bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structure Maps and Phase Stability in AlTi3 Alloyed with Rare-Earth Elements
Authors: Liu C. T. , Horton J. A. , Petitifor D. G. 
Published: March 2011

ABSTRACTRare-earth elements including Y, Er and Sc were added to AlTi3 for stabilizing the Ll2 ordered crystal structure, as predicted by the AB3 structure map. The crystal structure and phase composition in the AlTi3 alloys were studied by electron microprobe analysis, X-ray diffraction and TEM. The solubility limit of the rare-earth elements were determined and correlated with the atomic size factor. The results obtained so far indicate that rare-earth additions are unable to change the crystal structure of AlTi3 from DO19 to Ll2. The inability to stabilize the Ll2 structure demonstrates the need to characterize the structure map domains with a further period-dependent parameter.
Investigation of B2 and Related Phases in the Ti-Al-Nb Ternary System
Authors: Bendersky Leonid A. , Boettinger William J. 
Published: March 2011

ABSTRACTAlloy compositions around Ti2 AINb were studied to establish phase equilibria and transformations during cooling from 1100°C and 1400°C. In addition to general results obtained on a wide range of compositions, which include evidence for a broad B2 phase field, transformation of BCC Ti4 Al3 Nb to a phase with an omega-type structure is reported. Detailed analysis indicates that this phase has the B82 structure after annealing at 700°C.
Recrystallization Behavior of Ni3 AI(B)
Authors: Gottstein G. , Kim W. 
Published: March 2011

ABSTRACTThe recrystallization kinetics, structure development, stored energy of cold work, and rolling and recrystallization textures were studied on boron doped Ni76Al24. The recrystallization kinetics were very slow compared to pure metals or disordered solid solutions, but similar to other intermetallic compounds. The development of the deformed and recrystallized microstructure is similar to metals with intermediate stacking fault energy. Despite a lack of massive deformation twinning the rolling texture is a typical brass type texture. The recrystallization texture is not a brass type recrystallization texture, but consists of components, which are related by a 25°<100> rotation among each other and with the deformation texture. The observed phenomena are attributed to the constraints of grain boundary motion in long range ordered structures. It is further shown that Ni3Al does undergo dynamic recrystallization during high temperature deformation.
Grain Boundary and Cavity Surface Segregation in Crept Ni3Al + 0.2at% B AND Ni3 (AI,Hf) + 0.2at% B
Authors: Au-Yeung Patrick H. , Lukowski John T. , White Calvin L 
Published: March 2011

ABSTRACTCreep strengths and ductilities of boron-doped nickel aluminides are significantly improved by small additions of hafnium. Since creep failure in these alloys proceeds by growth and coalescence of grain boundary cavities, effects of Hf additions on the compositions of grain boundaries and creep cavity surfaces were examined using Auger electron spectroscopy (AES). In order to facilitate intergranular fracture in the AES analysis chamber, gage sections from creep specimens were hydrogen charged and copper plated.
Grain boundaries in crept specimens were not flat, and the grains did not exhibit a normal polyhedral appearance. The overall levels of boron detected on the fracture surfaces of the creep specimens were significantly higher than those from uncrept specimens. Additionally, boron was found to segregate more strongly to the grain boundaries while higher concentrations of residual sulfur and phosphorus were detected on the cavity surfaces in both alloys. These results are discussed in terms of the effects of impurity segregation on high temperature grain boundary cavitation.
The Effect of Boron on Microhardness in Ni3 Al Polycrystals
Authors: Qian X. R. , Chou Y. T. 
Published: March 2011

ABSTRACTIn a recent MRS symposium, the effect of boron on grain boundary hardness (GBH) in Ni3Al was reported. Addition of 0.2 at.% of boron decreased the GBH in all three sets of alloys tested (24, 25, and 26 at.% Al). The present paper summarizes the study of the effect of boron on hardness within grains. Boron-induced softening was again observed in grain interiors. However, it occurred only in alloys with 24 and 25 at.% Al, but not in the alloy with 26 at.% Al. An explanation for this behavior is presented.
The effect of Anti-Phase Domain Size on the Ductility of a Rapidly Solidified Ni3Al-Cr Alloy
Authors: Carro G. , Bertero G. A. , WlTTIG J. E. , Flanagan W. F. 
Published: March 2011

