bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructure and Mechanical Properties of Ni3Al-Ai2O3 Composites Produced by Hot Extrusion
Authors: McKamey C. G. , Lee E. H.
Published: March 2011

Hot extrusion of premixed charges of 10–20 vol% chopped A12O fiber and Ni3Al powder has resulted in composite alloys of near theoretical density. In tensile tests at room temperature, density-compensated yield strengths of some of these composite alloys are as good or better than those of as-cast Ni3Al without reinforcement; however strengths at 1000°C in vacuum are lower. The low strength at 1000°C and fine grain size (2–3/μm) suggest the presence of superplastic behavior and the accompanying diffusional creep and grain boundary sliding. This presentation discusses our findings to date and includes microstructural studies and tensile properties, both at room temperature in air and 1000°C in vacuum.
Ductility Enhancement from Interface Dislocation Sources in a Directionally Solidified β (γ + γ′) Ni-Fe-Al Composite Alloy.
Authors: Larsen M. , Misra A. , Hartfield-Wunsch S. , Noebe R. , Gibala R.
Published: March 2011

A directionally solidified β + (γ + γ′) Ni-Fe-AI in-situ composite alloy of composition Ni50Fe30Al20 (at.%) has been used to investigate the effect of a plastically soft second phase on the mechanical behavior of a B2 ordered intermetallic alloy. This material exhibits extensive plasticity during compressive deformation at room temperature and fails in shear with extensive γ + γ′ lamellar or rod pull-out. The material also exhibits ∼10% tensile elongation to fracture at room temperature, with final fracture that includes substantial necking of the γ + γ′ lamellae or rods. Observation of slip lines and dislocation substructures discloses that the normally brittle β matrix undergoes extensive plasticity in order to deform compatibly with the more ductile γ phase. The plasticity of the β matrix is accomplished by the generation of glissile dislocations into the β matrix from the β/γ interface region and is enhanced because of a favorable β - γ orientation relationship for slip transfer. Ductility enhancement from interface-generated mobile dislocations generated from β-γ interfaces is compared to that observed in film-coated β-NiAl single crystals and FeAl polycrystals.
Development of Highly Impact Resistant NiAl Matrix Composites
Authors: Nardone Vincent C. , Strife James R. , Prewo Karl M.
Published: March 2011

The ability to produce a NiAl intermetallic base composite with dramatically higher energy absorption capability and damage tolerance has been demonstrated. The approach consists of incorporating continuous tubular 304 stainless steel toughening regions throughout the NiAl matrix. To compensate for the increase in density resulting form the 304 stainless steel, B4C particulate was added to the NiAl so that the overall composite density was within 5% of the value for monolithic NiAl. The notched Charpy impact energy absorption of the B4C/NiAl/304 composites was in the range of 15 to 90 J/cm2, compared to a value of 0.8 J/cm2 for NiAl. The higher energies were measured on samples that deflected the crack front more extensively during failure. For a given interfacial condition, the energy absorption increased as the wall thickness of the 304 tubular toughening regions increased. Finally, room temperature tensile testing of the composites resulted in very large failure strains (20–35%) owing to the 304 stainless steel being able to sustain the applied load once the NiAl regions had completely cracked.
1300 K Compressive Properties of a Reaction Milled NiAl-AlN Composite
Authors: Whittenberger J. Daniel , Arzt Eduard , Luton Michael J.
Published: March 2011

Cryomilling (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

A 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

Ti-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

Panel 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

NiAl 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

Arc-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

Among 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

Reinforcing 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

The 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

An 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

In 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

Reaction 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

Pressureless 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

The 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

The 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

The 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

Randomly 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

Low-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

Achieving 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

Numerical 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

We 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

The 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.
Anisotropy and Simple mechanics of the Flesh of Apples.
Authors: Vincent Julian F. V.
Published: March 2011

