bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Effect of Cerium on Superplasticity of AL-6CU-0.35 MG-0.2ZR Alloy
Authors: Jingtao Wang , Qingling Wu , Jianzhong Cul , Haitao Zhou 
Published: March 2011

ABSTRACTThe effect of Cerium addition on the superplasticity of Al-6Cu-0.35Mg-O.2Zr alloy is investigated. The superplastic elongation of the alloy is increased from 450% to 500–700% by the addition of 0.5wt% Cerium, with some decrease in superplastic tensile resistance, when the alloy is deformed at 789K(516°C) with a strain rate of 8.33×10−4S−1. Microstructure observation shows that the addition of Cerium decreases the grain growth rate both in static annealing and during superplastic deformation. This is considered to be the result of the enhanced pinning of fine Zirconium-rich precipitates and the additional pinning of Cerium-rich phase particles. TEM and X-ray diffraction analysis show that Cerium in the alloy forms Cerium-rich phases (AlgCu4Ce and Al4CuCe), and these phase particles join in the pinning of second phase particles on grain boundary, stablizing the microstructure. The addition of Cerium also affects the distribution of Zirconium and Zirconium Aluminide in the alloy.
Observations on Historical and Contemporary Developments in Superplasticity
Authors: Sherby Oleg D. , Wadsworth Jeffrey 
Published: March 2011

ABSTRACTThe history of superplasticity is reviewed. The first scientific observation of superplasticity dates back to 1912. Sporadic reports of subsequent observations appear in the literature up to the review by Underwood in 1962. Since that time there have been a number of milestone achievements that have propelled the technology of superplasticity forward. These include commercial developments based on nickel, titanium, iron, and aluminum alloys. In more recent times the advent of superplasticity in ceramics and intermetallics has stimulated yet further interest in the field. At the present time there are major research efforts underway in the USA, USSR, Japan, China, and Europe to apply superplastic forming technology to the manufacture of complex components.
Microstructures, Grain Boundaries and Superplasticity in Fine Grained Ceramics
Authors: Carry C. 
Published: March 2011

ABSTRACTDeformation studies in compression and in tension have clearly shown evidence for superplasticity for a wide range of fine grained ceramics from both macroscopic and microscopic points of view. The main purpose of this paper is to focus attention on chemical effects in ceramic grain boundaries which can lead to a great variety of behavior. Grain boundary segregation or precipitation, residual impurities or doping elements, and glassy or liquid phases at grain boundaries can strongly affect the macroscopic flow properties of superplastic fine grained ceramics. Some microstructural and grain boundary features, mainly in two oxide materials (alumina and yttria doped zirconia), are analyzed, compared, and discussed in connection with their observed superplastic behavior. Special attention is devoted to the relation between the overall chemistry of the materials (impurities and doping elements) and to the grain boundary structure and chemistry (segregation, precipitation, intergranular phases). Some consequences and implications on the tailoring of ceramic microstructures for superplasticity are discussed. In addition, some recent hot forming and hot bonding experiments are also reported.
An Investigation of the Mechanical Behavior of a Superplastic Yttria-Stabilized Zirconia
Authors: Ma Yan , Langdon Terence G. 
Published: March 2011

ABSTRACTExperiments were conducted to determine the mechanical characteristics of an yttria-stabilized tetragonal zirconia containing 3 mol % Y2O3. Specimens were pulled in tension at elevated temperatures over a range of strain rates. It is demonstrated that this material exhibits good superplastic ductility, with tensile elongations >100% when the tests are conducted at low strain rates. Internal cavities are formed during deformation and it is shown that the cavitated area decreases with decreasing strain rate. At fast strain rates, of the order of 10−3 s−1, the cavities tend to link preferentially in a direction perpendicular to the tensile axis.
Superplastic Properties of Hipped and Extruded Iron Carbide
Authors: Kim W. J. , Ruano O. A. , Wolfenstine J. , Frommeyer G. , Sherby O. D. 
Published: March 2011

