bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Solutes on Phase Stability in A13 Nb
Authors: Subramanian P. R. , Simmons J. P. , Mendiratta M. G. , Dimiduk D. M. 
Published: March 2011

ABSTRACTAlloying transition metal trialuminides such as Al3Nb with appropriate ternary elements may stabilize the ordered cubic Ll2 structure relative to the DO22 structure. This may enhance the symmetry related contributions to plastic flow, thereby aiding in overcoming the low ductility in the trialuminide systems. The present investigation was directed towards exploring the potential for obtaining new ternary Al3Nb-based intermetallics with the Ll2 structure. The effects of various ternary elements on the phase stability of A13Nb were studied by SEM, XRD, and EPMA. Results of the A13 Nb-X phase relationship studies are presented. Preliminary microhardness results on the ternary DO22 Al3Nb-X phases are also reported. The predictive capabilities of Pettifor's structural stability scheme are evaluated in the light of the present investigation.
Simultaneous Chromizing-Aluminizing Coating of Nickel and Nickel-Base Superalloys
Authors: Ravi V. A. , Rapp R. A. 
Published: March 2011

ABSTRACTNi and Ni-base alloys have been simultaneously chromized-aluminized by a halide-activated pack cementation coating process. The computer program SOLGASMIX was used to calculate the equilibrium partial pressures of the gaseous species. Chloride-activated packs are predicted to be chromizingaluminizing while fluoride-activated packs are not. Codeposition of Cr and Al occurs in packs containing 90–95 w/o Cr in the masteralloy and either NaCl, CrCl2 or NH4 C1 as the halide salt activator at 1273K.
Fatigue/Creep Interactions in Ni3Al-Base Alloys
Authors: Camus G. M. , Duquette D. J. , Stoloff N. S. 
Published: March 2011

ABSTRACTStress-controlled fatigue tests and fatigue crack growth rate tests respectively have been carried out on two Ni3Al Cr/Zr alloys, IC 218 at 600°C and 800°C, and IC 221 at 800°C, in vacuum, at various test frequencies. Decreasing the test frequency and/or increasing the temperature leads to a decrease in the number of cycles to failure, and a gradual disappearance of a fatigue fracture zone. In fatigue crack propagation tests, the crack growth rate only decreases at the lowest frequency and remains constant in the major part of the frequency range investigated. The fatigue propagation mode in all cases is intergranular. These trends are shown in both cases to be related to a true creep component but, under fatigue crack growth test conditions, crack blunting intervenes gradually as the frequency is decreased, leading therefore to a less severe frequency effect.
Oxidation Behavior of Ni3Al-8Cr-0.1B Alloy Containing Zr Addition
Authors: Jiangting Guo , Chao Sun , Hui Li , Hengrong Guan 
Published: March 2011

ABSTRACTThe isothermal oxidation behavior of Ni3A1 + 8Cr + 0.1B alloy containing zirconium addition was studied over a temperature range 850 to 1150°C and for periods up to 100 h. The results show that isothermal oxidation kinetics of the alloys at various temperatures obey a parabolic law. The addition of zirconium to Ni3A1-8Cr-0.1B alloy improves oxidation resistance at 850 to 950°C. However, the additive results in a considerable weight gain at 1050 to 1150°C. The structure of scale and phase transformation of the surface zone beneath the scale have been investigated. The addition of zirconium leads to the formation of adherent scale at all temperatures, since the internal oxides, like “tree roots” between the oxide scale and the substrate, are developed during oxidation.
The Tensile Behavior of a Ni3Al-Based Composite with TiC Reinforcement
Authors: Fuchs Gerhard E. 
Published: March 2011

ABSTRACTThe tensile properties of a powder processed intermetallic matrix composite (IMC) and a similarly processed matrix alloy were investigated in the temperature range 298–1273K. The matrix alloy utilized in the study was the advanced nickel-aluminide IC-221 (Ni-16Al-8Cr-1Zr-0.05B). The composites contained 25 vol% TiC particulate reinforcement. The specific modulus of the composites was 20–30% higher than that of typical Ni-base superalloys. The yield strength of the composites were 10–20% greater than that of the matrix at all test temperatures. However, the composites exhibited lower ductility than the matrix. SEM fractography revealed that tensile failure occurred at the matrix/particulate interface. However, remnants of the matrix was observed on TiC particles on the fracture surface, suggesting good matrix/particle bonding. The strengths of the composites were very competitive with Ni-base superalloys.
Effect of Vanadium on Plastic Deformation in Llo TiAl Compound Alloys
Authors: Whang Sung H. , Hahn Yoo-Dong 
Published: March 2011

