bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of Dry-Solids-Blend Material Source Variation on the Compressive Strength of a Cement-Based Waste form
Authors: Gilliam T. Michael , Spence Roger D. , Francis Charles L , Osborne Steve C.
Published: March 2011

A preliminary evaluation of the impact on waste-form performance characteristics due to variations in dry-solids-blend material source has been performed. The statistical treatment technique utilized for data evaluation, described herein, provides a technically sound method of comparing the effects of material source and can be used to assess the statistical significance of effects of other variables on waste-form characteristics.
Evaluation of Thermal Conductivity of Backfill Material
Authors: Xu D.M. , Mohamed A.M.O. , Yong R.N. , Cheung S.C.H.
Published: March 2011

A series of tests have been performed at the Geotechnical Research Centre on backfill material under imposed temperature gradients. It has been demonstrated that the water content distribution during the transient process does not affect the temperature distribution. The Trial Function Technique (TFT) has been applied to calculate the thermal conductivity of the backfill material. Using these values and the proposed method of solution, the temperature profiles have been calculated. The comparison between the theoretically predicted and the experimentally measured temperature profiles shows good agreement except in the vicinity of the heating boundary, where a thin thermal boundary layer exists. The vaporization process in this thin layer contributes to the turbulent effect that can be modeled by using a thermal shock condition.
Basic Research for Assessment of Geologic Nuclear Waste Repositories: What Solubility and Speciation Studies of Transuranium Elements Can Tell US
Authors: Nitsche Heino
Published: March 2011

Solubility and speciation data are important in understanding aqueous radionuclide transport through the geosphere. They define the source term for transport retardation processes such as sorption and colloid formation. Solubility and speciation data are useful in verifying the validity of geochemical codes that are part of predictive transport models. Results from solubility and speciation experiments of 237NpO2+, 239Pu4+, and 241Am3+/Nd3+ in J-13 groundwater (from the Yucca Mountain region, Nevada, which is being investigated as a candidate high-level nuclear waste disposal site) at three different temperatures (25°, 60°, and 90°C) and pH values (6, 7, and 8.5) are presented and compared with published modeling calculations. The comparison results indicate that there is a great need for experimental data on the solubility and speciation of transuranium elements under a wide range of conditions, for example, pH, Eh, temperature, and composition of groundwaters. Additionally, the influence of alpha radiation and the radiolysis of the secondary transuranium solids on solubility and speciation should be studied. Solubility studies and model calculations should be extended to other important long-lived nuclear waste radionuclides such as nickel, zirconium, cadmium, radium, and thorium.
Actinide Speciation by Photothermal Spectroscopies: Instrumentation Development
Authors: Berg J.M. , Tait C.D. , Morris D.E. , Woodruff W.H.
Published: March 2011

Photoacoustic spectroscopy using pulsed laser excitation is being developed by a number of research groups as one of the most promising methods for studying speciation of actinides in solution at environmentally relevant concentrations. We present details of a number of hardware and software techniques we have implemented which, once fully developed, we believe will improve the sensitivity of the method. Our approach is based on more extensive waveform analysis. While most signal processing techniques extract the analytical signal from only a small portion of the acoustic waveform produced in the detector by an absorption event, we describe two methods that use more of the waveform. Other methods of minimizing noise sources using both hardware and software are also described.
Studies of the Effects of Degradation Products on the Sorption of Tin and Radium
Authors: Berry J.A. , Baston G.M.N. , Bond K.A. , Linklater C.M. , Pilkington N.J.
Published: March 2011

The effects on sorption on geological media caused by the presence of materials derived from a cementitious repository have been studied. This work includes an investigation of the influence of cellulosic degradation products on the sorption of tin and radium on London clay and Caithness flagstones and the sorption of radium as a function of calcium concentration.

Experimental conditions were chosen to simulate those expected close to a cementitious repository (pH=l1) and at the edge of the zone of migration of the calcium plume (pH=8). Work was carried out, (i) under baseline conditions in the absence of organic materials; (ii) with gluconate, acting as a well-characterized organic degradation product simulant; (iii) with authentic cellulosic degradation products.

This investigation has shown that the sorption of tin can be affected by the presence of cellulosic degradation products whereas the sorption of radium is little affected. The sorptive behaviour of radium is however strongly influenced by the calcium concentration.
Application of Sphagnum Peat, Calcium Carbonate, and Hydrated Lime for Immobilizing Uranium Tailings Leachate
Authors: Longmire P. A. , Brookins D. G. , Thomson B. M. , Eller P. G.
Published: March 2011

