bluuebunny/crossref_metadata_2025_split huggingface dataset:
Design and Preliminary Results of Redox Capacity Measurements of Granitic Rocks and Minerals
Authors: Pirhonen Veijo O. , Pitkänen Petteri , Takala Jukka , Arilahti Esko 
Published: March 2011

ABSTRACTA procedure for the measurements of the redox capacity of rocks and minerals is presented. Both solid and pulverized samples are used. In a preliminary test described in this paper, an oxygen loss of an aqueous solution in contact with pulverized granodiorite was measured directly on-line, with an oxygen sensor.The increase of Fetot in the solution responded relatively well to the oxygen consumption. The maximum rate varied from 3.0 × 10−4 to 9.0 × 10−11 mol l−1 s−1 correspondingly. Oxygen loss of 0.04 mmol (O2) and iron increase of 0.1 mmol were recorded in the solution. Fe(II) reduction in the solid phase was also examined. Fe(II) was inferred to have partially dissolved during the experiment. When the system was equilibrated at the ambient conditions, the vessel was pressurized upto 100 bar with oxygen gas. Three weeks later, the additional decrease of Fe(II) in the solid phase was minimal, only 0.07 % Fe(II) was dissolved or oxidized on the rock surfaces. At this point, the Fetot in the solution, had decreased down to the background level. According to the total oxygen loss at the ambient coditions, the maximum redox capacity of the examined granodiorite (BET 1.0 m2/g) is 0.002 mmol/m2.
Gas Formation in ILW and HLW Repositories, Evaluation and Modelling of the Production Rates and Consequences on the Safety of the Repository
Authors: Besnus François , Voinis Sylvie 
Published: March 2011

ABSTRACTThis paper summarizes the main gas formation mechanisms in deep radioactive waste repositories. Production rates and overall gas volumes were estimated and showed predominance of hydrogen production by anoxic corrosion and radiolysis for French wastes. Gas evolution in the near field has been modeled. First results issued from a sensitivity analysis showed desaturation of the storage cavities for a wide range of parameter values.
Microstructure and Mechanical Properties of a Single Crystal NiAl Alloy with Zr or HF Rich G-Phase Precipitates.
Authors: Locci I. E. , Noebe R. D. , Bowman R. R. , Miner R. V. , Nathal M. V. , Darolia R. 
Published: March 2011

ABSTRACTThe possibility of producing NiAl reinforced with the G-phase (Ni16X6Si7), where X is Zr or Hf, has been investigated. The microstructures of these NiAl alloys have been characterized in the as-cast and annealed conditions. The G-phases are present as fine cuboidal precipitates (10 to 40 nm) and have lattice parameters almost four times that of NiAl. They are coherent with the matrix and fairly resistant to coarsening during annealing heat treatments. Segregation and non-uniform precipitate distribution observed in as-cast materials were eliminated by homogenization at temperatures near 1600 K. Slow cooling from these temperatures resulted in large plate shaped precipitates, denuded zones, and a loss of coherency in some of the large particles. Faster cooling produced a homogeneous fine distribution of cuboidal G-phase particles (≤10 nm) in the matrix. Preliminary mechanical properties for the Zr-doped alloy are presented and compared to binary single crystal NiAl. The presence of these precipitates appears to have an important strengthening effect at temperatures≥1000 K compared to binary NiAl single crystals.
Oxidation Kinetics Of Mosi2 And Mosi2/Reinforcement Mixtures
Authors: Meschter P. J. 
Published: March 2011

ABSTRACTAn oxidation study of pure, dense MoSi 2 at 400-600°C and MoSi2/20 vol. % (TiB2, Al2O3, Nb) mixtures at 400–1200°C has been performed. Dense MoSi2 does not fail catastrophically (“pest”) in dry air, wet air, or oxygen, and oxidizes heavily only near 500°C. Heavy oxidation is related to the slow growth of a protective, amorphous SiO2 layer; a low rate of Mo removal as vapor species; and cracking of an initially protective Mo9O26-SiO2 layer. Pre-oxidation of MoSi2 at 1200°C prevents subsequent heavy oxidation at 500°C. MoSi2/TiB2 and MoSi2/A12O3 mixtures oxidize more slowly than MoSi2 for T < 600°C and more rapidly for T > 600°C. Protective oxides are formed on MoSi2/reinforcement mixtures except at 500°C, for which high-temperature pre-oxidation is again effective. MoSi2/Nb mixtures suffer severe mass losses upon oxidation at both 500 and 1200°C owing to rapid oxidation of the Nb and spalling of the product Nb2O5 Only the latter case poses problems for the application of MoSi2-matrix composites as high-temperature materials.
Microstructure and Mechanical Properties of Near Eutectic Β-Nial Plus α-Re Alloys Produced by Rapid Solidification and Extrusion
Authors: Mason D.P. , Van Aken D.C. 
Published: March 2011