ABSTRACTTensile tests on splat-quenched Ni3Al-Cr alloys showed a sharp decrease in ductility with long-time annealing. The growth of the initially very-fine size anti-phase domains showed a tenuous correlation with ductility up to a critical size, where ductility was lost. The grain size was relatively unaffected by these annealing treatments, but the grain-boundary curvature decreased, implying less toughness. An important observation was that for the longest annealing time a chromium-rich precipitate formed, which our data indicate could be a boride. Miniaturized tensile tests were performed on samples which were all obtained from the same splat-quenched foil, and the various domain sizes were controlled by subsequent annealing treatments.
Titanium-Aluminide Alloys Between the Compositions Ti3 Al and TiAl
Authors: Mishurda J. C. , Lin J. C. , Chang Y. A. , Perepezko J. H. 
Published: March 2011

ABSTRACTMany questions still remain about the Ti-Al phase diagram, particularly for the compositions between the intermetallic compounds Ti3Al and TiAl. In an experimental study of the phase equilibria, titanium-aluminum alloys with 44, 46, 48, 50 at.% aluminum were produced by drop casting, HIP, and a double forging process method. Differential thermal analysis (DTA), optical metallography, and residual oxygen analysis were performed in order to characterize the low and high temperature phase equilibria of the alloys. The experimental results are compared with the calculated Ti-Al phase diagram which is being modeled concurrently. For the bcc, hcp and liquid phases, the Margules type of equations are used to represent the excess Gibbs energies. A maximum of six parameters are used for each of the phases. For the TiAl (Llo) and Ti3Al (D019 ) phases, the Wagner-Schottky type of equations are used to represent the Gibbs energies. All of the other phases are treated as line compounds. Values of the solution parameters were obtained by optimization using existing thermochemical and phase boundary data reported in the literature. The calculated results show that the high temperature hcp phase field is stable between approximately 34 at% Al, in equilibrium with β and α2 up to about 48 at% Al in equilibrium with γ and L and forms from the liquid by a peritectic reaction β+L-α. The experimental results obtained to date for the four alloys are consistent with the calculated equilibria which is being refined and also allows for an estimate of the metastable equilibria.
Improvement of Elevated Temperature Material Properties in Intermetallic Compound Ni3Al
Authors: Fujita Akitsugu , Matsumoto Tatsuki , Nakamura Makoto , Takeda Yorimasa 
Published: March 2011

ABSTRACTIntermetallic compound Ni3Al(γ′) is one of the major constituents in Ni-base superalloys. But it is not used by itself for structural use because of its low ductility and low strength.In the present study, the improvement of elevated temperature mechanical properties of Ni3Al intermetallic compound is pursued by addition of such elements as Fe, Ti, Cr, V, Nb, Ta, Mo, W, Zr and Hf. These results show that Ni 3AI which contains some elements substituting for Al has better mechanical properties and creep rupture properties than commercial Inconel 713C.
Corrosion, Wear, and Galling Tests of IC218, a Chromium-Bearing Alloy of Ni3Al
Authors: Dulmaine Bradford A. 
Published: March 2011

ABSTRACTIC218 contains about 8.4% aluminum and about 7.8% chromium by weight and forms a tenacious alumina scale. In this work the ability of the scale to protect against aqueous corrosion and abrasive and adhesive wear was evaluated. Wrought IC218 was heat treated at 1150°C, yielding a microstructure of ordered FCC islands in a disordered FCC matrix. This material was more resistant to corrosion than common stainless steels in 96% or 98% sulfuric acid and in 5% hydrochloric acid. It was approximately equivalent to stainless steels in 10% sulfuric acid, 50% acetic acid, 50% sodium hydroxide, 5% sodium chloride, and in a sodium chloride + ferric sulfate + hydrochloric acid mixture used to test for pitting resistance. The IC218 performed poorly in 45% sulfuric acid, 20% or 65% nitric acid, 20% phosphoric acid, and in electrolytic 10% oxalic acid. It did not exhibit sensitivity to intergranular corrosion. It resisted stress corrosion cracking at a stress level equal to its yield strength, 645 MPa, in 45% magnesium chloride and in NACE TM0177, a test that simulates an oil well environment. IC218 wore more quickly than austenitic stainless steels do in a dry-sand-rubber-wheel test, but resisted galling as well as or better than most of them do.
Strength and Toughness of Composite Materials Based on Nickel Aluminide Matrices
Authors: Rigney J. D. , Khadkikar P. S. , Lewandowski J. J. , Vedula K. 
Published: March 2011