Batch experiments, mineralogical studies, and geochemical modeling were conducted to evaluate the effectiveness of sphagnum peat, calcium carbonate, and hydrated lime in removing dissolved concentrations of As, Mo, NO3, and U present in uranium-tailings pore water at Gunnison, Colorado. Amounts of As, Mo, and U removal by sphagnum peat, calcium carbonate, and hydrated lime at 5.0, 2.5, and 2.5 wt.%, respectively, were typically above 97 %. Nitrate removal ranged between 55 and 80 %. Significant contaminant removal was achieved by sphagnum peat alone at pH 3.18. Addition of 2.5 wt.% calcium carbonate to the sphagnum peat-tailings system resulted in formation of soluble uranyl carbonato complexes, which decreased the amount of U(VI) fixed onto sphagnum peat by a factor of 2. Addition of 2.5 wt.% hydrated lime to the acidic tailings increased Mo concentrations by a factor of 2 under moderately alkaline conditions (pH 12). During neutralization of tailings-pore water, precipitation of ferric oxyhydroxides may provide additional removal of As, Mo, and U(VI) from solution through adsorption and coprecipitation processes.
Leach Rate Excursions in Borosilicate Glasses: Effects of Glass and Leachant Composition
Authors: Barkatt Aa. , Olszowka S. A. , Sousanpour W. , Adel-Hadadi M. A. , Adiga R. , Barkatt Al. , Marbury G. S. , Li S.
Published: March 2011

Leach tests on borosilicate glasses using a partial-replenishment technique show that in certain cases large excursions in leach rate may appear at the end of periods ranging between 1 and 20 months. The extent and time of these leach rate transients are very sensitive to glass and leachant composition and to S/V ratio, and they may be eliminated by slight increases in Si and Al levels in the glass or by using a neutrally buffered leachant. This phenomenon, which may reflect cracking of the initial surface layer, can have a considerable effect on the results and complicate the modeling of leach tests which strongly reflect the extent of leaching during the early stages of glass/leachant interaction. However, these effects appear to have relatively little significance in the long term.
Prediction of Uranium Adsorption by Crystalline Rocks: The Key Role of Reactive Surface Area
Authors: Wanty Richard B. , Rice Cynthia A. , Langmuir Donald , Briggs Paul , Lawrence Errol P.
Published: March 2011

Adsorption processes are important in controlling U concentrations in ground water. Quantifying such processes is extremely difficult in that in situ conditions cannot be directly measured. One rock characteristic that must be known to quantify adsorption is the specific surface area of reactive minerals exposed to the ground water. We evaluate here three methods for estimating specific surface area in situ. The first is based on the dissolution kinetics of sodium feldspars, the second on emanation of radon-222 and the third on adsorption of naturally-occurring U. The radon-222 method yields estimates 5 to 8 orders of magnitude greater than those obtained via the other two methods; too large probably because of effects related to fracture geometry. Estimates of specific surface area based on modelling adsorption of natural U by aquifer materials are of comparable magnitude to those from the feldspar-dissolution kinetics approach. These conclusions are based on analyses of water from 145 wells in crystalline-rock aquifers from Pennsylvania, New Jersey, Maryland, and Colorado. Computer modelling of the chemical data using PHREEQE [1] showed that uraninite or coffinite approach saturation in reducing water, limiting total U to <2 × 10−9 m. Generally, U minerals are below saturation in oxidizing ground water, where uranyl-carbonate complexes are the dominant dissolved U species. Autoradioluxographs of thin sections show areas of concentration of radioactivity in the rocks and establish that U is concentrated along fracture boundaries and on ferric oxyhydroxide grain coatings. Because U minerals generally are undersaturated, U mobility is limited by adsorption onto ferric oxyhydroxides and other mineral surfaces. Calculations of uranyl adsorption from the ground water onto goethite using the program M1NTEQ [2] show that adsorption decreases with increased carbonate concentrations due to the formation of uranyl-carbonate complexes. Results of this paper improve our understanding of the mobility of U that might be released into oxidized ground water in crystalline rock from a breached radioactive-waste repository.
Temporal Changes in Decay-Series Isotope Concentrations in Response to Flow Conditions in the Sssdp Well, Salton Sea, California
Authors: Leslie Bret W. , Hammond Douglas E. , Ku Teh-Lung
Published: March 2011

Several radionuclides of the naturally occurring 238U, 235U and 232Th decay series have been measured in high-temperature (300–350 °C) brines from several flow tests of the Sal ton Sea Scientific Drilling Project (SSSDP) well. Activities (dpm/kg) at the initial flow test of the well were 222Rn (2130), 226Ra (2200), 228Ra (1120), 224Ra (1010), 223Ra (6), 210Pb (3260), and 212Pb (2250). In contrast, activities of U and Th isotopes were much lower (< 1 dpm/kg). Following the first flow test (12/85), the well was deepened and sampled again during a short flow test (3/86). Radium and uranium concentrations were about two times lower during the second flow test, while other elements had similar concentrations. During a subsequent 20 day flow test of the well (6/88), flow rates were regulated at the wellhead to investigate reservoir characteristics, and 226Ra and 210Pb activities were found to be negatively correlated with the flow rate and positively correlated with the wellhead pressure. The 226Ra activity varied by a factor of five, roughly the variation in total flow rate, while well-head pressure varied only by 25% and 210Pb activity varied by a factor of two. Ratios of short-lived daughters to longer-lived parents increased in these flow tests. Results from mass balance calculations incorporating reaction kinetics suggest that differences in the degree of radium adsorption, rates of precipitation and dissolution of reservoir minerals exist in different flow zones.
Study on Role of 234Th in Uranium Series Nuclides Migration
Authors: Ohnuki Toshihiko , Watanabe Shoji , Murakami Takashi
Published: March 2011

