bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microcrack Nucleation and Crack Propagation in Equiaxed γ TiAl
Authors: Crimp Martin A. , Ng Boon-Chi , Simkin Benjamin A. , Bieler Thomas R. 
Published: April 2011

ABSTRACTTo gain a better understanding of the ductility limitations in TiAl alloys, the mechanisms involved in deformation strain transfer and/or microcrack initiation at grain boundaries have been examined in an equiaxed near-γ alloy. These studies have been carried out on both in-situ and ex-situ deformed bulk samples using scanning electron microscopy (SEM) techniques for both orientation analysis and deformation defect imaging. Selected area electron channeling patterns (SACPs) have allowed determination of grain orientations, eliminating ambiguity between the a and c axes. Deformation twins and dislocations have been imaged in the bulk samples using electron channeling contrast imaging (ECCI). A combination of ECCI contrast analysis and trace analysis based on orientations determined from SACP has allowed identification of the active deformation systems. Microcracks have been found to initiate at γ-γ boundaries as a result of an inability to adequately transfer twin strain from grain to grain. Once initiated, cracks propagate through cleavage and re-nucleation of grain boundary microcracks in front of the advancing crack. A geometric based predictive factor has been developed that accounts for microcrack initiation at γ-γ boundaries based in deformation twinning and strain accommodation by ordinary dislocations.
Microstructural Effect on Environmental Embrittlement of Isothermally Forged TiAl-Based Intermetallic Alloys
Authors: Takasugi T. , Tsuyumu T. , Kaneno Y. , Inoue H. 
Published: April 2011

ABSTRACTThe TiAl-based (Ti-46Al-7Nb-1.5Cr (at%)) intermetallic alloy was tensile tested in vacuum and air as a function of temperature to investigate microstructural effect on the moisture-induced embrittlement. The reduction in tensile strength (or elongation) due to testing in air diminishes as testing temperature increases. From the fracture strength (or elongation)-temperature curves, it was found that the near gamma grain microstructure was most resistant, and the dual-phase microstructure most susceptible to moisture-induced embrittlement. Also, the moisture-induced embrittlement of the TiAl-based intermetallic alloy with fully lamellar microstructure depends on the lamellar spacing, and reduced with decreasing lamellar spacing.
The Heterogeneous Character of Phase Transformations Caused by Limited Vacancy Mobility
Authors: Püschl Wolfgang , Soffa William A. , Pfeiler Wolfgang 
Published: April 2011

ABSTRACTIn homogeneous phase transformations the order parameter proceeds towards equilibrium uniformly in all microvolumes of the system. However, defect-mediated diffusion (vacancy mechanism) involving local atomic jump processes during the early stages of transformation kinetics can produce discrete regions within which the order parameter has changed significantly embedded in an unperturbed matrix. This effect is evident in order-order transformations in B2 FeAl as measured by residual resistivity. An estimate of the heterogeneity regime is calculated in terms of vacancy diffusion parameters.
HRTEM Observation of Partially Ordered Long-Period Superstructures in Al-Rich TiAl Alloys
Authors: Hata S. , Higuchi K. , Mitate T. , Kuwano N. , Itakura M. , Tomokiyo Y. , Nakano T. , Nagasawa Y. , Umakoshi Y. 
Published: April 2011

ABSTRACTAtomistic microstructures of long-period superstructures in Al-rich TiAl alloys were investigated by high-resolution transmission electron microscopy. The multi-slice image simulation revealed that Al-atoms in Ti-rich (002) layers of the superstructures are imaged as very bright dots under appropriate observing conditions. By enhancing the contrast of the very bright dots using an image processing technique, partially ordered long-period superstructures were clearly characterized. For the short-range order state, A4B, A2B and A3B type ordered-clusters are generated in the Ti-rich (002) layers. These ordered-clusters are in contact with each other, and form local microdomains of various superstructures, such as Al5Ti3, h-Al2Ti and so on. For the Al5Ti3 and h-Al2Ti ordered states, the ordered-clusters are tiled periodically to form the Al5Ti3 or h-Al2Ti domains and characteristic anti-phase boundary structures.
Effect of Antiphase Boundary on the Pseudoelasticity in Fe3Al Single Crystals
Authors: Yasuda Hiroyuki Y. , Nakano Kazuaki , Ueda Masato , Umakoshi Yukichi 
Published: April 2011

