bluuebunny/crossref_metadata_2025 huggingface dataset:
Plasma Enhanced Chemical Vapor Deposition of Dielectric Films: Correlation of Stress to Film Structure and Plasma Characteristics
Authors: Srinivasan Radhika , Nguyen B. C. , Short A. P.
Published: March 2011

Stress in dielectric films, including silicon dioxide, borosilicate glass, and silicon nitride, deposited using Plasma Enhanced Chemical Vapor Deposition have been studied. In each case the total stress was found to be strongly dependent on processing conditions. Deposition rates and film characteristics, such as refractive index, -OH content, (in the case of SiO2), total H content, Si-H and N-HI concentration (in the case of nitride), boron concentration (for BSG), have also been determined as fuctions of processing parameters. In addition, the emission spectra from the plasma itself has been studied. Correlations have been established whereever relevant.
Correlation between Processing, Composition, and Mechanical Properties of PECVD-SiN, Thin Films
Authors: Yu D. C. H. , Taylor J. A.
Published: March 2011

The inter-relationship between plasma processing, composition, and mechanical properties of PECVD-SiNx, thin films was investigated. Results showed that by varying the gas feeding ratio of NH3/SiH4N2, one can obtain PECVD-SiNx, films of different composition and streu levels. For high stress films, the deposition rate is low, values of index of refraction and Si/N ratio are small. On the other hand, film density of such films is high; values of Young's modulus and N-H/Si-H relative bond density are large. A model which correlates film stress to that contributed by (1) lattice distortion induced by Si-H and NH bondings, (2) ion bombardment, (3) thermal mismatch between PECVD-SiNx films and silicon substrate, and (4) intrinsic stress introduced during the formation of covalent Si-N bonding is proposed and examined in this work.
Intrinsic Stress of Pecvd Silicon Oxynitride Films Deposited in a Hot-Wall Reactor
Authors: Aite K. , Koekoek R.
Published: March 2011

Plasma enhanced chemical vapor deposited ( PECVD ) silicon oxynitride films with refractive indices varying from 1.65 to 1.85 have been deposited in a hot-wall reactor using a SiH4/NH3/N2O gas mixture. A systematic investigation of the variation of the intrinsic stress of the deposited films with the parameters of deposition and the properties of the films, has been carried out. Our results show that silicon oxynitride films deposited in optimal conditions can support annealing temperatures of 900°C without cracking. The mechanical stresses in the films were determined by the Newton's fringes technique and a surface profiler. The film thickness was measured by ellipsometry at a wavelength of 632.8 nm. Fourier transform infrared spectroscopy ( FTIR ) was used to measure the hydrogen content of the films. The composition of the silicon oxynitride films was determined by Auger electron spectroscopy ( AES ) and Rutherford backscattering spectrometry ( RBS ).
Internal Stresses and Adhesion Properties of Film/Substrate Interfaces
Authors: Ignat M. , Chouaf A. , Normandon Ph.
Published: March 2011

The evolution of internal stresses in Tungsten films deposited on Silicon substrates submitted to external stresses is discussed here. The stresses are estimated and measured by theoretical and experimental methods. The discussion of the internal stress evolution is shown to be dependent of the film/substrate interfaces, and of the loss of adhesion inducing stress relaxation.
Ab-Initio Calojiations of Phase Diagrams of Binary Simplemetal Alloys
Authors: Hafner J.
Published: March 2011

The combined application of electronic and thermodynamic perturbation theories allows for an ab-initio calculation of the phase diagrams of binary simple-metal alloys.
Simple Solution Approaches in Phase Diagram Evaluation
Authors: Kaufman Larry
Published: March 2011

In the beginning there were ideal solutions (Geneva 1966) [1] and lattice stability values were deduced for the transition elements. Next regular solution interaction parameters for second and third row transition elements were predicted from simple models (Cambridge 1970)[2] combined with the lattice stability values via computer methods to calculate binary and ternary phase diagrams. Line compounds were introduced for comparison with experimental phase diagram data. At Brunel (1971)[3] and Munster (1972)[4] the regular solution models were expanded to include subregular and higher order terms and since the origin of CALPHAD (1973)[5]many coupled sets of thermochemical and phase diagram descriptions have been derived and published. Examples of multicomponent phase diagram calculations applied to solution of industrial problems have been illustrated in the subject areas of transformations and stability in steels and superalloys, uranium alloys, SIALON materials, metallic and fluoride glasses, electronic materials, and novel materials refining and processing methods. [6-19]
The Sublattice Model
Authors: Sundman BO , Ågren John
Published: March 2011

A thermodynamic model, based on the regular solution approximation is presented and a formalism, suitable for phases with an arbitrary number of elements and sublattices is described. A new concept, the component array, is introduced in order to simplify the analytical expressions for the Gibbs energy. The mathematical complexity of the model has been solved by the implementation of the model as a part of a general software system for thermochemical and phase diagram calculations by computer.

