bluuebunny/crossref_metadata_2025_split huggingface dataset:
1300 K Compressive Properties of a Reaction Milled NiAl-AlN Composite
Authors: Whittenberger J. Daniel , Arzt Eduard , Luton Michael J. 
Published: March 2011

AbstractCryomilling (high intensity mechanical ball milling in a liquid nitrogen bath) of the B2 crystal structure nickel aluminide leads to a NiAl-AlN composite containing about 10 vol pct second phase which is dispersed as very small diameter (< 50 nm) AlN particles in a mantle surrounding particle-free NiAl grains. The AlN particles are the result of reaction milling, where nitrogen incorporated into the matrix during cryomilling reacts with Al during subsequent thermomechanical processing to form a composite. Compressive testing at 1300 K of such materials densified by either hot extrusion or hot isostatic pressing have indicated that strength at relatively fast strain rates (>10−7 s−1 ) is dependent on the method of consolidation; however no clear dependency on densification technique appears to exist at slower rates. In addition deformation at 1300 K occurs by two distinct mechanisms, where at high strain rates the stress exponent is greater than 13 while at slower rates (< 10−7 s−1) a much lower stress exponent (∼6) was found.
Micromechanical Model of Crack Growth in Fiber Reinforced Brittle Materials
Authors: Rubinstein Asher A. , Xu Kang 
Published: March 2011

AbstractA model based on the micromechanical mechanism of crack growth resistance in fiber reinforced brittle matrix composites is presented. The formulation of the model is based on a small scale geometry of a macrocrack with a bridging zone, in this case the process zone, which governs the resistance mechanism. The effect of high toughness of the fibers in retardation of the crack advance, and the significance of the fiber pullout mechanism on the crack growth resistance, are reflected in this model. The model allows one to address issues such as influence of the fiber spacing and fiber-matrix friction.Two specific cases are analyzed. One represents the fracture initiation and concentrates on the development of the first microcrack between fibers. The second case deals with the development of an array of microcracks forming the bridging zone. In both cases a discrete fiber distribution is assumed. The analysis is based on an exact solution of the corresponding. boundary value problem.
Constant Stress Creep of XD™ TiAl Containing Nitrogen
Authors: Robertson Erica , Martin Patrick L. 
Published: March 2011

AbstractTi-47at%Al+7vol%(TiN+TiB2) alloys, produced by the Martin Marietta XD™ process, were subjected to tensile constant stress creep deformation in the range 760-850°C temperature and 138–276 MPa (20–40 ksi) stress. These alloys have a matrix of TiAl and Ti3Al initially containing 1 to 10 μm diameter equiaxed particles of Ti2B and Ti2AlN. Microstructures were examined using optical, SEM and TEM methods in an attempt to correlate the substructures with the property data. In particular, fine coherent particles have been observed to decorate dislocations and the interior of TiAl grains. The presence of these particles is thought to explain the creep resistance of this alloy.
Heat Treatments and Thermal Fatigue of Scs-6/Alpha-2 Titanium Aluminide Composites
Authors: Kim Y-W. , Kleek J. 
Published: March 2011

AbstractPanel composites made of alpha-2 titanium aluminide (Ti-25A1-9Nb-1.6Ta-1.6Cr-lMo) foils and SCS-6 (SiC with carbon core and carbon double coatings) fibers were investigated to determine the influence of postprocessing heat treatments on the thermal fatigue behavior in air. The 4-ply composite panels with 22 vol% fiber showed no edge cracks after 1000 thermal cycles between 150°C and 816°C in alpha+beta or beta-solution plus isothermal-aging treatments. The thermal cycling, however, embrittled the fiber carbon core and coatings in the composites given post-processing heat treatments, with the degree of embrittlement increasing progressively with heat treatment temperature/exposure. The detrimental effects of heat treatments on the matrix were also observed in that beta treatments reduced both the strength and tensile ductility of the matrix alloy when compared with alpha+beta treatments.
Initial Evaluation of Continuous Fiber Reinforced NiAl Composites
Authors: Noebe R. D. , Bowman R. R. , Eldridge J. I. 
Published: March 2011

