bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microstructure and Mechanical Properties of Mechanically Alloyed NiAl
Authors: Hwang S. J. , Nash P. , Dollar M. , Dymek S. 
Published: March 2011

ABSTRACTMechanical alloying (MA) has been used to produce NiAl powders from either elemental or prealloyed constituents. The powders were consolidated by hot extrusion resulting in material which was fully dense, with a grain size around 1 μm and a homogeneous distribution of oxide particles with sizes in the range 10 to 100 nm. TEM observation indicates the presence of a significant dislocation density after consolidation. Mechanical properties have been studied by compression testing from room temperature to 1300 K in air. Yield strengths ranged from 1453 MPa to 32 MPa depending on material and test temperature. Work hardening was observed at all test temperatures for both materials. Substantial ductility was observed even at room temperature where it exceeds 7.5 %. The effects of microstructure on the mechanical properties are discussed.
The Mechanical Properties of A Ni-30Al-2OFe-0.05Zr Intermetallic Alloy in the Temperature Range 300–1200 K.
Authors: Raj S. V. , Noebe R. D. , Locci I. E. 
Published: March 2011

ABSTRACTTensile tests were conducted on an extruded Ni-30(at.%)Al-20Fe-0.05Zr intermetallic alloy in the temperature range 300–1200 K and the microstructures were characterized by optical, scanning and transmission electron microscopy. The alloy did not exhibit any room temperature ductility and failed by transgranular cleavage at a stress of about 710 MPa. This mode of fracture was observed at and below 873 K with the total ductility being less than 2.5%. However, the failure mode changed to dimpled fracture, triple point cracking and rupture above 873 K. Scanning electron microscopy of the fracture surfaces revealed that transgranular cleavage failure had always originated at pre-existing defects. In these cases, the fracture stress exhibited a good correlation with the defect size in accordance with linear elastic fracture mechanics, where the critical stress intensity factor was estimated to be about 4 MPa m1/2.
Structure/Property Relationships in a Rapidly Solidified and Annealed Ternary Iron Aluminide
Authors: Décamps B. , Gibsont M.A. , Morton A.J. , Wolfenden A. 
Published: March 2011

ABSTRACTRapidly solidified strips of Fe66.5-A128.5-Cr5 alloy with the addition of 0.5wt.% TiB2, were produced by planar flow strip casting. Correlations of the microstructure and room temperature mechanical properties were made for strips in the as-cast condition and after annealing at 1273K for periods up to 4hrs. The results showed that grain size, tensile strength, ductility, hardness and Young's modulus were very stable for the times investigated. Studies of tensile fracture surfaces revealed essentially 100% transgranular cleavage in the ascast strip with a greater tendency for intergranular failure after prolonged exposure to high temperatures. TEM studies of this alloy revealed diffraction patterns characteristic of DO3 ordering but the dislocations observed in both ascast and deformed specimens were those typical of the B2 structure without any extended APBs. This is attributed to the very fine DO3, domain size . At room temperature <111> slip is predominant.
High Temperature Measurements of Neutron Diffuse Scattering in a FeAll9.Sat% Single Crystal. Influence of Magnetism on Chemical Order.
Authors: Pierron-Bohnes V. , Cadeville M.C. , Schaerpf O. , Finel A. 
Published: March 2011

ABSTRACTThe influence of magnetism on atomic short range order is shown in a single crystalline FeAl19.sat% alloy in the disordered phase. The short range order has been measured in the paramagnetic state between 973 and 1573 K on D7 at ILL through neutron diffuse scattering in the [110] plane. The effective pair interaction potentials V1 , V2, V3 and V5 are calculated through an inverse cluster variation method. The results are compared to those obtained through X-ray diffuse scattering on the same alloy frozen in the ferromagnetic order state at 772 K. The effect of magnetic coupling on the atomic order is the most important on the 1st effective potential, which is smaller by about a factor 2 in the ferromagnetic phase than in the paramagnetic one.
Electronic Structure of Planar Faults in Tial
Authors: Woodward C. , Maclaren J. M. , Rao S. 
Published: March 2011