ABSTRACTHipped and extruded materials were prepared from atomized-powders containing 5.25C, 1.5Cr and balance Fe. The materials consist of a matrix of 80 volume percent of iron carbide and 20 volume percent of a discontinous iron base phase. Both processed materials were reduced in thickness (6:1) at 720°C. The grain size was about 2 μm for the hipped-and-pressed material and about 4 μm for the extruded-and-pressed material. Compression tests were used to evaluate the strain-rate-sensitivity exponent, m, in the temperature range from 725°C to 950°C, over the strain rate range of 10−5 to 2 × 10−2 s−1. The as-hipped material does not exhibit superplastic behavior because the grain shape is not equiaxed. At low stresses, in the superplastic range (m≈0.5), the hipped-and-pressed material was weaker than the extruded-and-pressed material as a result of the fine grain size. At high stresses, when slip dominates the deformation process, m is about 0.2 and a reversal in the relative strength is obtained. Tensile tests were performed and elongations in excess of 600% were achieved. The hipped-and-pressed material was shown to be more ductile than the extruded-and pressed-material which is attributed to its fine grain size.
Superplastic Hobbing of Die Cavity and Its Numerical Simulation
Authors: Kaifeng Zhang , Wang Z. R. , Dianjian Guo , Yanwu Xu 
Published: March 2011

ABSTRACTIn this paper, the superplastic and isothermal hobbing process for manufacturing die cavities is described. The technical parameters, the design method of the set-up and the lubrication are also mentioned. Recently, these technologies have been applied in hobbing automobile link rod dies and other parts. By means of finite element analysis and experiments, the deformation paramaters for superplastic hobbing are obtained. They can be used in determining the process and choosing the blank sizes.
A Re-Appraisal of Cavity Growth Processes in Superplasticity
Authors: Ma Yan , Langdon Terence G. 
Published: March 2011

ABSTRACTIt is well known that cavities are nucleated and grow during the superplastic deformation of many materials. The various theories for cavity growth are examined with special emphasis on the role of growth by diffusion. It is demonstrated that the normal model for the diffusion growth of cavities is inadequate for superplastic materials when the grain boundary lengths are very small. By developing a new model for the growth of an isolated cavity to sizes exceeding the grain size, it is shown that the diffusion process may play a major role in cavity growth under a range of experimental conditions.
Lignins: Structure and Distribution in Wood and Pulp
Authors: Obst John R. 
Published: March 2011

ABSTRACTLignin is the stuff that makes trees “woody.” Usually constituting from one-fifth to one-third of wood, lignin strongly influences its chemical and physical properties. A major use of wood is for the production of pulp for paper and paperboard products. The residual lignin in pulp fibers greatly affects paper properties and, therefore, the uses of these pulps.Lignin is a rather unusual substance. Polymerized through radical coupling of propenylphenols, it forms several types of interunit bonds and a three-dimensional network may result. The lignin of gymnosperms (softwoods) is made up mostly of a single monomer type. As a result, the lignins of gymnosperms do not differ much from species to species. However, the lignins of angiosperms (hardwoods) do vary considerably among species because these lignins are derived from two monomer types which are often present in differing proportions. Furthermore, the ratio of monomer types may vary among different cell types and between cell regions within a species.This review, intended mainly for those unfamiliar with the details of lignin chemistry, will provide an overview of the formation, structure and distribution of lignins in wood and of the distribution of lignin in pulp fibers.
Fibre Quality Factors in Papermaking — I The Importance of Fibre Length and Strength
Authors: Seth R.S. 
Published: March 2011

ABSTRACTIndependent effects of fibre length and strength on the properties of pulp, and on the physical properties of the dry sheets have been demonstrated. Apart from improving formation, which indirectly influences many sheet properties, reducing fibre length has little direct effect on the sheet structural and optical properties, but does reduce mechanical properties. The loss in fibre strength also has little direct effect on the sheet structural and optical properties, but severely reduces those mechanical properties which are controlled by the breaking of fibres. Implications for market pulps are discussed.
The Differences Between Sonically and Mechanically Determined Elastic Moduli of Paper
Authors: Batten George L. 
Published: March 2011

ABSTRACTThis paper examines the differences between sonically- and mechanically-determined paper elastic moduli. Four factors are examined for their contributions to observed differences. Two factors, thermodynamics and the low frequency approximation, relate to the sonic method; the other two factors, load cell stiffness and paper viscoelasticity, relate to the mechanical method. When all four factors are given proper consideration, the differences between the two methods are reduced to the order of experimental error. Quantitative relationships between the two moduli are given.
The Structure and Properties of Vicinal Water
Authors: Etzler Frank M. , Conners James J. , Ross Russell F. 
Published: March 2011

