bluuebunny/crossref_metadata_2025 huggingface dataset:
Parametric Investigation of Rock Salt Behaviour Resulting from Disposal of High Level Radioactive Waste
Authors: Caramelle D. , Gaudez M.T. , Monig J. , Ouzounian G. , Simonet G.
Published: March 2011

The liberation and generation of gases from rock salt due to heat and gamma irradiation is investigated in order to obtain some of the data needed for the development of the concept for the disposal of high level waste in rock salt.

Our work is concerned with the influence of various parameters on gas production, e.g. salt composition and grain size, total absorbed dose, dose rate, temperature and gas atmosphere. Some of these parameters have not been studied previously in detail.

The original gamma irradiator employing spent fuel elements and capable of exposing samples at temperatures up to 250°C will be described. Experimental results from some 150 experiments will be given. The two major gases found were CO2 and N2O.CO, H2, CH4, Hydrocarbons, CI2, HCl and SO2 were also detected. The dependence of the gas yields on the various parameters will be presented and discussed.
A Review Process and a Database for Waste-Package Documents
Authors: Interrante Charles G. , Messina Carla A. , Fraker Anna C.
Published: March 2011

The work reported here is part of a program conducted by the Nuclear Regulatory Commission on the efficacy of proposed plans for radionuclide containment for long-term storage of high-level nuclear waste (HLW). An important element of that program is the review and evaluation of available literature on components of a waste package. A review process and a database have been developed and tailored to provide information quickly to an individual who has a question about a particular material or component of a waste package. The database is uniquely suited to serve as a guide to indicate special areas where data and information needs exist on questions related to radionuclide containment. Additions to the database are made as information becomes available, and this source is as current as the published literature. A description of the review process and the database is given.
Effects of Alpha and Gamma Radiation on Glass Reaction in an Unsaturated Environment
Authors: Wronkiewicz David J. , Young John E. , Bates John K.
Published: March 2011

Radiation may effect the long-term performance of glass in an unsaturated repository site by interacting with air, water vapor, or liquid water. The present study examines (1) the effects of alpha or gamma irradiation in a water vapor environment, and (2) the influence of radiolytic products on glass reaction. Results Indicate that nitric and organic acids form in an irradiated water vapor environment and are dissolved in thin films of condensed water. Glass samples exposed to these conditions react faster and have a different assemblage of secondary phases than glasses exposed to nonirradiated water vapor environments.
Microstructure and Properties of Eutectic Composites Based on (Ti, Nb)3 (Al, Si) and (Ti, Nb)5 (Si, Al)3
Authors: Wagner R. , Es-Souni M. , Chen D. , Dogan B. , Seeger J. , Beaven P. A.
Published: March 2011

Previous work has shown that ternary Ti-Al-Si alloys with hypoeutectic and eutectic microstructures containing the intermetallic phases Ti3 (Al,Si) and Ti5 (Si,Al)3 have promising high temperature mechanical properties [1]. In the present investigation alloying additions of Niobium have been made to selected Ti-Al-Si alloys based on hypoeutectic compositions and the effects of Niobium on the microstructure and mechanical properties have been studied. The high temperature creep and oxidation behaviour of such alloys appears to be superior to that of currently available Ti3Al-based alloys.
First-Principles Calculations of Phase Stability for High Temperature Intermetallics
Authors: Becker J.D. , Sanchez J.M. , Tien J.K.
Published: March 2011

Total energy electronic structure calculations are performed for the elements and selected binary ordered compounds of the ternary system Nb-Ru-Zr. These calculations provide binding energies, atomic volumes, bulk moduli, Debye temperatures, and Grüneiesen constants for the selected structures and compounds. Volume dependent pair and many-body chemical interactions are also obtained from the total energy results which, in turn, are used to study partially ordered alloys at finite temperatures. The stability of all the binary intermetallic compounds experimentally observed at low temperatures is correctly predicted by the first-principles calculations. The solid state portion of the Nb-Ru binary phase diagram is calculated using the chemical interactions obtained from the total energy calculations, a Debye-Grüneisen model for the vibrational free energy and the cluster variation method (CVM) for the configurational entropy with a local volume relaxation scheme. The calculations reproduce the experimentally observed ordering temperature of the NbRu3 intermetallic to within 2%.
First Principles Calculation of Phase Stability of High Temperature Intermetallic Alloys
Authors: Mikalopas J. , Sterne P.A. , Sluiter M. , Turchi P.E.A.
Published: March 2011

One way to calculate the coherent phase diagram of an alloy based on first principles methods is to compute the ground state total energy for various ordered configurations, from which many-body interactions can be calculated and employed in a thermodynamic model. If the Connolly and Williams method (CWM) is used to extract the many-body interactions from the calculated total energies, the resulting many-body interactions can exhibit a strong dependence on the choice of ordered configurations and multi-site clusters, and the accuracy and convergence of the CWM energy expansion is not assured. To overcome this difficulty, a successful systematic method for implementing the CWM is proposed. This approach is applied to a study of the fcc-based Ni-V and Pd-V substitutional alloys and these interaction parameters together with the cluster variation method (CVM) are used to calculate phase diagrams.
Relation of Phase Stability Boundary to the Fill-Up Bonding States In Ni3V,Co3V and Fe3V
Authors: Lin W. , Xu Jian-Hua , Freeman A.J.
Published: March 2011