ABSTRACTTernary Ti-Al-V (Llo) alloys containing vanadium up to 10 at.% and aluminum in the range of 50–55 at.% were prepared. Miniature specimens machined from these alloys were deformed in uniaxial compression at room temperature.The yield stress, and fracture stress and strain were determined with respect to vanadium and aluminum concentration. The deformed alloys were electropolished into thin foils and studied by TEM. In particular, the types of dislocations, stacking faults and twins in the Ti-Al-V alloys were investigated by TEM.
Experimental Determination of the Ti-Nb-Al Phase Diagram At 1200°C.
Authors: Jewett T. J. , Lin J. C. , Bonda N. R. , Seitzman L. E. , Hsieh K. C. , Chang Y. A. , Perepezko J. H. 
Published: March 2011

ABSTRACTStudies consisting of both bulk sample and diffusion couple experiments have been conducted in order to establish an isothermal section of the Ti-Nb-Al system. Bulk samples were prepared by arc-melting and then annealed in a gettered, flowing, argon atmosphere for extended equilibration periods. The results obtained so far have established the existence of two ternary phases with the following approximate compositions, TI (Ti-18 at% Nb-34 at% Al) and T2 (Ti-ll at% Nb-44 at% Al). Moreover, several of the binary phases were found to have extensive solubilities, including the TiAl phase. The phases TiAl3 and NbAl3 form a continuous solid solution. Several heterogeneous equilibria were also determined. Determination of these phase fields was accomplished through the use of electron microprobe analysis (EMPA), x-ray diffraction, microstructural observations and backscatter electron imaging (BEI).
Annealing Studies of B2 FeAl
Authors: Schmidt Berndt , Nagpal Pavan , Baker Ian 
Published: March 2011

ABSTRACTRods of five FeAl alloys whose compositions span the B2 phase field (34–51 at. % Al) were produced by multiple hot extrusions of ingots. Samples of each alloy were annealed in air at 1173K and 1473K in order to study the effect of alloy composition on both the grain growth kinetics and on the rate of oxidation. Little oxidation occurred at 1173K but at 1473K the oxidation rate was found to decrease with increasing aluminum concentration. The predominant oxide was found to be α-A12O3. The grain size was found to increase rapidly during the first hour of annealing at both temperatures after which it increased more slowly. The grain growth rate was found to decrease with increasing aluminum content.Hardness measurements were made on both as-extruded and annealed samples of FeAl. Hardness increased with increasing aluminum content. The hardness was higher in annealed and air-cooled samples due to vacancy retention. Compression tests of air-cooled, annealed samples also showed higher yield strengths than as-extruded samples. Yield strength and strain hardening rate were found to increase and the ductility was found to decrease with increasing aluminum content.
Effect of Aluminum Level on Boron Clustering in Ni3Al
Authors: Horton J. A. , Miller M. K. , Liu C. T. , George E. P. , Bentley J. 
Published: March 2011

ABSTRACTIn alloys containing 0.24% boron, atom-probe field-ion microscopy (APFIM) revealed the presence of boron clusters in Ni-25 at. % Al and Ni-26 Al but not in Ni-24 Al. The observed boron clusters generally consisted of two to three boron atoms with a maximum size of 10 atoms. Quench rates that ranged from rapid solidification to furnace cooling had little effect on the clustering. The occurrence of the clustering coincides with a higher rate of boron strengthening as measured by an increase in the yield stress per atomic percent boron, and it also coincides with a reduced amount of boron segregation to grain boundaries. The levels of nickel and boron were highly variable on grain boundaries in rapidly solidified material and therefore no consistent indication of nickel enrichment at the grain boundaries associated with boron segregation was found. This result suggests that cosegregation of nickel with boron may not be necessary for the ductilization of Ni3Al by boron, since the rapidly solidified material is also ductilized by boron and exhibits segregation of only boron to the grain boundaries.
Synthesis and Structural Characterization of Rigid Rod-Like Unsubstituted Quinoline Oligomers
Authors: Chiang Long Y. , Kastrup Rodney V. , Hsu Chang S. , Swirczewski John W. 
Published: March 2011