ABSTRACTPseudoelasticity in Fe3Al single crystals with the D03 structure was investigated focusing on the type of thermally-induced antiphase domain boundaries (APDB) developed in the crystals. Fe3Al single crystals containing 23.0at%Al and 28.0at%Al were produced by a floating zone method. Fe-23.0at%Al single crystals with an appropriate heat treatment demonstrated perfect strain recovery during unloading after compression to plastic strains below 5.0%. In contrast, Fe-28.0at%Al single crystals exhibited little strain recovery. The ordering process and the type of thermal APDB depended strongly on the alloy composition. As a result, B2-type APDB having a displacement vector (R) of 1/4<111> was frequently observed in Fe-23.0at%Al, while D03-type APDB with R=1/2<111> was dominant in Fe-28.0at%Al. In Fe-23.0at%Al, the strong interaction between B2-type APDB and 1/4<111> superpartial dislocations led to the individual motion of the superpartials dragging deformation-induced antiphase boundary (APB). The restoring force due to the deformation-induced APB resulted in the pseudoelasticity in Fe-23.0at%Al single crystals. Moreover, the refinement of antiphase domains surrounded by B2-type APDB was found to be effective in the enhancement of shape recovery in the crystals. Thus, the thermally-induced APDB in the D03 phase played an important role in the pseudoelasticity in Fe3Al single crystals.
Modeling Dislocation Dissociation and Cutting of γ′ Precipitates in Ni-Based Superalloys by the Phase Field Method
Authors: Shen Chen , Mills Michael J. , Wang Yunzhi 
Published: April 2011

ABSTRACTWe incorporate γ-surface data of both γ and γ′ phases from ab initio calculations into the phase field model to study dislocation dissociation and interaction with γ′ particles in Ni-based superalloys. Through three examples we demonstrate the unique capabilities of the model in characterizing the core structure of a dissociated superdislocation in γ′ phase, the creation and annihilation of planar defects such as CSF and APB caused by dislocation cutting through the γ′ phase and the interplay between the cutting and looping mechanisms.
The Role of Cluster Formation on the Magnetic Properties of Nd-Fe-Al-based Magnetic Alloys
Authors: Betancourt I. , Valenzuela R. 
Published: April 2011

ABSTRACTWe present a detailed investigation of the role of the disorder degree on magnetic properties for melt spun and die cast intermetallic Nd-Fe-Al-based alloys. For melt spun alloys, the roll speed was varied between 30 m/s and 5 m/s, which resulted in a clear dependence of coercivity on increasing roll speed, showing a steep decrease (from 250 kA/m to 10 kA/m). The results are interpreted in terms of a gradual transition from fully disordered microstructure (30 m/s sample) to short range ordered one (i.e., a clustered microstructure at 5 m/s), which is a consequence of a diminished cooling rate. On the other hand, die-cast alloy affords cluster formation due to this very low cooling rate compared with the melt spinning process and in consequence, coercivity values of 284 kA/m were observed. Further alloying addition (B, Cu, Dy) on the original Nd-Fe-Al composition, exhibited coercivity enhancement (up to 388 kA/m) due to the presence of small Nd-based crystallites, which act as pinning centers.
Defects Formation in LaNi5-based Alloys Investigated by In-situ X-ray Diffraction
Authors: Nakamura Yumiko , Akiba Etsuo 
Published: April 2011

ABSTRACTDefects formation in LaNi5-based alloys was investigated by X-ray diffraction (XRD). In-situ XRD data measured along the first hydriding-dehydriding P-C isotherms were analyzed by the Rietveld method. Lattice strain and crystallite size were evaluated from the peak profile. In LaNi5hydride phase formed accompanying with 2 % of anisotropic lattice strain in <hk0> direction caused by dense dislocations. Coexisting solid solution phase was not affected by the strain in the hydride phase. Lattice parameterabecame smaller after cycles than before hydriding, which is related with vacancies formation.Only 5 % of Al substitution for Ni dramatically changed the defects formation behavior. Hydride phase did not show lattice strain in the first hydriding but showed small strain during dehydriding. Formation of both dislocations and vacancies are strongly affected by substitution of other elements for a part of Ni.
Interactions of Mechanical Twinning and Dislocation Glide with Polytwin-Interfaces in L1o-Ordered Iron-Palladium Intermetallics
Authors: Xu Huiping , Wiezorek Jörg 
Published: April 2011