ABSTRACTTwo β-NiAl plus α -Re alloys with near eutectic composition were produced by rapid solidification and then consolidated through a powder extrusion process. Microstructures of the rapidly solidified, as-consolidated, and deformed alloys were characterized by transmission electron microscopy. Both compression and tensile properties of these alloys were determined over the temperature range of 300–1300 K. The Re additions were found to greatly enhance low and intermediate temperature yield strengths when compared to other β-NiA1 alloys. This enhancement was attributed to a combination of solid solution strengthening, precipitate hardening, and grain size refinement. Above 1200K the strength of these Re-modified alloys was comparable to the binary β-NiAl compound.
The Dislocation Structure and Deformation Mechanism of Tib2/Nial Composites
Authors: Wang L. , Arsenault R.J. 
Published: March 2011

ABSTRACTDislocation structures in 0, 10, and 20 V% TiB2/NiAl composites have been thoroughly investigated with a 1 MeV HVEM after compression testing at 760–1000° C. Samples with 0 and 10 V% TiBl2/NiAl additions have almost identical dislocation structures which can be described as a<100> screw dislocations with extensive jogs and superjoqs. Prismatically punched dislocations were observed in all of the deformed composites and deformed samples of 20 V% TiB2/NiAl had extensive dislocation generation around the particles. Dislocation density, grain size, and the tendency for dislocation reactions or networks forming during deformation decrease as the volume fraction of TiB2 increases. Also, since a predominance of screw dislocation was observed, the rate controlling process is not likely to be dislocation annihilation or climb, but dislocation generation. The grain size refinement could play an important role in the strengthening of the composites.
LMTO/CVM and LAPW/CVM Calculations of the Nial-Niti Pseudobinary Phase Diagram
Authors: Burton Benjamin P. , Osburn Jean E. , Pasturel Alain 
Published: March 2011

ABSTRACTLinear Muffin Tin Orbital and Linearly Augmented Plane Wave calculations of equations of state were performed for observed and hypothetical ordered structures in the NiAl-NiTi system. Total energies were parameterized in both the Connolly-Williams and ∈-G approximations, and the resulting parameters were used to calculate theoretical phase diagrams by the cluster variation method. Third nearest neighbor Al-Ti pairwise interactions are predicted to be strongly repulsive, and to be a major cause of observed B2+L21 two phase fields.
Dislocation Core Structures and Mechanical Behavior of DO22 Type Alloys
Authors: Khantha M. , Vitek V. , Pope D.P. 
Published: March 2011

ABSTRACTWe investigate the structures of dislocation cores in a model DO22 type intermetallic alloy in the absence of external stresses. The tetragonal distortion produces sessile configurations of superpartial dislocations even when the energies of planar faults are reasonably low. The influence of the core configurations on the mechanical behavior at low temperatures is discussed.
Calculation of Electronic Structure of Ordered and Disordered Binary (Ab) Alloys using the Lmto Parameters for Pure A And B Components
Authors: Bose S.K. , KudrnovskÝ J. , Jepsen O. , Andersen O.K. 
Published: March 2011

ABSTRACTWe discuss how, in the linear-muffin-tin-orbitals (LMTO) method, the potential parameters for an intermetallic compound can be estimated from those of the constituents. For ordered alloys we illustrate the scheme by comparing the electronic density of states (DOS) obtained in self-consistent calculations with that obtained with the potential parameters transferred from the pure components. Several examples are discussed. We discuss how the scheme can be used in performing almost self-consistent calculations for disordered alloys, and present some results obtained by using this scheme with the LMTO-CPA(coherent potential approximation) method.
The Influence of Strain Rate on Dislocation Structures in γ/α2 Titanium Aluminides Deformed at 815°C
Authors: Donlon W.T. , Dowling W.E. , Allison J.E. 
Published: March 2011