The role of 234Th, a daughter nuclide of 238U having a half life of 24 days, in the migration of uranium series nuclides has been studied to understand the mechanism which gives a higher migration velocity of 238U than that of 234U. We assume that 234Th is adsorbed at two different sites; one, where 234Th is reversibly adsorbed, and the other, where 234Th is irreversibly fixed. Calculations have shown that the fixation of ^Th to a rock can cause the apparent migration velocity of 234U to be reduced compared to that of 238U and this agrees with observed field data. Changes in the fixation rate constants affect the relative mobility of 238U and 234U, and this can account for the different migration behavior at different depths in the Koongarra ore deposit.
Migration of Radionuclides in Geologic Media: Fundamental Research Needs
Authors: Reed D. T. , Zachara J. M. , Wildung R. E. , Wobber F. J.
Published: March 2011

An assessment of the fundamental research needs in understanding and predicting the migration of radionuclides in the subsurface is provided. Emphasis is on the following three technical areas: (1) aqueous speciation of radionuclides, (2) the interaction of radionuclides with substrates, and (3) intermediate-scale interaction studies. This research relates to important issues associated with environmental restoration and remediation of DOE sites contaminated with mixed radionuclide-organic wastes.
The Role of Surface Layers in Glass Leaching Performance
Authors: Bates J. K. , Ebert W. L. , Mazer J. J. , Bradley J. P. , Bradley C. R. , Dietz N. L.
Published: March 2011

The examination of reacted layers that form as glass reacts can provide insight into reaction mechanisms that control long-term glass reaction, and into processes by which radionuclides are released to solution. Examples are given for the natural glasses obsidian and tektite, and the nuclear waste glasses 131 and 165, where the layers form bothin-situand precipitated from solution, where they are both amorphous and crystal 1ine, where selective incorporation of actinide elements Into stable phases may offer a barrier to release, and where sloughing of the layers from the glass acts as an alternative radionuclide release process to solubility-limited control.Several reaction processes occur simultaneously as glass reacts, and the projection of glass performance to long time periods requires the identification of those processes that dominate the long-term reaction.
Demonstration of a System Performance Assessment Process
Authors: Dormuth Kenneth W.
Published: March 2011

To help evaluate the concept of nuclear fuel waste disposal in plutonic rock of the Canadian Shield, the long-term performance of a hypothetical disposal facility is being studied. This case study uses information from a Shield research area, laboratories, and conceptual engineering. It illustrates the use of performance assessment to derive constraints on the siting, construction, and operation of a disposal facility, and to demonstrate the feasibility of safe disposal of nuclear fuel waste.
On the Problem of Consistency of Chemical Thermodynamic Data Bases
Authors: Wanner Hans
Published: March 2011

The geochemical modelling in support of the performance assessment of radioactive waste disposal systems calls for a large number of chemical thermodynamic data. For realistic modelling it is essential that the data used are fully consistent. The verification of consistency of existing data bases is complicated by the fact that it requires the knowledge of a considerable amount of primary information to ensure:

1.

Consistency with the fundamental laws of thermodynamics

2.

Consistency within a chemical model

3.

Consistency with auxiliary data

4.

Consistency in the data correction procedures

This paper includes selected examples for each of the four items to visualize the problems. It should be noted that there are numerous other systems that could serve as examples as well, and the range of cases reported here is far from being exhaustive.

Realistic geochemical modelling depends not only on the quality of the data base, but also on the quality of the chemical model used. For the establishment of a chemical model, additional information is needed that is not contained in thermodynamic data bases.
Estimation of the Migration Parameters for the Boom Clay Formation by Percolation Experiments on Undisturbed Clay Cores
Authors: Put Martin J. , Monsecour Marcel , Fonteyne Alfons , Yoshida Hidekazu
Published: March 2011

The safety assessment of the repository for high level radioactive waste in the Boom clay formation requires reliable data for the migration parameters. The experimental set-up and the interpretation method is briefly described for percolation experiments on undisturbed clay cores drilled from the formation and results are reported. The undisturbed clay cores are drilled perpendicular and parallel to the stratification of the formation to study the isotropy of the formation. To represent the real situation as close as possible, in-situ interstitial clay pore water is used as percolating liquid.

Parameter values determined in the percolation experiments are presented for bromine, iodine and tritiated water. Darcy velocity and effective stress are used as variables. Anisotropy of the formation is demonstrated for the hydraulic conductivity, but is found to be trivial for the dispersion parameters. A general relation between the apparent dispersion constant, the diffusion accessible porosity and the Darcy velocity is also given.
Comparison of Granite, Tuff, and Basalt as Geologic Media for Long-Term Storage of High-Level Nuclear Waste
Authors: Grandstaff D. E. , Grassi V. J. , Lee A. C. , Ulmer G. C.
Published: March 2011

Systematic differences in pH, cation/proton ion activity ratios, and redox have been observed between solutions produced in rock-water hydrothermal experiments with tuff, granite, and basalt. Stable pH values in tuff-water experiments may be as much as 1.5 pH units more acidic than basalt-water experiments at the same temperature and ionic strength. Redox (log fO2) values in 300°C tuff experiments are 4–7 orders of magnitude more oxidizing than basalt experiments and ca. 4 log units more oxidizing than the magnetite-hematite buffer. Such fluid differences could significantly affect the performance of a high-level nuclear waste repository and should be considered in repository design and siting.
Heat-Pipe Effect on the Transport of Gaseous Radionuclides Released from a Nuclear Waste Container
Authors: Zhou W. , Chambré P. L. , Pigford T. H. , Lee W. W.-L.
Published: March 2011