ABSTRACTThe defect structures in polytwinned (PT) FePd have been studied after room temperature deformation by transmission electron microscopy (TEM). Interactions between gliding dislocations and mechanical twins with the {101}-conjugated PT-interfaces have been identified. Based on crystallographic analyses of shear transfer of dislocations and microtwins across the PT-interfaces in FePd boundary reactions have been identified that are consisted with the TEM observations. A model has been proposed, which is suitable to rationalize significant contributions to strain-hardening from these defect-interface interactions in PT-FePd.
Effects of elastic strain energies on a hydride precipitation in LaNi5-based compounds
Authors: Tanaka K. , Inui H. , Yamaguchi M. , Koiwa M. 
Published: April 2011

ABSTRACTThe elastic energies associated with hydride formation have been calculated using coherent elasticity theory. The energies modify the required condition for hydride nucleation to lower temperatures or higher hydrogen gas pressures. Since the elastic energies are quite large, hydride cannot form in a crystal or on a planer surface without assistance of a lattice defect. Hydride can form with reasonable excess hydrogen gas pressure only at a corner of specimen at which the most part of elastic energy is released.
Magnetic Structure and Thermal Expansion of Eu4Ga8Ge16
Authors: Birkedal Henrik , Daniel Bryan J. , Stucky Galen. D. , Christensen Mogens , Iversen Bo B. 
Published: April 2011

ABSTRACTThe orthorhombic clathrate compound Eu4Ga8Ge16 orders antiferromagnetically at about 8 K. The magnetic structure is established by neutron powder diffraction while the thermal expansion and atomic displacement parameters are studied by synchrotron powder diffraction. The Eu spins align along the a-axis and achieve a zero-temperature magnetic moment equivalent to that of the free Eu2+ ion. The thermal expansion is largest along the a-axis while the expansion along c has almost the same magnitude as that along b. The Eu displacement parameters display significant residual values at 0 K, largest in the c direction.
Negative Thermal Expansion
Authors: Sleight Arthur W. 
Published: April 2011

ABSTRACTNegative thermal expansion behavior has been found in many oxides where oxygen or a cation has a coordination number of two. The MO2, AM2O7, A2M3O12, AMO5, and AO3 families, where A is an octahedral cation, M a tetrahedral cation, and the oxygen coordination is two, have been investigated for their thermal expansion properties. Negative thermal expansion has been found in all families except the AO3 family, where very low thermal expansion was found in the case of TaO2F. Open networks are necessary to allow free transverse thermal motion of oxygen, which is the apparent cause negative thermal expansion in these families. This openness leads to two problems. One is that structure collapse transitions tend to occur as the temperature is lowered. There is little or no thermal expansion below this transition. A solution to this problem is to maintain sufficient ionic character in the bonds holding the network together. The other problem is that when the networks become sufficiently open, they tend to hydrate. This hydration destroys the negative thermal expansion of the network.
Selective Preparation of Nickel Silicides and Germanides Using Elemental Multilayers as Reactive Precursors
Authors: Jensen Jacob M. , Ly Sochetra , Kyablue Xavier , Johnson David C. 
Published: April 2011

ABSTRACTUsing elemental multilayers with designed composition and ultrathin repeating subunits (λ=20 A) we have prepared nickel monosilicide and nickel germanide directly without the formation of any intervening phases. When the same synthetic strategy is used to prepare nickel-silicon-germanium compounds the first nucleated phase is a ternary phase with the NiAs structure.
Oxidation-Protection Methodology for Long-Term use of Carbon-Carbon Fiber-Matrix Composites in Oxidizing Ambients
Authors: Golecki Ilan , Fuentes Karen , Walker Terence 
Published: April 2011

ABSTRACTA methodology is described for protecting Carbon-Carbon fiber-matrix composite (C-C) components from oxidation for extended use in oxidizing ambients for lifetimes of the order of 10,000 hours, from room temperature to 650°C. This time-temperature profile is relevant to applications such as airborne heat exchangers. Weight changes of oxidation-protected, pitch-fiber based C-C coupons in flowing dry air at 650°C are presented. Two types of external protective approaches are compared: (a) multi-phase, borophosphate-based fluidizing overseal coatings applied directly to C-C, and (b) the same overseal coatings applied to CVD SiOxCy coated C-C. The latter, dual-coating approach provides an effective engineering solution for the above temperature-time profile and is particularly applicable to thin (0.1–3 mm thick), complex-shaped articles. The behavior of inert substrates (oxidized silicon) with the same overseal coatings is compared to the behavior of the C-C substrates. This approach can be applied with optional modifications to suit other environmental conditions, and other carbon-containing materials, such as carbon foams and C-SiC composites.
Synthesis and Characterization of New Iron and Zinc Phosphate Materials with Open Framework
Authors: Song Yanning , Chernova Natasha A. , Zavalij Peter Y. , Stanley Whittingham M. 
Published: April 2011

