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In developing the Griffith–Irwin fracture mechanics of chapters 2 and 3 we presumed that equilibrium brittle fracture properties are governed by invacuo surface energies. In practice, most fractures take place in a chemically interactive environment. The effects of environment on crack propagation can be strongly detrimental. One of the most distinctive manifestations is a rate-dependent growth, even at sustained applied stresses well below the ‘inert strength’, with velocities sufficiently high as to be clearly measurable but too low as to be considered inertial. We use the term kinetics (typical velocity range ≈ m s -1 down to and below nm s -1 ) to distinguish from true dynamics (velocity range ≈ m s -1 to km s -1 ). Kinetic crack propagation (alternatively referred to as ‘slow’ or ‘subcritical’ crack growth) is notable for its extreme sensitivity to applied load, specifically to G and K . It tends also to depend on concentration of environmental species, temperature, and other extraneous variables. How does kinetic behaviour reconcile with the Griffith concept? A crack growing at constant velocity at a specific driving force implies a condition of steady state, whereas Griffith deals explicitly with equilibrium states. Experimentally, it is found that velocity diminishes with decreasing G or K until, at some threshold , motion ceases. On unloading the system still further the crack closes up and, under favourable conditions, heals , even in the presence of environmental species.

The phase behavior of a blend containing poly(hydroxypropyl L-glutamine) (PHOPG), a rod-like polypeptide, and a coil-like random copolymer with 1.5% hydrogen bonding monomer is studied using light scattering, DSC, and optical microscopy. The results show that this system has an LCST. The phase behavior of this binary system is complicated by a glass transition and an ordering transition. Evidence is also observed of a possible change in phase demixing process, from nucleation and growth to spinodal decomposition, for a 50/50 blend with a change in temperature.

Publisher Summary This chapter focuses on the chemical bonding of the elements. Chemical bonding is the technique through which the atoms of the elements are held together in molecules. The type of bonding that binds the atoms of the metallic elements together is called metallic bonding. X-ray crystallographic studies have shown that the metal atoms are closely packed together in such a way that they occupy a minimum volume, and hence a minimum potential energy exists among atoms. An ordered arrangement of spheres can be used to represent the types of bonding that occur. Some of the physical properties of most metals are that they are malleable, ductile, good conductors of heat and electricity and in addition the majority of the metals are dense and have high melting points and boiling points. The nonmetallic elements in their pure states are held together by a different type of bonding called covalent bonding. This involves the snaring of two electrons between two different atoms that holds the electrons in a distinct position relative to each other. Each element can share as many electrons as are necessary to achieve a stable electronic configuration. These stable electronic configurations are those of the inert or noble gases, neon, argon, krypton, or helium. The number of bonds formed is thus dependent on the electronic configuration of the particular element.

Conventional hydrophilic and hydrophobic bonding processes involve high-temperature annealing above 700~1000oC that would cause undesirable effect on the bonded structure and devices (1). Surface activation prior to bonding has been carried out using dry plasma treatment. However, low-temperature annealing (200~400oC) is generally necessary to strengthen the bonding (2). Although plasma activation followed by wet chemistry treatment can enhance the bonding strength, voids are often raised at bonding interfaces during the annealing step (3). Alternatively, several vacuum wafer bonding methods have been reported in recent years for achieving reliable bonding even at room temperature, e.g. surface activated bonding (4) and ultra-high vacuum bonding (5). They are capable of room-temperature bonding without annealing but the whole bonding process requires high-vacuum condition that makes these processes expensive and less applicable for mass production. This paper presents a simple fluorine containing plasma activated bonding process at room temperature in ambient air without requiring annealing step and wet chemical cleaning processes. Moreover, we focus on several critical issues, such as effects of plasma treatment parameters on bonding strength, characterizations of bonding surface and interface, and bonding mechanism. In the first part of this paper, the bonding parameters are optimized to improve the bonding strength. Silicon and silicon oxide wafers are successfully bonded at room temperature. In the second part, the physical effects of plasma treatments on wafer surfaces are investigated using atomic force microscopy (AFM) and surface profiler. And the chemical states of surfaces are analyzed by X-ray photoelectron spectroscopy (XPS). Si/Si bonding interfaces are characterized by transmission electron microscopy (TEM) as well as Fourier Transform infrared (FT-IR) spectroscopy to understand the role of water molecules for bonding mechanism. A bonding model is proposed to illustrate the roles of fluorine and water molecules, which can be explained by the reaction between reactive fluorinated silicon oxide layers resulting in partial covalent bonding at room temperature.