We present analytic studies of the transport of gaseous species released from a spent-fuel waste package, as affected by a heat-pipe of counterflowing liquid and vaporized water in the surrounding rock. A heat-pipe is caused by heating which vaporizes pore water near the waste, releasing vapor into the fractures. Driven by its pressure gradient, the vapor flows away from the waste and condenses where the rock is cooler. Because of capillary pressure gradient due to non-uniform liquid saturation, condensate flows towards the waste through the porous rock. We first develop analytic solutions for the time-dependent transport of energy and fluid from the waste container to the surrounding fractured porous rock. From the mass fluxes of liquid and vapor, we solve the advective-diffusive transport of a gaseous species released from the waste. The major assumptions are quasi-steady-state, local thermodynamic equilibrium, no noncondensable gases, and no sorption. Our results include the extent of the heat-pipe zone as function of time, the vapor velocity distribution in the heat-pipe zone, radionuclide concentration in water vapor, and the flux of radionuclide at the waste surface normalized to the surface concentration. We find that the vapor velocity in the heat-pipe zone is 1000-fold greater than the local air velocity if there were no heat pipe. If the gaseous species release mechanism maintains a near-constant concentration of gaseous species in the gas outside and near the waste container surface, the mass rate of transport of that species would be increased 1.3 to 7 times greater than if there were no heat pipe. However, if the release rate of the gaseous species is affected little by the concentration of that species outside the container, the heat-pipe can have little affect on the transport rate of that species.
Loading Rate Effects on Ductile-Phase Toughening in In-Situ Niobium Silicide-Niobium Composites
Authors: Rigney J.D. , Lewandowski JJ , Matson L. , Mendiratta M.G. , Dimiduk D.M.
Published: March 2011

Brittle silicide intermetallics such as Nb5Si3 have been significantly toughened by Nb particles incorporated during in-situ processing techniques. Ten-fold increases in toughness as well as resistance-curve behavior have been realized at conventional testing rates with these ductile Nb particles. Under more rapid loading rates the efficiency of the body-centered cubic (bcc) Nb particles in enhancing the toughness may be affected due to the strain-rate sensitivity of the Nb and/or the possible strain-rate sensitivity of interfacial debonding. Toughness tests conducted at loading rates of 0.0042 to 8.5 mm/sec have indicated a significant sensitivity to testing rate, with a drop in fracture toughness from 28 to 9 MPa√m over this range accompanied by a change in fracture mode from primarily ductile to cleavage failure in the Nb.
The Role of off-Diagonal Disorder on Alloy Phase Stability: An Application To The Ni-Pt System
Authors: Sluiter M. , Turchi P.E.A.
Published: March 2011

The occurrence of ordering in the Ni-Pt alloy system seems to violate theoretical predictions based on a tight-binding description of the electronic structure [1,2,3]. In these descriptions of transition metal alloys, ordering is predicted if the d-band is about half filled, and phase separation is predicted if the d-band is almost empty or almost full. This so-called bandfilling argument clearly fails in the case of Ni-Pt alloys, which order despite an almost filled d-band. The band filling rule is derived under the assumption that off-diagonal disorder (ODD), that is, the difference in d-bandwidths of the constituents, can be ignored. In Ni-Pt that is not the case, the d-bandwidths of the pure elements Ni and Pt are 0.32 Ry and 0.57 Ry, respectively [4]. However, it has been argued that taking ODD into account would result in an even stronger phase separation tendency in the theoretical prediction [2]. Magnetism is not a factor in equiatomic Ni-Pt alloys, and thus can not be invoked to correct the erroneous prediction. Other factors, such as spin orbit coupling in the relativistic description of Pt can change the prediction only if very large spin orbit splitting is assumed on the Pt atom [5].
Phase and Microstructure Morphologies in Combustion Synthesized Nb-Al-B Composites
Authors: Ho C.T. , Sekhar J.A.
Published: March 2011

Results of an experimental study on unidirectional wave combustion synthesized Nb-Al-B composite alloys are described. The effect of combustion initiation temperature and composition on the microstructural morphology and phases is studied. Correlations with the initial parameters and reaction velocities have been sought to understand the kinetics of the rate controlling step for sustained combustion and for the explanation of the synthesized microstructures. Strategies for controlling the distribution of the reinforcement phases (both ductile and hard) in the composite are discussed.
Empirical Interatomic Potentials for L1O Tial and B2 Nial
Authors: Rao Satish I. , Woodward C. , Parthasarathy T.A.
Published: March 2011