The electronic structures and cohesive properties of the intermetallics Ni3V, Co3V, and Fe3V in the L12 structure have been studied using the self-consistent total energy linear muffin-tin orbital method based on the local density approximation. The simple rigid-band concept appears to be adequate to explain the structural stability of these compounds. Further,the structural stability of the pseudobinary compounds (Ni,Co,Fe)3V has been investigated based on the rigid-band scheme. The correlation between the electronic concentration and the crystal structure is shown to be related to the fill-up of the bonding states.
Computer Simulation of the Elastic Energy Contribution to Antiphase Boundary Energy Anisotropy
Authors: Van Der Heide Robert G. , Allen Samuel M.
Published: March 2011

The results of computer simulations on the effect of elastic energy on APB anisotropy are presented. The model used treats composition and order parameter as local variables defined at crystal planes parallel to the APB. The set that minimizes the free energy, including elastic energy terms, defines the equilibrium APB structure. It was found that, despite their high elastic anisotropy, elastic effects would not result in any substantial APB anisotropy in Fe-Al alloys. However, a model with different parameters did show a high degree of anisotropy.
A Model for the Yield Behavior of Ni3Ai Alloys
Authors: de Bussac Arnaud , Webb Graham , Antolovich Stephen D.
Published: March 2011

Current models for predicting the unusual deformation characteristics of Ni3Al alloys are based upon the idea of cross-slip pinning of screw dislocation segments. These models assume an Arrhenius type framework which employs a stress-modified activation barrier for forward cross slip. Use of such models has been successful in describing the orientation, asymmetry and temperature characteristics of yielding. A limitation of current models is their inability to predict the apparent lack of a strain rate effect in Ni3Al alloys. The current model approaches the problem using both kinetic and thermodynamic arguments to describe the physical process. It is then demonstrated that the driving force for cross-slip controls the process. The model describes all aspects of deformation including apparent strain rate insensitivity. An additional feature of the model is its ability to provide analytical and physical justification for the use of Arrhenius type equations for representing experimental data.
A Mechanism of the Positive Temperature Dependence of Yield Stress in Tial
Authors: Kawabata T. , Kanai T. , Izumi O.
Published: March 2011

The positive temperature dependence of yield stress (PTYS) has been observed (Kawabata et al., Acta Metall., 33, 1355 (1985)) in TiAl single crystals in all orientations operating ordinary dislocations with the Burgers vector 1/2<110] and superdislocations with the Burgers vectors <101] and 1/2<112]. A mechanism for the PTYS is proposed, which is a cross-slip and pinning mechanism of Shockley partials with the Burgers vector 1/6<112] or/and 1/6<121]. The results of strain rate dependence of yield stress, K value dependence of critical resolved shear stress (CRSS) and transmission electron microscopy support the theory. Here, K value is the Schmid factor ratio of a Shockley partial on {101) or {110) plane and a perfect ordinary dislocation or a perfect superdislocation on {111) plane.
Dislocation Structure in Single Crystal L1o Type Ti-Al-V Compound
Authors: Hahn Y.D. , Li Z.X. , Whang S.H. , Kawabata T.
Published: March 2011

Single Crystals of L1o type Ti44Al54V2 alloy were deformed at high temperatures and various orientations. The dislocations thus produced by single slip were studied by TEM. 1/2<110] dislocations produced at 1073 K consist of dislocation loops and curled dislocations with spiral segments, which is in agreement with those shown in the polycrystalline Ti-Al-V, and -Nb alloys deformed under the same conditions. The normal dislocations produced at 873 K pile up in groups, each of which contains several straight dislocations with a screw character. On the other hand, the majority of superdislocations produced at 873 K were found in a dipole form, indicating that the dipole is a favorable configuration at this temperature.
Dislocations with Non-Planar Locked Structures in the L12Ordered Alloys
Authors: Sun Y.Q. , Hazzledine P.M. , Crimp M.A.
Published: March 2011

In the L12structure, the Kear-Wilsdorf lock on screw superdislocations is the best known example of a dislocation with a non-planar locked structure. Recent high resolution TEM work on Ni3Al and Ni3Ga has shown locked structures on the following dislocations: 30-degree <112>/3 super-Shockley partials, edge <110> {001} dislocations, and 45-degree <100>{001} dislocations. Dislocation reactions among intersecting <100>{001} and <110>{001} slip systems have also been found to form product dislocations with locked structures. This paper summarizes these locked structures and outlines their effects on the operation of related slip systems.
A Tem Study of the Dislocation Structure in a Ni3Al-Based Alloy at Temperatures Below the Peak in Flow Stress
Authors: Wen Mao , Lin Dongliang
Published: March 2011

Dislocation structure in a directionally solidified Ni3Al-based alloy deformed at temperatures below the peak in flow stress has been studied by the weak beam TEM technique. At room temperature, the screw superdislocations are partly transformed into Kear-Wilsdorf configurations. With increasing temperatures, the transformed Kear-Wilsdorf parts increase until the temperature reaches 450°C, at which the screw superdislocations are wholly transformed. Bending of the Kear-Wilsdorf configurations on {0101} planes is observed at 450°C, which is believed to be the cause of interaction of Kear-Wilsdorf configurations with superkinks. The Contribution of superkink motion to deformation is discussed. The results suggest that deformation in this temperature range occurs primarily by the slip of non-screw components on {lll} planes, which is consistent with the widely accepted cross slip pinning model.
Micromechanisms of Deformation and Fracture in Rapidly Solidified Ni3Al Alloys
Authors: Liu G. , Bond G.M.
Published: March 2011

Rapidly solidified Ni76 Al24 ribbons, with and without boron, have been the subject of in-situ TEM deformation studies, as well as X-ray and TEM characterization and TEM fractography. The aim has been to gain a better understanding of the influence of a reduced degree of order on grainboundary behavior and ductility. This, in turn, allows fresh insights to be gained, both into the manner in which boron additions can enhance ductility, and into the potential usefulness of sequential ordering in intermetallic alloys with a tendency to intergranular failure. Lower degrees of order are found to reduce stress concentrations at grain boundaries; this effect is due to easier generation of dislocations from boundary sources, and, to a lesser extent, the braking action of thermal APB's on dislocation motion. The beneficial effect of boron on ductility is seen to result, at least in part, from enhanced boundary cohesive strength.
Dislocations Microstructures and Disorientation of Cubic Planes in Samples of a Superalloy Submitted to Bending Tests
Authors: Buffiere J.Y. , Ignat M. , Bastie P.
Published: March 2011

Single crystal samples of a nickel base superalloy have been deformed by cyclic bending tests. At the higher temperatures of our experiments, an evolution of the apparent modulus as the advancement of disorientation of cubic planes has been detected.