AbstractNiAl is being evaluated as a potential matrix material as part of an overall program to develop and understand high-temperature structural composites. Currently, continuous fiber composites have been fabricated by the powder cloth technique incorporating either W(218) or single crystal Al2O3 fibers as reinforcements in both binary NiAl and a solute strengthened NiAl(.05 a% Zr) matrix. Initial evaluation of these composite systems have included: fiber push-out testing to measure matrix/fiber bond strengths, bend testing to determine strength as a function of temperature and composite structure (e.g. fiber volume fraction and number of fiber plies), and thermal cycling to establish the effect of matrix and fiber properties on composite life. The effect of matrix/fiber bond strength and matrix strength on several composite properties will be discussed.
Microstructural Studies of β-NiAl and α-Re Composites Produced by Eutectic Solidification
Authors: Mason D. P. , Van Aken D. C. , Webber J. G. 
Published: March 2011

AbstractArc-melted alloys of stoichiometric β-NiAl with additions of up to 1.5 atomic percent Re were examined to determine the nature of the quasi-binary phase diagram. Analysis of the Re segregation during solidification confirmed the eutectic nature. Solubility of Re in the β-NiAl structure was limited to approximately 0.5 atomic percent and precipitation of α-Re was observed in the hypoeutectic alloys. An orientation relationship with (101)β // (0001)α and [111]α // [1210]βwas determined for these rod-like precipitates.
Studies of Titanium Aluminide Composites Containing Metallic Fiber/Matrix Interface Layers
Authors: Rhodes C. G. , Bampton C. C. , Graves J. A. 
Published: March 2011

AbstractAmong the more serious problems arising from the use of SiC as a reinforcement for titanium aluminides are chemical instability and thermal expansion mismatch. In this work, metallic layers (Pd + W or Pt + W) have been included in the interface between SCS6 type SiC reinforcing fibers and Ti-48A1-1V (gamma TiA1) matrix to reduce interdiffusion and to retard crack propagation. Pd reacted with the SCS layer on the SiC fibers as well as with the titanium aluminide matrix by diffusion through the W layer. Cracks were found in the resulting Pd-Ti-Al reaction product. Pt did not react with the SCS layer, and reacted with the titanium matrix only in those regions where the W layer was fractured. No cracks were present where the W layer successfully protected the matrix from the Pt. Ti and Pt reacted extensively with the underlying SiC fiber in those areas where the SCS layer was fractured.
Chemical Stability of Fiber-Metal Matrix Composites
Authors: Norman J. H. , Reynolds G. H. , Brewer L. 
Published: March 2011

AbstractReinforcing phases used to strengthen a metal matrix cannot be appreciably chemically reactive for the times and temperatures expected during the service life of the composite. Where accurate phase diagrams exist that describe the interactions of the metal matrix and the reinforcing phase, the evaluation process can be completed with these diagrams and, if reactivity is encountered, with appropriate kinetic parameters. These complete phase diagrams are rarely available for complex materials systems. Therefore, we have adopted several ways of using available thermochemical data to estimate the compatibility of various metal matrix composite systems. Usually evaluations involve comparing matrix component activities, using reinforcing phase component thermochemistry to decide whether or not a reaction is expected by examining product chemical activities. Other methods use integral thermochemical properties of reactants and possible products in estimations. In either case a single thermodynamically favored reaction will disqualify a reinforcing phase on an energetic basis if not a kinetic basis. Where no disqualifying reactions are found, the reinforcing phase-metal matrix system is considered a candidate to be proved or disproved in experimental studies which may reveal reaction products not included in the extensive but still limited thermochemical literature. This approach has been advantageously applied to several systems. The study of Ti-Al metal matrices with selected reinforcing phases is discussed as an example.
Chemical Compatibility of High Temperature Intermetallic Compounds with Various Potential Reinforcements
Authors: Yang J.-M. , Jeng S. M. , Yang C. J. , Anton D. L. 
Published: March 2011

AbstractThe chemical compatibility between five high temperature intermetallic compounds and six potential reinforcements are investigated. Diffusion couples are prepared by vacuum hot pressing. The most promising reinforcements or coating for each intermetallic compound are identified.
Phase Stability of Sigma + Beta Microstructures in the Ternary Nb-Ti-Al System
Authors: Hoelzer D. T. , Ebrahimi F. 
Published: March 2011