Recent studies have suggested a particular relationship between the degree of covalent bonding in TiAl and the mobility of dislocation[1,2]. Ultimately such electronic effects In ordered compounds must dictate the dislocation core structures and at the same time the dislocation mobility within a given compound. However, direct modelling of line defects Is beyond the capability of todays electronic structure techniques. Alternatively, significant steps toward extending our understanding of the flow behaviour of structural intermetallics may come through general application of empirical interatomic potential methods for calculating the structure and mobility of defects. Toward this end, we have constructed semi-empirical interatomic potentials within the embedded atom formalism for L1O and B2 type structures. These potentials have been determined by fitting to known bulk structural and elastic properties of TIAl and NiAl, using least squares procedures. Simple expressions that relate the parameters of the potentials to the bulk properties are used in the fitting procedure. Calculations of dislocation core structures and planar fault energies using these potentials are considered. The differences between the optimized bulk properties predicted from the potentials and the values for these properties are discussed in terms of non-spherical nature of the electron density distribution. Empirical methods which incorporate these effects into interatomic potentials are briefly discussed.
Alloying Behavior of Ni3Si and the 900°C Isotherms of Several Ni-Si-X Systems At Ni-Rich Corner
Authors: Tianxiang Zhang , Yundong Li , Zhi Zheng , Yaoxiao Zhu
Published: March 2011

The solid solubilities of 15 common alloying elements in the L12-type intermetallic compound Ni3Si have been determined at 900°C, and their substitution mode has been deduced from the direction of solubility lobe of the compound. It is shown that the alloying behavior in Ni3Si is determined by both size and electronic factors, i.e, the substitution mode is governed by electronic configuration and solubility by the both. The solubilities of alloying elements can be explained on the two dimensional map proposed by Alonso and Simozar.

Four isotherms of Ni-Si-X (X = Fe,Cr, Co,Cu) have been obtained. They are very similar in structure.
Microstructure of Titanium-Aluminides after Thermomechanical Treatment
Authors: Seeger J. , Hartig C. , Bartels A. , Mecking H.
Published: March 2011

Forging in the α2+γ-phase field results in grain refined zones by dynamic recrystallization, but still coarse γ-grains and a residual amount of α2/γ-lamellae are observed. During subsequent heat treatment in the α+γ-phase field the recrystallization leads to inhomogeneous distributions of α2-Ti3Al and grain sizes of γ-TiAl. Due to these inhomogeneities a significant increase of the room temperature ductility is not found.
Short-Range to Long-Range Ordering Reactions in a Ni-25Mo-8Cr Alloy
Authors: Kumar Mukul , Vasudevan Vijay K.
Published: March 2011

The transformation from short-range↔long-range order in Haynes® Alloy 242, a nominal Ni-25Mo-8Cr (in wt.%) alloy, during both continuous heating and cooling and isothermal holding at temperatures between 550 and 750°C is reported using dilatometry and microhardness measurements, and optical and transmission electron microscopy The long-range to short-range order transformation temperature was observed to increase with an increase in the degree of prior order. Aging below the transformation temperature led to considerable hardening; this hardening was associated with the formation of a very high volume fraction of Ni2Mo domains/precipitates. On aging at 700°C and below, the hardness initially increases and then levels off, with no evidence of overaging for times to 2000 hours. The role of both short- and long-range order on the transformation temperature, thermal expansion and hardening behavior and the mechanisms of transformation from short-range to long-range order were established and will be discussed.
Dislocation Nucleation Versus Cleavage in Ni3AI and Ni
Authors: Sun Yuemin , Rice James R. , Truskinovsky Lev
Published: March 2011

Recent advances in the modelling of dislocation nucleation from a crack tip are used here to compare the critical energy release rate associated with emission in Ni3Al and Ni. The method for analyzing nucleation makes use of a Peierls-type stress versus displacement relation ahead of the crack tip. It has been shown recently by Rice [1] that the energy release rate for emission scales with γus, the “unstable stacking” energy associated with the sliding of atomic planes past one another. The advantage of this approach is that it allows for an extended dislocation core during nucleation, thus eliminating the need for a core cutoff radius. Preliminary calculations which take into account only the shear stress on a slip plane show that it is more difficult to emit a dislocation in Ni3Al than in Ni. Working within the framework of the competition between atomic decohesion and blunting by dislocation emission, the implications for explaining the brittleness of Ni3Al are also discussed.
Deformation Microstructures in B2-Type CoTi Single Crystals
Authors: Yoshida M. , Takasugi T.
Published: March 2011

B2-type CoTi single crystals which exhibit the yield strength anomaly were deformed at various temperatures and on various compression axis in order to investigate the deformation microstructures. The morphological feature and Burgers vectors of the activated dislocations were investigated by means of transmission electron microscopy. At a low temperature of 300 K, relatively straight dislocations with the <001>-type Burgers vector were observed. They consisted of the mixed components of edge and screw, and strongly tended to form the dipoles. At a temperature of 773 K where the yield stress increases with increasing temperature, the screw components of dislocations with a <001>-type Burgers vector were dominant and showed peculiar morphology revealing the pinning or cross slip. However, the examination using the weak-beam method could not show the evidence of any dissociation. At a high temperature of 973 K above the peak temperature, the Burgers vectors of activated dislocations were determined to be a <001>- type for compressive orientation axes close to [111] and [011] whereas a <110>-type for orientation axis close to [001]. These dislocation microstructures were discussed in correlation with the yield strength anomaly observed in these intermetallics.
Phase Stability and Role of Ternary Additions on Electronic and Mechanical Properties of Aluminum Intermetallics
Authors: Freeman A.J. , Hong T. , Lin W. , Xu Jian-Hua
Published: March 2011

