farghalli A. 
Published: March 2011

ABSTRACTAn investigation was conducted on the superplastic Zn-22% Al alloy to examine the effect of impurity level on mechanical behavior and cavitation in the alloy. In conducting the investigation, three grades of Zn-22% Al containing different levels of impurities (6 ppm, 100 ppm, and 180 ppm) were used. The results show that the deformation behavior of Zn- 22% Al at low stresses is influenced by the impurity level of the alloy, and that the extent of cavitation increases with increasing impurity content. These two findings lend support to the concept of attributing low-stress superplastic deformation to strong impurity segregation at boundaries.
Is Superplasticity in the Future of Nanophase Materials?
Authors: Siegel R. W. 
Published: March 2011

ABSTRACTThe ultrafine grain sizes and high diffusivities in nanophase materials assembled from atomic clusters suggest that these materials may have a strong tendency toward superplastic mechanical behavior. Both small grain size and enhanced diffusivity can be expected to lead to increased diffusional creep rates as well as to a significantly greater propensity for grain boundary sliding. Recent mechanical properties measurements at room temperature on nanophase Cu, Pd, and TiO2, however, give no indications of superplasticity. Nonetheless, significant ductility has been clearly demonstrated in these studies of both nanophase ceramics and metals. The synthesis of cluster-assembled nanophase materials is described and the salient features of what is known of their structure and mechanical properties is reviewed. Finally, the answer to the question posed in the title is addressed.
Processing of Nanocrystalline Ceramics
Authors: Ciftcioglu Muhsin , Mayo Merrilea J. 
Published: March 2011

ABSTRACTMethods of preparing non-agglomerated powders for three systems -- yttria, titania, and yttria-stabilized zirconia -- are reviewed. The non-agglomerated nature of these powders should make it possible to sinter them into dense ceramic bodies with nanocrystalline grain sizes. Experiments with yttria-stabilized zirconia have shown that this is indeed the case, with mean linear intercept grain sizes of 60 nm resulting from original powder particle diameters of 13 nm. This ultrafine-grained zirconia is shown, in turn, to have superplastic forming rates 34 times faster than a 0.3 μm-grained commercial zirconia of the same composition.
Grain Growth During Sintering of Nanocrystalline Y and/or CE-Doped Tetragonal Zirconia
Authors: Boutz Michel M. R. , Theunissen G. S. A. M. , Winnubst A. J. A. , Burggraaf A. J. 
Published: March 2011

ABSTRACTA non-isothermal analysis of grain growth in tetragonal zirconia ceramics doped with various amounts of yttria and/or ceria in the temperature range 700–1150°C is presented. In these nanocrystalline ceramics, prepared by the gel precipitation technique, two grain growth regimes are recognized. At temperatures up to 900–1000°C grain growth proceeds slowly at high values of porosity (55%→35%); probably by means of a surface diffusion mechanism. At higher temperatures grain growth is much faster and occurs in locally dense regions by a normal grain growth or an impurity drag mechanism. Apparent activation energies are given for five compositions in both regimes.The isothermal sintering behavior of 3 mol% Y2O3-containing TZP at 1050°C is analysed. A dense ceramic with a crystallite size in the nanometer regime (< 100nm) is obtained.
The Role of Dislocations in the Superplastic Deformation of a Duplex Stainless Steel
Authors: Parayil T. R. , Dunlop G. L. , Howell P. R. 
Published: March 2011

ABSTRACTTransmission electron microscopy (TEM) has been employed to examine the role of dislocations in the superplastic deformation of a duplex stainless steel. In particular, matrix, grain boundary and interphase interface dislocation distributions have been documented after testing in region II. It is concluded that dislocation activity is of importance during superplastic flow and both loop sources and dislocation pile-ups have been observed. The presence of highly distorted dislocation arrays also suggests that grain and interphase boundary sliding is intimately linked to the motion of grain and interphase boundary dislocations. Finally, it is argued that dislocation multiplication in interphase interfaces can involve the operation of loop sources.
Application of a Continuous Annealing Process to the Production of Superplastic High-Carbon Steels
Authors: Seto K. , Kato T. , Abe H. 
Published: March 2011