The dislocation microstructures show that the development of dislocation networks is more advanced in the compressive zones than in the tensile ones.
Effects of Alloying Additions on Intergranular Fracture of Ordered Intermetallics
Authors: Takasugi Takayuki
Published: March 2011

The majority of ordered intermetallics generally exhibit brittle fracture and poor ductility at ambient temperatures, and their brittleness is strongly associated with grain boundary properties. Recent efforts on alloying approaches and microstructural modifications gave promising results to improve the ductility of ordered intermetallics. This article summarizes recent studies on understanding the intergranular brittle fracture from the point of view of compositional and resultant structural (and electro-chemical) properties of grain boundaries. Significant improvement in ductility has been established by the control of chemical composition, that is, by the selection of constituent elements, the control of alloy stoichiometry, the addition of substitutional elements, the change of degree of ordering and the doping by the interstitial elements. Also, the gaseous atoms hydrogen and oxygen from environment or as residue are shown to strongly affect the grain boundary fracture behaviour. Emphasis will be placed on the L12-type ordered intermetallics including Ni3Al, Ni3Si and Co3Ti.
Mechanical Properties of Fe-Modifie Ll2-Type Al3Ti
Authors: Inoue H. R. P. , Cooper C. V. , Favrow L. H. , Hamada Y. , Wayman C. M.
Published: March 2011

The room temperature ductility of an L12-type A13Ti alloy containing 7.5 at.% Fe has been improved substantially by hot isostatic pressing (HIP) after arc casting. This L12-type alloy can be deformed in compression to 11.4 % at room temperature after HIPing, retaining the original shape of compressive specimens, while compressive specimens without HIPing following heat-treatment for homogenization (HHT) fracture into small pieces when deformed to similar strain. At temperatures higher than 400°C, specimens for both HHTed and HIPed conditions show similar behavior, having strains to failure of greater than 12 % plastic strain. Fracture occurs at room temperature by brittle transgranular cleavage with a smooth surface in HHTed specimens, while in HIPed specimens, fracture occurs by both transgranular and intergranular modes. Transgranularly fractured surfaces in the latter case have rough surfaces with fine structure, indicating ductile fracture as compared with that for HHTed specimens. In both HIPed and HHTed specimens, no fracture surfaces are flat and parallel to any crystallographic planes. High resolution electron microscopy has revealed that a pair of superlattice partial dislocations on a (111) plane have a spacing of approximately 11 nm (2–3 times larger than that for Al-23Ti-6Fe-5V) giving an antiphase boundary energy of 95 mJ/m2. Since this energy is relatively low, the present alloy may be ductile because of its ready emission of dislocations at crack tips, according to the Rice-Thomson criterion. Improvement of room-temperature ductility of this alloy is attributed primarily to the reduction of a large population of cavities formed upon arc casting.
Free Energy Simulation of Grain Boundary Segregation and Thermodynamics In Ni3−xAl1+x
Authors: Najafabadi R. , Wang H. Y. , Srolovitzt D. J. , LeSar R.
Published: March 2011

The free energy simulation method is employed to study segregation to Σ5 and Σ13 (001) twist grain boundaries and their free energies in ordered Ni3−xAl1+x. In the temperature range studied (300–900K), it is shown that there is almost no segregation, strong Al segregation, and weak Ni segregation to the grain boundary for the stoichiometric, Al-rich, and Ni-rich bulk compositions respectively. It is also shown that the segregation is limited to a few (002) planes around the grain boundary and its magnitude decreases with increasing temperature. For Al-rich bulk composition, it is demonstrated that segregation at low temperature substantially lowers the grain boundary free energy.
The Effects of Alloy Addittons of Si and Transitton Metal Elements on the Mechanical Properties Of B-Doped Ds Ni3Al
Authors: Zhang Yun , Lin(T.L.Lin) Dongliang
Published: March 2011

The temperature dependence of the flow stress in the B-doped DS Ni3Al containing Si as well as transition metal elements was systematically investigated by tensile tests. The effects of the alloy elements on the magnitude of the positive temperature dependence of the flow stress were evaluated. The calculated activation energy which results in the anomalous mechanical behavior the Ni3Al decreases for each element addition. The flow stress near liquid nitrogen temperature, taken as a measure of the degree of solid solution strengthening, increases linearly with the element concentration. The influences of the element additions on the solid solution strengthening were discussed. Also discussed were the mechanisms of the anomalous mechanical behavior in the Ni3 Al affected by the element additions.
The Effect of Strain Rate on the Mechanical Properties of Single Crystal NiAl
Authors: Lahrman D.F. , Field R.D. , Darolia R.
Published: March 2011