First principles total energy local density method have addressed the problems of (i) bonding, cohesion and phase stability and (ii) the role of ternary additions, anti-phase boundaries (APB's) and other faults in determining the structural, electronic and mechanical properties of aluminum intermetallic alloys. A key goal has been to attempt to understand, at the electronic level, fundamental quantities that may be related to the crucial brittleness vs. ductility issue in high temperature Ni and Ti and other aluminides. Other contrasts between observed ductility properties of related systems (e.g., NiAl and RuAl) are related to their differing electronic and bonding properties, particularly the nature of p-d hybridization and the directional properties of their electronic charge distrubutions - especially for states near the Fermi energy.
Bonding Energies and Long-Range Order in the Trialuminides
Authors: Sparks C. J. , Specht E. D. , Ice G. E. , Zschack P. , Schneibel J.
Published: March 2011

The degree of long-range order in the trialuminides is determined by X-ray powder diffraction techniques. Long-range order exists to their melting points. For the binary trialuminides Al3Ti, Al73Ti27, and Al3Sc, the degree of long-range order is nearly perfect and is a measure of the lack of mixing of the aluminum atoms onto the sublattice occupied by either Ti or Sc. A calculation of the bond energy between neighboring pairs of atoms from the ordering (melting) temperature is made following the Bragg-Williams mean field theory approach. These bond energies compare favorably with more sophisticated calculations. Bond energies are found to be larger than the energy difference between the crystal structure forms DO22, Ll2, and DO23, and therefore, more relevant to understanding the mechanical and chemical behavior of the trialuminides. Ordering or melting temperatures of these intermetallics reflect the strong Al-metal near-neighbor pair potentials and may provide insights to their brittle properties.
X-Ray Determination of Site Occupation Parameters in Ordered Ternaries Cu(Aux.M1x.)M = Ni,Pd
Authors: Kumar R. , Sparks C. J. , Shiraishi T. , Specht E.D. , Zschack P. , Ice G. E. , Hisatsune K.
Published: March 2011

X-ray scattering data obtained for multiple wavelengths with synchrotron radiation were analyzed by the Rietveld method to determine Ni and Pd distributions on the Cu(000) and Au(½½½) sites in the CuAuI tetragonal P4/mmm structure. Alloys of CuAuxM1-x containing 6 at. % Ni or 10 and 25 at. % Pd were processed to obtain maximum ordering. Nickel is predominantly found on the Cu site and most all the Pd is found on the Au site. The uncertainty in site occupation parameters is discussed for various contributions which affect powder intensity measurements. For highly absorbing materials, an observed powder roughness effect decreases the low angle (2θ) intensities relative to the high 2θ intensities. This effect reduces the reliability of the thermal parameters and obscures a proper description of the thermal motion of the two sublattices. Corrections to the X-ray intensity data for surface roughness/porosity effects reduce uncertainties to about ±1 at. % on the refined value of the site occupations. This use of variable wavelength X-rays with simultaneous refinement of the corresponding data is capable of distinguishing site occupations even between two elements of almost equal scattering factor as, for example, Cu and Ni atoms in this investigation. Chemical phase stability is related to the site occupation parameters.
Theoretical Investigation of Phase Stability in Non-Magnetic Fe-V Substitutional Alloys
Authors: Sluiter M. , Turchi P.E.A.
Published: March 2011

The assessed phase diagram of Fe-V exhibits a continuous high temperature bcc solid solution intersected at lower temperatures by a complex sigma phase centered around equiatomic composition [1]. Slow kinetics of the bcc to sigma transformation make it possible to retain the bcc solid solution at low temperature. It has been observed that this metastable solid solution has a tendency to order with a CsCl type structure (B2) below 970 K [1,2]. As a first attempt to describe this behavior from an electronic structure approach, this paper will study the phase stability on the bcc lattice using a realistic tight-binding Hamiltonian. Details of the tight-binding description have been given elsewhere [3]. Main features are as follows: Element and structure specific Slater-Koster parameters are used [4] and lattice parameter effects are incorporated through scaling [5]. Charge transfer is set to zero by rigidly shifting the onsite energies of one constituent. The Coherent Potential Approximation (CPA) is invoked with four levels corresponding to states with s, p, t2g and eg like symmetry. Effects of off-diagonal disorder (ODD) have not been included, instead, an average alloy Hamiltonian was defined using the Slater-Koster parameters of the components weighted by concentration. At equiatomic composition the effect of this approximation has been evaluated by repeating the electronic structure calculation with inclusion of ODD effects (see also [6]). Effective pair interactions, as defined within the Generalized Perturbation Method (GPM) [7], have been computed and have been used to evaluate the ground states of configurational order on the bcc lattice in the Fe-V system. Furthermore, the theoretically derived energetic properties have been used to determine the phase diagram pertaining to the (metastable) bcc lattice with the Cluster Variation Method (CVM) [8] in the tetrahedron approximation
The Structure and Properties of Boundaries in Bicrystals of Boron-Doped Ni3(Al,l at% Ta)
Authors: Mills M. J. , Goods S. H. , Foiles S. M.
Published: March 2011