ABSTRACTThe mechanical behavior of intermetallic alloys is related to crystal bonding and the influence of bonding on the core structure of dislocations formed in these compounds. These combined effects influence the deformation behavior in an, as yet, undefined manner. However, in a way that gives rise to unusual behavior, such as the anomalous temperature dependence of flow stress observed in TiAl. Recent studies have suggested a particular relationship between the directional bonding in TiAl and dislocation mobility. To better understand the flow behavior of intermetallics, and as a beginning toward bridging the gap between electronic structure and flow behavior, we have calculated the electronic structure of various planar faults in TiAl. The self consistent electronic structure has been determined using the layered Korringa Kohn Rostoker (LKKR) method which embeds the region containing the defect between two semi-infinite perfect crystals. Calculated defect energies agree reasonably well with other theoretical estimates, though overestimating experimental values. The changes in bonding taking place in the vicinity of the planar defect will be discussed and illustrated through the density of states and charge density plots.
Structure Dependence of Tensile Creep Behavior in Thermo-Mechanically-Treated Ti-50Mol%Al Intermetallics
Authors: Takahashi Tohru , Oikawa Hiroshi 
Published: March 2011

ABSTRACTTensile creep properties have been studied in Ti-50mol%Al intermetallics prepared by ingot metallurgy. Four types of structure were obtained in as-cast material (C), homogenized material (CA), isothermally forged material (F) and forged-and-recrystallized material (FA). Structural effects was investigated by comparing creep properties such as minimum creep rates, fracture strains and creep life among C, CA, F, and FA materials. Creep characteristics were strongly dependent upon the structure.
High-Temperature Deformation Behavior of the γ Alloy Ti-48Ai-2Cr-2Nb
Authors: Shih Donald S. , Scarr Gary K. 
Published: March 2011

ABSTRACTThe hot-workability of a two-phase (γ+α2) alloy, Ti-48A1-2Cr-2Nb, has been studied by conducting isothermal compression tests to 0.8 true strain over the temperature range of 975–1200°C at strain rates between 1×l0−1 and 3×10−3s−1. A deformation map showing temperature, strain rate, soundness of deformation, and isostress contours was constructed. Good workability is found from the low temperature/low strain rate regime to combinations of high temperature and either high or low strain rate. The upper-limit flow stress for good workability is between 450 and 500 MPa. Deformation induced softening occurs at all conditions. SEM and TEM examinations of the deformed specimens reveal that non-uniform deformation takes place at all strain rates, but cracking occurs mostly at high strain rates (e.g. 1×10−1s−1), especially combined with low temperatures. The cracking appears to progress primarily along γ/α2interfaces. It is thought that non-uniform deformation develops channels of shear bands, which in turn promote localized recrystallization, thus accommodating higher strains.
Preliminary Indications of a Slight Improvement in the Ductility of Ni3Ge With Boron
Authors: Fang J. , Schulson E. M. 
Published: March 2011

ABSTRACTPreliminary work was conducted to investigate whether 0.1 at% boron affects the ductility of Ni-rich Ni3Ge (Ni-23.5 at%Ge). Cracks were observed in the unmodified alloy around hardness indentations and on fresh surfaces upon abrasive cutting. No cracks appeared in the modified alloy. Also, SEM fractographs showed that with the boron addition the morphology changed from pure intergranular fracture to a mixture of intergranular and transgranular fracture, albeit predominantly intergranular. Tensile tests indicated that the boron addition slightly improves the ductility of Ni-rich Ni3 Ge.
Cavitation-Erosion Resistance of Thick-Film Thermally Sprayed Niti
Authors: Peter Jardine A. , Horan Y. , Herman H. 
Published: March 2011

AbstractThermal spray technologies provide a method for depositing high temperature intermetallics. Deposits of Shape Memory Effect NiTi were produced by Electric-Arc Spraying (EAS) of NiTi wire, Vacuum Plasma Spraying (VPS) of NiTi powder, and codeposition of Ni and Ti using VPS. NiTi deposits displayed shape memory effect properties, which are highly sensitive to processing conditions. They were found to also exhibit superior cavitation-erosion resistance. Under identical cavitation erosion conditions, weight losses of 0.41, 1.65 amd 7.71 mg were found VPS, arc-sprayed and blended Ni-Ti deposits respectively. Minimal amounts of NiTi was formed from co-spraying both Ni and Ti powders onto steel substrates.
Structures and Properties of Gamma-Tial Alloys Containing Interstitial Elements
Authors: Huang S.C. , Hall E.L. 
Published: March 2011

ABSTRACTThis paper reports on the effects of carbon, nitrogen, boron, and oxygen on the microstructure and properties of gamma-TiAl alloys. It has been found that nitrogen and boron are capable of altering the solidification structure, whereas the others are not. The additions of >1 at.% B or 0.5 at.% N changed the cast structure from columnar to equiaxed with fine grain sizes. As a result, the strength has been significantly increased. Additional results on phase and structural stabilities will be presented.
Effect of APB Microsegregation on the Strength of Ni3Al with Ternary Additions
Authors: WU Y.P. , Sanchez J.M. , Tien J.K. 
Published: March 2011