ABSTRACTSeveral nickel aluminide matrix composites were prepared using vacuum hot pressing techniques. The matrix compositions, based on Ni3Al, Ni3Al+B and NiAl, were reinforced with 10 volume % TiB2 particles. Both smooth and notched bend tests were conducted at room temperature on the monolithic as well as the reinforced materials in order to determine the effects of TiB2 reinforcement on both the smooth bend and notched bend properties. TiB2 additions were shown to improve the smooth bend strengths regardless of the matrix composition while notched bend tests, conducted to provide estimates of fracture toughness, revealed somewhat lower values for the composites in comparison to the monolithic materials. Fractographic analyses and in-situ fracture observations of the composites revealed that preferential fracture in regions of clustered TiB2 particles may significantly affect the measured toughnesses.
Improving the Low Temperature Ductility of NiAl
Authors: Guha Sumit , Munroe Paul R. , Baker Ian 
Published: March 2011

ABSTRACTAs part of a study aimed at developing a ductile NiAl-based alloy, ingots of Ni-Fe-Al alloys were cast and hot extruded to rods. The purpose of the iron additions was two-fold viz; to produce a change in the slip vector from <001> to <111> and, in one alloy, to add a L12-structured ductile second phase. Extruded Ni-20A1–3OFe was two-phase, containing a pro-eutectic B2 phase in a fine lamellar structure (< 0.5 μm spacing) of B2+L12phases. Room temperature tensile testing of both single extruded and double extruded alloys resulted in 8% and 22% plastic elongation and yield stresses of 850 and 760 MPa respectively. Fracture in both cases occurred by ductile tearing of the eutectic and transgranular cleavage of the proeutectic phase at 1350 MPa. The ductility in double extruded condition is higher than that reported earlier in rapidly solidified wires by Inoue et al., J. Mat. Sci.,19, (1984), 3097. By comparison, extruded single-phase B2-structured Ni- 30AI-2OFe exhibited a fracture strength of 780 MPa, no plasticity and a mixture of intergranular fracture and transgranular cleavage. This is in contrast to earlier work by Inoue et al. (ibid) where a yield stress of 400 MPa, 5% plastic strain and a mixture of dimple and intergranular fracture was reported.
Strain-Induced Recrystallization of Tial
Authors: Feng C. R. , Michel D. J. , Crowe C. R. 
Published: March 2011

ABSTRACTTransmission electron microscope investigation of extruded and rolled XD™ titanium aluminide sheet has shown the development of recrystallized TiAl regions adjacent to grains which exhibit submicron scale TiAl twins. Detailed diffraction analysis confirmed that the TiAl twins were separated by a layer of Ti3Al. This is consistent with previous observations of the microstructure of extruded XD™ titanium aluminide. In the extruded material, however, the scale of the twins was larger, but the extent of the recrystallized region was smaller. The evidence suggests that the recrystallization of the TiAl regions may result from the impingement of twins from adjacent grains.
Plastic Deformation of Ti3Al and Ti3Al/TiA1 Polycrystals
Authors: Court S. A. , Löfvander J. P. A. , Stucke M. A. , Kurath P. , Fraser H. L. 
Published: March 2011

ABSTRACTSamples of polycrystalline Ti3Al-base alloys, and a two phase Ti3Al/TiAl mixture have been deformed at room temperature and at elevated temperatures and examined subsequently by transmission electron microscopy in order to determine the influence of temperature and alloy content on the relative activity of the various slip systems. In particular, the detailed influence of covalent bonding on dislocation mobility in Ti3Al has been identified.
Effects of Structure on Creep of Ti-53.4mol%Al Intermetallics
Authors: Takahashi Tohru , Oikawa Hiroshi 
Published: March 2011

ABSTRACTConstant stress compression creep behavior at elevated temperature was investigated on Ti-53.4mol%Al polycrystalline intermetallics of gamma single phase in different grain morphologies: coarse columnar grains, fine recrystallized grains and equiaxed grains. The shape of creep curves depended on the applied stress: normal primary transient followed by steady creep was found at higher stresses, but at lower stresses steep acceleration was observed after taking minimum creep rates. This behavior was common to all the grain morphology. The creep rate itself was not greatly different among the three types of structure, and the stress exponent of about 4 and the apparent activation energy of about 340kJ/mol at 0.3 true strain were common to all three types. The shape and size of grains do not affect the essential creep features of this material.
Effect of Hydrogen on the Behavior of Y-TiAl Atomized Powders
Authors: Shong D. S. , Kim Y-W. , Yolton C. F. , Froes F. H. 
Published: March 2011