The effect of boron on the structure and macroscopic properties of an isolated grain boundary in bicrystals of a non-stoichiometric Ni3Al alloy (76 at% Ni, 23 at% Al, 1 at%Ta) has been studied. The room temperature tensile ductility and fracture mode of the bicrystals varies dramatically with the rate of cooling after elevated temperature heat treatment. In the absence of significant segregation of boron to the boundary, the bicrystals fail via brittle interfacial fracture with little or no ductility. When the segregation of boron to the boundary is maximized, the bicrystals are highly ductile. High resolution transmission electron microscopy reveals that this ductile state is achieved without the formation of a detectable region of compositional disorder at the boundary. Atomistic calculations using a Monte Carlo scheme predict that only partial disordering of the planes immediately adjacent to the boundary should occur for Ni-rich alloys both with and without boron. These results suggest that the presence of boron causes an increase in the cohesive energy of the boundaries rather than a change in the local compositional ordering.
Stress-Assisted Discontinuous Precipitation during Creep of Ti3Al-Nb Alloys
Authors: Rowe R.G. , Hall E.L.
Published: March 2011

Stress-assisted discontinuous precipitation was observed during creep of Ti- 25Al-12.5Nb at.% and associated with microstructures in which large primary creep strains were observed [1]. It was found that a large shift between the equilibrium βo (B2) phase composition at the heat treatment temperature and disordered β(bcc) phase at the creep temperature provided a driving force for discontinuous precipitation of disordered beta phase. Applied stress accelerated the growth of discontinuous β phase at grain boundaries perpendicular to the principal stress axis, but did not produce a significant shift in composition. The difference between beta and ordered beta phase boundaries in the Ti-Al-Nb system at 650°C and 1040°C suggests that discontinuous precipitation or related dissolution should occur in all Ti3Al-Nb alloys.
Deformation Mechanisms and Solid-Solution Strengthening in Ordered Alloys
Authors: Dimiduk Dennis M. , Rao Satish
Published: March 2011

Fundamental to understanding the results of alloy design studies, is the need for understanding the intrinsic role of solutes in a particular compound. For many compounds such an understanding must be built from a systematic exploration of the role of deviations from the stoichiometric composition as well as the role of ternary solute additions on the variation of flow behavior. Within most intermetallic systems the problem is complicated since the fundamental mechanisms of flow are not well established and, in those systems where these mechanisms are known, thermal activation can lead to dislocation-core transformations and changes in the operative slip systems with temperature. In general, flow may be governed by more than one dislocation process at a given temperature and deformation twinning may be a major contributing deformation mechanism. The problem of isolating the mechanisms of solid-solution hardening may, therefore, require treatment as a problem of combined strengthening mechanisms operating in parallel. This paper reviews the key aspects of deformation mechanisms and solute strengthening in intermetallic alloys. Classical elastic theories of solute hardening serve as an origin, from which, the progress made to date in isolating the mechanisms of solute hardening in ordered alloys is discussed.
Cleavage Fracture and Dislocation Structures of Ductile L12 Type Ni3Ge Single Crystals
Authors: Inoue H.R.P. , Wayman C.M. , Saburi T.
Published: March 2011

Fracture and dislocation structures of single crystals of the L12-type compound Ni3Ge deformed in tension-compression at room temperature are investigated by optical and electron microscopy. After considerable plastic deformation, cracks nucleate along primary (111) planes of [245]-oriented single crystals and grow in zigzag manner by connecting one octahedral plane to another. Fracture occurs by brittle cleavage. Similar cleavage fracture also occurs when thin films (whose plane is (111)) prepared from cyclically deformed specimens are further deformed at room temperature. These observations are different from those reported in a previous study where the cleavage plane is claimed to be {001} for single crystals deformed in tensio at room temperature. A number of piled-up dislocations are emitted due to stress concentration at and ahead of crack tips, evidencing that this compound is intrinsically ductile. Superlattice intrinsic stacking faults are observed in front of crack tips along with a moire structure. Although there is argument that such moire structures are formed in persistent slip bands during cyclic deformation of Ni3Al, this is unlikely in the present case. The moire structure observed is believed to be formed by deformation of the thin (111) film.
First-Principles Calculations of Stacking Faults and Grain Boundaries in Metals
Authors: Hampel K. , Vvedensky D.D. , Crampin S.
Published: March 2011

A detailed understanding of planar defects plays an important role in the search for a comprehensive description of the mechanical behaviour of metals and alloys. We present calculations for isolated stacking faults and grain boundaries using the layer Korringa-Kohn-Rostoker method including an assessment of the force theorem, which has already proven itself in evaluating defect energies for elemental close-packed metals. These ab initio total energy calculations will be supplemented by a study of the changes in bonding and local magnetic properties near a symmetric Σ5 (310) grain boundary in Fe
Hydrogen Embrittlement of FeAl and Fe3Al
Authors: Shea M. , Castagna A. , Stoloff N. S.
Published: March 2011

This paper deals with the role of charging conditions and strain rate on the embrittlement of several Fe.Al and Fe3Al alloys. Fracture paths are transgranular or mixed mode in both air and after precharging of the iron aluminides, unlike the intergranular cracking typical of Ll2 superlattices exposed to hydrogen. The fractographic observations are consistent with a decohesion mechanism. The role of long range order in transport of hydrogen will be discussed.
Alloying of Al3Ti With Mn and Cr to Form Cubic L12 Phases
Authors: Nic J.P. , Zhang S. , Mikkola D.E.
Published: March 2011