ABSTRACTSolid solution strengthening for stoichiometric and non-stoichiometric alloys is studied using a microscopic model that takes into account the micro-segregation of the alloying additions and of the host atoms to antiphase boundaries. Experimental results for four ternary intermetallic compounds, Ni-Al-Si, Ni-Al-Ti, Ni-Al-Hf and Ni-Al-V, are analyzed in the light of the theoretical model. It is found that the athermal increment of yield strength for both stoichiometric and non-stoichiometric alloys can be explained using solid solution strengthening theory provided that the local concentration at the {111} antiphase boundaries between superpartial dislocations is used.
Homogenization of Ingot Metallurgy Near-Gamma Titanium Aluminides
Authors: Semiatin S.L. , Mcquay P. , Stucke M. , Kerr W.R. , Kim Y-W. , El-Soudani S. 
Published: March 2011

ABSTRACTThe elimination of microsegregation and subsequent breakdown of the lamellar structure in near-gamma titanium aluminides was investigated through a series of high temperature homogenization heat treatments and isothermal hot compression tests. The homogenization heat treatment studies revealed that microsegregation could be eliminated after approximately five hours or one and one-half hours at temperatures either 15 C or 40 C, respectively, above the transus in the single phase alpha field. Subsequent attempts to breakdown the coarse prior alpha grain, lamellar structure were successful at low strain rates (∼ 10−3 s−1) and temperatures low in the alpha + gamma phase field, but led to wedge cracking and gross fracture at high strain rates (∼ 1 s−1) high in the alpha + gamma phase field. Subsequent annealing treatments to globularize the hot-worked structure in order to obtain a uniform, fine, and stable grain structure were also identified.
Tensile Fracture Behavior of a Cast Gamma-Titanium Aluminide
Authors: Seetharaman V. , Goetz R. L. , Semiatin S. L. 
Published: March 2011

ABSTRACTThe fracture behavior of a cast gamma-titanium-aluminide alloy (Ti-49.5A1–2.5Nb-l. 1Mn) during deformation processing was investigated using hot-tension testing and isothermal-forging experiments. In uniaxial tension, fracture ductility increased with an increase in the test temperature and a decrease in the imposed strain rate. During open-die forging of this alloy under isothermal conditions, tensile stresses generated due to frictional effects and the associated inhomogeneous plastic deformation led to free-surface fracture via intergranular cracking. The failure observations under these two deformation modes were correlated successfully using a tensile-damage criterion.
High Temperature Corrosion Behaviour of Intermetallic Phases based on Ni3Al
Authors: Brill U. , Klöwer J. 
Published: March 2011

ABSTRACTNickel aluminides based on Ni3Al were continuously cast into 12.4 mm diameter wire in an industrial production machine. Cyclic corrosion tests were carried out on this material in oxidizing, carburizing, sulfidizing and chloridizing atmospheres at temperatures between 750°C and 1100 °C in order to study the time and temperature dependence of high temperature corrosion. The results show, that Ni3Al has a very good oxidation resistance up to 1000 °C. The sulfidation resistance is poor, while resistance against carburization and chlorination is significantly better than that of the commercial alloy 800H andalloy 617.
Crystallization and Matrix Effects on the Electronic Properties of Polymers Doped with CT Salts of TCNQ
Authors: Fann Yang-Cheng , Jansen Susan A. , Hutchins Marygail 
Published: March 2011

ABSTRACTMolecularly doped polymer films have shown potential for applications in electrophotography and molecular electronics. The electrooptical and magnetic properties as well as conductivities are enhanced significantly by doping chargetransfer(CT) complexes or dye into a polymeric matrix, by comparison with nondoped polymer films.Polycarbonate films doped with CT complexes based on 7,7′,8,8′- tetracyanoquinodimethane( TCNQ) were studied from 100K to 450K. Crystallization and formation of ‘nearly’ spaced aggregates within the polymer matrix were observed. These phenomena were affected by several factors such as the film thickness, evaporation process, temperature and concentration within the polymer matrix. Discontinuities in magnetic properties at 200K, possibly due to solvent encapsulation in the matrix, and at about 385K due to glass transition of the polymer were observed.Characterization, conductivity measurements in comparison with pristine complexes, and photoirradiation studies on these doped films are presented.
Ab-Initio Calculations on PPS Oligomers
Authors: Musso G.F. , Piaggio P. , Cuniberti C. , Dellepiane G. , Borghesi A. 
Published: March 2011