ABSTRACTElevated temperature (815°C) compression tests were performed at strain rates between 10−2 & 10−5 sec−1 on a γ/α2 alloy, Ti-48Al-1V-0.2C (at%), for two different α2 volume fractions. A large change in the flow stress was observed to occur for strain rates between 1.10−5 & 1.10−3 sec−1. The dislocations observed in the primary γ grains deformed at the high strain rates were “regular” 1/2<110]; screw dislocations. The dislocations observed at slow strain rates were also regular 1/2<110] dislocations, however their orientation was changed so that they were aligned close to [001]. Dislocation structures produced during high cycle fatigue are identical to those observed during high strain rate compression tests, while dislocation structures produced during tensile (ė- 8.10−4 sec−1 ) tests are identical to those observed in the slow strain rate compression tests. Analysis of the orientation of deformed primary γ-TiAl grains shows that the CRSS for {111}<101] slip must be at least 1.4 times the CRSS of {111}1/2<110] slip.
Deformation and Ductility in Alloys Based on Al3Ti
Authors: Morris David G. , Lerf Reto 
Published: March 2011

ABSTRACTTitanium trialuminide alloys suffer problems of intense segregation during solidification and extreme brittleness when subjected to tensile stresses. In this study, spray forming techniques have been used to obtain homogeneous materials of fine microstructure, containing various second phase particles, and the deformation behaviour of these materials examined over a range of temperatures.The microstructure and deformation behaviour of an iron-modified titanium trialuminide with the L12structure is reported here.Deformation mechanisms are interpreted by analysis of dislocation structures and further confirmation is obtained by activation volume measurements: the importance of Peierls effects at low temperatures and cross slip at high temperatures is shown. The material remains brittle in tension both at room temperature and at high temperatures: the second phase particles in the material are yet not present in sufficient volume fraction to greatly affect plastic behaviour.
Energetics and Structural Effects of Boron Additive to Intermetallic Compound: γ-Tial
Authors: Khowash P.K. , Price D.L. , Cooper B.R. 
Published: March 2011

ABSTRACTImproving the low temperature ductility of the intermetallic compound γ - TiAl by alloying with small concentrations of an additive is of great practical importance. The difference in site selection energy of the additive plays an important role in the stability and behavior of the alloy. For boron in L10 TiAl, we have calculated the site selection energy using linearized combination of muffin-tin orbitals (LMTO) total energy calculations. For pure γ - TiAl, we found the equilibrium lattice structure by minimizing the total energy, and obtained good agreement with the experimental values. With the introduction of boron, a relaxation of the lattice around the boron additive is expected. For boron additives, we have calculated the forces on each atom leading to the minimization of the total energy as a function of the ionic positions in order to obtain the “true” stable structure of the alloy.
Computer Simulation of ao<110> Screw Dislocations in Ni3Al
Authors: Parthasarathy T.A. , Dimiduk D.M. , Woodward C. , Diller D. 
Published: March 2011

ABSTRACTDissociation of the ao<110> screw dislocation in Ni3Al was studied using the embedded atom method of computer simulation. The dissociation occurred predominantly along the {111} plane, however, a {001}-plane step occurred in the APB at the center of the configuration. When a pair of ao/2<110> superpartials initially separated in the {111} plane was relaxed, the step formed once again but with a reduced height. When the pair was relaxed from larger distances the step was not formed. The results indicate that the elastic interaction “torque” due to elastic anisotropy is responsible for the formation of the {001} APB step. When a stress was applied to these dislocation configurations by simulation, results confirmed that the step in the APB and the octahedral cross-slipped-core dissociations can be significant barriers to glide of the screw dislocation.
Deformation Mechanisms in TiAl-Based Alloys Containing Low Oxygen
Authors: Sriram S. , Vasudevan Vijay K. , Dimiduk Dennis M. 
Published: March 2011

ABSTRACTThe effects of oxygen on the deformation behavior of Ti-(48-52)Al alloys is reported. Two types of studies were conducted. In the first, high purity alloy buttons containing low oxygen (~250 ppm) were prepared, whereas in the second, alloys with additions of 1 at.% Er to scavenge the oxygen from the matrix were prepared. The alloys were heat treated to produce large grains and the microstructures characterized by analytical electron microscopy. Samples prepared from the heat treated alloys were electropolished and deformed in compression to a plastic strain of 1.0-1.5% at temperatures between 25 and 800°C and the yield stress measured. The morphology of deformation, that is, slip lines and the presence of twinning, was studied by optical microscopy and the dislocation structures were characterized by weak-beam imaging in the transmission electron microscope. The results of these various studies are presented and discussed in terms of recent developments regarding the factors that appear to control the dislocation structure and the mobility of dislocations.
The Effect of Grain Boundary Geometry on Intergranular Cracking in Ni3A1 at Room Temperature
Authors: Lin Hui , Pope David P. 
Published: March 2011