ABSTRACTHigh-carbon steels with carbon content of more than 0.8wt% have been known to be superplastic by refining their microstructure. Many methods such as warm rolling have been proposed to refine the microstructure. But most of them are considered to be difficult to use as an actual production method. To make high-carbon steels superplastic and economical, application of a cold rolling and continuous annealing process has been examined.Changes in microstructure of high-carbon hot rolled steels during the cold rolling and continuous annealing was investigated. By cold rolling with a reduction of more than 50%, a lamellar pearlite structure is deformed and heavily sheared, and a large strain energy is stored. Rapid annealing at temperatures just below the A1 temperature(1000K) is shown to spheroidize the sheared pearlite and to recrystallize the ferrite grains. After processing, the final structure consists of very fine cementite particles with 0.05–0.2μm diameter in a very fine equiaxed ferrite matrix with 0.1–0.5μm diameter. The processed steel shows total elongations of more than 700% and a strain rate sensitivity index of about 0.5 when deformed at 973K.
On the Interaction Between Moisture and Wood Fibre Materials
Authors: Salmén Lennart 
Published: March 2011

ABSTRACTThe effect of water on wood fibre materials is described from the standpoint of how the water is absorbed by the individual wood polymers. The main influence on physical properties are thus associated with water acting as a plasticizing agent for lignin and carbohydrates. Effects of drying restraints on paper are discussed in relation to a molecular orientation of the constituent polymers, made possible in the vicinity of the water-induced softening points.
An Investigation of Factors Effecting Coating Structure
Authors: Kline James E. 
Published: March 2011

ABSTRACTThe properties of coatings have been studied on a theoretical level using model systems of spherical polymeric pigments applied to a mylar substrate. Using binderless coatings, the expected void filling, gloss and light scattering relationships to particle size and polydispersity were observed. The addition of binders to the coatings yields results which depart from those expected and observed without binders. These results have led to two seemingly opposed views that the binder either coats the pigment and causes expansion of the structure or fills the voids without greatly effecting the pigment structure. Pigment blends were selected which were expected to show a difference between the two conflicting theories, and starch and latex binders added. The data obtained failed to favor one theory over the other, indicating that both are probably operative. Greater decreases in gloss were observed with the polymeric pigments, probably due to an undesirable interaction between the pigments and binders causing agglomeration of the coating materials and severe disruption of the coated surface. The data obtained is reviewed in light of the “real world” behavior of paper coatings to examine reasons why the theoretical contributions of pigments and binders are not often observed.
Materials Science of Lignocellulosics
Authors: Rowell Roger M. 
Published: March 2011

ABSTRACTWood and other lignocellulosics have been used as “engineering materials” because they are economical, low in processing energy, renewable, and strong. In some schools of thought, however, lignocellulosics are not considered “materials” in that they do not have consistent, predictable, reproducible, continuous, and uniform properties. This is true for solid lignocellulosics such as wood, but not necessarily true for composites made from lignocellulosics. The chemistry of the components of lignocellulosics can be modified to produce a material with consistent, predictable, and uniform properties. Properties such as dimensional instability, biodegradability, flammability, and degradation due to ultraviolet light, acids, and bases can be altered to produce property-enhanced composites.
Preparation of In Situ Magnetically Loaded Cellulose Fibers
Authors: Ricard Serge , Marchessault Robert H. 
Published: March 2011

ABSTRACTMagnetic paper handsheets with pigment loadings in the order of 10–30%, depending on the experimental conditions, have been made using the established “lumen-loading” technology. These sheets have bulk magnetic properties comparable with the computer floppy-disk products. In order to minimize the particle size of pigments and thereby explore a new level of optical and magnetic properties, in situ synthesis of pigment particles is a second approach. This chemistry starts with a carboxymethylcellulose substrate with ion-exchange properties for Fe(ll). The substrates, before and after oxidation reactions to produce ferrite particles, are characterized by: conductimetric titration, x-ray diffraction, thermogravimetric analysis, and magnetization determination. Electron microscopy and diffraction provide insight on the ferrite morphologicals. These specialty fibers allow exploration of new concepts in papermaking, information storage, security printing and paper handling.
The Structures of Cellulose
Authors: Atalla Rajai H. 
Published: March 2011

ABSTRACTThis report presents an overview of studies on the structures of cellulose. After presenting a brief historical perspective, the report reviews diffractometrically based structural models and then describes recent developments based on models that are consistent with both diffractometric and spectroscopic observations. The primary impetus for development of these models was provided by Raman and 13C NMR (CP-MAS) spectral results that could not be rationalized on the basis of classical structural models, which are constrained by diffractometric data alone. The structures derived from integrating the spectral information into the data base, which constrain the models, represent relatively small but very significant departures from those structures derived on the basis of diffractometry alone. In addition to rationalizing all the structurally sensitive information, the new models provide a basis for complementary use of spectroscopic and diffractometric methods to monitor variations of the states of aggregation of celluloses with source and history. Thus, it is now possible to investigate the effects of different processing variables, which are important in industrial practice, on both secondary and tertiary levels of structure in celluloses. These levels of structure have a major influence on the material properties of commercial celluloses, yet adequate characterization of these levels has been quite elusive.
Heteroepitaxy Between Lattice Mismatched Materials with Van Der Waals Interactions
Authors: Koma Atsushi 
Published: March 2011