Based on studies of several binary trialuminides, it has been concluded that those with the L12 structure offer the best prospects for developing useful mechanical properties. Further, evaluation of a series of cubic ternary alloys produced by alloying Al3Ti with fourth period transition elements from Cr to Cu has shown that the mechanical properties and lattice parameters of the cubic alloys vary in a consistent manner with the location of the ternary alloying element in the periodic table. These structure/property relationships have been interpreted in terms of the number of d-shell electrons available for bonding. The Cr- and Mn-modified alloys have been shown to be the most attractive in terms of hightemperature structural applications. Finally, the work has resulted in a suggested mechanism for the D022 to Ll2 transformation on alloying.
Microcracking Development in the L12 Ternary Titanium Trialuminide
Authors: Winnicka M.B. , Varin R.A.
Published: March 2011

Development of microcracking in a ternary titanium trialuminide modified with copper (Al5CuTi2) has been investigated. It has been observed that indenting the material by diamond pyramid indenter (Vickers) causes two types of cracking: (a) on the faces of the indentation and (b) on the surface around the indentation. Compression tests carried up to various levels of permanent deformation have shown a different response of low porosity (2.6±0.5%) and high porosity (5.3±1.5%) material to the formation of microcracks.
L12 Ordering in Disordered NiAIFe Alloys
Authors: Yavari A.R , Baro M.D. , Fillion G. , Surinach S. , Gialanella S. , Clavaguera-Mora M.T. , Desriè P. , Cahn R.W.
Published: March 2011

Ordering of the disordered state (obtained by cold-working or by meltspinning) of L12 type Ni,AI,Fe alloys has been monitored by calorimetric, magnetic and X-ray diffraction measurements .It is found that the magnetic moment per atom of the Ni,Al,Fe alloys in the γ-disordered state is about half of that of the LI2 -γ'state. Magnetic measurements such as ours constitute a new tool for studyingthe γ→γ' transition below the Curie temperature.
Effect Of Ceramic Dispersoids On The High Temperature Strength Of Mechanically Alloyed MoSi2
Authors: Kim Y.S. , Johnson M.R. , Abbaschian R. , Kaufman M.J.
Published: March 2011

Mechanical alloying (MA) has been used to synthesize MoSi2 from elemental Mo and Si powders. SiC and A12O3 dispersoids were also incorporated as a means of increasing high temperature strength. After synthesis, the powders were consolidated using vacuum hot pressing. It is shown that the size and volume fraction of porosity increases anomalously with increasing hot pressing temperature over the range 1200 to 1700°C. The strengths of the A12O3 composite are, in most instances, considerably higher than the monolithic material produced under similar conditions.
Deformation Mechanisms Associated with Annealed Structures in a Ti-24Al-Nb Alloy
Authors: Morris Maria A. , Morris David G.
Published: March 2011

Crystallographic and chemical analysis of the microstructures obtained by annealing a heavily deformed Ti-24Al-11 Nb alloy have been performed. The influence of the niobium distribution within the different phases present and the variation of degree of long range order caused by this distribution have been related to the deformation mechanisms leading to strain hardening at the early stages of deformation. In particular, slip band formation and twinning have been observed to occur within the (α2 phase according to the different degree of order measured.
Electronic Structure of Ordered and Disordered Cu50Pd50 and Cu75Pd25 Alloys
Authors: Bose S.K. , KudrnovskÝ J. , Jepsen O. , Andersen O.K.
Published: March 2011

We present the electronic density of states (DOS) in ordered and disordered Cu50Pd50 and Cu75Pd25 alloys calculated by using the linear muffin-tin orbitals (LMTO) method. For ordered alloys the results are obtained via self-consistent LMTO method. We then show how the LMTO parameters for pure Cu and pure Pd can be appropriately transferred to the ordered alloy calculation to produce results in excellent agreement with the self-consistent calculation. For disordered alloys we present the electronic DOS calculated via LMTO-recursion and LMTO-CPA methods, and study the effect of the deviation from the ideal lattice structure, due to different sizes of the Cu and the Pd atoms, on the DOS of these alloys. We also discuss how the scheme of transferring parameters from the pure components to the alloy can be used in the calculation for the disordered phase.
The Effect of Yttrium Ion Implantation on the High Temperature Oxidation Properties of NiAl
Authors: Pint B.A. , Jain A. , Hobbs L.W.
Published: March 2011

NiAl was ion implanted with yttrium (2×1016 cm−2) in order to study its effect on the very high temperature (1000–1500°C) oxidation properties. At 1000°C, implanted Y stabilizes the faster growing θ-Al2O3 phase, thus slightly increasing the oxidation rate. At 1200°C, where predominantly α-Al2 O3 is formed with and without Y, there is a factor of 4 reduction in the oxidation rate. However at higher than 1200°C, there is little effect by Y on the oxidation rate. Cyclic testing showed that the Y implant had an imperfect and short-lived improvement on adherence relative to other Y-containing alloys. Variations in aluminum content from 23.5 to 36.0wt%(40–55at%) had little effect on the oxidation properties. Initial experiments at 1500°C with a novel Rh marker indicate that alumina grows at least partially by outward cation diffusion both with and without Y.