ABSTRACTAb-initio STO-3G* geometry optimizations have been carried out on the first two oligomers of poly (p-phenylene sulfide) (PPS), namely diphenyl sulfide (I) (neutral species, radical cation and dication) and 1, 4-bis(phenylthio)benzene (II) (neutral species and radical cation). Aim of the work is to obtain a first theoretical insight into the geometry relaxation effects occurring in the doping of PPS. The results show that i) geometry changes in the radical cation of I are rather small, being much more pronounced in the dication, and ii) in the radical cation of II a strong geometry modification occurs, the central phenyl ring now lying in the plane of the C-S bonds with a clear quinoid-type structure. These findings are in agreement with our experimental results on the same two oligomers.
Helical Sense and Twisting Power in Thermotropic Side–Chain Copolymers
Authors: Krishnamurthy Sushil , Chen Shaw H. 
Published: March 2011

ABSTRACTThermotropic chiral nematic copolymers containing (S)–(–)–1–phenylethyl alcohol and (R)–(–)–methyl mandelate with methacrylate backbone and those containing (S)–(–)–1–phenylethylamine and cholesterol with acrylate/methacrylate mixed backbone structures have been synthesized and characterized. It is found that the helical sense is dictated by chiral/nematic molecular interactions of a steric nature, and that the helical twisting power (HTP) is favored by the structural similarity between the chiral and nematic components. Furthermore, it is shown that HTP can be optimized with a suitable nematogenic comonomer by regulating the backbone flexibility within the acrylate/methacrylate series, which facilitates supramolecular arrangement without affecting the HTP.
A Novel Unsymmetrical Poly(1-N-Carbazolyl) Diacetylene for Non Linear Optics
Authors: Garbarino G. , Dell'erba C. , Cuniberti C. , Piaggio P. , Musso G.F. , Comorefito D. , Lanzani G. , Dellepiane G. 
Published: March 2011

ABSTRACTPhotoinduced absorption spectra of poly(1-N-carbazolyl-penta-1,3.diyne-5-acetoxy) show absorption peaks which depend on the sample preparation and on the temperature. The low temperature spectra show two well resolved absorptions centered at ∼0.5 and ∼1.2 eV respectively. In view of other experimental results on these systems, we have interpreted our data as evidence of charged bipolarons stabilized by interchain interactions.
Birefringence and Order of Liquid Crystal Polymer Solutions
Authors: Mattoussi Hedi , Srinivasarao Moran , Kaatz Philip G. , Berry Guy C. 
Published: March 2011

ABSTRACTBirefringence measurements of nematic solutions of the poly(p-phenylene benzobisthiazole), PBT, using interference between the ordinary and extraordinary waves created when a plane polarized wave enters the crystal, are described. The measured birefringence is high, e.g., ne – no varies from 0.05 to 0.09 at 633 nm for polymer concentrations 4×10−2 < c < 10×10−2(g/cm3). These data are discussed with the implications they have on the order parameter in these solutions.
Steady State and Transient Photoconductivity of Thin Film Polydiacetylene Single Crystals
Authors: Yang Y. , Lee J. Y. , Miller P. , Li L. , Kumar J. , Tripathy S. K. , Matsuda H. , Okada S. , Nakanishi H. 
Published: March 2011

ABSTRACTCharge carrier generation and transport mechanisms in polydiacetylene thin film single crystals., poly-PTS (2,4-hexadiyne-1,6-diol bis(p-toluenesulfonate)) and poly- BTFP (bis-(4-n-butyl-2,3,5,6-tetra-fluorophenyl) butadiyne), are studied by using steady state and transient photoconductivity techniques. The electric field dependence of the steady state photocurrent is superlinear for both samples. Dependence of photocurrent on incident light polarization has been investigated. The polarization dependence of photocurrent has completely different behavior for the polydiacetylene PTS and BTFP. Single-gap transmission line experiment has been designed to directly measure the drift velocity of PTS single crystals. A drift velocity of the order of 106cm/s was measured.
Nonlinear Optical Properties of Polyphosphazenes
Authors: Ferris K.F. , Risser S.M. 
Published: March 2011

ABSTRACTTheoretical second hyperpolarizabilities for a series of iso-electronic conjugated inorganic systems, including polyphosphazenes, have been evaluated using electronic structure methods. The nonlinear optical properties of these molecules are controlled by the electronegativity difference along the backbone, which may be modulated by the electron donating/accepting properties of the ligands.
Optimized Processing Condition for a Photocrosslinkable Stable Nonlinear Optical Polymer
Authors: Lee Jun Y. , Kim Woo H. , Mandal Braja K. , Kumar Jayant , Tripathy Sukant K. 
Published: March 2011