The sublattice model is suitable for describing phases where the difference in size, charge or electronegativity causes a deviation from random mixing of the atoms in a manner which can be described as long range order. This is the case for interstitial solutions and many intermetallic phases, but also for ionic liquids and slag systems. The application of the model to several alloy system will be described.
A Pair-Wise Interaction Model for Multi-Sublattice Phases
Authors: Pratt J.N. , Jones I.P.
Published: March 2011

The use of simple nearest neighbour pair-wise interaction models for the description of the thermodynamic properties of ordered alloys is reviewed and extended to the treatment of phases containing several sublattices. Employing individual sublattice occupation parameters to define atomic distributions, enthalpies corresponding to these are described by the summation of pair-wise interaction energies over all the resulting first co-ordination shell neighbours. Invariant like and unlike bond energies are assumed, their respective values being estimated using heats of vaporisation of the elements and a heat of formation of the phase at a single composition. Combination of the enthalpies with corresponding configurational entropies yields an expression for the free energy of the phase which may be minimised with respect to variation of the sublattice occupation parameters. This leads to the prediction of the stable atomic distributions and the variation of these and the thermodynamic properties with composition. The application of the model to sigma phases and other multi-sublattice structures is discussed
Association Model for Liquid Alloys
Authors: Sommer Ferdinand
Published: March 2011

The concentration and the temperature dependence of thermodynamic mixing functions of liquid alloys with compound formation tendency, which often exhibit large deviations from a regular behavior, can be calculated according to an association model using only a few parameters which have a definite physical significance. The results obtained for binary and ternary alloy melts with one ore more, simultaneously occurring, binary or ternary associates are in good accordance with the experimental values. For the calculation of phase diagrams, the association model enables a correct extrapolation into concentration and temperature regions for which no experimental results are available. The occurrence and the borderline of miscibility gaps in liquid alloys with strong compound forming tendency can be quantitatively described.
Cohesion, Compound Formation and Phase Diagrams from First Principles
Authors: Williams A. R. , Gelatt C. D. , Connolly J. W. D. , Moruzzi V. L.
Published: March 2011

The physical picture of cohesion and compound formation provided by parameter-free, self-consistent, energy-band calculations will be described. For transition-metal elements, the calculations allow us to “see” which electrons are holding the solid together and which are holding it apart. For compounds, calculated heats of formation agree well with available measurements and are in general agreement with those given by Miedema's empirical formula. (The agreement with Miedema is paradoxical, in that Miedema's conception of the formation process differs qualitatively from ours.) Preliminary, but very encouraging, results of efforts to extend the analysis to disordered materials and to the calculation of phase diagrams are described.
Magnetic Ordering and Phase Separation in Binary Alloys with One Magnetic Component
Authors: Moran-Lopez J.L. , Urias Jesus
Published: March 2011

Magnetic ordering and phase separation in binary alloys with one magnetic component are studied within the mean field approximation. The influence of ferromagnetic ordering on the phase separation temperature (TCS) is examined in detail. In general it is found that magnetism increases TCS and causes strong asymmetries in the phase diagram. In particular, it is found that in systems with only ferromagnetic interactions, the Curie temperature (TCM) and TCS are the same. Results for the phase diagrams and for the temperature dependence of the magnetic and spatial order parameters are presented.
Phase Diagram Features Associated with Multicritical Points in Alloy Systems
Authors: Allen Samuel M. , Cahn John W.
Published: March 2011

Many features in the vicinity of critical points in phase diagrams can be illustrated using a Landau type free energy expansion as a power series in one or more order parameters and composition. This simple approach can be used with any solution model. It also predicts limits to metastability, and is useful for understanding mechanisms of phase change. The theory is applied to all the critical points that can occur in binary systems according to a Landau theory: critical consolute points, order-disorder transitions, tricritical points, critical end points, as well as to systems in which two transitions such as chemical and magnetic ordering occur.
A Thermodynamic Approach to the Calculation of the C-Cr-Nb-Ni-W Phase Diagram
Authors: Chevalier P.Y. , Barbier J.N. , Ansara I.
Published: March 2011

The phase boundaries of the C-Cr-Nb-Ni-W system are calculated from the available thermodynamic properties of the limiting binary systems. The methods of calculation and the models used in the description of the ternary and quaternary systems are presented as well as the influence of tungsten on the solubility of the M23C6phase in the nickel rich alloys.
Prediction of Solid + Liquid Equilibrium Diagrams for Binary Mixtures Forming Solid Solutions with an Extremum
Authors: Brostow Witold , Antonieta Macip M.
Published: March 2011

Convenient methods of correlation and prediction of S+L diagrams exist only for systems forming eutectics. To deal with solid solutions, we have adopted the model of strictly regular solutions of Guggenheim [3–5]. Our key assumption is that values of the Gibbs function of interchange w are different in the two coexisting phases: wS and wL. The assumption is based on the fact that the average interatomic distances R are also different, and this affects the averages of the interatomic (or intermolecular) potentials. The input parameters are enthalpies and temperatures of melting of pure components and any pair of experimental points on the diagram. For a number of binary alloy systems the agreement with the experiment is good. Since we believe in the basic unity of materials (see Chap. 1 in [7]), calcuations have also been made for organic mixtures, again with good results.
Use of Metastable Phase Diagrams in Rapid Solidification
Authors: Perepezko J. H. , Boettinger W. J.
Published: March 2011