In this study, the strain rate sensitivity of single crystal NiAl has been investigated by performing tensile tests as a function of temperature and two strain rates. Three crystallographic orientations, [100], [110], and [111] were studied. The tensile test results investigated include yield strength, work hardening rate and plastic strain to failure. The data are discussed in terms of deformation mechanisms in NiAl.
Effect of Boron Content on Mechanical Properties of Monocrystalline Ni3Al
Authors: Jianting Guo , Chao Sun , Hui Li , Zhiya Zhang , Yajun Tang , Zhuangqi Hu
Published: March 2011

The microstructure and the mechanical properties at room and high temperatures of monocrystalline Ni3Al containing 0, 0.52, 1.37, 2.22 and 3.00 at%B have been studied. The results show that the ultimate and yield strengths at 20°C and 800° C of monocrystalline Ni3Al obviously increase with the increase of B content, and reach maxima when B content is 1.37 and 0.52 at% respectively. With further increasing the B content to 2.22 at%, they slowly drop. The tensile ductilities at 20°C and 800°C of monocrystalline Ni3Al when the B content is 0 and 0.52 at% respectively are the best in five kinds of Ni3Al studied, then they continuously decrease with the increase of B content due to the precipitation of boride eutectic. The rupture life and elongation at 850°C and 100 MPa markedly drop as the B content is raised in the monocrystalline Ni3Al, but they are still higher by 1 to 2 orders of magnitude as compared with those of polycrystalline Ni3Al with the same compositions. When B content exceeds 1.37 at%, the eutectic structure of Ni20Al3B6 and Ni3Al is formed, which is enhanced by the B content and is harmful to the strength and the ductility.
On Improving the Fracture Toughness of a Niai-Based Alloy by Mechanical Alloying
Authors: Kostrubanic J. , Koss D.A. , Locci I.E. , Nathal M.
Published: March 2011

Mechanical alloying (MA) has been used to process the NiAl-based alloy Ni-35Al-2OFe such that a fine-grain (∼2 μm) microstructure is obtained through the addition of 2 v/o Y2O3 particles. When compared to a conventionally processed, coarse-grained (∼;28 μm) Ni-35–20 alloy without the Y2O3 particles, the MA alloy exhibits two to three times higher fracture toughness values, despite a 50% increase in yield strength. Room temperature KQ values as high as 34 √Pa m are observed accompanied by a yield strength in excess of 1100 MPa. Fractography confirms a change in fracture characteristics of the fine-grained MA alloy.
Mechanical Properties of Ordered Fe-Al-X Alloys
Authors: Prakash Ujjwal , Buckley Robert A. , Jones Howard
Published: March 2011

Fe-Al-X alloys (X = Cr, Mo) in the composition range 50 to 80 at. % Fe, 0 to 20 at. % X were rapidly solidified by chill-block melt-spinning. As-spun and heat treated ribbons were characterised by optical and electron microscopy and X-ray diffraction. Strengthening mechanisms were identified using microhardness measurements. Tensile fracture surfaces of ribbons reveal ductile to cleavage to intergranular fracture transitions with increasing Al-content. An increasing preponderance of cleavage fracture with increasing ternary substitution for Fe was observed.
Tensile and Creep Behavior of Ordered Orthorhombic Ti2A1Nb-Based Alloys
Authors: Rowe R.G. , Konitzer D.G. , Woodfield A.P. , Chesnutt J.C.
Published: March 2011

Titanium aluminide alloys with compositions near Ti-25A1-25Nb at.% were prepared by both rapid solidification and ingot techniques. Their tensile and creep properties were studied after heat treatment to produce various microstructures containing ordered orthorhombic (O) [1], ordered beta (βo), and α2 phases. It was found that these alloys had higher specific strength from room temperature to 760°C than conventional α2 alloys. Ductility and tensile strength of O+βo alloys were strongly dependent upon heat treatment, with the highest strength observed as-heat-treated, and the highest ductility after long term aging. The creep resistance of single phase O and two phase O+βo alloys was strongly dependent upon heat treatment.
The High Temperature Deformation Behavior of A Cr2Nb Ordered Intermetallic System
Authors: Vignoul G. E. , Sanchez J.M. , Tien J. K.
Published: March 2011

A basic characterization of the deformation behavior of Cr2Nb by microindention at ambient and elevated temperatures (up to 1400 °C) was undertaken. The microhardness of this system was seen to decrease with increasing temperature, from 1040 MPa at 25°C to 322 MPa at 1400 °C. Further, the microindention creep behavior of this system was studied by varying time on load at T = 1000 and 1200°C. Analysis of the data showed that m = 24 and Qapp = 477.61 kJ/mole. These unusually high values are indicative of the existence of an effective resisting stress against creep. When the data was fit against a microindention creep deformation law which was modified to incorporate an effective resisting stress term, it was determined that m = 4.5, Qcreep = 357 kJ/mole and the resisting stress term σr = 300 MPa.
A Comparative Study of Short Range Order in Fe-Cr and Fe-V Alloys Around Equiatomic Composition
Authors: Turchi P.E.A. , Sluiter M. , Stocks G. M.
Published: March 2011

Configurational energies have been calculated for equiatomic Fe-Cr and Fe-V alloys possessing the high temperature bcc crystalline structure, within a first principles electronic band structure approach. In agreement with experimental facts, a tendency towards order, with a B2 ordered structure of CsCI type, is found for FeV whereas phase separation characterizes FeCr. These results suggest that the nature of short range order in the high temperature bcc solid solution is not the primary driving force for describing the structural transformation from bcc to sigma which takes place in both alloys upon decreasing temperature.
Recent Advances in Gamma Titanium Aluminide Alloys
Authors: Kim Young-Won (Y-W.)
Published: March 2011