ABSTRACTOpen framework materials are of great interest due to the applications in the fields of adsorption, ion exchange, molecular sieving and catalysis. Metal phosphates are very important open framework materials due to the rich crystallography. Several new iron phosphate materials have been synthesized and characterized in our lab. Two new iron (III) phosphates, FePO4, have been synthesized from careful dehydration of hydrothermally prepared monoclinic and orthorhombic hydrated phosphates FePO4·2H2O. Reversible insertion and extraction of lithium into new iron phosphate hydroxide materials with 3-d rod-packing framework shows it to be an excellent intercalation material. Several other transition metals are also incorporated successfully into these compounds without changing the structure. With ethylenediamine as template, 1-D chain, 2-D layered and 3-D network iron phosphate materials were synthesized. The structure, electrochemical and magnetic properties of these compounds were studied. Meanwhile, two new zinc phosphates with methylammonium templates were also synthesized. There are infinite Zn-O-Zn chains in one of the compounds, while closed 4-member circuits made up from Zn-O-Zn linkage present in the other.
Temperature-Dependent Magnetic Properties of SiO2-Coated Ni75Fe25 Nanoparticles
Authors: Wu Mingzhong , Zhang Y.D. , Hui S. , Ge Shihui 
Published: April 2011

ABSTRACTSiO2-coated Ni75Fe25 nanoparticles were prepared using a wet chemical method and their structure and magnetic properties were investigated using x-ray diffraction, high-resolution transmission electron microscopy, and a superconducting quantum interference device magnetometer. The SiO2 material was in an amorphous state. The Ni75Fe25 nanoparticles were in a simple cubic state and contained inner oxide (Ni-oxide and Fe-oxide) cores whose size decreased with increasing calcination temperature. The nanoparticles were basically in the ferromagnetic state. Their saturation magnetization increased with increasing calcination temperature, whereas their coercivity decreased with increasing calcination temperature. The nanoparticles exhibited strong temperature-dependent magnetic behaviors. The Bloch exponent fell from 1.5 for the bulk to smaller values and decreased with increasing oxide content, while the Bloch constant was much bigger than that for bulk and increased significantly with oxide content. The value of coercivity decreased with increasing temperature, and this decrease was more pronounced for the nanoparticles containing high oxide content. The exchange anisotropy arising from the exchange coupling across the Ni75Fe25/oxide interfaces was examined and was used to interpret the observed temperature-dependent behaviors.
Anion Intercalation and Anion Exchange in Bismuth Compounds
Authors: Tsuji Masamichi , Yamaguchi Makoto , Murao Satoshi 
Published: April 2011

ABSTRACTBismuth nitrate basic, which chemical content is given by 4BiNO3(OH)2.BiO(OH), was studied for anion-intercalation or anion-exchange properties. A crystal structure of the bismuth nitrate basic has not been known. In the present study, its XRD pattern was indexed using a possible orthorhombic system having the lattice parameters of ao=3.021(1) nm, bo=3.029(1) nm and co=0.9572(3) nm. This compound was found to incorporate CH3COO-, halides and several oxyanions including CO32-. Incorporation of these anions by this solid was evidenced by broadening of infrared absorption band by NO3-, suggesting involvement with NO3- ions. Intercalation of CO32- by the bismuth nitrate basic in full extent yielded a bismutite represented by the chemical composition Bi2O2CO3. The bismuth nitrate basic will serve as a new host for anion-intercalation and anion-exchange.
Synthesis of Several Tungsten (VI) Complex Perovskites, Ba(BIII2/3W1/3)O3 (B = In, Y, Dy, Gd, Sm) by the Polymeric Precursors Method
Authors: Fuentes Antonio F. , Mendoza-Suarez Guillermo , Iván Escalante-García J. , Amador Ulises , Boulahya Khalid 
Published: April 2011