Although its morphology is complex, the mechanical properties of the flesh of apples can be understood qualitatively in terms of the way the cells are assembled. There is no quantitative model for structures of turgescent cells which are not totally adherent.
Impact Behaviour of Metallic Fibre Reinforced Concrete and Mortar
Authors: Hamelin P. , Razani M.
Published: March 2011

This 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.
Effect of Fibres on Bond Behaviour Under Impact Loading
Authors: Yan Cheng , Mindess Sidney
Published: March 2011

The bond between concrete and reinforcing bars under impact loading was studied for plain, polypropylene fibre reinforced, and steel fibre reinforced concretes. It was found that adding steel fibres significantly improved the bond behaviour under impact loading; polypropylene fibres had a much smaller effect.
Methods of Evaluating the Performance of Fiber-Reinforced Concrete
Authors: Johnston Colin D.
Published: March 2011

Three of the most important properties of fiber-reinforced concrete (FRC) are strength, toughness and resistance to cracking. The various methods of evaluating them are compared in terms of underlying rationale, ability to characterize composite material behavior in a readily understandable manner minimally affected by testing variables, and suitability for routine use in specifying and controlling concrete quality. The scope includes dynamic loading tests, slow-rate (static) loading tests, and tests to evaluate cracking induced directly by load or indirectly by restraint during shrinkage or thermal change.

Consideration of the advantages and disadvantages of the various alternatives shows that slow flexure testing in accordance with the rationale developed by the writer and incorporated into ASTM standard C1018 effectively characterizes the FRC in terms of first-crack strength, toughness, and residual strength after first crack up to any predetermined level of serviceability expressed in terms of maximum permissible deflection. Although not part of the standard, resistance to cracking under load may also be assessed by measuring crack widths at appropriate deflections.
First and Second Order Structural Approaches to Steel Fibre Reinforced Concrete
Authors: Stroeven Piet
Published: March 2011

Global and local information on distribution parameters of steel fibres in fibre reinforced concrete form essential ingredients in pursuit for further development of micromechanical, fracture mechanical or even composite modelling of such materials in the pre- and postcritical ranges. Additionally, quantitative image analysis approaches to specimens of such composites can be executed more effectively when based on proper structural models. This paper outlines first and second order stereological methods for that purpose.
The Interface Between Zinc Phosphate-Deposited Steel Fibers and Cement Paste
Authors: Sugama Toshifumi , Gray Gwen
Published: March 2011

In an attempt to protect steel fiber reinforcements from corrosion and improve the adherence of cement pastes to steel fiber reinforcement, we deposited a zinc phosphate (Zn-Ph) conversion coating on the surface of the fibers. At the interfacial contact zones between the cement paste and Zn.Ph, the alkali-induced dissolution caused the dissociation of abundant PO43- ions from the Zn-Ph. The interaction of PO43- ions with Ca2+ ions from the pastes led to the formation of hydroxyapatite and brushite in the vicinity of the dissolved Zn.Ph surface. Such intermediate Ca-phosphate compounds played important roles 1) in improving the cement-fiber interfacial bonds, and 2) in repairing the damage of the Zn.Ph surface dissolved by alkali. These processes protected the steel fiber from corrosion.
Influence of Interface Modification in Fiber Reinforced Cement Composites on Their Properties
Authors: Yuan Chen Zhi , Hua Cheng Qing , Feng Gao
Published: March 2011

This research aims at a further exploration of surface treatments of carbon fibers to improve the performance of CFRC. Two approaches to treat carbon fibers were used in this study. SEM, IR, XRD were used to analyse the CFRC prepared with treated carbon fibers. Because of strong adhesion, CFRC prepared using CF with treatment has a better performance than that without treatment. Flexural strength is 30% higher, tensile strength is 48% higher, impact strength 63% higher, and deflection is increased.
Development of Composites Reinforced by Polyester Fibres
Authors: Jelidi Ahmed , Chabannet Michel , Ambroise Jean , Pera Jean
Published: March 2011

Until now, the use of untreated polyester fibres in concrete has been delayed because these fibres are not alkali-resistant. To understand the fundamental mecanisms of degradation of such fibres in a cementitious matrix, some physico-chemical experimental techniques (SEM - EDAX - I.R. Spectrometry) associated with flexural tests were used. The degradation of polyester is caused by a saponification reaction and the toughness of the fibre-reinforced composite is quickly reduced.