During rapid solidification, the nucleation and/or growth of a thermodynamically stable phase may be difficult. In this case the liquidus, solidus or other thermodynamic data for a metastable phase are important for the interpretation and prediction of the phases present in rapidly solidified materials. In this paper various techniques are described to obtain information about metastable equilibrium from measured stable equilibrium data. Extrapolations of phase boundaries as functions of temperature, pressure or composition (including a new component) into regions of metastability can often be constructed directly on the equilibrium diagram. These constructions can be performed more quantitatively with analytical methods using thermodynamic modelling of the free energy functions consistent with measured data. A number of examples are considered including a discussion of metastable liquid miscibility gaps, metastable eutectic and peritectic reactions, pressure diagrams and metastability in ternary alloys to indicate the possible product phase selection. A coupling of metastable phase diagrams with a solidification kinetics analysis can contribute towards effective alloy design and processing during rapid solidification.
Crystal Chemistry of Metastable Alloy Phases
Authors: Glessen B. C.
Published: March 2011

Knowledge of the metastable crystalline alloy phases that can be prepared from the liquid or vapor by non-equilibrium methods is useful because the descriptive crystal chemistry of an alloy system should include metastable phases stable with respect to the components but unstable respective to other intermediate phases [1]. Alloy phases within a certain range of positive free energy of formation are also of interest, especially for systems without equilibrium phases. Accordingly, there have been some systematic “hunts” for metastable alloy phases (MAP's) that can be prepared by rapid liquid quenching, reviewed in Refs. 2–7. The principal results of these studies on disordered (element-like) and ordered MAP's and some additional data are presented here.
Theory of Surface Effects in Binary Alloys
Authors: MoráN-LóPez J.L. , Falicov L.M.
Published: March 2011

The chemical, ordering and magnetic properties of binary alloys at the surface are examined in terms of a model of pairwise interacting atoms. Both the case of segregating alloys and the case of alloys which form intermetallic compounds are examined. Some surprising results about surface concentration and surface ordering are found. Applications to a number of systems, including ferromagnets, are presented.
Paraequilibrium and other Restricted Equilibria
Authors: Hillert Mats
Published: March 2011

After a review of the historic development of the concept of paraequilibrium in the field of alloyed steels, the basic principles of restricted thermodynamic equilibrium at a migrating interface during phase transformations are outlined. As a demonstration they are first applied to classical nucleation. In addition to the case of paraequilibrium they are then applied to adiabatic and to isochoric conditions. It is argued that a full equilibrium model, with a spike of the intensive property in front of the migrating interface may be more realistic. It is shown that the full equilibrium conditions require about twice as much undercooling or underpressure as the restricted equilibrium conditions because of the consumption of driving force in the spike.
The concept of restricted equilibrium only applies to heterogeneous phase transformations. For homogeneous reactions, the same experimental conditions will give full equilibrium.
Phase Reeationships for Adsoreed Layers on Surfaces
Authors: Lu T.-M. , Lagally M. G.
Published: March 2011

Ordering phenomena of adsorbed atoms that are commensurate with the substrate structure can be described by a two-dimensional lattice gas. The major features of temperature-coverage phase diagrams for commensurate overlayers are reviewed and illustrated with several experimental examples. For overlayers with net attractive interactions, a two-phase region consisting of ordered overlayer and nearly empty substrate surface forms at low coverage. Substrate extended defects such as steps can create diffusion barriers, thus forming thermodynamic subsystems by eliminating communication between adsorbed atoms on either side of the steps. Steps can also prevent the growth of a reconstructed layer. Experimental examples are presented.
Spin Glassiness and Ferromagnetism in Disordered Ni-Mn Alloys
Authors: Kouvel James S.
Published: March 2011

From magnetic measurements, the alloy Ni78Mn22 is found to undergo a field-induced transition from spin glassiness to ferromagnetism at a critical field that decreases from ∼140 Oe to zero as the temperature is raised from 4.2 K to 40 K, the ferromagnetic Curie point being ∼270 K. The alloy Ni74Mn26 is found to transform at 80 K from a spin glass to a state of infinite initial susceptibility but no spontaneous magnetization and to remain so up to 155 K, where it becomes paramagnetic. The spin-glass properties of Ni78Mn22 below 40 K and of Ni74Mn26 below 80 K include displaced hysteresis loops produced by cooling in a field. The changes in the hysteresis loops upon subsequent warming correspond to a gradual conversion of a unidirectional anisotropy to a uniaxial anisotropy.
Phase Transformation Under Intense Shock Pressure Loading
Authors: Grady Dennis E.
Published: March 2011

Solids subjected to high velocity impact or explosive loading may undergo polymorphic phase transformation or melting within time periods appreciably less than 10-8s due to the intense shock-pressure environment. Although criteria for equilibrium phase transformation on the Hugoniot are satisfied, other nonequilibrium features unique to the shock-wave environment have been identified in the shock transformation process. These features include shear and heterogeneous deformation effects which control the transformation kinetics and microstructure of the transformed material. Transformation under shock loading leads to unusual microstructure in the recovered materials and can result in interesting and useful changes in physical and mechanical properties.
The In–Sn Phase Diagram
Authors: Evans Dain S , Prince Alan
Published: March 2011