From molecular-dynamics simulations, it is demonstrated that the structure factor has a second-peak splitting feature not only for glass states but also for supercooled-liquid states in some metallic cases. This appears to be due primarily to the presence of icosahedronlike clusters in these cases. This suggests that a laboratory or simulated metallic glass is generally a distorted metallic solid including a significant amount of icosahedra, each consisting of 13 atoms. This lends strong support to one of various existing structural models, namely, the Briant model.

It is necessary for the proper understanding of materials technology to have some knowledge of the underlying science and the fundamental principles that control the properties of materials. There are many thousands of materials available for use by today’s engineers and, clearly, it is impossible for one person to have a full and detailed knowledge of all of them. However, as we have seen in Chapter 1, materials can be classified within several well-defined groups. There is a further common feature—all substances are composed of atoms. There is a comparatively limited number of different atomic species or chemical elements (the total number of elements, including the artificially created transuranic elements, is 103) and all these elements are composed of the same basic sub-atomic particles. The manner in which these sub-atomic particles are assembled into atoms and the ways in which the various atoms are bonded to one another in the make-up of bulk materials play a major part in determining the final properties of any material. For example, it is the different nature of the interatomic bonding in metals, as compared with polymer materials, which allows for electrical conduction in the former while making the latter dielectrics or insulators.

Workers engaged in a wide range of investigations of charge transport in non-metallic solids came together at a meeting of the Institute of Physics Dielectric Group, held in London on 2 April 2008. Topics included both ionic and electronic conduction, investigations of the fundamental mechanisms of charge transport, percolation, modelling the conduction process in both natural and man-made composite electrical and electromagnetic materials, the design and development of solids with specified conduction properties and the ac characteristics of non-metallic solids. In the first session, the long-standing problem of the anomalous power law increase in ac conductivity with frequency was addressed by a set of four presentations. Jeppe Dyre, an invited speaker from Roskilde University, Denmark, introduced the problem and stressed the universality of the frequency dependence observed in the ac conductivities of disordered non-metallic materials. He showed that it could be obtained from a simple random barrier model, independent of the barrier distribution. Darryl Almond, University of Bath, showed that the electrical responses of large networks of randomly positioned resistors and capacitors, simulating the microstructures of disordered two-phase (conductor insulator) materials, exhibit the same frequency dependence. He demonstrated their robustness to component value and distribution and suggested that it was an emergent property of these networks and of two-phase materials. Klaus Funke, an invited speaker from the University of Munster, Germany, presented a detailed model of ion motion in disordered ionic materials. He stressed the need to account for the concerted many-particle processes that occur whilst ions hop from site to site in response to an applied electric field. The conductivity spectra obtained from this work reproduce the same frequency dispersion and have the additional feature of conductivity saturation at high frequencies. Tony West, University of Sheffield, UK, discussed the analysis of the ac electrical response data of ionically or electrically conducting ceramics, using constant phase elements to deal with power law dispersions. He presented strategies for dealing with data made complex by the overlapping, in the frequency domain, of different materials response components: bulk, grain boundary, electrode, etc. The final morning paper concerning space charge measurement was given by Kaori Fukunagwa, NICT, Japan. The closely linked but diverse nature of the morning papers stimulated healthy debate between the presentations and during the lunch break and poster session, during which the Mansel Davies prize was awarded to Dr Shahid Hussain from QinetiQ for his poster entitled Dielectric relaxation of glass particles with nanoscale metallic coatings. In the second session, again through a set of four presentations, the electrical and electromagnetic properties of composite materials were more broadly considered. Isaac Balberg, an invited speaker from The Hebrew University in Jerusalem, gave a detailed and in many ways philosophical review of critical behaviour in composites near the percolation threshold. He focused on the validity of using critical response developed from the classic Scher and Zallen model of a regular lattice when considering the more realistic situation of composites in which hopping and tunnelling are prevalent, the key to observing universal or non-universal critical behaviour being the significance of nearest neighbour versus non-nearest neighbour conducting paths and the distribution of resistances in the composite. Ian Youngs, from Dstl, described the microwave response of conductor--insulator percolating composites and especially the observation of novel plasma-like response under certain circumstances. It was shown that the standard low frequency approximation of the dielectric function of the metallic phase impedes modelling of this response. Christian Brosseau, Universite de Bretagne Occidentale, France, presented an invited paper discussing electromagneto-mechanical coupling in ferrite-filled plastics. A model for the changes to the electromagnetic properties of the composite as a function of applied mechanical stress was presented and linked to the elastic network response of the composite. The work is relevant to flexible materials such as circuits and for smart sensor applications. Rolf Pelster, Universitat des Saarlandes, Germany, concluded the meeting with a comparison of micro- and nano-composites of magnetic particles dispersed in polymer. Broadband dielectric spectroscopy was used to highlight the particle-size differences and the likely modification of the host polymer when nano-sized filler particles were used. The dielectric data was used to infer the microstructural contribution to the effective properties of each composite and this information was used to extract an estimate of the intrinsic magnetic properties of the filler particles, again showing a difference between micro- and nano-sized particles. This cluster issue of Journal of Physics D: Applied Physics contains four of the above-mentioned papers presented at the meeting. We would like to thank those authors for preparing their contributions to this special cluster. Their papers provide a cross section of the topics presented at the meeting and we hope you enjoy reading them.