Gamma titanium aluminide alloys of current interest are two-phase alloys consisting of γ-TiAl phase as the matrix and a α2-Ti3Al phase as the second phase. The properties of these alloys depend on alloy composition, processing, microstructure, and their combination. Two major microstructural constituents are gamma grains and lamellar grains, the latter of which contain alternate layers of gamma (γ) and alpha-2 (α2) thin plates. The relative amounts and distribution of these two constituents are the main factors controlling mechanical properties. This paper reviews our current understanding of the composition/microstructure/property relationships. An extended discussion will be made on the fundamental aspects of the formation of lamellar structure during cooling and the evolution of microstructure occurring during thermomechanical treatments.
Effect of Interstitials on the Phase Stability of Selected Intermetallics
Authors: Kassem M. A. , Koch C. C.
Published: March 2011

The possibility of modifying the complex crystal structure of selected refractory metal aluminides and silicides of AB3 stoichiometry by interstitial alloying additions was investigated. The compounds Nb3Si, V3Si, Mo3Si, Cr3Si, and Nb3Al were alloyed with oxygen or carbon up to about 20 atomic %. Alloying with oxygen or carbon in V3 Au was studied as a model for the A15 to Ll2 (or L'l2) structural change induced by interstitial alloying. Oxygen and carbon stabilized the perovskite, L'l2, structure in V3Au. Oxygen stabilized a L12 phase in Nb3Si while carbon induced a hexagonal structure phase. No L12 or L'12 phases were stabilized with the addition of oxygen or carbon in V3Si, Mo3Si, Mo3A1, Cr3Si, or Nb3Al. The Pettifor structural map for AB3 compounds was used to predict the structural changes in these compounds on alloying of oxygen or carbon.
Development Of Fe3Si Alloys
Authors: Langhong Lou , Tianxiang Zhang , Yaoxiao Zhu
Published: March 2011

The partial phase diagram of the Fe-Mn-Si system at 900°C was obtained by electron microprobe measurement. In addition, the effect of carbon on these equilibrium were also studied. Depending on these, a series of Fe-Mn-Si-C alloys with the matrix of Fe3Si were designed. It was found that they all have some plasticity and can satisfy the engineering requirement. Moreover, after appropriate heat treatment, all these alloys have good corrosion resistance in sulphuric acid with various concentrations.
Microstructure of Rapidly Solidified Nb3Al-X Ribbons
Authors: Yasuda Ken , Fujiwara Tetsuo , Kodama Hideyo , Suwa Masateru
Published: March 2011

Nb-Al and Nb-Al-X(X is Cr,Ti or Zr) ternary alloys ribbons, with compositions around the A15 (Nb3Al) structure, a candidate intermetallic as an advanced high temperature material, were rapidly solidified by an arc melt spin process. The rapid solidification structure of these tri-niobium aluminide alloys and the relationship between formed phases and compositions of ribbons are investigated.
Hot Extrusion of A Ti-Al-Nb-Mn Alloy
Authors: Seetharaman V. , Malas J. C. , Lomibard C. M.
Published: March 2011

Forward extrusion of a gamma-TiAl alloy (Ti-49.5A1-2.5Nb-l.lMn) was investigated, with special reference to the role of preheat temperature, ram velocity, and can material. Cylindrical billets were sealed in evacuated cans, soaked at extrusion temperatures ranging from 1050 to 1350°C for 2 hr and then extruded through streamlined dies held at 260°C. Microstructural features of the extruded billets which evolved under steady-state conditions were characterized. In conjunction with these observations, a coupled (thermal-deformation) finite-element analysis procedure was used to predict the local distributions of strain, strain rate, temperature, and stress present during extrusion. The microstructures of the extruded products are compared with those obtained in samples subjected to isothermal constant-strain-rate compression tests.
Oxidation Behavior of Gamma-Titanium Aluminide Alloys
Authors: Mckee Douglas W. , Huang Shyhchin C.
Published: March 2011

The oxidation behavior of a number of gamma-TiAl alloys with ternary additions has been studied for extended periods during rapid thermal cycling to temperatures of up to 1000°C in flowing air. Under these conditions, binary alloys, such as Ti-48a/oAl and Ti-52a/oAl form flaking scales with sub-scale embrittlement, although the initial oxidation rate decreases with increasing aluminum content. Ternary Ti-Al-Cr and Ti-Al-Ta alloys with up to 4 a/o Cr or Ta also show a tendency to form spalling scales at these temperatures. On the other hand, the addition of niobium or tungsten results in a dramatic improvement in oxidation resistance at 850 °C, although at 1000°C even these alloys begin to spall after an induction period of several hundred hours.
Oxidation Behavior of Ni Aluminides Using X-ray Absorption Spectroscopy
Authors: Greegor R.B. , Lytle F.W.
Published: March 2011

XAS was used to investigate the oxidation behavior of Ni3Al aluminides with and without the addition of Cr. At 450 C the Cr formed a Cr2O3 like oxide layer which inhibited the oxidation of the Ni at the surface. Ni oxidation did occur in the sample without Cr at 450 C. At higher temperatures the Ni at the surface oxidized to NiO, but in the bulk no oxidation of the Ni was observed whether Cr was present or not. When no Cr was present a minimum was observed at 700 C in the fraction of oxidized Ni. The Cr (8at.%) did not cluster and substituted for Ni or Al in the Ni3Al aluminide.
The Methods of Investigation of Complex Dielectric Permittivity of Layer Polymers Containing Conductive Inclusions
Authors: Kalachev A.A. , Kukolev I.V. , Matitsin S.M. , Novogrudskiy L.N. , Rozanov K.N. , Sarychev A.K. , Seleznev A.V.
Published: March 2011