ABSTRACTThe structure of quinoline oligomers synthesized by the catalytic dehydrogenative condensation reaction of 1,2,3,4-tetrahydroquinoline was elucidated on the basis of various spectroscopic data including the 2D COSY 1H NMR. The x-ray crystal structural study of two quinoline dimers successfully isolated from the bulk material resolved the puzzle of ring conjunction positions between quinoline units of the oligomer product. A reaction mechanism is proposed. From this mechanism a delicate balance between dehydrogenation and polymerization activity of the catalyst is required to optimize the yield and the molecular weight of the product.
The Synthesis of Benzothiazole Polymers with Perpendicularly Attached Phenyl Substituents
Authors: Feld William A. , Chang YiHua , Peak John D. , Wierschke Scott G. , Chen Join Pin 
Published: March 2011

ABSTRACTA series of 2-aryl-4,7-benzothiazoledicarboxylic acids have been synthesized from the corresponding dimethyl derivatives. These derivatives contain the phenyl, and the p-bromo-, mchloro-, p-chloro-, m-methoxy-, and p-methoxyphenyl aryl substituents. The phenyl, pchlorophenyl and p-methoxyphenyl substituted diacids were polymerized with 2,5-diamino-1,4- benzenedithiol dihydrochloride to yield the corresponding poly(benzothiazole)s. The polymers were of low molecular weight (intrinsic viscosity as high as 1.7) and did not show enhanced solubility in common solvents.
An Heterocyclic Aromatic Polymer and Its Mechanical Properties
Authors: Mukai Seiichi , Nozawa S. , Kimura M. , Tayama T. 
Published: March 2011

ABSTRACTA novel polyimide-based heterocyclic polymer, polyimide benzobisthiazole (PIBT), was prepared from diaminophenylene benzobisthiazole (DAPBT) and pyromellitic acid dianhydride (PMDA). Fibers with tensile modulus of 220 GPa were obtained from PIBT; this modulus value is consistent with the 430 GPa modulus determined by wide-angle x-ray diffraction (WAXD) analysis. Unoriented isotropic films exhibited significantly lower modulus values in the range of 10 GPa. Block copolymers of PIBT with thermoplastic segments were synthesized in an effort to prepare molecular composites. These materials showed a dramatic decrease in melt viscosity and had modulus values lower than observed in isotropic PIBT films.
Lattice Simulation of Mixtures of Flexible and Semi-Flexible Chains
Authors: Cifra P. , Karasz F.E. , Macknight W.J. 
Published: March 2011

ABSTRACTMiscibility behavior in a binary polymer mixture composed of flexible and semiflexible chains has been examined by Monte Carlo simulations on a cubic lattice. It is shown that as the flexibility of one component in an initially miscible mixture of flexible chains of both kinds is reduced the miscibility of the system is not necessarily lost. In fact, flexible chains in the mixture can adjust to this situation and the equilibrium number of segmental contacts between the blend components is retained. The situation is changed in systems in which the loss of flexibility is coupled with an aggregation tendency of the semiflexible chains. The disparity between blend components due to the presence of orientational correlations between the semiflexible chains to a certain extent drives the system towards demixing. However, the dominant role in miscibility behavior in mixtures of flexible and semiflexible chains is played by intermolecular interactions between blend components.
Film Processing and Applications for Rigid-Rod Polymers
Authors: Lusignea Richard W. 
Published: March 2011

ABSTRACTHigh strength, high modulus (2 GPa, 270 GPa, respectively) films have been produced with controllable planar orientation. Films were extruded from high viscosity nematic polymer solutions using rigid-rod aromatic heterocyclic polymers. Novel solution processing and treatment were used to control orientation, microfibrillar structure and texture, and physical properties. The coefficient of thermal expansion of these films was tailored by orientation and addition of secondary materials. This resulted in applications for dimensionally stable electronic substrates and structures for spacecraft. Other applications include high temperature barrier films, thin-walled structures, lightweight capacitors, high temperature insulation and cryogenic tanks.
Some Physical and Mechanical Properties of Pbo Fiber
Authors: Im J. , Percha P.A. , Yeakle D.S. 
Published: March 2011