The In–Sn system has been redetermined using dta, metallography and X-ray diffraction techniques. It is confirmed that the B and y intermediate 8hases are formed by peritectic reactions, at 141.0° and 222.6°C respectively. β and γ form a eutectic at 47.4 at% Sn and 119°C. The kink in the γ–phase solidus proposed by Heumann and Alpaut is not confirmed.
Modification of Al-Si Microstructure - The Al-Si-Sr Phase Diagram from 0–20 WT. % Si and 0–5.0 WT. % Sr
Authors: Hanna M. D. , Hellawell A.
Published: March 2011

It is well known that the morphology of primary and eutectic silicon resulting from solidification is sensitive to minor impurity additions: “modification” by alkali and alkaline earth metals is common foundry practice and the use of strontium is of recent and current interest because its effect is retained in liquid metal for relatively long times. The mechanism for modification remains obscure and is not necessarily the same from one elemental addition to the next, but it is essential to separate the equilibrium and kinetic influences if the phenomenon is to be better understood. Accordingly, the liquidus surface and eutectic reactions have been located in the relevant part of the Al-Si-Sr system by careful thermal analysis and the results correlated with the microstructure. Comparison is made with the parallel behavior of alkali metal additions.
Phab - An Alloy Phase Diagram Bibliographic Database: A Part of the Asm/Nbs Data Program for Alloy Phase Diagrams
Authors: Cuthill John R. , Baker Hugh
Published: March 2011

PHAB is intended to be a complete bibliographic file of the phase diagram data papers pertaining to the experimental determination, evaluation and calculation of phase diagrams of binary, ternary and higher-order alloy systems. Metastable as well as stable equilibrium data, crystal structure, thermodynamic and high pressure data are included. The database will provide a service to the scientific community as well as serving the ASM/NBS Data Program for Alloy Phase Diagrams. The PHAB Database will serve as a source of data to the other activities and outputs of the Program, including alloy system evaluations, the Bulletin of Alloy Phase Diagrams and bound volumes of evaluated phase diagrams. as well as other databases.
Electronic Energy and Short-Range Order in Binary Alloys
Authors: Robbins Mark O. , Falicov L.M.
Published: March 2011

An electronic theory for the total energy of binary alloys is presented. It treats the entire range of concentration and short-range order. The method in not ab initio, but requires only information about the pure elemental constituents of the alloy. Results for two very different metal series, monovalent metals and 4-d transition metals, are calculated and compared to experiment and other models. The model calculation allows us to examine the physical basis for experimental trends.
Quantitative Predictions from Solid-State Physics - What do Phase Diagram Calculators Want?
Authors: Rand Malcolm
Published: March 2011

The types of information required for the calculation of phase diagrams are discussed by considering the computation of typical ternary sections from the constituent binary systems. Such calculations require a knowledge of the Gibbs energy of transformation (lattice stabilities) and Gibbs energies of mixing of wholly metastable, as well as the stable phases in binary systems. Similarly, the stabilities of metastable compounds such as Fe7C3 would be required for computations in the C-Cr-Fe system.

These requirements are compared to the information provided by solid-state theoreticians. Essentially such calculations provide enthalpy values at 0 K (or some unspecified temperature for semi-empirical models); however the lattice dynamics and configurational entropy of simple phases have been included in some recent computations. The importance of predicting the entropy and thus heat capacity of metallic phases - particularly metastable phases - is therefore emphasized. Identification of those contributions to the heat capacity which are responsible for the differences between metal polymorphs is discussed, particularly the formalism for magnetic and atomic ordering phenomena. Predictions of ordering temperatures and magnetic moments as a function of composition would be of considerable help for phase diagram calculations.

Ab-initio calculations already have considerable success in predicting molar volumes of both stable and metastable phases, so that such information will undoubtedly be of considerable value in studying alloy behaviour at high pressures.
Ductile-Phase Toughening in Niobium-Niobium Silicide Powder Processed Composites
Authors: Nekkanti Rama M. , Dimiduk Dennis M.
Published: March 2011

The Nb-Si system offers a possibility of ductile-phase toughening of the brittle Nb5Si3 intermetallic with the terminal niobium-silicon solid solution. Powder composites have been made in which the volume fraction of the terminal Nb-Si phase is systematically varied in a matrix of Nb5Si3 in order to study the extent of toughening. The Nb-Si solid-solution phase was observed to exhibit cleavage failure under both as hot pressed and heat treated conditions, thereby limiting the toughening attained by the presence of this phase. Hot working of the composite results in a dramatic improvement in toughness because of a change in the plastic behavior and fracture mode of the terminal Nb-Si phase from brittle cleavage to a mixed mode of cleavage and ductile microvoid growth and coalescence (dimpled) fracture.
Ductile-Phase Toughening of Cr3Si with Chromium
Authors: Newkirk Joseph W. , Sago J. Alan
Published: March 2011