ABSTRACTThe lattice matching condition encountered usually in the heteroepitaxial growth has been proved to be relaxed drastically, if one uses the interface having van der Waals nature. Such interface can be realized on a cleaved face of a layered material or a quasi-one dimensional material and on a surface of a dangling-bond-terminated three dimensional material. Various kinds of heterostructures, which cannot be made by conventional growth methods, can be fabricated by using a variety of layered transition metal dichalcogenides, in which there exist superconducting, metallic, semiconducting or insulating layered materials. Moreover those heterostructures have been found to be grown on such an ordinary three-dimensional material as GaAs, if the dangling bonds on its surface are terminated by suitable atoms.
Dislocation Arrays in Epitaxial Interfaces.
Authors: Beanland R. , Pond R. C. 
Published: March 2011

ABSTRACTA method for analysing the form of dislocation arrays which accommodate misfit at epitaxial interfaces based on the Frank-Bilby expression of the dislocation content of an interface is presented. Emphasis is placed on the deformation of a crystal in the presence of a dislocation array, and ease of formulation through use of an orthogonal reference frame. Several aspects of epitaxial growth are subsequently addressed, including the uniqueness of a dislocation array accommodating a given misfit. In the case of growth on vicinal cubic surfaces, it is shown that dislocations generated to relieve misfit may also lead to misorientation of the overlayer. From experimental measurements of dislocation densities using transmission electron microscopy, it is possible to calculate the state of strain in a metastable misfitting epitaxial layer. When misfit is not isotropic in the interface (such as for silicon or niobium grown on sapphire) it is shown that dislocation line directions may not lie along low index directions in either crystal, a point which is particularly important with regard to studies of interfacial structure by high resolution electron microscopy.
Characteristics of Mocvd-Grown AlGaAs/GaAs Sqw Lasers and GaAs Mesfetsfabrication on Si Substrate with SiO2-Back Coating
Authors: Egawa Takashi , Tada Hitoshi , Kobayashi Yasufumi , Nozaki Shinji , Soga Tetsuo , Jimbo Takashi , Umeno Masayoshi 
Published: March 2011

ABSTRACTWe discuss room temperature CW operation of AlGaAs/GaAs SQW lasers and GaAs MESFETs with good pinch-off characteristic on SiO2 -back coated Si. The all-MOCVD-grown,SQW laser on Si with thermal-cycle annealing, which has the EPD of 1.5 × 107 cm−2, has the threshold current as low as 55 mA (1.41 kA/cm2) under CW operation at room temperature. The pinch-off and the sidegating effect characteristics of GaAs MESFETs on Si have been improved by using SiO2-back coating of Si and higher growth temperature. The maximum transconductance of 160 mS/mm has been obtained for the MESFET with a 2.5 × 15 µm gate. The main origin of sidegating effect associates with the channel layer-undoped GaAs layer beneath it interface. The SiO2 -back coating is found effective to obtain a lower background electron concentration in undoped GaAs layer and to control doping of the active layer in GaAs/Si.
Study of the Tnfluence of Structural Properties on Si and Be Doping of Heteroepitaxial InAsSb on GaAs-Coated Si Substrates for Infrared Photodiodes
Authors: Boeck J. De , Dobbelaere W. , Hove M. Van , Vanhellemont J. , Raedt W. De , Vandervorst W. , Mertens R. , Borghs G. 
Published: March 2011

ABSTRACTThe behavior of Si and Be impurities in InAsx Sb1−x (0.05<x<0.45) heteroepitaxial layers grown on GaAs-coated Si by MBE is characterised. Siis found to act as an n-type dopant for the growth conditions used. The calibration of the Si n-type doping as a function of the Sisource temperature is obtained by infrared absorption spectrometry, stripping Hall and SIMS depth profiling. At high doping levels the amphoterical characterof the Si impurities becomes evident. SIMS is used to investigate the dopant incorporation and the formation of diode structures. The influence of the mismatched epitaxy on the transport properties is investigated by stripping Hall measurements. In order to establish the correlation between crystalline properties of the epilayers and the ability to fabricate diodes, we compare the defect structure of InAs and In(As)Sb p-'i'-n diodes.
Buried Metal/III-V Semiconductor Heteroepitaxy: Approaches to Lattice Matching
Authors: PalmstrØM C.J. , Harbison J. P. , Sands T. , Ramesh R. , Finstad T. G. , Mounier S. , Zhu J.G. , Carter C.B. , Florez L.T. , Keramidas V.G. 
Published: March 2011