AbstractAn alloy with the nominal composition 42Nb-28Ti-30Al (at.%) was heat treated in the sigma + beta phase region. The evolution of σ phase from the metastable β phase and the stability of the two-phase microstructure at various aging temperatures were evaluated using TEM techniques. The results indicate that the β phase in equilibrium with the σ phase at high temperatures decomposes to the orthorhombic phase at temperatures below 1200°C.
Decomposition Reactions and Toughening in NiAl-Cu Alloys
Authors: Allen W. P. , Foley J. C. , Cooper R. F. , Perepezko J. H. 
Published: March 2011

AbstractIn the NiAl-Cu3 Al pseudobinary section of the Ni-Al-Cu ternary system, the structural similarity of the binary phases yields a miscibility gap between NiAl (B2 structure with ao≃0.2880 nm) and Cu3 Al (bcc structure above 567° C with ao≃0.2946 nm). Due to the extensive mutual solubility, alloys can be solution-treated as single-phase NiAl and then aged at temperatures within the miscibility gap to investigate possible decomposition reactions. Several NiAl-Cu alloys (containing up to 30 at% Cu) were solution-treated at 1000° C, water-quenched, and then aged at either 475° C or 525° C. The decomposition of the supersaturated NiAl was characterized using XRD and SEM. A modulated microstructure was observed for an initial aging of 24 hours, and is consistent with the presence of a conditional spinodal between the NiAl and the Cu3Al. Long term aging resulted in the formation of equilibrium fcc Cu-rich precipitates. In comparison with the brittle nature of the as-quenched samples, the initial aging treatment yields samples which exhibit extensive slip development during hardness testing. Analysis of the deformation/fracture zone produced with a diamond cone indenter suggests that the ductile phase produced by the aging treatment, yielding an in-situ composite, enhances the resistance of NiAl to both crack initiation and propagation.
Reaction Zone Growth in Ti-Base/SiC Composites
Authors: Ritter Ann M. , Hall Ernest L. , Lewis Nathan 
Published: March 2011

AbstractReaction zone phases and kinetics over a temperature range of 650-1200°C have been characterized for Ti-14Al-21Nb/SiC and Ti-6Al-2Sn-4Zr-2Mo/SiC fibrous composites. The matrix of the Ti-1421/SiC materials was α2 with varying amounts of beta phase and transformed beta phase, and the Ti-6242 matrix consisted of alpha plus beta. The reaction zone in the as-HIP Ti-1421/SiC contained fine-grained TiC, a region of coarser-grained TiC, a carbide layer containing Ti, Al and Nb, and a region of(Ti, Nb)5(Si, Al)3. The matrix adjacent to the reaction zone was α2-Ti3Al with no beta phase. In the as-HIP Ti-6242/SiC composites, the reaction zone contained TiC near the fiber, and a layer of (Ti,Zr)5Si3 adjacent to the matrix. In heat-treated samples, the reaction zone thicknesses varied in a linear fashion with the square-root of aging time, indicating diffusion-controlled growth. Incubation periods for reaction zone growth were observed in Ti-1421/SiC samples aged at 760-1000°C. The overall kinetics for the two matrix alloys were approximately the same, and the activation energy was measured as 63-73 kcal/mole for Ti-1421/SiC and 73kcal/mole for Ti-6242/SiC.
Reaction Sintering of Molybdenum Disilicide Based Composites
Authors: Weiser Martin W. , Smelser Sherisse R. , Petrovic John J. 
Published: March 2011

AbstractPressureless reaction sintering was investigated as a fabrication method for composites composed of a MoSi 2 based matrix with up to 20 vol% SiC reinforcement. Up to 10 vol% of a number of reactants including Mo+2Si, CrSi2, and Cr+2Si were utilized. In nearly all cases the reactants greatly enhanced pure matrix densification at temperatures as low as 1400°C. The composites containing SiC reinforcement did not densify nearly as well. For some reactants it appears that an adverse reaction occurred between the SiC and the additives resulting in swelling.
Intermetallic Matrix Composites by Physical Vapor Deposition
Authors: Hardwick Dallis A. , Cordi Richard C. 
Published: March 2011