A set of methods for measure complex dielectric permittivity of layer materials at microwaves is suggested. These methods allow one to measure dielectric permittivity of composite materials in with the mean size of inhomogeneities is comparable with the wavelength and materials with high dielectric permittivity.
Third – Order Nonlinear Optical Properties of Polysilane Films
Authors: Kaatz P.G. , Patterson G.D. , Kim H.K. , Frey H. , Matyjaszewski K.
Published: March 2011

Results are presented from third harmonic generation, (THG), experiments on a number of polysilane films. The polymers studied include poly(di-n-hexylsilylene) PDHS, and copoly(di-n-hexyl, hexylmethylsilylene) PDHS / PHMS. These polymers exhibit positive thermochromism, where the transition temperature and spectral properties are dependent on the copolymer ratio. The nonlinear susceptibility, , in the low temperature phase of the polymer increases by approximately 4 − 5 times that of the high temperature phase where the absorption maximum decreases by ∼ 60 nm. The polymers are prepared as neat, solid films on fused silica substrates. Thickness and refractive index measurements of these polymers were made by UV-VIS-NIR spectroscopy.
Structure and Optical Property of Polymers Obtained by Solid-State Polymerization of a Tetraacetylene Compound
Authors: Okada Shuji , Matsuda Hiro , Masaki Atsushi , Nakanishi Hachiro , Hayamizu Kikuko
Published: March 2011

The polydiacetylene having diacetylenic substituents has been prepared by γ-ray irradiated solid-state polymerization of 15, 17, 19, 21- hexatriacontatetrayne. It has been found that the polymer can be converted into the di(polydiacetylene), i.e., a new type of the fused-ring polymer of conjugated 10π-electron system, by the subsequent heat-treatment in the solid-state.
Doped Polymers as Third-Order Nonlinear-Optical Materials
Authors: Kuzyk Mark. G. , Paek U. C. , Dirk Carl W. , Andrews Mark P.
Published: March 2011

Recently, there has been much interest in doped polymeric materials owing to their suitability for optical device applications.[1] While most of this effort has been centered on poled polymers and their applications to electrooptics, doped polymers are beginning to emerge as a promising material class for all-optical device applications. In this contribution, we discuss the status of doped polymers as third-order optical materials. Particular attention is focused on those properties that make doped polymers attractive as device materials such as optical nonlinearity and loss and their suitability for nonlinear-optical fiber devices.
Photocross-Linked Second Order Nonlinear Optical Polymers
Authors: Chen Y. M. , Mandal B. K. , Lee J. Y. , Miller P. , Kumar J. , Tripathy S.
Published: March 2011

We report a novel method to obtain stable second order nonlinear optical (NLO) properties in polymeric thin films. Photocross-linking between the NLO active molecules and a photoreactive polymer is achieved by UV irradiation subsequent to poling. The thin film exhibits a nonlinear coefficient d33of 16.5 pm/V at a doping level of 20% by weight of NLO active molecules and possesses quite stable second order nonlinear optical properties
Determination of Linear and Nonlinear Optical Properties of a Polymer Thin Film
Authors: Koerkamp H.M.M. Klein , Hoekstra T.H. , Driessen A. , Popma Th.J.A. , Mohlmann G.R. , Horsthuis W.H.G. , Akzo E.W.P. Erdhuisen
Published: March 2011

The second- and third-order nonlinear susceptibilities χ(2) and χ(3) of a polymer thin film are determined for three wavelengths (543.Snm, 632.8nm and 1523nm) using a method based on the linear and quadratic electro-optic effect. The frequency dependences of χ(2) and χ(3), deduced from a simple two-level electron-spring model, are consistent with our experimental results. Using this frequency dependence the intensitydependent refractive index, determined by nonlinear grating coupling, is transformed to a χ(3) value for the quadratic electro-optic effect. This value is in good agreement with our experiments. The layer structure used is simple and consists basically of a polymer layer sandwiched between thin metal electrodes.
Nonlinear Optical Properties of Ladder Polymers and Their Model Compound
Authors: Jenekhe Samson A. , Roberts Michael , Agrawal Ashwini K. , Meth Jeffrey S. , Vanherzeele Herman
Published: March 2011

The third order nonlinear optical properties of thin films of polybenzimidazobenzophenanthroline ladder (BBL) and semi–ladder (BBB) polymers and their model compound cis–BBB were investigated by picosecond, third harmonic generation. The χ(3) (−3ω, ω ω, ω) spectrum of BBL, BBB, and cis-BBB was obtained in the wavelength range 1.0–2.4µm and shown to exhibit a three–photon peak at respectively 1.695, 1.695, and 1.50 µm. The magnitude of the three–photon enhanced χ(3) was 6.40×10−11, 3.15×10−11, and 0.77×10−11 esu, respectively, for BBL, BBB, and cis–BBB. The results show that the χ(3) of BBL and BBB is enhanced by a factor of 50 and 17, respectively, relative to the model compound cis–BBB at 1.05µm.
Asymmetrical Diphenylpolyene Pendant Polymers for Nonlinear Optical Activity
Authors: Sapochak Linda S. , Polis David W. , Dalton Larry R. , Spangler Charles W.
Published: March 2011

Recent activity in the development of nonlinear optical (NLO) materials with high second order susceptibilities has prompted the development of a wide variety of pendant polymers which possess desirable properties for device development, including high Tg minimal relaxation of the poled matrix, and high laser damage threshold. Ideal candidates for such systems are asymmetrically substituted oligomers of polyacetylenes such as dimethylaminonitrostilbene (DANS) and corresponding higher order oligomers. We report here a preliminary study of the synthesis of asymmetrically substituted donor/acceptor diphenyl-capped polyenes and thienylene vinylene oligomers attached as pendant moieties on polyvinylphenol (PVP) for second harmonic generation.
Broadband Microwave Dielectric Properties of Polymers
Authors: Robertson W. M. , Pastol Y. , Arjavalingam G. , Halbout J.-M. , Kopcsay G. V.
Published: March 2011