ABSTRACTThe properties of water near surfaces are known to differ from those of the bulk. For instance, in 140 A diameter silica pores the density has been found to be 3% lower than that of the bulk while the heat capacity is 25% greater than that the bulk. Etzler [15] has proposed a statistical thermodynamic model for vicinal water. This model has been able to correlate a number of thermodynamic properties of water in silica pores. Furthermore, some of the microscopic implications of the model have been found to be consistent with molecular dynamics simulations. Here we discuss the results of a statistical geometric analysis of a molecular dynamics simulation which, as first suggested by Roentgen (1892), indicates that water indeed exists in “bulky” and “dense” states. Furthermore, recent results concerning the temperature dependence of the heat capacity of water in silica pores is discussed.
Effect of Synthetic Fiber and Binder Addition on the Strength Losses Associated with Corrugating Medium
Authors: Waterhouse John F. 
Published: March 2011

ABSTRACTThe investigation is concerned with strategies to reduce losses in medium compressive strength during corrugating.Medium handsheets with a non-random fiber orientation were made using a NSSC pulp and different levels of synthetic fiber addition, including glass and Kevlar pulp, at two levels of wet pressing. Corrugating was performed using a concora fluter, and compressive strength measurements were made in the tip and flank regions of the corrugated medium.Forming losses are reduced by increased wet pressing with a greater improvement in the flank than the tip region of the flute. A small reduction in tip forming losses is found, for a given furnish when a film forming latex is used. However, a greater reduction is evident when a non-film forming latex is employed.Forming loss measurements were also made on non-bonded and bonded laminates. The non-bonded laminates resulted in much lower forming losses, while the heat-activated laminates resulted in large forming losses similar to those found with conventional medium.These experiments suggest that forming losses can be reduced if cost-effective systems are designed which do not activate until the fluting process is complete.
Chitosan-Coated Fibers for Use in Papermaking
Authors: Allan G. G. , Carroll J. P. , Hirabayashi Y. , Muvundamina M. , Winterowd J. G. 
Published: March 2011

ABSTRACTChitosan was precipitated onto wood pulp, glass and polypropylene fibers suitable for papermaking. The coating which formed on the fibers was characterized by photomicrography after the formation of colored derivatives, and by scanning electron microscopy. The most uniform and adherent coatings were formed on the wood pulp fibers and the least were formed on the polypropylene fibers. Paper handsheets were readily formed from the chitosan-coated wood pulp and glass fibers, but not from the chitosan-coated polypropylene fibers.
A New Emphasis in Strategies for Developing Lignin-Based Plastics
Authors: Dutta Sunil , Sarkanen Simo 
Published: March 2011

ABSTRACTLignins, a truly abundant group of biopolymers exhibiting some significant diversity, are usually thought to be constituted by a random proportionate distribution of ten different linkages between p-hydroxphenylpropane units. Over 20 million tons of kraft lignin derivatives are produced annually in the United States by the pulping industry, but 99.9% of these aromatic polymeric materials are consumed as fuel. Such industrial byproducts are generally viewed as being almost hopelessly complicated mixtures of partially degraded and condensed chemical species. However, a very different picture has begun to emerge from a more coherent understanding of the physicochemical behavior exhibited by kraft lignin preparations. Noncovalent interactions between the individual molecular components under a variety of solution conditions orchestrate pronounced associative processes that are characterized by a remarkable degree of specificity. Their consequences may be readily observed both size-exclusion chromatographically and electron microscopically, and are reflected in an anomalous variation of glass transition temperature, Tg, with molecular weight of paucidisperse kraft lignin fractions. How these effects may influence the mechanical properties of lignin-based polymeric materials is presently being scrutinized at the University of Minnesota.
Heteroepitaxy of Inp on Si for Optical Devices
Authors: Mori Hidefumi , Sugo Mitsuru , Tachikawa Masami , Itch Yoshio , Yamaguchi Masafumi 
Published: March 2011