ABSTRACTThe effect of hydrogen on the phase stability of γ-TiAl and α2-Ti3Al phases was studied, with emphasis on the investigation of decomposition of a metastable α2 phase to a stable γ phase in gamma alloy powders. In this work, progressive decomposition of α2 → γ was observed to occur during aging with increasing temperatures or time under vacuum and under H2. The microstructural analysis indicated that hydrogen may facilitate such decomposition to occur at lower temperatures and shorter aging time.
Electronic Structure and Mechanical Properties of Intermetallics: Apb Energies in Ni-Al-Based Systems
Authors: Hong Tao , Freeman A. J. 
Published: March 2011

ABSTRACTThe possible origin of the high degree of brittleness (i.e., low ductility) of the Ni-Al-based alloys in the B2 structures is investigated by means of all-electron self-consistent total energy LMTO calculations. Using a supercell approach, the energetics of the two simplest anti-phase boundaries (APB) for NiAl in the B2 structure - namely the ½<111> on {110} and ½<111> on {112} - are calculated for the first time assuming no relaxation at the interface. We find APB energies of order of 800 ergs/cm2 for both cases. Since the calculated APB energies are very high, <111> slip is hardly likely to occur - as suggested experimentally. By substituting Ni or Al with V, Cr or Mn at the APB interface plane, remarkably decreased APB energies are obtained. These first results on these simplified model systems may suggest a way to decrease the APB energy contribution to the ductility of NiAl-based alloys.
Stacking Fault Energies, Crystal Elasticity and Their Relation to the Mechanical Properties of L12-Ordered Alloys
Authors: Fu C. L. , Yoo M. H. 
Published: March 2011

ABSTRACTFirst-principles calculations of the stacking fault energies of Ni3Al, and the linear elastic constants of Ni3Al and Pt3Al are presented. The anomalous (positive) temperature dependence of flow stress in Ni3Al and its absence in Pt3Al are fully rationalized in terms of the present results and cross-slip pinning mechanism. It is found that the elastic shear anisotropy factor plays an equally (or even more) important role than the anisotropy of antiphase-phase boundary energy in determining the plastic flow behavior of L12-ordered alloys.
Conformational Rearrangement in the Nematic Phase of a Polymer Comprising Rigid and Flexible Sequences in Alternating Succession. II. Theoretical Results and Comparison with Experiments
Authors: Yoon D. Y. , Flory P. J. 
Published: March 2011

ABSTRRACTTheory predicts that the nematic state of a homopolymer comprising rigid and flexible sequences in alternating succession depends critically on the tendency of the flexible units to reconform to ordered extended conformations. When the relative statistical weight s* of such extended conformations is very small (very flexible), the chains undergo only a minor conformational rearrangement in the nematic state. Moreover, the clearing temperature and the orientational order of these nematic polymers are not much different from those of the monomeric liquid crystals. Hlowever, as the value of s* becomes larger than a certain critical value, an ordered (nematic) state exhibiting perfect orientational order and completely rodlike conformations becomes more stable than the state of only partial order. Hlence, an extensive conformational rearrangement is predicted to occur in nematic melts of the polymers when the flexible sequences are niot very flexible. These predictions are in good qualitative agreement with the conclusions from the thermodynamic and NMR measurements on two thermotropic polymers comprising identical rigid groups joined by flexible sequences of substantially different flexibility.
Synthesis of New Nitrogen Substituted Polybenzimidazoles
Authors: Kane James J. , Akmal Naim , Jariwala Chetan , Sinsky Mark 
Published: March 2011

ABSTRACTN1,N4-diphenyl-1,2,4,5-tetraaminobenzene was condensed with the di-acid chlorides of terephthalic acid, isophthalic acid and 2,5-pyridine-dicarboxylic acid in polar aprotic solvent to give the poly(o-phenylamino)amides which, after cyclodehydration in polyphosphoric, acid gave three new N,N'-diphenyl substituted polybenzimidazoles (PBI). The syntheses and certain of the solution and thermal properties of the PBI's are discussed. The synthesis of three new tetraamine monomers and their related model compounds is also described.
Properties of Solutions of Rodlike Chains from Dilute Solutions to the Nematic State
Authors: Berry Guy C. 
Published: March 2011