Cr-Si alloys offer important advantages as an aerospace material, including high service temperature and good oxidation resistance. This in-situ composite combines a hard, brittle silicide phase with a softer chromium phase. The soft phase is intended to add damage tolerance. Alloys with high volume percents of the silicide phase had good strength values at temperatures up to 1200C or more. Microhardness indents were used to demonstrate that the chromium phase could act as a crack bridging material. In addition the microstructural stability of these materials was studied with encouraging results.
Simple Measurements of Toughness and Crack Formation in Several Intermetallic-Matrix Composite Systems
Authors: Fleischer Robert L.
Published: March 2011

Chisel-and-hammer (C.T.) and microhardness tests have been used to examine trends in toughness and crack formation in several intermetallic-based two-phase equilibrium systems. High fracture toughness, as defined by the chisel test, correlates with the presence of some ductility; and the lack of crack formation, or its limitation by a second phase in the microstructure, are prerequisites for fracture resistance. Equilibrium systems have desirable stability for use at elevated temperatures. Comparison of Tbd and C.T. is now possible for a wide range of intermetallics. Intuition suggests that Tbd and C.T. would anti-correlate. Observation, however, contradicts that hypothesis. There are significant numbers of alloys with low Tbd and low C.T. and with high Tbd and high C.T. Possible explanations are noted. Systems that have been studied include Al-Ru with Sc additions, Be-Ti, Be-Zr, Cr-Ti, with Al, Nb and Zr, Ge-Ti, Ir-Nb with Co, Fe, Ni, and V, and Ru-Ta with Co and Fe. Compositional effects on chisel toughness, hardness-vs-temperature, and crack information are presented.
Determination of Fiber/Matrix Interface Mechanical Properties in Brittle-Matrix Composites
Authors: Kerans Ronald J. , Jero Paul D. , Parthasarathy Triplicane A. , Chatterjee Amit
Published: March 2011

It has been evident for some time that the mechanical properties of the fiber/matrix interface play an important role in determining the mechanical behavior of ceramic composites (for reviews, see [1], [2], and [3[). Recently there has been a growing interest in the role of the fiber/matrix interface in intermetallic matrix composites. While ceramic and intermetallic composites are certainly very different materials, understanding the behavior of one will provide insight into the other. Furthermore, the basic issues regarding the determination of interface properties are the same. The accuracy of micromechanics models of any composite system is dependent upon the accuracy of all the constituent and interface properties. It is far preferable to measure actual materials constants rather than test-specific quantities. The tests described here are intended to measure the interfacial shear strength (or mode II toughness) and the interfacial tensile strength. The objective of this work is to briefly outline a few of the approaches which are being evaluated for and applied to ceramic composites, and which may be of interest to investigators working in intermetallic composites.
The Effect of Notches on the Fatigue Life of SCS-6/Ti3Al Composite
Authors: Bain Kenneth R. , Gambone Mary Lee , Zordan Richard D.
Published: March 2011

Low cycle fatigue tests were performed on Ti-24Al-11Nb titanium aluminide composite unidirectionally reinforced with SCS-6 fiber. (SCS-6 is a SiC-based fiber manufactured by Textron-SMD in Lowell, Massachusetts.) The effect of circular holes onthe fatigue life of this composite system was measured with respect to fiber orientation, temperature, and frequency. Longitudinal and transverse specimens with and without holes were tested at 26°C and 649°C at 0.33 Hz. In addition, longitudinal specimens were also tested at 30 Hz and 649°C to determine the effect of frequency.

A degradation in fatigue life due to the presence of holes was observed in specimens loaded in the fiber direction (longitudinally). This effect is independent of frequency. The notch sensitivity factor, Q, associated with the reduction in life ranges from 0.33 to 0.50 over the range of temperature tested.

The specimens oriented with the load axis perpendicular to the fiber direction (transverse) demonstrated no sensitivity of fatigue life to the presence of holes at room temperature but did possess a finite sensitivity at 649°C with a Q=0.45.
Models for the Strength of Ductile Matrix Composites
Authors: Bao Gang , Genna Francesco , Hutchinson John W. , Mcmeeking Robert M.
Published: March 2011

Numerical results have been obtained for the plastic flow of a metal matrix composite material reinforced by rigid spheres, cylinders and ellipsoids. Aligned geometries have been investigated and 2-d and 3-d cellular calculations carried out using the finite element method. The relative effect of particulates, disks and needles used as reinforcements are compared. Needles in aligned arrangements are found to produce the greatest strengthening. Additional results are presented from plane strain slip line solutions. Such results provide insight into the relative importance to strength of the reinforcement end regions versus the narrow side ligaments.
Particle-Reinforced Nb-26at%Ti-48at%Al Composites
Authors: Aikin R. M. , Mccubbin P. E. , Christodoulou L.
Published: March 2011

Composites based on Nb-26at%Ti-48at%Al have been produced in situ by the XDTM process with nitride and silicide particulates, boride whiskers, and carbide plates. The alloy microstructure is a two-phase matrix of γ (TiAl) and σ (Nb2Al) with a uniform distribution of the ceramic phase. The room and elevated temperature strength of these alloys have been investigated and the role that the nondeforming particles play on the deformation of the two-phase γ-σ matrix will be discussed.
Feasibility Study of Intermetallic Composites
Authors: Shah D. M. , Anton D. L. , Musson C. W.
Published: March 2011