AbstractThe feasibility of producing layered composite sheet material, in which the matrix is the intermetallic compound TiAl, using physical vapor deposition (PVD) has been demonstrated. The PVD techniques of sputtering and electron beam evaporation were both investigated. Films were deposited by alternately sputtering from targets of composition Ti-53A1–3Nb and TiB2 or were co-deposited from separate electron beam heated hearths containing Ti and Al. In the latter case, nitrogen gas was pulsed into the deposition chamber at controlled intervals resulting in the formation of a TiAl/TiAlN layered composite. The composition of the films was determined using Auger analysis and Rutherford backscattering spectroscopy and the crystal structure was checked using X-ray and electron diffraction. Cross-sections through the films were prepared for examination by transmission electron microscopy so that the layered microstructure of the films could be verified.
Tailored Microstructures of Niobium-Niobium Silicides by Physical Vapor Deposition
Authors: Bhattacharya Rabi S. , Rai A. K. , Mendiratta M. G. , Cheng Y. T. 
Published: March 2011

AbstractThe feasibility of fabricating Nb-Nb silicide microstructure by Physical Vapor Deposition with sufficient control of impurities has been investigated. It is demonstrated that electron beam evaporation can satisfy the requirement of impurity control under appropriate vacuum condition. In elemental layered structure of Nb and Si, NbSi2 is the first phase formed upon annealing. It was found that, at 600°C, the growth rate of NbSi2 phase at the interface of Nb and Si is 35Å/min. The Nb5Si3 phase nucleates at a higher temperature (around 900°C) at the interface of Nb and NbSi2. In the case of co-deposited film with overall composition around Nb5 Si3, NbSi2 formation is by-passed. Thus, multilayers of Nb/NbSi2 or Nb/Nb5Si3 can be formed from layered elemental deposition and subsequent heat treatment under controlled conditions by adjusting the starting thicknesses of the films. Alternate elemental and co-deposition and subsequent or in-situ heat treatment can directly form the layered Nb/desired silicide composite. Multilayers of Nb/NbSi2 and Nb/Nb5Si3 with layer thicknesses below 500Å have been formed from layered elemental deposition.
Axial Alignment of Short-Fiber Titanium Aluminide Composites by Directional Solidification
Authors: Kampe S. L. , Swope G. H. , Christodoulou L. 
Published: March 2011

AbstractThe floating zone directional solidification technique has been applied to an XDTM short-fiber-reinforced titanium aluminide ingot in an effort to produce in situ alignment of the reinforcement. Microstructural evaluation reveals that a general alignment of the high aspect ratio (>100:1) fibers occurs under specific imposed solidification conditions. These metallographic observations are supported by 800 ° C mechanical data, which indicate higher axial and reduced transverse strengths relative to the unprocessed base material which contains a dispersion of randomly oriented fibers. The increased strengths are observed to be a consequence of an increase in the matrix hardening due to accommodation of plastic strain around the fiber reinforcement.
Rigidity of Layered Random Alloys
Authors: Jin Wei , Mahanti S. D. , Thorpe M. F. 
Published: March 2011

AbstractRandomly intercalated layered alloys are excellent models for two-dimensional microporous systems. We have studied the nonlinear gallery expansion and the gallery height fluctuations by constructing a double layer model that describes the layer rigidity and the size and stiffness of the intercalant species. Exact solutions, simulations and an effective-medium theory (EMT) results are compared. Applications of the results to ternary intercalation compounds are discussed.
Microcellular Foams Prepared From Demixed Polymer Solutions
Authors: Aubert J. H. 
Published: March 2011

AbstractLow-density, microcellular polymer foams have numerous applications as structural supports in high-energy physics experiments, in catalysis, ion exchange, and filtration, and for a variety of biomedical uses. A versatile method to prepare such foams is by thermally-induced phase separation (TIPS) of polymer solutions. Demixed solutions can be transformed into a foam by freezing the demixed solution and removing the solvent by freeze-drying. The morphology of these foams is determined by the thermodynamics and kinetics of phase separation. A model of both the early and late stage structure development for demixed polymer solutions will be presented. For semi-crystalline polymers, gels can be prepared by crystallizing the polymer from solution, either a homogeneous solution or a demixed solution. Foams can be prepared from these gels by the super-critical extraction of the solvent. By understanding and utilizing the phase separation behavior of polymer solutions, engineered microcellular foams can be prepared. To design the foams for any application one must be able to characterize their morphology. Results will be presented on the morphological characterization of these foams and the relationship of the morphology to their processing history.
Stress-Density Variations in Alumina Sediments: Effects of Polymer Chemistry
Authors: Schilling C. H. , Lannutti J. J. , Shih W.-H. , Aksay I. A. 
Published: March 2011