To prevent such a damage and develop tougher composites, the authors modified the cementitious matrix. Adding burnt clays (kaolin and montmorillonite) to OPC enabled the polyester fibre to withstand the alkaline attack.
Toughening of Cement-Based Materials with Fiber Reinforcement
Authors: Shah S. P.
Published: March 2011

Toughening of cement-based materials when reinforced with relatively high fiber volume is studied in the paper. Toughening mechanisms of composites have been experimentally studied by quantitative image analysis, laser holographic interferometry, and acoustic emission. It is found that damage localization in cement-based materials can be greatly reduced by the use of fibers. Based on fracture mechanism observed, an R-curve approach has been proposed to predict toughening of matrices due to fiber reinforcement. Theoretical predictions show good agreement with experimental results.
Evaluation of Toughness and Flexural Strength of Fiber Reinforced Concrete
Authors: Kubo Mitsuru , Mashima Mitsuyasu , Iwamoto Kaoru
Published: March 2011

Fiber reinforced concrete was developed to improve the mechanical properties of cementitious materials. Especially by using FRC, the structural mechanical properties after the maximum load can be improved. In the present study the mechanical properties of the fiber reinforced concrete are evaluated by investigating the influence of various parameters on the complete load-deflection curve, including the descending branch.
High Durability Glass-Fiber Reinforced Modified Cementitious Matrix
Authors: Thiery J. , Vautrin A. , Francois-Brazier J.
Published: March 2011

In AR-GFRC growth of hydration products around the filaments plays a dominant role in inducing embrittlement of the fibers and loss of toughness of the composites.

The purpose of this paper is to present the way to limit the anchorage of the fibers in the matrix and to obtain a long term flexural strength of 30 MPa and an ultimate strain of 0,7 %. The improvement of the matrix is obtained by using selected metakaolinites and acrylic polymers in order to optimize the nature of the hydrates in the interface between the fibers and the matrix.

The mecanical properties and durability behaviours are reviewed using three accelerated ageing tests based on warm water, wet-dry cycles and freeze-thaw cycles. The toughness indices proposed by Shah, Ludirdja and Daniel [12] are calculated, pointing out the improvements of toughness and durability of the new V~trotex-Saint-Gobain AR-GFRC system.
Glass Fiber Composites Made with a Cement Based on a Hydraulically Active CaO-SiO2-Al2O3 Glass
Authors: Hommertgen C. , Odler I.
Published: March 2011

Glass fiber reinforced cement pastes were prepared using a cement based on a hydraulically active glass in the system CaO-SiO2-Al2O3. The properties of such composites were compared with those made with ordinary portland cement.In all the studied materials the MOR and WOF values declined with time, however for different reasons.
Formation of Titanium Silicide by Multiple Arsenic Implantations and Ion Beam Mixing
Authors: Chen Po-Ching , Lin Jian-Yang , Hwang Huey-Liang
Published: March 2011

Titanium silicide was formed on the top of Si wafers by arsenic ion beam mixing and rapid thermal annealing. Three different arsenic-ion mixing conditions were examined in this work. The sheet resistance, residue As concentration post annealing and TiSi2 phase were characterized by using the* four-point probe, RBS and electron diffraction, respectively. TiSi2 of C54 phase was identified in the doubly implanted samples. The thickness of the Ti silicide and the TiSi2/Si interface were observed by the cross-sectional TEM.
Temperature Uniformity Optimization Using Three-Zone Lamp and Dynamic Control in Rapid Thermal Multiprocessor
Authors: Apte Pushkar P. , Wood Samuel , Booth Len , Saraswat Krishna C. , Moslehi Mehrdad M.
Published: March 2011