A particulate silicon carbide—titanium metal-matrix composite (MMC) has been joined successfully using both solid-state and transient-liquid-phase (TLP) diffusion bonding. A thin-film diffusion model was developed to predict bonding times and temperatures for TLP bonding using a copper interlayer. Good agreement with experimental data was seen. Also, bonding conditions of relatively high temperatures for short times minimise matrix-reinforcement interfacial reactions. The α/β phase stability of the Ti matrix is of particular relevance when bonding and affects the extent of the interfacial reactions.

We review the phenomenology of laser-induced particle emission at sub-bandgap photon energies from the surfaces of halides and compound semiconductors, which are representative of solids with strong and weak electron-lattice coupling, respectively. In the former a multi-hole localized state generated by cascade excitation of self-trapped excitons can cause nonlinear dependence of the desorption or ablation yield on the laser fluence. In weak-coupling systems, multi-hole localization on surface defect sites by the negative-U interaction can lead to ejection of atoms. The contribution of these electronic processes to laser ablation is discussed.

In the course of a general investigation of the particular case of the copper-alumina bonding Transmission Electron Microscopy (TEM) has been used to follow the interfacial reactions through a detailed characterization of compounds at the metal-ceramic interface.

In the 1950’s, Slater introduced the concept of the electron-gas approximation as a simplification of the Hartree-Fock equations (Slater, 1951). The goal was to make energy band structure calculations practical for crystalline solids such as bulk Cu. The exchange term of the Hartree-Fock equations needed to be approximated while the kinetic energy and the Coulomb repulsion terms of the Fock operator could be treated rather well within a periodic lattice, particularly if the so-called muffin-tin approximation (Slater, 1937) was made.

Solid-state physics is the physics of that state of matter in which a large number of atoms are chemically bound to produce a dense solid aggregate. The emphasis in this statement is placed on the large number of atoms involved, since that number is of the order of 1023 cm-3. At first sight it would seem to be a hopeless task to try to apply traditional scientific methods for the description of such a vast number of atoms. However, it is exactly the large number of atoms involved that in fact makes a quantitative description possible by means of new models, applicable specifically to solids. A prerequisite, though, for the success of these models, is that the participating atoms are not simply chosen at random from the periodic table of elements; the solid must be composed of a limited number of different elements whose atoms are arranged in space with a certain order. Thus, for the solid state physicist, the showpieces are the “elementary” crystals, i.e., three-dimensional periodic arrangements of atoms of one type, or chemical compounds of two elements. An understanding of solids and of their characteristic properties thus requires that we first achieve a fundamental understanding of two particular phenomena: the first is that of the forces that hold together the atoms of a solid, in other words, the chemical bonding between atoms. The second important aspect is the structural ordering of the atoms within the solid. A consideration of these two basic questions forms the content of the first two chapters. In both cases it will only be possible to give a short introduction and for a more detailed discussion of these phenomena the reader is referred to textbooks on quantum chemistry and crystallography.