ABSTRACTThe relation between intergranular fracture and grain boundary character was studied in Ni3Al using the electron backscattering pattern (EBSP) technique. A new and improved set of experiments have been performed in which the problems of forced crack propagation and statistical validity of numerical results encountered in the earlier study were eliminated. It was found that low angle and σ3 boundaries do have a substantially lower propensity for cracking as compared to other boundaries, but there is no correlation between grain boundary σ value and the propensity for cracking for low σ boundaries. These results are in general agreement with recent theoretical predictions of grain boundary structure.
The Microstructure of Titanium Beryllide, Tibe12
Authors: Banerjee D. , Jacobson L. , Zindell J. , Mitchell T.E. 
Published: March 2011

ABSTRACTTitanium beryllide (TiBe12) has been processed by various techniques, including inert gas arc melting, sputter deposition and as second phase particles in atomized powder of alloys ranging in composition from 1 to 35 weight percent Ti. The TiBe12 that formed in the various alloys was characterized by transmission electron microscopy. Defect structures such as microtwinning, antiphase domain boundaries and dislocations have been observed within the beryllide phase. Descriptions of these defect structures will be presented in this paper, together with a discussion of their origin.
Temperature Effects on the Strength and Toughness of Be12Nb
Authors: Bruemmer Stephen M. , Arey Bruce W. , Jacobson Rodney E. , Henager Charles H. 
Published: March 2011

ABSTRACTStrength and toughness of single-phase Be12Nb have been assessed at temperatures from ambient to 1200°C using four-point-bend and hardness tests. Vacuum-hot-pressed beryllide exhibits low bend strengths (∼110 MPa) and fracture toughnesses (∼2.5 MPa√m) at temperatures up to 500C. Measured bend strength then increases to a maximum at 1000°C, while KlC slowly increases through 1100 C. Significant plastic deformation is only observed at 1200 C for the test strain rate of 2×10−6/s. Hardness values were found to remain relatively constant at temperatures up to 800 C and then sharply decrease at higher temperatures. Results indicate that low toughness limits bend strength at temperatures below ∼1000 C and prompts the observed increase in strength at high temperatures.
Compression, Bend, and Tension Studies on Forged Al67Ti25Cr8 and Al66Ti25Mn9 L12 Compounds
Authors: Kumar K.S. , Brown S. A. , Whittenberger J.D. 
Published: March 2011

ABSTRACTCast, homogenized, and isothermally forged aluminum-rich L12 compounds Al87Ti25Cr8 and Al66Ti25Mn9 were tested in compression as a function of temperature and as a function of strain rate at elevated temperatures (1000K and 1100K). Three-point bend specimens were tested as a function of temperature in the range 300K to 873K. Strain gages glued on the tensile side of the ambient and 473K specimens enabled direct strain measurements. A number of “buttonhead” tensile specimens were electro-discharge machined, fine polished, and tested between ambient and 1073K for yield strength and ductility as a function of temperature. Scanning electron microscope (SEM) examination of fracture surfaces from both the bend and tensile specimens revealed a gradual transition from transgranular cleavage to intergranular failure with increasing temperature.
Mechanical Behavior of Single Crystalline A166.8Ti27.4Fe5.8
Authors: Wu Z.L. , Pope D.P. , Vitek V. 
Published: March 2011

ABSTRACTThe operating slip systems and flow behavior of single crystalline A166.8Ti27.4Fe5.8 having the L12 structure were investigated at elevated temperatures using specimens with compressive axes near [001], [113], [112], [013] and [133]. Plastic deformation was carried exclusively by octahedral slip at low temperatures, and by both octahedral and cube slip at high temperatures. The yield stress is roughly temperature-independent at intermediate temperatures, but changes rapidly with temperature at high and low temperatures. At 770°C fracture occurs by cleavage on {011}, {001}, {013} and {111} planes. Al2Ti and AlTi3 were found in the single crystal matrix. The effects of these second phases on the mechanical behavior are not the same: Al2Ti does not embrittle the material but AlTi3 does.
The Role of Twinning in Brittle Fracture Of Ti-Aluminides
Authors: Yoo M. H. , Fu C. L. , Lee J. K. 
Published: March 2011