Rapid thermal processing (RTP) can play an important role in in situ single-wafer thermal multiprocessing, since it allows for a rapid wafer throughput rate. Conventional dedicated RTP equipment, where temperature uniformity is achieved by optimized reflector and chamber geometries for a specific process, typically cannot provide uniformity for different processes, or for a range of processing conditions. In this work we present a new flexible lamp system, in which tungsten-halogen lamps are configured in three concentric rings that are independently and dynamically controlled. The resultant circularly symmetric flux, which can be varied and controlled both temporally and spatially, offers significantly improved temperature uniformity. This is demonstrated using thermocouples as well as actual processes such as implant annealing, thermal oxidation and chemical vapor deposition of silicon. Through added flexibility and more precise control, this approach offers a powerful tool for multiprocessing and rapid process prototyping.
Contactless Measurements of Slip Lines Intentionally Introduced in Si Wafers During Rapid Thermal Processing
Authors: Usami A. , Shiraki H. , Fujiwara H. , Abe R. , Osamura N. , Ichimura M. , Wada T.
Published: March 2011

The slip lines introduced in Si wafers during rapid thermal processing (RTP) were revealed with focused reflectance microwave probe (RMP) method. The signal intensity of RMP which is related to optically injected excess carrier concentration decreases at slip lines. The region in which the signal intensity decreased is in good agreement with results of X-ray topography and theoretical analysis considering thermal stress caused by temperature drop at the wafer periphery during RTP. According these results, it is considered that carrier lifetime is decreased by slip dislocations which are effective recombination centers.
Ripple Technique; a Novel Non-Contact Wafer Emissivity and Temperature Method for RTP
Authors: Schietinger C. , Adams B. , Yarling C.
Published: March 2011

A novel wafer temperature and emissivity measurement technique for rapid thermal processing (RTP) is presented. The ‘Ripple Technique’ takes advantage of heating lamp AC ripple as the signature of the reflected component of the radiation from the wafer surface. This application of Optical Fiber Thermometry (OFT) allows high speed measurement of wafer surface temperatures and emissivities. This ‘Ripple Technique’ is discussed in theoretical and practical terms with wafer data presented. Results of both temperature and emissivity measurements are presented for RTP conditions with bare silicon wafers and filmed wafers.
Application of RTP-CVD Technology to Ulsi Device Fabrication
Authors: Jung K. H. , Hsieh T. Y. , Kwong D. L.
Published: March 2011

Rapid thermal processing chemical vapor deposition (RTP-CVD) has received considerable attention as a novel in-situ multi-processing tool capable of meeting the stringent requirements of ULSI device fabrication. In this paper, we review the progress made in developing and applying RTP-CVD to ULSI device fabrication. Research areas discussed include epitaxial Si and poly-Si growth, in-situ doping, selective growth, in-situ multi-processing, and novel dielectrics. In addition, the extension of RTP-CVD to novel materials such as GexSi1−x has produced device quality films with successful application in HBTs and Si-based optoelectronics.
Si and GexSi1−x Epitaxial Growth on SOI Structures by Rapid Thermal Processing Chemical Vapor Deposition
Authors: Hsieh T. Y. , Jung K. H. , Kwong D. L. , Lin S. , Marcus H. L.
Published: March 2011

A short time high temperature H2 pre-bake resulted in an undulating SIMOX surface, which planarized after epitaxial growth by rapid thermal processing chemical vapor deposition (RTPCVD). However, a short time, high temperature N2 pre-bake resulted in severe surface pitting. From dilute Schimmel etch results, no significant changes in the defect densities of the Si layers occurred after RTPCVD. Auger depth profiles of the SOI substrate prior to epitaxial growth show an oxygen peak in the SIMOX Si layer. However, the peak flattens out after epitaxial growth. Oxygen was not observed in the epitaxial film, even though oxygen was still observed in the SIMOX top Si layer.