ABSTRACTIn situ measurements of dislocations at growth temperature have been made on the heteroepitaxial systems of GaAs/Si and GaP/Si. It was found that the etch pit densities of heteroepitaxial layers were as low as those of bulk wafers at the growth temperature and increase to 107 cm−2 when the layers cool down to room temperature. This means that the thermal stress determines the quality of heteroepitaxial layers.The InP on Si system, in which the thermal expansion coefficient difference is smaller than other heteroepitaxial systems, has been studied. High quality InP has been obtained using a GaAs buffer layer, strained-layer superlattice insertion, and thermal cycle annealing and regrowth. Full width at half maximum of X-ray rocking curve was 110" at 13 µ thickness.An InGaAsP laser diode emitting at 1.55 µm was successfully made on Si. The threshold current was 46 mA at room temperature for a ridge waveguide laser with a 4 µm width and a 200,µm cavity length.
In-Situ Patiterning and Regrowth of InP Based Heterostructures using a Native Oxide Mask
Authors: Wang Y. L. , Harriott L. R. , Temkin H. 
Published: March 2011

ABSTRACTWe have successfully used an ultrathin (20-50 Å) native oxide layer on the surface of InP as an etch mask for transferring patterns onto the substrate. The oxide mask is grown in situ in O2 atmosphere, and the mask pattern is created by locally removing the oxide with a focused ion beam. Depending on the thickness of the mask, the required ion dose varies from 2×1014 to 2×1015 Ga/cm2. C12 etches the exposed areas selectively. Features as deep as 3 microns have been produced with such an ultrathin mask. High quality InGaAs and InP epitaxial layers have been overgrown on such patterned substrate. We have studied the formation and desorption of the oxide mask with Auger analysis. We also demonstrate that the secondary charged particle emission from a substrate during ion exposure provides a useful signal for the determination of the required dose.
Defects in Mbe-Grown GaAs/ScxEr1–xAs/GaAs Layers
Authors: Zhu Jane G. , Palmstrdøm Chris J. , Carter C. Barry 
Published: March 2011

ABSTRACTThe microstructure and the structure of defects in GaAs/ScxEr1–xAs/GaAs (x=0 and 0.3) heterostructures grown on (100) GaAs substrates by molecular beam epitaxy have been characterized using transmission electron microscopy. The top GaAs layer forms islands on ScxEr1–xAs at the initial growth stage, and the area covered by GaAs varies with the growth temperature. In addition to regions of epitactic (100) GaAs, regions of {122}- and (111)-oriented GaAs are observed on (100)-oriented ScxEr1–xAs. A high density of stacking-fault pyramids is found in epilayers of GaAs grown on a thin epilayer of ErAs, where the ErAs layers are only one or two monolayers thick. The apex of each stacking-fault pyramid is located at the ScxEr1–xAs/GaAs interface.
InGaAs/AWAsSb Heterostructures Lattice-Matched to InP GRown by Molecular Beam Epitaxy
Authors: Nakata Y. , Sugiyama Y. , Inata T. , Ueda O. , Sasa S. , Muto S. , Fujii T. 
Published: March 2011

ABSTRACTWe have successfully grown InGaAs/AIAsSb quantum-well (QW) structures lattice-matched to InP by molecular beam epitaxy for the first time. We studied the band-edge discontinuity and the interface abruptness of these heterostructures. A cross-sectional lattice image of InGaAs/AlAsSb QWs taken along the [100] axis showed atomically smooth heterointerfaces. The photoluminescence (PL) peak energy of the 20-nm-thick InGaAs well (0.758 eV) was lower than that of InGaAs bulk (0.799 eV), indicating that the InGaAs/AlAsSb system has a staggered lineup. The conduction band-edge discontinuity, ΔEc, was evaluated to be 1.74 ± 0.04 eV, which was derived from parameter fitting to the 4.2 K PL peak energy shifts of QWs as a function of InGaAs well width between 2.1 nm and 20 nm. The corresponding valence band-edge discontinuity, ΔEv, was 0.07 ± 0.02 eV. We also fabricated a resonant tunneling barrier structure of InGaAs (4.4 nm)/AlAsSb (2.9 nm), and obtained a very high peak-to-valley current ratio of 15 at 300 K.
Rapid Thermal Chemical Vapor Deposition: Selective Epitaxial Silicon Growth (SEG)
Authors: Osenbach J. W. , Ku Y. H. , Kermani A. 
Published: March 2011

ABSTRACTRapid Thermal Chemical Vapor Deposition (RTCVD) offers great promise for deposition of high-quality, thin, abrupt interface epitaxial films. In addition, RTCVD systems operate under cold wall environment to minimize particles and cross contamination. SEG of silicon provides both isolation and active device wells with fine dimensional control. A combination of RTCVD and SEG holds great promise for future VLSI circuit technologies. In this paper, we present our results on selective growth of single crystal silicon using RTCVD.
Optical Approaches to Real-Time Analysis and Control of Crystal Growth
Authors: Aspnes D. E. 
Published: March 2011