ABSTRACTThe important roles of (111)[112] twinning in cleavage fracture of single-phase γ-TiAl and TiAl3 are assessed on the basis of theoretically calculated elastic constants, shear fault energies, and cleavage energies. The importance of elastic anisotropy in both homogeneous twin nucleation theory and dislocation models for twin nucleation is emphasized. The twin-slip conjugate relationship makes an important contribution to the strain compatibility for localized plasticity at a crack tip of Mode-I type. The intrinsic brittleness of these aluminides is attributed to a combined effect of the low mobility of slip and twin dislocations and the relatively low cleavage strength. The effect of the resolved normal stress on the twin plane is to enhance twinning activity at a (110) crack tip, leading to transformation toughening of shear type.
Does A Threshold Stress For Creep Exist in Hfc-Dispersed Nial?
Authors: Daniel Whittenberger J. , Ray Ranjan , Jha Sunil C. 
Published: March 2011

ABSTRACTRecently it was proposed [S.C. Jha, et al., Mater. Sci. & Eng. A119 (1989) 103 & J.D. Whittenberger, et al., J. Mat. Sci. 25, (1990) 2771] on the basis of constant velocity testing at 1300 K that dispersion strengthened NiAl composites containing about 4 wt pct HfC possess threshold stresses for creep. Further 1300 K compression testing has been conducted on NiAl+4HfC,and diametrically opposite behavior has been found: for constant load creep tests normal power law behavior was observed (strain rate proportional to the stress raised to the power n); however additional constant velocity testing still indicates that the flow stress is essentially independent of strain rate below 10−6 s−1. Examination of NiAl+4.3HfC specimens after being deformed under constant velocity conditions revealed that the original hot extruded small grain structure could be converted to large, elongated grains during testing. Such a transformation appears to be responsible for the apparent threshold stress behavior in HfC dispersed NiAl.
Effect of Off-Stoichiometry on the Creep Behavior of Binary and Ternary Ni3Al
Authors: Hayashi Tohru , Shinoda Tetsumori , Mishima Yoshinao , Suzuki Tomoo 
Published: March 2011

ABSTRACTCompressive creep behavior is investigated In polycrystalline Ni3Al intermetallic compounds in which the focus is put on the effect of offstoichiometry and ternary additions of Ti, Ta, V and Co on the creep resistance of the compounds. In all cases, the steady-state creep rate has the power-law type dependence on the applied stress. The stress exponent thereby obtained leads us to regard the creep behavior of the compound to be of the Class I type. It is shown that the creep resistance Increases with increasing Ni concentration on both sides of the stoichiometric Ni3Al composition and a discontinuity exists in the variation at stoichiometry. The gap at the discontinuity becomes clearer by the addition of ternary element in most cases as compared to the binary Ni3Al. Although the exact reason for the phenomenon is not clearly understood at present, it is shown that it could be interpreted by the concentration dependence of activation energy in the power-law type creep equation.
Ternary Alloying of Refractory Intermetallics
Authors: Shah D. M. , Anton D. L. 
Published: March 2011

ABSTRACTOne of the most attractive attributes of intermetallics is their potential for alloying to achieve the desired balance of engineering properties via the creative use of in-situ composite processing. Following our initial investigation of 20 binary refractory intermetallics, selected primarily on the basis of structure type; seven systems were down selected for ternary alloying, based on a balanced consideration of room temperature toughness, high temperature creep strength, oxidation resistance and ultimate strength. These systems were Nb3Al and Cr3Si with A15 structure, CO2Nb and Cr2Nb Laves phases with C14/C15 structure, MoSi2 with C11b structure, and Nb2Al and Mo5Si3 sigma phases.The alloying potential of each of these binary systems is evaluated with respect to solubility limits, phase relationships, melting point suppression with alloying, and potential for enhancement of creep resistance. The results show that, with alloyed intermetallics, realistic creep strength is attainable and several opportunities exist for in-situ processing of intermetallic based composite systems to improve room temperature toughness.
Improvement of Room Temperature Ductility of Ni3Al by Unidirectional Solidification
Authors: Hirano Toshiyuki , Chung Sea-Sung , Mishima Yoshinao , Suzuki Tomoo 
Published: March 2011

ABSTRACTWe present the new promising method to improve the ductility of intermetallic compound, Ni3Al. Stoichiometric and Alrich Ni3A1 were unidirectionally grown at the growth rate of 24 mm/h by a floating zone method (FZ-UDS). The stoichiometric Ni3Al had a columnar-grained and single phase structure, whereas the Al-rich Ni3Al had a Ni3Al matrix with martensite-like precipitates. These alloys exhibited a large tensile elongation along the growth direction at room temperature. Fracture mode is a complete transgranular fracture in the stoichiometric Ni 3Al alloy, and a mixture of transgranular fracture of the matrix and cleavage of the martensite-like precipitates with cracking at the phase boundary in the Al-rich Ni3Al alloys.