ABSTRACTThe optimum processing condition for a photocrosslinking Nonlinear Optical(NLO) polymeric system was established. Parameters such as change in heat capacity at glass transition temperature, rate of decrease of absorbance of residual uncrosslinked chromophores, and measurement of mass loss upon heating were used to set up the optimum condition. Poly(vinyl cinnamate) was used as the photocrosslinkable polymer and 3- cinnamoyloxy-4-[4-(N, N-diethylamino)-2-cinnamoyloxy phenyl azo] nitrobenzene was used as the NLO molecule. Poling at 70°C for 5 minutes followed by photocrosslinking with a dose of 2.5 mW/cm 2 for 10 minutes results in a stable second order nonlinear optical material.
Theoretical Models of Cooperative Dynamics Near the Glass Transition
Authors: Jäckle Josef 
Published: March 2011

AbstractIt is shown that diffusion in the hard-square and hard-octahedron lattice gases at high particle concentration has cooperative properties resembling molecular relaxation in undercooled liquids near the glass transition. For these models a characteristic length of cooperativity is introduced by an underlying percolation problem, which determines whether permanently blocked particles exist in lattices of finite size. The percolation problem belongs to a general class of bootstrap percolation models. Salient Monte Carlo results for the concentration and size dependence of self diffusion in the hard-square lattice gas are presented. Similarities with the n-spin facilitated kinetic Ising models are also pointed out.
Physical Aging and Isothermal Relaxation in Glassy Polycarbonate Measured by Positron Annihilation Lifetime Spectroscopy
Authors: Hill A. J. , Jones P. L. 
Published: March 2011

AbstractThe free volume behaviour of polycarbonates annealed above and below the glass transition temperature, Tg, is studied. The free volume behaviour as a function of temperature and as a function of time during isothermal relaxation is compared for the different heat treatments. The relaxations which occur during contraction experiments performed after cooling from the heat treatment temperature result in a decrease in free volume for both sets of samples; however, the general decrease is much greater in the polycarbonate annealed below Tg. For the polycarbonate annealed below Tg, the free volume is partially recoverable if the samples are reheated to the original annealing temperature. Differences in the free volume relaxation behaviour during contraction experiments are discussed.
Free Volume Distribution in Polymer Liquid and Glass Evaluated by Molecular Dynamics Simulation
Authors: Roe R. J. , Rigby D. 
Published: March 2011

AbstractMolecular dynamics simulation has been performed with dense systems of alkane-like chain molecules. Distribution of occupied and unoccupied space in the system was then evaluated by the technique of Voronoi tessellation of space and by enumeration of the cavities formed when hard spheres of diameter D were assumed placed on atomic centers. The distribution of cavity volumes is extremely broad and often exhibits a bimodal or trimodal character. These cavities change shape and size with time even at temperatures much below Tg.
Structural Relaxation, “Memory Behaviour”, Specific Heat Anomaly and Localized Motions in Amorphous Solids
Authors: Johari G. P. 
Published: March 2011

AbstractDielectric and mechanical relaxation spectroscopy of thermoplastics and thermosets show that, in the former, ageing is related only to the spontaneous structural relaxation towards a lower energy, but still disordered, structure and decreases the strength of the β- relaxation process. Ageing of a thermoset initially increases the strength of its (dielectric) β-relaxation as a result of diffusionallowed chemical reactions, which increase the number of dipolar groups, and later decreases it towards a limiting value. The decrease in the strength of β-relaxation on ageing of polymers and other amorphous solids suggests that structural relaxation causes a collapse of low-density, high-entropy, regions or “soft-sites” randomly distributed in the structure of a glassy material. The increase in the strength of β-relaxation observed in thermosets is higher than calculated from the extent of chemical reactions that occur during their structural relaxation at T<Tg. It is suggested that these effects should be included in the phenomenological theories for both the physical ageing and “memory behaviour” - the latter can be conveniently studied by both dielectric and mechanical spectroscopy and by differential scanning calorimetry. Structural relaxation also decreases the magnitude of the specific heat anomaly in amorphous solids and can be used to experimentally test the postulate that tunneling centres involved in the low-temperature phonon properties are related to the presence of “islands of mobility” or “soft-sites” in an otherwise rigid glassy matrix.