ABSTRACTMetallic transition metal aluminides and gallides with the CsCI structure and semi-metallic rare earth monopnictides with the NaCi structure have been grown as buried conducting layers in III-V compound semiconductor heterostructures. The criteria for achieving (100) oriented epitaxial growth on (100)111-V semiconductor surfaces is different for each class of materials. The methods used to achieve III-V/metal/llI-V heteroepitaxial structures are discussed here with emphasis on the different approaches needed for the aluminides or gallides and the monopnictides. Work producing exact lattice matching between the buried metal and surrounding semiconductor layers makes possible the separation of lattice mismatch effects from those due to other interface parameters. Results to date indicate that defect structures in the overgrown semiconductor layers arise more because of differences in crystal symmetry, interface chemistry and bonding across the interface than lattice mismatch.
The Influence of Initial Growth on Defect Generation in Mocvd Grown GaAs/Si Heteroepitaxial Layers
Authors: George T. , Weber E.R. , Nozaki S. , Wu A.T. , Umeno M. 
Published: March 2011

ABSTRACTThe structural quality of GaAs/Si layers deposited directly at the normal growth temperatures (650°C,750°C) is compared with that of layers grown by the standard two-step growth process using Metalorganic Chemical Vapor Deposition (MOCVD). The directly grown layers are highly twinned and polycrystalline in nature whereas the two step growth process produces single crystal layers even at growth temperatures as high as 800°C. The origin of these effects is related to the initial growth of the GaAs, which is in the form of highly defective separate islands, for the case of direct growth, and connected single crystal islands for the case of two-step growth. The directly grown islands exhibit a “ripening” type behavior, with a strong dependence of the Si substrate surface coverage by the GaAs layer, on the growth temperature. The generation of structural defects such as stacking faults and microtwins, which destroy the epitaxial relationship could be triggered by the presence of surface imperfections on the Si substrate.
GaAs Heteroepitaxy on Substrate-Engineered Silicon Using SixGe1–x Multilayer Structures
Authors: Posthill J.B. , Venkatasubramanian R. , Malta D.P. , Hattangady S.V. , Fountain G.G. , Timmons M.L. , Markunas R.J. 
Published: March 2011

ABSTRACTThe novel concept of using a SixGe1–x multilayer structure as a buffer layer between a silicon substrate and a GaAs epitaxial layer to accommodate the GaAs/Si 4.1% lattice mismatch is introduced. Initial results using a 340 nm trilayer SixGe1–x multilayer structure are presented and are critically assessed. Significant potential is demonstrated, and the work to date indicates that certain guidelines and procedures must be adhered to for this method of threading dislocation reduction to be effective.
Nucleation and Defect Structures of GaAs Films Grown on Reactive Ion Etched Si Substrates
Authors: Lee Henry P. , George Thomas , Sohn Hyunchul , Tu Jay , Weber Eicke R. , Wang Shyh 
Published: March 2011

ABSTRACTThe nucleation and interfacial defect structure of thin GaAs films grown on reactive ion etched Si substrates by normal molecular beam epitaxy (MBE) and modulated molecular beam epitaxy (MMBE) at 300°C were studied by plan view and high resolution cross-sectional electron microscopy (TEM). Plan view TEM micrographs show a pronounced three-dimensional (3-d) island type nucleation for the MBE grown sample. A high density of microtwins is also found in these nucleated islands from high resolution cross-sectional TEM micrographs. The 3-d nucleation and the interfacial twinning is suppressed however in the MMBE grown samples. The FWHM of the (400) Bragg peak for 3 μm thick GaAs on Si films shows a reduction of 60 arcseconds when the initial buffer layer is grown by MMBE as compared to normal MBE.
Semiconductor Resonant Tunneling Device Physics and Applications
Authors: Reed Mark A. , Seabaugh Alan C. , Kao Yung-Chung , Randall John N. , Frensley William R. , Luscombe James H. 
Published: March 2011

ABSTRACTA discussion of resonant tunneling physics in both diode and transistor heterojunction structures is presented. It is evident the In(GaAI)As/InP system is significantly superior for this application. We also present results on resonant tunneling in lower dimensional systems.