ABSTRACTThe tensile properties of poly (paraphenylene benzobisoxazole) or PBO fiber strands were studied using two variables: gage length and the number of twists per inch. The gage length was varied from 1 to 10 inches with 2 twists of the fiber per inch. The effect of the number of twists per inch was studied by varying the number of twists from zero to 10 along a 5-inch gage length. The trends of tensile strength and modulus due to these variables were established and appropriate explanations of these behaviors are provided.The coefficient of thermal expansion (CTE) was studied on bare strands of PBO and Kevlar 49 (a product of Du Pont de Nemours & Co.) fibers, using a Du Pont 943 Thermomechanical Analyzer (TMA) equipped with a film and fiber tension assembly. The axial CTE of both fibers exhibited a dependence on the small dead load employed to keep the fibers straight. Kevlar 49 fiber, when wet, attained a much less negative value of CTE than when dry. In contrast, PBO fiber absorbed very little moisture, and the CTE remained unchanged.
Computational Predictions of the Tensile and Compressive Properties of Rigid-Rod Polymers
Authors: Wierschke Scott G. 
Published: March 2011

ABSTRACTThe Austin Model 1 (AM1) semiempirical molecular orbital method has been used to calculate tensile moduli and molecular tensile and compressive deformation for several rigid-rod polymers and a graphite model. The calculated moduli are an improvement over previous Modified Neglect of Differential Overlap (MNDO) calculations. These are the ultimate moduli or the perfectly aligned bulk systems. By analyzing the deformation of polymer molecules in tension and compression, the failure modes and weak points in the molecules can be determined. In compression, all the heterocyclic rigid-rod polymers exhibit a “bending” failure mode. In tension and compression, the phenyl group in the rods undergoes in-plane deformation more easily than the heterocyclic moiety, thus causing a lowering of the modulus. The hypothetical “ladder” polymer, polyacene, shows higher tensile and compressive resistance than any of the rods, suggesting that further study into the ladder polymers is warranted.
Molecular Packing and Crystalline Order in Polybenzobisoxazole and Polybenzobisthiazole Fibers
Authors: Fratini Albert V. , Lenhert P. Galen , Resch Timothy J. , Adams W. Wade 
Published: March 2011

ABSTRACTThe structures of poly(p-phenylenebenzobisthiazole) (PBZT) and poly(p-phenylenebenzobisoxazole) (PBO) fibers have been investigated by fiber diffraction techniques. d-spacings were obtained from equatorial and meridional scans recorded on a four-circle diffractometer. Intensity data were derived from x-ray rotation patterns taken on Weissenberg and vacuum cylindrical cameras. Unit cells were found to be monoclinic and non-primitive, each containing two chains per cell of dimensions a = 11.79(2), b = 3.539(5), c = 12.514(9) A, γ = 94.0(2)o for PBZT; and = 11.20(1), b = 3.540(2), c = 12.050(3) Å, γ = 101.3(1) for PBO. The fiber axes correspond to c. The conformational torsion angle between the bisthiazole and phenylene units and the orientation of chains within the unit cells were obtained from a ‘linked-atom least-squares’ (LALS)refinement procedure. A packing model is proposed for each polymer in which two independent molecular chains are displaced longitudinally by discrete rather than random increments. Primitive unit cells (Z = 1), besides requiring perfect axial registry of molecular chains, suffer from the occurrence of short intermolecular contacts and are rejected from further consideration.
Structure Analysis of a Rodlike Macromolecule: Poly(2,2'-(p,p'-Biphenyl)−6,6'-bis(4-Phenylquinoline))
Authors: Burkhart Craig W. , Lando Jerome B. , Stille John K. 
Published: March 2011

ABSTRACTUniaxially oriented, crystalline fibers of poly(2,2'-(p,p'-biphenyl)- 6,6'-bis(4-phenylquinoline)) [PBPQ], were subjected to structure analysis via x-ray diffraction and molecular packing analysis. Packing analysis was required due to the sparse and diffuse nature of the fiber diffraction photographs. The combination of the two techniques allowed us to resolve the crystal structure. PBPQ packs in a syn conformation, in a modified herringbone structure. It has a unit cell of a = 16.2Å, b = 5.31Å, c = 21.4Å. There are two independent chains in the unit cell. An overview of the refinement of the crystal structure, the packing analysis and the crystallography are presented.
The Dynamics of Phase Separation in Rigid-Rod Molecular Composites
Authors: Chuah Hoe Hin , Kyu Thein , Helminiak T. E. 
Published: March 2011