The feasibility of developing high-temperature intermetallic composites for use as gas turbine engine components is assessed for a wide range of high temperature intermetallic matrices including aluminides, silicides, Laves and Sigma phases along with Al2O3, SiC, TiC, Si3N4 and Y2O3 as well as ductile refractory metals as either reinforcing phases or coatings. Preliminary evaluations of fabricability and observations of matrix/reinforcing phase compatibility are presented and discussed in terms of various factors, including interstitial impurities, equilibrium phase relationships, kinetics, and physical and mechanical properties of both matrix and reinforcing phases.
High Temperature Oxidation of Ni3Al Composites
Authors: Tortorelli P. F. , DeVan J. H. , McKamey C. G. , Howell M.
Published: March 2011

As part of an effort to develop oxidation-resistant metal matrix composites, the influence of reinforcement materials on the oxidation of Ni3Al was studied. Thermogravimetric measurements and microstructural analyses were used to determine the 800°C oxidation behavior of Ni3Al and composites based on this material. The presence of fiber (Al2O3)- or particle (TiN or TiC)- reinforcement material in the Ni3Al increased susceptibility to oxidation as measured by the amount of reacted material, rate constants, and/or extent of internal attack. The orientation of fibers with respect to the free surfaces was found to affect the oxidation behavior by providing, in certain cases, reactive paths along the fiber-matrix interface that led to significant internal penetration. The results suggest that the choice of reinforcement material and the method of materials processing will be important considerations in the design of oxidation-resistant Ni3Al composites. However, ways to minimize the detrimental influence of the reinforcement material on oxidation resistance often conflict with requirements for obtaining attractive mechanical and physical properties of the composite.
Compatibility of Potential Reinforcing Ceramics with Ni and Fe Aluminides
Authors: Moser J. A. , Aindow M. , Clark W. A. T. , Drapert S. , Fraser H. L.
Published: March 2011

The compatibility of candidate ceramic reinforcement materials with intermetallic matrices for high temperature composite systems has been evaluated. Powders of FeAl and NiAl were mixed with ceramic powders and consolidated by hot isostatic pressing and subsequent heat treatment. The microstructures of these composites and the nature of the ceramic/matrix interfaces were assessed using a wide variety of electron-beam techniques. The system FeAl/TiB2 was found to be particularly promising. The matrix appears to be bonded to the ceramic particles, which may be the result of diffusion of Fe into the ceramic. The particles stabilized in a previously unreported monoclinic crystal structure, rather than the equilibrium hexagonal form exhibited by the binary compound.
Reactive Synthesis of NbAl3 Matrix Composites
Authors: Lu L. , Kim Y. S. , Gokhale A. B. , Abbaschian R.
Published: March 2011

NbA13 matrix composites were synthesized “in-situ” via reactive hot compaction (RHC) of elemental powders. It was found that the simultaneous application of pressure during synthesis was effective in attaining a near-theoretical density matrix at relatively low temperatures and pressures. Using this technique, two types of composites were produced: (1) matrices containing a uniform dispersion of second phase particles (either Nb3Al or Nb2Al with an Nb core or Nb2Al) and (2) matrices reinforced with coated or uncoated ductile Nb filaments. It was found that a limited amount of toughening is obtained using the first approach, while composites containing coated Nb filaments exhibited a significant increase in the ambient temperature fracture toughness. In this paper, various aspects of RHC processing of NbAI3 matrix composites, the effect of initial stoichiometry and powder size on the microstructure, as well as the mechanical behavior of the composites will be discussed.
Solidification Processing Routes to High Aspect Ratio Reinforcements in γ-TiAl
Authors: Valencia J. J. , Löfvander J. P. A. , Rösler J. , Levi C. G. , Mehrabian R.
Published: March 2011

Additions of ∼5%B1 and ∼9%Ta to binary γ-TiAl result in the formation of a monoboride isomorphous with TiB but containing Ta in solid solution. This boride exhibits strongly anisotropic growth from the melt, producing rod-like primary phases which are of potential interest for creep strengthening of the γ matrix. Fibrous borides with aspect ratios larger than ∼20 and volume fractions of ∼0.12 have been produced in arc-melted Ti-48AI-9Ta-4.3B alloys. Creep testing at 1255 K indicates that these “in-situ” composites have much higher creep strength than γ-TiAl, but the contribution of the reinforcements is relatively small compared with the solute-strengthening of the matrix.
Densification Models for Plasma Sprayed Metal Matrix Composite Foils
Authors: Elzey D. M. , Kunze J. M. , Duva J. M. , Wadley H. N. G.
Published: March 2011

The development of a constitutive model describing the deformation response of plasma sprayed metal matrix composite (MMC) foils during hot isostatic pressing (HIP) is described. A representative volume element of the composite is chosen whose constitutive behavior, including inelastic compressibility, is analyzed for the particular case of constrained uniaxial compression. Results of this preliminary model for the case of a SCS–6/Ti–14wt%Al–21wt%Nb intermetallic matrix composite are presented in the form of a density–pressure HIP map.
Testing of Impact Limiters for Transportation Cask Design
Authors: Maji A. K. , Donald S. , Cone K.
Published: March 2011

‘Soft Impact Limiters’ such as polyurethane foams and aluminum honeycombs are being studied to assist the Sandia National Lbiatory's Transportation Base Technology Program. The aim of this research is to study the mechanical behavior of these materials, which are being used as impact absorbers in nuclear waste transportation containers.