The recently developed coherent microwave transient spectroscopy (COMITS) technique is capable of determining the complex dielectric properties of materials over a broad frequency range (15–140 GHz), in a single experiment. COMITS is based on the radiation and detection of picosecond duration electromagnetic transients by optoelectronically pulsed antennas. The essential features of the COMITS technique are described and representative results on dielectric and conducting polymers are presented.
Adam-Gibbs Formulation of Nonlinear Enthalpy Relaxation
Authors: Hodge Ian M.
Published: March 2011

The Adam-Gibbs (AG) expression linking relaxation times with configurational entropy gives an excellent account of the nonlinearity observed in enthalpy relaxation of amorphous polymeric, inorganic, and simple molecular materials near and below Tg. Data analyses yield zero entropy temperatures that are comparable with available Kauzmann values. The AG formulation, when coupled with a few plausible ancillary assumptions, predicts correlations between the Arrhenius parameters x, Δh*, and the KWW exponent β that are observed experimentally. It is suggested that the AG primary activation energy, Δμ, is the single causative factor that generates these correlations.
New NMR Methods that Probe the Structure of Glasses
Authors: Tycko Robert , Dabbagh Gary
Published: March 2011

Two-dimensional NMR methods allow a determination of the relative orientations of nearby molecules in polycrystalline and noncrystalline solids. We describe these methods and present applications to the determination of the crystal structures of two forms of polycrystalline methanol and to the investigation of short range molecular orientational ordering in methanol glass and in atactic PMMA.
Permeation of Selected Organic Compounds Through Untreated and Barrier-Treated High-Density Polyethylene
Authors: Kathios Daniel J. , Ziff Robert M.
Published: March 2011

The permeation rates of alkanes, alcohols, and aromatic hydrocarbons through untreated, fluorinated, and sulfonated high-density polyethylene (HDPE) were measured at a variety of temperatures and solvent compositions. The results were then analyzed to separate the individual contributions that solubility and diffusion make to the overall permeation rate. These results are discussed in terms of the chemical characteristics of the permeating constituents, and the barrier treatments on the HDPE surface.
Application of a Classical Force Field for Polyvinylchloride Derived from Ab initio Calculations.
Authors: Ludovice Peter J. , Jaffe Richard L. , Yoon Do Y.
Published: March 2011

Ab initio calculations were used to characterize the inter- and intramolecular energy surfaces for polyvinylchloride (PVC) model compounds and a classical force field was fit to these energy surfaces. This new force field will be used in molecular mechanics and stochastic dynamics simulations to analyze the atomic level morphology of PVC.
Strong and Fragile Behavior in Liquid Polymers
Authors: Angell C. A. , Monnerie L. , Torell L. M.
Published: March 2011

In the light of the strong and fragile classification of simple liquids we review some of the relaxation data for some well-known polymers to see the extent to which a similar pattern may be manifested. Relaxation time data rather than viscosity data are used in the polymer case to avoid complications from long chain effects on the Vogel-Fulcher equation pre exponent. A combination of light scattering and 13C NMR data seem to provide the most reliable guide to the microviscosity of interest to the classification. A pattern similar to that for viscous liquids is recovered with polyisobutylene, the “strongest” chain polymer and bisphenol polycarbonate, the most fragile. The extent to which correlations of other properties with fragility, found in the non-polymeric liquids cases, will carry over to the polymer case is still being evaluated, though the work of Hodge on the analysis of the more complicated problem of non-linear thermal relaxation, suggests the carry over may be extensive.
Thermal Treatment of Hg Containing I-VI Semiconductors by Annealing in a Mercury Bath (AMEBA)
Authors: Kalish R. , Uzan-Saguy C.
Published: March 2011

An extremely simple and inexpensive technique (AMEBA) for the thermal treatment of Hg containing specimens which permits short or long time annealing in a Hg rich atmosphere is described. It is based on the immersion of the sample, properly protected by proximity caps in, or above, a hot mercury bath. The sample assembly is such that it permits Hg vapors, but not the liquid, to reach the specimen's surface.

The usefulness of AMEBA in improving the electrical and structural properties of as-grown Hg1-xCdxTe (x = 0.21) and in removing ion implantation related damage as well as electrically activating B implants in various p-type HgCdTe samples is demonstrated. All the data presented show that AMEBA treatment yields results which are comparable or superior to those obtainable by convensional annealing methods.
Ohmic Contacts on N-Type Hg0.4Cd0.6Te.
Authors: Leech Patrick W. , Reeves Geoffrey K. , Kibel Martyn H.
Published: March 2011

The electrical characteristics of In, Sn, Au and Pt contacts on n-type Hg0.4Cd0.6Te formed in the presence and absence of prior In2+ implantation have been examined. Measurements of specific contact resistance made using a Transmission Line Model have shown that the unimtlanted In/Hg0.4Cd0.6 and Sn/Hg0.4Cd0.6 junctions gave values of pc = 3.0x10−3 to 4.0x10−3 ohm.cm2. Auger sputter profiles of the asdeposited In/Hg0.4Cd0.6 and Sn/Hg0.4Cd0.6 interfaces have shown a significant in-diffusion of the metal overlayer. The influence of shallow In2+ implantation prior to metallization was an increase in pc which occurred above a dose of 1013 ions/cm2. In contrast, Pt and Au formed Schottky barrier diodes on n-type Hg0.4Cd0.6 with øb=0.69eV for Pt and øb=0.79eV for Au. With prior In2+ implantation, both Pt and Au contacts exhibited an ohmic behaviour with pc= 2x10−1 ohm.cm2. These results have significance in the fabrication of devices for 1.0 -2.5μm optical communications.
Photoluhi Nescence of Inas/InAsPSb and InAs/Heterojunctions
Authors: Baranov A.N. , Bresler M.S. , Gusev O.B. , Moiseev K.D. , Sherstnev V.V. , Yakovlev Yu. P. , Yassievich I.N. , Ioffe A. F.
Published: March 2011