ABSTRACTWe show in this work the usefulness of the polymeric precursors method to obtain several Ba(BIII2/3W1/3)O3 (B = In, Y, Dy, Gd, Sm) complex perovskites. Solid resins obtained from solution were treated at different temperatures and characterized by XRD and thermal analysis. BaCO3 and Ba(NO3)2 were the only crystalline species found below 500°C. Tungstates with different stoichiometry evolve from the powdered precursors as the temperature is raised. Formation of perovskite-like phases is evident in all five cases, above 1000°C. XRD results suggest also that trivalent ions do not participate in chemical reactions below that temperature since the presence of any binary phase containing them could be confirmed.
Surfactant Templated Assembly of Cubic Mesostructured Semiconductors Based on [Sn2Se6] 4- and Pt2+ in Single-Crystal Form.
Authors: Trikalitis Pantelis N. , Kanatzidis Mercouri G. 
Published: April 2011

ABSTRACTMesostructured non-oxidic materials with cubic Ia-3d symmetry were prepared by linking [Sn2Se6] 4- clusters with Pt2+ in the presence of surfactant molecules. The use of long chain pyridinium-based surfactants (octadecyl- and eicosadecyl) afforded materials with exceptionally high cubic pore order and single-crystal particle morphology. By contrast trimethylammonium-based surfactants produced cubic mesostructured solids with inferior overall quality. We have also synthesized materials with significantly lower surfactant content by increasing the Pt2+:[Sn2Se6] 4- molar ratio, while maintaining the cubic pore symmetry. All materials are semiconductors with energy band-gap in the range 0.9<Eg<1.8 eV.
Photochemical Reactivity of Sr2Nb2O7 and Sr2Ta2O7 as a Function of Surface Orientation
Authors: Giocondi Jennifer L. , Zimbouski Ariana M. , Rohrer Gregory S. 
Published: April 2011

ABSTRACTSr2Nb2O7 and Sr2Ta2O7 have a (110) layered perovskite structure and are efficient photolysis catalysts. Aqueous silver and lead cations were photochemically reduced and oxidized, respectively, on the surfaces of Sr2Nb2O7 and Sr2Ta2O7 crystals with a wide range of orientations. Atomic force microscopy has been used to observe the distribution of photochemically reduced and oxidized products and determine the orientation dependence of the reactivity. On surfaces with the same orientation, reaction products frequently had a non-uniform distribution. The reactivity of both compounds proved to be only weakly anisotropic, with the highest relative reactivity for both oxidation and reduction occurring for surfaces oriented between (010), (110), and (011). These low index orientations have structures similar to the ideal {110} and {100} planes in the perovskite structure, respectively. The relationship of the perovskite structure to the reactivity is discussed.
On the nature and structure of new MoVTeO and MoVTeNbO crystalline phases
Authors: García-González E. , López Nieto J. M. , Botella P. , Solsona B. , González-Calbet J.M. 
Published: April 2011

ABSTRACTNew TeMoV and TeMo(V,Nb) bronze type phases have been obtained during the heat-treatment (600° C in N2) of the corresponding precursor mixture. Both mixed oxides seem to be structurally related to one of the crystalline phases proposed in Mo-V-Te-Nb-O catalysts. Chemical and microstructural characterization revealed the formation of an orthorhombically distorted cell deriving from a bronze type HTB structure, which does not behave as a bronze type structure in the chemical sense. Microstructural details responsible for the new unit cell are discussed in terms of tellurium location inside the hexagonal tunnels and based on the structural model proposed.
Orientation Dependence of the Photochemical Reactivity of BaTi4O9
Authors: Giocondi Jennifer L. , Samadzadeh Shahrzad , Rohrer Gregory S. 
Published: April 2011

ABSTRACTBaTi4O9 is a photocatalyst with a pentagonal prism tunnel structure. It has been hypothesized that the tunnels promote the separation of photogenerated carriers and, therefore, lead to the spatial separation of oxidation and reduction half reactions. This hypothesis has been tested by observing the distribution of reduced and oxidized reaction products on BaTi4O9 surfaces over a wide range of orientations. The surface orientations were determined by electron backscattered diffraction and atomic force microscopy was used to examine the structure of the surface both before and after the deposition of reaction products. Reduction products (Ag0) are distributed uniformly. The distribution of oxidation products (PbO2) is also not correlated to the surface orientation or to the orientation of the tunnels with respect to the surface. Based on these observations, we conclude that the tunnels in this structure do not separate photogenerated charge carriers and that this mechanism is not responsible for this compound's relatively high photocatalytic activity.