A series of tests were performed along various loading paths using an Instron, servo-controlled, multi-axial loading machine and Soiltest triaxial testing apparatus. Static tests included uniaxial tension, uniaxial compression, triaxial compression, hydrostatic compression and fracture toughness testing. The purpose of using different loading paths was to generate an extensive test data which is being used to develop constitutive models for these materials, under a separate research program.

Dynamic tests were conducted at strain rates of 100 strains/sec., to generate experimental data relevant to accident situations. These tests were conducted on an instrumented Charpy impact testing apparatus. Results of these tests were subsequently used to conduct scale-model tests of transportation casks of different industrial designers.

Different densities of Polyurethane foams, aluminum honeycombs, and corrugated aluminum honeycombs were tested in different orientations. The paper discusses the experimental program, instrumentation and test results for the nuclear waste transportation industry and other potential applications.
A Comparison of Mechanical Properties and Scaling Law Relationships for Silica Aerogels and their Organic Counterparts
Authors: Pekalaa R. W. , Hrubesh L. W. , Tillotson T. M. , Alviso C. T. , Poco J. F. , LeMay J. D.
Published: March 2011

Aerogels are a unique type of ultrafine cell size, low density foam. Traditional aerogels are inorganic, but the synthesis of organic aerogels has also been reported. In all cases, solution chemistry can be used to tailor the structure and properties of the resultant aerogels. This study examines the microstructural dependence of the compressive mechanical properties of silica, resorcinol-formaldehyde, carbon, and melamine-formaldehyde aerogels.
Mechanical Structure-Property Relationships of Microcellular, Low Density Foams.
Authors: Lemay James D.
Published: March 2011

High energy physics applications at the Department of Energy National Laboratories require unique low-density foams of demanding homogeneity specifications (cell sizes on the order of 10 μm or smaller). These delicate and fragile foams are machined and shaped into specimens to exacting tolerances. In this work, the mechanical properties of a variety of these low density microcellular foams are reported as functions of foam density and morphology.
The Porosity Dependence of Mechanical and other Properties of Materials
Authors: Rice Roy W. , Grace W. R.
Published: March 2011

Though the volume fraction (or %) porosity is commonly used as the exclusive porosity variable to describe the porosity dependence of physical properties, it is not sufficient. The average minimum solid area, i.e., of the bond or sintered area between sintering particles, or the minimum web or strut cross-sections is the most appropriate second porosity parameter. Pore shape-stress concentration effects have, at best, limited direct effect on mechanical properties, but generally correlate with minimum solid area effects. Methods of combining effects of different types of porosity within the same body are important and result in quite reasonable descriptions of mechanical properties across a broad range of porosities.
Thermal Shock Behavior of Open Cell Ceramic Foams
Authors: Orenstein Robert M. , Green David J. , Segall Albert E.
Published: March 2011

Specimens of heated alumina foams were thermally shocked by immersion in water or oil. Two distinct temperature profiles were found to exist during liquid quenching: a macroscopic gradient due to heating of the fluid during infiltration into the foam and a microscopic gradient across each individual strut. Thermal stresses were calculated using a semi-empirical, finite element model. The peak thermal stresses were coupled with the two-parameter Weibull distribution of the strut strengths to calculate the probability of crack extension on a strut for eight cellular geometries. Experimentally, the thermal shock resistance increased with increasing relative density and increasing cell size. The predicted critical temperature differences were in fair agreement with measured values.
Multiaxial Failure Criteria for Cellular Materials
Authors: Triantafillou T. C. , Gibson L. J.
Published: March 2011

Cellular materials are increasingly used in engineering. Proper design requires an understanding of the response of the materials to stress; and, in real engineering design, the stress state is often a complex one. In this paper we model the elastic buckling, plastic yield, and brittle fracture of cellular solids under multiaxial stresses to develop equations describing their failure surfaces. Comparison of the analysis with data shows that the models describe the main features of the multiaxial behavior of foams well.
Oxynitride Glass Reinforced Cement Composites
Authors: Leatherman Gary. L. , El-Korchi Tahar , Holmes Thomas M. , Katz R. Nathan
Published: March 2011

Glass fiber reinforced composites made with an oxynitride analogue of alkali resistant glass were tested in tension after accelerated aging. The results were compared to composites made from oxide alkali resistant glass. The strength of the oxynitride glass reinforced composites was almost double that of the oxide glass based material. The results are related to the improved properties of oxynitride glass over oxide glass. In particular previous work has shown that surface chemistry of the oxynitride glass inhibits the formation of a strong bond between fiber and matrix. The difference in surface chemistry was examined by measuring the contact angle of aqueous solutions with respect to nitrogen content of the glass.
Effect of Aging on Interfacial Properties of Glass Fiber Reinforced Concrete
Authors: Shah S. P , Li Z. , Mobasher B.
Published: March 2011