ABSTRACTCertain aspects of the physical chemistry of solutions rodlike polymers are reviewed. The range of concentrations includes infinite dilution ([ŋ]c<<l), dilute solutions ([ŋ,]c<l), moderately concentrated solutions (l<[ŋ]c<[ŋ]cNI), and concentrated solutions (c<cN,), where [ŋ] is the intrinsic viscosity and cNI. is the concentration required for a stable nematic phase. Studies of chain conformation are emphasized at infinite dilution, and rheological behavior is emphasized for more concentrated isotropic and nematic solutions. Both theoretical and experimental considerations are included.
Film Formation by Electrodeposition of Ionized Aramids
Authors: Takayanagi Motowo , Koga Keiko 
Published: March 2011

ABSTRACTPoly(p-phenylene terephthalamide) (PPTA) recognized as rigid-rod polymer is converted into polyanion by the reagent of sodium methylsulfinylcarbanion in dimethylsulfoxide (DMSO), which is dissolved in DMSO to form a dark red colored homogeneous solution. The electrolysis of PPTA polyanion in DMSO, which has also rigid-rod shape due to resonance effect, gives a PPTA gel swollen by DMSO on the anode. The gel is easily converted to a PPTA film. The structural change during the process was followed by the Xray diffraction. The PPTA film neutralized with acidic water and dried has the hydrogen-bonded sheet in crystal standing perpendicular to the film surface, whereas the same film annealed at temperatures above 300°C has the hydrogen-bonded sheet parallel to the film surface. The latter form is the stable structure. The orientational transition was energetically discussed by taking into the activation energy of the crystalline relaxation. A uniform and homogeneous film was prepared by using a coaxial rotating electrode cell. The modulus was 11 GPa and the strength was 150 MPa. The addition of polyacrylonitrile to the electrolytic solution as the frictionproviding polymer which was removed from the gel after electrolysis, provided the mechanical anisotropy, especially after annealing at 350°C: the modulus along the orientation direction was 14 GPa and the strength was 370 MPa.The PPTA film unannealed or annealed below 200°C in an unstable orientational tate was used as a matrix of electropolymerization of electroconductive polymers such as polypyrrole, polyaniline and polythiophene, resulting in the electroconductive composite film of PPTA with improved mechanical properties. The PPTA/polyyyrrole with p-toluenesulfonate as a dopant had the conductivity of 50 Scm−1, the modulus of 6.2 GPa and the strength of 140 MPa. The conductivity was stabilized as high as 150°C. The SEM observation and the analysis of dynamic viscoelasticity proved the composite film being composed of two-phase structure.A novel aramid, poly(p-phenylene[2,5-bis(4-carboxyphenyl)pyrazine]amide) (PPPA), was synthesized. PPPA is soluble in pure sulfuric acid to form liquid crystal. The X-ray diffraction pattern of the oriented PPPA film predicts that the conformation of the PPPA chain in crystal takes all-trans form, giving the good agreement of the fiber period with the calculated one. It is noticeable that PPPA is dissolved into DMSO with formation of polyanion by the reagent of sodium methylsulfinylcarbanion and the electrolysis of the solution is conducted, resulting in a PPPA film on the anode like PPTA. The aramid copolymer of PPTA forming a molecular coil was unable to be electrodeposited. Thus, it is believed that only the rigid-rod polyelectrolytes are capable of film formation by electrolysis.
X-ray Diffraction Studies of the Axial Tensile Modulus of Rigid-Rod Polymer Fibers
Authors: Lenhert P. Galen , Adams W. Wade 
Published: March 2011

ABSTRACTWe report the design and use of a device to measure the axial tensile modulus of high modulus fibers by following the change in the meridional X-ray spacings as a function of applied tension. The device, which mounts on a Picker 4-circle automated diffractometer, applies tension to the fiber sample by a cantilever arrangement. Tension is measured by a strain gauge bridge on the cantilever arm. The tension is adjusted and read by the control computer, a VAX 11/730. Measurements made on PBZT and PBO fibers before and after heat treatment are reported. For PBZT fibers (as spun, and heat treated at 525° C and 650° C) with tensile moduli of 186, 283 and 290 GPa, the X-ray determined moduli are 348, 385 and 395 GPa. For PBO fibers (as spun and heat treated at 600° C and 665° C) with tensile moduli of 166, 318 and 290 GPa, the X-ray determined moduli are 387, 477 and 433 GPa. These modulus values are to be compared with theoretical values presented by Wierschke in the previous paper and sonic modulus values discussed by Jiang et al in the following paper.