ABSTRACTThe thermally induced phase separation of poly(p-phenylene benzobisthiazole)/ Nylon 66 molecular composites was followed by small-angle light scattering which showed the development of a scattering ring. The intensity increased and the ring moved towards the main beam as a function of time.The scattering vector qm and intensity maxima Im scaled as qm~t−∝ and Im~tβ with ∝~ 0.33 and β = 0.91-0.95, in close agreement with the cluster dynamics prediction of Binder. However, at longer times, the increase in both qm and Im slowed down dramatically indicating a different mechanism. The structure function S(x) was used to test the validity of universal scaling for a rigid-rod/flexible coil polymer blend. At large x, S(x) scaled to the power of −2.4 in x, which is in between values predicted for systems with one and two-dimensional diffusion.
Orientational Order of α-Helical Poly (γ-Benzyl L-Glutamate) in the Lyotrao-Phiecl Ilciaqlu Idp Oclryy(yS-Tbaelnlziynle Ls-Tate and Conformation of the Pendant Side Chain
Authors: Abe Akihiro , Yamazaki Toshimasa 
Published: March 2011

ABSTRACTDeuterium NMR studies have been performed on variously labeled PBLG samples in the lyotroplc liquid crystalline state. The orientational orders S of the a-helical backbone were estimated from the observed quadrupolar splittings ∆v of the N-D and Cα-D bond. The values of S decrease gradually by dilution until the upper equilibrium concentration (B-point) is reached. The concentration dependence of Scrit has been compared with those derived from standard theories. The relatlve orientation of side chains with respect to the backbone was elucidated by the rotational isomeric state analysis of the ∆v/S data observed for the γ-, γ-, and ζ-methylene, and p-benzyl deuterons. The results indicate that the steric overlaps between adjacent side chains play an important role in determining the preference of conformations in the PBLG system. A similar analysis has been extended to poly(L-glutamic acid) esters carrying a homologous series of ester residues, -C(O)O(CH2)nC6D5 with n = 2 and 3. A distinct odd-even oscillation was observed for the orientation of the terminal phenyl groups with n.
Distribution and Transport of Charge Carriers in Heterogeneous Electrolyte Systems
Authors: Maier Joachim 
Published: March 2011

AbstractThe thermodynamic point defect concentrations for both ionic (majority) as well as electronic (minority) charge carriers are considered for different types of heterogeneities appearing in ionically conductive solid materials systems. Particularly, the electrical conductivity is discussed for different types of composite electrolytes. Quantitative space charge arguments are shown to be able to explain a variety of different phenomena such as: unusual enhancement of ionic conductivity in two phase samples and in polycrystalline materials, additional conductivity effects in microsized systems; change from cationic to anionic conduction due to heterogeneous doping; simultaneous enhancement of n- and p-conductivity in different electrolyte/ alumina samples, catalytic effects in composite electrolytes as well as chemical interface effects.
Spectroscopic Studies of a Superionic Plastic Phase Crystal: Lithium Sulfate
Authors: Frech Roger 
Published: March 2011

AbstractTemperature dependent Raman spectroscopic studies of single crystal lithium sulfate are summarized. Coupling between sulfate ion bending modes and the lithium ion translatory modes becomes weaker with increasing temperature until the lithium modes can no longer be observed above 250° C. The temperature interval above 450° in the monoclinic phase is marked by the onset of significant sulfate ion reorientational motion, as evidenced by the bandshape studies of the sulfate ion v1, mode and the librational modes. Bandshape analysis of the v3mode in the plastic phase strongly suggests that the symmetry of the sulfate ion potential energy environment has planar anisotropy.The lithium ion-sulfate ion interactions are modeled for correlated sulfate ion configurations as a function of lithium ion position. The results support the role of the octahedral site in lithium ion transitions contributing to the ionic conductivity.
Neutron Diffraction in Superionic Glasses
Authors: Börjesson L. , Elmroth M. , Torell L.M. , Howells W.S. 
Published: March 2011

AbstractNeutron diffraction experiments have been performed on AgI and LiCI doped borate glasses. The experiments reveal a substantial progressive increase of the medium range structural ordering when Agl is introduced into the glass, which is manifested in the appearance of an intense diffraction peak at anomalously low Q-values (0=0.8 Å−1). The observation might be attributed either to density deficits within the boron-oxygen network or to the presence of small clusters of AgI. The conduction path model proposed to explain the high ion conductivity may therefore hold for the AgI doped glasses. In contrast, no additional medium range ordering can be observed when LiCI is used as the dopant salt, which casts some doubts on the microdomain model as an explanation of the high ionic conductivity in superionic glasses.