This paper explores the behavior of the interface of glass fiber and cementitious matrix under the effect of aging. Pull-out tests of multiple alkali resistant glass fiber strands embedded in portland cement paste matrix were conducted. Four different curing regimes of 3 and 14 days normal curing, in addition to 3 and 7 days accelerated aging were employed. A recently developed method of characterizing interfacial properties was used to identify and evaluate the important parameters at interface. The experimental data are presented on the parameter of shear stiffness of a fiber-matrix boundary layer, the shear bond strength, the frictional bond strength and the specific surface energy as a function of fiber embedded length. It was observed that aging had a larger effect on the stiffness of the interface, the shear bond strength and the specific surface energy than on the frictional bond.
Durability of FRC-Materials
Authors: Larsen Erik Stoklund , Krenchel Herbert
Published: March 2011

Asbestos cement was the first type of FRC-material that was ever made. It consisted of neat, hardened Portland cement reinforced with asbestos fibres (Vt - 7 vol-%). The most outstanding and valuable property of a high quality asbestos cement was the highly improved durability of this composite material in comparison to what would have been the case, if no fibres had been added or the fibre reinforcement of this extremely brittle matrix had been carried out incorrectly.

This paper describes an analysis of the variation in time of the fracture energy, GF, of different types of FRC-material exposed to various climatic conditions.

The following types of fibres were examined: steel fibre, ar-glass fibre, synthetic fibre (polypropylene) and natural fibre (sisal fibre and paper pulp cellulose).

The climatic exposure conditions were natural out-door weathering or laboratory tests in a special weather-o-meter. Three test series were carried out at the Danish Building Research Institute. The results from these tests have been compared to results from five test series taken from the literature (ar-glass-, steel-, polypropylen-, sisal-fibres and neat concrete).

It is concluded that natural and glass fibres are losing strength and ductility in a cementitious matrix. This results in a drastically reduced fracture energy of the composite material over the years. In the worst cases practically no fibre effect is left after some ten years of normal out-door exposure.

For the best types of fibres examined (steel fibre, high tenacity, high bond polypropylene and combinations of these two types) the ductility and fracture energy of the composites are increasing significantly even after very long time of exposure.
Fibrous Concrete - Sensitivity of Workability to Percentage and Type of Fibre
Authors: Debicki G. , Bouchekouk M. , Clastres P. , Hamelin P.
Published: March 2011

Workability is measured with the LCL consistometer. The device is an open rectangular mould with an external vibrator and a removable vertical partition dividing it into two compartments. When the partition is removed, the vibrator is triggered at the same time as a chronometer. The time, t, that the concrete takes to flow to a reference line is measured.

For a matrix with a given composition (mortar and concrete), we study how workability varies when the percentage of fibres increases. The curves thus obtained take the form Ln(t)= A + B %. We show that the value of coefficient A is linked to the matrix composition while coefficient B is especially sensitive to the type of fibre used and to the gravel -fibre interaction.

Mortar and concrete compositions reinforced by fibres of very different types with different lengths and geometries (rods or ribbons) are tested and are used to validate the proposed model. The types of fibres studied are: glass fibres coated with thermoplastic, PVC fibres, steel fibres and amorphous cast iron fibres. The results can be used to optimize the geometry of very different types of fibres and thus obtain a better workability.
Noninvasive Diagnosis of Toughening Mechanisms in Fiber Reinforced Concrete
Authors: Maji A. K. , Wang J. L.
Published: March 2011

Various physical phenomena are involved in the fracture process of steel fiber reinforced concrete (SFRC). Although pullout of the fiber has been the most intensively investigated parameter in studying the micromechanics of these materials, other mechanisms could be dominant, depending on the nature of the loading and the fiber orientations. Pullout tests were conducted on isolated fibers embedded in a mortar matrix with different orientations to the direction of loading.

The specimens were loaded in the chamber of a scanning electron microscope (SEM), and on an optical table with instrumentation for Laser holographic interferometry (HI). The relative contribution of the various mechanisms, such as: fiber debonding and pullout, mortar crushing, friction at comers, and plastic energy dissipation on the fibers were evaluated. When the specimens were tested in the SEM, it was observed that compressive failure with crushing of the mortar is an important physical phenomenon, in addition to plastic bending of the fiber. HI studies also indicated the crushing of mortar prior to interface debonding.

The relative amounts of energy dissipated by the various mechanisms were evaluated using experimental observations and analytical approximations. The importance of the different mechanisms at progressive stages of fiber pullout was estimated.
Total Anchorage Fibres for Concrete: Fibre-Reinforced Cementitious Materials
Authors: Destree X. , Sahloul M.
Published: March 2011

Steel fibre reinforced concrete is a composite material consisting of a brittle matrix reinforced and randomly oriented fibres. The concrete matrix is brittle and the engineered steel fibres are ductile (elasto-plastic). When these two materials are mixed, the importance of the bond between the steel fibres and concrete becomes obvious.