Photol uminescence of p-P InAs/InAsPSb and InAs/InAl AsSb heterojunctions grown by LPE method was studied at liquid helium temperature. The recombination spectra contained a new broad band lying between the substrate and the layer lines which was identified as an emission from the interface. This line is characterized by a strong blue shift when the excitation intensity increases. The intensities of bulk and interface lines show an unusual dependence on the pumping power. On the basis of experimental findings the interface line is attributed to emission from electrons confined at the interface due to reflection of elecctrons moving above the barrier.
The Growth Mechanisms of GaSb Epitaxial Film by MOCVD
Authors: Ueng H. Y. , Chen S. M. , Su Y. K. , Juang F. S.
Published: March 2011

The growth reaction mechanism was experimentally investigated for TEGa and TMSb used for MOCVD GaSb epitaxial growth. The variations of growth rate, substrate temperature, the V/III ratio and the mole-fraction of III and V source gases, were detailly considered and investigated with regard to their effect on electrical and optical properties were measured during the epitaxial process. The experimental results were used to provide an inspection on defects interaction mechanisms and on the type of conductivity. Based on the investigation of growth mechanism, at 470°, a high quality GaSb epitaxial film 1 with 3 mobility, 634 cm2/V*sec and low hole concentration, 1.67x1016 cm−2 was obtained.
Mev Ion Beam Applications In III-V Semiconductors
Authors: Elliman R.G. , Ridgway M.C. , JOHNSON S.T. , Williams J.S.
Published: March 2011

This paper reviews some key areas where MeV ion beams can be applied to III-V semiconductor materials. In particular, ion damage is assessed for various III-V materials in terms of implantation parameters, especially substrate temperature and dose rate. Implant isolation, involving the introduction of damage to remove carriers and achieve highlyresistive layers, is assessed for MeV irradiation. It is concluded that MeV ions can provide deep, uniform damage with a single-energy implant. Finally, improved epitaxy of amorphous InP with MeV ions is demonstrated.
Temperature Dependence of the Linewidth and Peak Position of the Intersubband Infrared Absorption in GaAs/Al0.3Ga0.7As Quantum Wells
Authors: Manasreh M. O. , Stutz C. E. , Evans K. R. , Szmulowicz F. , Fischer D. W.
Published: March 2011

The linewidth and peak position (vo) of the intersubband transition (IT) in GaAs/Al0.3Ga0.7As multiple quantum wells are studied as a function of temperature using the infrared absorption technique. We find that electrons in the GaAs well are weakly coupled to the GaAs normal optical phonon mode. The total integrated area of IT absorption is found to be approximately constant in the samples that were doped in the well but temperature dependent in the samples that were doped in the barrier. We also find that vo increases as the temperature decreases. This blue shift is found to increase as the dopant concentration is increased. We calculated the absorption spectrum in a nonparabolic-anisotropic envelope function approximation including temperature dependent effective masses, nonparbolicity, conduction band offsets, the Fermi level, and lineshape broadening. Our results indicate that a large manybody correction, in particular an exchange interaction (Eexch) for the ground state, is necessary to account for the observed blue shift as the dopant concentration increases.
High-Quality InGaAsP Crystals Grown by MOVPE Using TBA and TBP
Authors: Kuramata A. , Yasmazaki S. , Nakajima K.
Published: March 2011

TBA and TBP are attractive candidates for group V sources for MOVPE growth from the viewpoint of safety. We studied how the composition of InGaAsP crystals depends on growth conditions, and investigated its electrical and optical properties. The relationship between group V sources and crystals indicates that TBA and TBP decompose into AsH and PH. Since there is no carbon in AsH and PH, carbon contamination in the crystals is expected to be small. Carrier concentrations ranged from 5×1014 cm−3 to 1.5×1015 cm−3. Photoluminescence spectra at 4.2K showed strong band-edge emission with no acceptor-related emission. Based on the electrical and optical properties of the crystals, we conclude that high-quality InGaAsP crystals can be grown using TBA and TBP.
Peculiarities of the Far-Infrared Reflection Spectra of the Doped Lead-Tin Tellurides Revealing the Persistent Photoconductivity Effect
Authors: Belogorokhov Aleksander I. , Ivanchik Ivan I. , Khokhlov Dmitriy R. , Popovich Zoran V. , Romchevich Nebojsha
Published: March 2011

We measured the far-infrared reflectivity spectra of PbTe(Ga) and Pb1−xSnxTe(In) - materials revealing the Persistent Photoconductivity effect at the low temperatures T<Tc; Tc≈80K and 25K, respectively-The reflectivity spectra display the singuliarity nearby the plasmon-phonon minimum. The spectra may be fitted satisfactory by means of the introduction of an additional oscillator into the dispersion relation. The result is interpreted in the framework of the model taking into account the temperature change of the one-electron metastable impurity state Position in the configuration-coordinate space. The oscillator corresponds to the two-electron - one-electron state transitions. Some previously unexplained results find the satisfactory interpretation in the framework of the model Proposed.