AbstractAchieving spatially uniform and hierarchically structured microstructures during the shape-forming of colloidal ceramics depends largely on (i) the magnitude of the effective stresses (i.e., stresses that are supported by the particulate network) and (ii) plastic properties, which in turn are significantly altered by processing parameters affecting interparticle friction and adhesion. To quantify the effects of processing parameters on consolidation, we present a novel approach for analyzing sediments by gamma-ray densitometry and a fluid mechanics model. This method enables us to correlate processing parameters with spatial variations of the packing density and the local effective stress. These correlations are difficult to achieve by traditional techniques (e.g., rheometry, sedimentation kinetics modeling, soil mechanics tests), especially for the low stresses (< 1000 Pa) that are typically encountered in sediments. Aside from being destructive to samples, these techniques also tend to measure volume-averaged properties, and as a result they usually fall short of describing localized consolidation phenomena.
Mechanical Analyses of Wipp Disposal Rooms Backfilled with Either Crushed Salt or Crushed Salt-Bentonite
Authors: Wagner Ralph A. , Callahan G. D. , Butcher B. M. 
Published: March 2011

AbstractNumerical calculations of disposal room configurations at the Waste Isolation Pilot Plant (WIPP) near Carlsbad, NM are presented. Specifically, the behavior of either crushed salt or a crushed salt-bentonite mixture, when used as a backfill material in disposal rooms, is modeled in conjunction with the creep behavior of the surrounding intact salt. The backfill consolidation model developed at Sandia National Laboratories was implemented into the SPECTROM-32 finite element program. This model includes nonlinear elastic as well as deviatoric and volumetric creep components. Parameters for the models were determined from laboratory tests with deviatoric and hydrostatic loadings. The performance of the intact salt creep model previously implemented into SPECTROM-32 is well documented.Results from the SPECTROM-32 analyses were compared to a similar study conducted by Sandia National Laboratories using the SANCHO finite element program. The calculated deformations and stresses from the SPECTROM-32 and SANCHO analyses agree reasonably well despite differences in constitutive models and modeling methodology. These results provide estimates of the backfill consolidation through time. The trends in the backfill consolidation can then be used to estimate the permeability of the backfill and subsequent radionuclide transport.
Scaling Theory of Elasticity and Fracture in Disordered Networks
Authors: Duxbury P. M. , Kim S. G. 
Published: March 2011

AbstractWe discuss scaling theories for the elasticity and tensile fracture of random central force spring networks with bond dilution disorder. Effective medium theory works quite well for elasticity but needs very new ingredients to be even qualitatively correct for tensile fracture. A novel “extreme scaling theory” predicts a dilute limit singularity and a size effect in the tensile strength. These predictions are supported by numerical simulations.We extend the above arguments to networks with distributions of bond disorder, and compare the central force network theories to models currently used in the study of rigid cellular materials.
Mechanical Behavior of a Cellular-Core Ceramic Sandwich System
Authors: Van Voorhees Eric J. , Green David J. 
Published: March 2011

AbstractThe failure behavior and stress distribution of a novel ceramic sandwich system was investigated. A highly porous, open-cell A12O3 was used as the core material with relative densities ranging from 9% to 20%. The faceplates were dense A12O3 of varying thickness. The composites were tested in flexure and failure loads of the cellular core were shown to compare favorably to those predicted by theory when Weibull statistics were incorporated. Stresses in the tensile faceplates were also measured. For composites with relatively thick faces and low modulus cores, the stress distribution was significantly altered by a local bending effect. These stresses were predicted using a refined model.
Impact Behaviour of Metallic Fibre Reinforced Concrete and Mortar
Authors: Hamelin P. , Razani M. 
Published: March 2011

AbstractThis research work concerns the impact behaviour of metallic fibre reinforced concrete. After a description of the experimental apparatus used, an air compressed gun, we present the main results in terms of stress–strain diagrams as a function of the strain rate. Then, we establish equations of a specific damage model which take account of the different phases of the behaviour law.