ABSTRACTA variety of optical methods are now available for studying surface processes and for monitoring layer thicknesses and compositions during semiconductor crystal growth by molecular beam epitaxy (MBE), organometallic chemical vapor deposition (OMCVD), and related techniques. Spectroellipsometry (SE) and spectroreflectometry (SR), the older, primarily bulk-sensitive probes, are now augmented by new, primarily surface-sensitive probes such as reflectance-difference spectroscopy (RDS), second-harmonic generation (SHG), and laser light scattering (LLS). Examples of real-time growth studies now include SE determinations of thicknesses and compositions of AlxGa1–xAs layers on GaAs by organometallic molecular beam epitaxy (OMMBE) to 10 Å thickness scales, RDS determinations of surface dielectric anisotropy spectra of various (001) GaAs surfaces relevant to crystal growth by MBE, and LLS determinations of the evolution of surface roughness during chemical vapor deposition (CVD) growth on Si. Proven capabilities suggest new applications, particularly to growth-interrupted and metastable systems.
Heteroepitaxy of Ge on Vicinal Si(100)
Authors: Krishnamurthy Mohan , Drucker Jeff S. , Venables J.A. 
Published: March 2011

ABSTRACTThe initial stages of germanium heteroepitaxy on vicinal Si(100) have been studied using in-situ deposition in a UHV STEM. Germanium was deposited using molecular beam techniques onto substrates misoriented 1° and 5* toward <110> held at room temperature, 375°C and 525°C. Film thicknesses were in the range 4-6 ML, just greater than the stable intermediate layer of 3-4ML (1ML = 0.14nm). The Ge clusters were observed using biassed secondary electron (b-SE) imaging with nanometer resolution. Comparisons were made between deposition at the elevated temperatures, and room temperature deposition followed by anneals at the same temperatures.Annealing the low temperature deposits produces coarsening of the islands which is similar on the 1° and 5° samples. Island size distributions and other film growth parameters obtained from the 375°C and 525°C anneals indicate that the coarsening is different at these temperatures and is possibly affected by instabilities in the intermediate layer. Results of the high temperature depositions indicate that neither surface steps nor the edges of islands act as perfect sinks, and that diffusion distances are of the order of several microns. The nucleation density and size distributions are markedly different for deposition at 375°C and 525°C possibly due to competitive capture at strong sinks.In a parallel set of experiments in a standard UHV chamber, macroscopic wafer samples were analyzed with RHEED, Auger and secondary electron spectroscopy. These correlate well with the intermediate layer thicknesses previously reported in the literature, and the large contrast observed in the b-SE images. Ex situ TEM studies of samples grown in this chamber show islands with various contrast features including those of coherent strain.
An Electron Microscopic Characterization of Mbe-Grown ZnSe/CaAs and ZnSe/Ge Heterointerfaces
Authors: Sant S.B. , Smith R.W. , Weatherly G.C. 
Published: March 2011

ABSTRACTMolecular beam epitaxy (MBE) grown ZnSe/GaAs and ZnSe/Ge heterointerfaces have been studied by transmission electron microscopy (TEM). Defect characterization of cross-sectional and planar specimens showed that ZnSe epitaxial films contain numerous twins that predominantly arise at the interface. Planar specimens of ZnSe/Ge were in-situ TEM annealed, for 5.5 hours at 873K. The twins are thermally very stable which would indicate that they arise during the growth process. The occurrence of these twins in the ZnSe film is explained by nucleation and growth of normal and twinned nuclei. Some of the ZnSe films grown on (10O)Ge substrates have low-angle boundaries indicating that the initial growth of the film is by the formation of islands.
Strain Relaxation Mechanisms in Lattice Mismatched Epitaxy
Authors: Hull R. , Bean J.C. , Bonar J.M. , Peticolas L. 
Published: March 2011

ABSTRACTThe relaxation of strained epitaxial layers by the introduction of misfit dislocations is reviewed. Current theoretical and experimental understanding of the nucleation, propagation and interaction of misfit dislocations are summarized. The ramifications for applicability of strained layer epitaxy to practical device structures are discussed.