The use of GexSi1−x epitaxial layers to reduce threading dislocation densities was examined. A 1000°C Si buffer layer was first grown for 30s, followed by a GexSi1−x layer, and topped off by a 1000°C Si layer for 120s. The GexSi1−x layers were grown at temperatures varying from 850°C to 1000°C for 30s to 240s. The defect density was significantly reduced when the 900°C and 850°C GexSi1−x layers were used, although an increase in stacking fault densities (still small compared to threading dislocation densities) accompanied the lower deposition temperatures. The 1000°C GexSi1−x layer and a control sample in which pure Si was grown showed no significant decrease in defect densities.
Photo Induced Deposition of Thin Silicon Dioxide Films Using a Novel Large Area Excimer Lamp
Authors: Patel P. , Kogelschatz U. , Bergonzo P. , Boyd I. W.
Published: March 2011

There is a growing interest in the deposition and processing of thin films at low temperatures to eliminate the inherent problems associated with high temperature processing. Photo enhanced processing is one of the techniques which has received considerable interest. One of the major limitations of photo processing is the lack of sufficiently intense ultra-violet (UV) sources. To date the low pressure Hg lamp has been the only available source for large area UV processing and this has limited the types and quality of films deposited.

In this paper we will outline the design of a novel, variable wavelength excimer discharge lamp which can be used for depositing thin films over large substrate areas. We shall also discuss the direct (i.e. without intermediate photosensitisation reactions) photo induced deposition of thin silicon dioxide films using SiH4 and N2O which are photo dissociated by 126nm photons generated by the excimer lamp described.
ArF Excimer Laser-Enhanced Photochemical Vapor Deposition of Homoepitaxial Silicon from Disilane
Authors: Fowler B. , Lian S. , Krishnan S. , Jung L. , Banerjee S.
Published: March 2011

The 193 nm output of an ArF excimer laser has been used to selectively photodissociate Si2H6 to deposit homoepitaxial Si films in the temperature range of 250°C to 350°C. Photolytic decomposition of Si2H6 results in the generation and adsorption of growth precursors on a hydrogenated Si surface. A simple growth kinetic model has been developed based on the most likely primary photofragments upon single-photon absorption by Si2H6 at the ArF excimer laser wavelength of 193 nm, and gas kinetic transport of the resulting photofragments to the substrate surface. Growth rates are observed to vary linearly with laser beam power and Si2H6 partial pressure when the laser beam is tangentially positioned less than 0.5 mm from the Si substrate for Si2H6 partial pressures less than 40 mTorr, total chamber pressures of 600 mTorr, and laser beam photon flux densities less than 2×1016 photons/cm2.pulse. Under these conditions, gas-phase diffusion dominates over chemical reaction rates and laser beam absorption is in the optically thin limit. The model then reduces to a simple form that predicts a linear dependence of growth rate on Si2H6 partial pressure and gives an accurate estimate of the expected growth rate. The epitaxial films are specular, and appear to have very low defect density in terms of stacking faults, as determined by modified Schimmel etching and Nomarski microscopy, and dislocation loops as determined by TEM (less than 105 loops/cm2). The crystallinity has been confirmed both by in situ RHEED, where we see a (l×l) streaky pattern, as well as selected electron diffraction, which shows a (100) crystalline orientation.
The Behavior of Free-Carriers During Rapid Thermal Annealing of Doped Silicon
Authors: Lojek B.
Published: March 2011

Radiation and the resulting excess concentration of free carriers has a strong impact on several physical processes in silicon. New experimental results involving RTA are compared with previous experimental practice. Several aspects of the new result raise questions about the validity of the assumptions which were used in the past. It is concluded that radiation significantly enhances annealing processes, especially during the initial phase of RTA. Based on the study of the physical phenomena involved in the irradiated silicon, it is shown that the absorption and recombination rate are the most affected parameters and they are most likely the reason for the underestimation of the magnitude of excess free carriers.
Variation of Thermal Donors in Diffused Wafers by rapid Thermal Annealing
Authors: Sugiyama Takahide , Usami Akira , Ito Akira , Natori Taichi , Tokuda Yutaka , Wada Takao
Published: March 2011

Variations of thermal donors (TDs) in highly phosphorus-diffused n-type silicon wafers (diffused wafer) have been studied with deep-level transient spectroscopy and capacitance-voltage measurements. The introduction and annihilation of TDs have been performed with heat treatment at 450°C and rapid thermal annealing (RTA) in the temperature range 600-900°C,respectively. In diffused floating zone-grown (FZ) silicon wafer, TDs were observed. It is thought that oxygen diffuses into FZ silicon during the diffusion process, since no TDs are generally formed in FZ silicon for the low oxygen concentration. The behavior of TDs in diffused wafer corresponded with that in oxygen-rich bulk silicon. TDs were completely annihilated by RTA at 700 and 800°C for the as-diffused wafers and the heat-treated ones at 450°C for 24 h, respectively, and the annihilation rate for the as-diffused wafers was fast, as compare to that for the heat-treated ones. This results may be caused by difference in the total concentration and cluster size of TDs.
Temperature Control and System Design Aspects in Rapid Thermal Processing
Authors: Roozeboom Fred
Published: March 2011

The main factors influencing the thermal performance (and thus product yield) of a rapid thermal processor are the heat source, the reaction chamber, the temperature measurement system, and as complicating factors, their total configuration and the optical wafer properties.

The characteristics of 19 currently available commercial RTP systems are highlighted with focus on temperature control including the spectral characteristics and measures to suppress perturbations due to stray radiation.

In addition recent developments and trends in the system configuration and in the optimization of temperature or layer thickness control are discussed. The improvements in temperature control focus especially on in situ temperature control, irrespective of wafer condition, and at system constructions that optimize dynamic temperature uniformity. Some novel optical process control and novel system design aspects to compensate for emissivity changes and temperature non-uniformity are included.
Studies of Oxygen Introduced During Thermal Oxidation and Defects Induced by Rapid Thermal Annealing in Silicon Epitaxial Layers
Authors: Usami Akira , Natori Taichi , Ito Akira , Sugiyama Takahide , Hirota Seiya , Tokuda Yutaka , Wada Takao
Published: March 2011

Introduction of oxygen during thermal oxidation and production of defects by rapid thermal annealing (RTA) in n-type epitaxial Si layers were studied with deep-level transient spectroscopy measurements. We use oxygen-related thermal donors (TDs) as a monitor for introduction of oxygen in silicon epitaxial layers. It is found that oxygen is introduced from the substrate into the epitaxial layer after thermal annealing. The TD was almost annihilated by RTA at .700°C. However, a shallow trap (Ec−0.073±0.005 eV) was induced by RTA.
Kinetics of Vacancy Ordering in YSi2−x Thin Film on Silicon
Authors: Lee T. L. , Chen L. J. , Chen F. R.
Published: March 2011

High resolution and conventional transmission electron microscopy have been applied to study the interfacial reaction of yttrium thin films on Si. Epitaxial Ysi2−x film was grown on (111)Si by rapid thermal annealing at 500–1000 °C. The orientation relationship between yttrium silicide and (111)Si was determined to be [0001]Ysi2−x//[111]Si and (1010)Ysi2−x//(112)Si. The vacancies in the Ysi2−x film were found to be ordered in the Si sublattice plane and form an out-of-step structure. The range of M values of the out-of-step structure was found to narrow with annealing temperature and time. Defects along specific crystallographic directions were observed and analyzed to be intrinsic stacking faults.