This paper presents the pressure-induced solid-state lattice mending of nanopores in single-crystal copper by femtosecond laser annealing processes. The microscopic mechanism of lattice mending is investigated by a modified continuum-atomistic modeling approach. Three typical lattice mending phases, including (i) the incubation of dislocation nucleation, (ii) plastic deformation under the combined effect of pressure and atomic thermal diffusion, and (iii) lattice recovery and reconstruction, are characterized via the microscopic structure changes and transient thermodynamic trajectories. The simulation results reveal that the structural mending of a pore is originated in heterogeneous nucleation of dislocations from the pore surface. The shear-induced multiple lattice glides are found to significantly contribute to the mending of a nanopore in the process of solid-state structural mending. The mending rates of two different modes, the pressure-induced and the classical unsteady-state atomic diffusion, are estimated and found to be very different from each other, by an order of 10(4). In addition, the location of the pore is also found to significantly influence the annealing threshold. Since the largest amplitude of the pressure wave is built up at a characteristic depth of approximately 45 nm below the irradiated surface, the shock wave will directly impinge on the pore and induce a fast solid-state lattice mending if the pore is located within the lower limit of the range of the characteristic depth. Furthermore, it is also interesting to note that the mending of a nanopore close to the characteristic depth by annealing fluence is generally lower than that of a pore near the surface. These results provide vital insights of photomechanical interactions with the microstructure of metallic solid, and the proposed approach can be further considered and enhanced to predict the mending depth for various defects in the future.

Publisher Summary This chapter discusses the structure, bonding, rupture behavior, and strength of ceramics. It also discusses the time and temperature effects and role of heterogeneities on ceramics. Ceramics display inorganic crystal structures or, occasionally, glass-like amorphous structures. According to the chemical species involved, the bonds may be ionic, covalent, or metallic. Additional van der Waals bonds also may occur. Processes and properties will depend on the nature of the bonds and their structure. Ionic bonding occurs when one atom gives up one or more electrons that are accepted by one or several other atoms in such a way so that an overall electrical neutrality is maintained. Each atom thus gets a stable, filled electron shell. Metallic oxides and halides have mainly ionic bonding. Covalent bonding occurs when two or more atoms share electrons. Here again, this generally endows each atom with a stable and filled electron shell. Depending on the ceramic type, the shape, and the required characteristics, numerous forming processes can be resorted to. The main ones are die pressing, slip casting, injection molding, and extrusion molding.

We have studied the formation of molecular scale particles or “clusters” of alkali halides and semiconductors during laser vaporization of solids. By measuring the abundances of cluster ions produced in several different source configurations, we have determined that clusters are ejected directly from the source sample and do not need to grow from atomic or molecular vapor. Using samples of mixed alkali halide powders, we have found that unalloyed clusters are easily produced in a source that prevents growth from occurring after the clusters leave the sample surface. However, melting the sample or encouraging growth after vaporization lead to the production of alloyed cluster species.The sizes of the ejected clusters are initially random, but the population spectrum quickly becomes structured as hot, unstable-sized clusters decay into smaller particles. In carbon, large clusters with odd numbers of atoms decay almost immediately. The hot even clusters also decay, but much more slowly. The longest lived clusters are the magic C50 and C60 fullerenes. The mass spectrum of large carbon clusters evolves in time from structureless, to only the even clusters, to primarily C50 and C60. If cluster growth is encouraged, the odd clusters reappear and the population spectrum again becomes relatively structureless.The laser vaporization process in non-metallic systems closely resembles multiphoton laser photodissociation of clusters themselves. As a result, the best cluster source samples are powders or powder-like materials. We have found that carbon powder or exfoliated graphite sheet (Union Carbide Grafoil) are the best samples for the production of large carbon clusters. Many previous studies of carbon clusters formed in vacuum may have relied on the vaporization of carbon dust produced by repeated vaporizations in a small region of the sample.

Room temperature covalent bonds between bonded silicon oxide layers can be realized by forming surface and subsurface absorption layers followed by terminating outmost bonding surfaces with desired bonding groups prior to bonding. For example, by introducing fluorine into bonding oxide layers and NH2 groups onto surfaces of bonding oxide layers before bonding, bonding energy equivalent to silicon fracture energy (2500mJ∕m2) has been realized at room temperature after storage in air. Fluorine incorporation causes Si–O–Si ring breaking leading to fluorinated oxide formation with lower density, thus facilitating a higher diffusion rate of polymerization by-products and enhanced moisture absorptivity. Results indicate that by-products of the polymerization reaction between NH2 groups on mating surfaces appear to be more easily diffused and dispersed away from the bonding interface by the low density fluorinated oxide than are polymerization by-products of OH groups. This enhanced by-product removal results in...

There has been substantial progress in the development of properties in high-temperature in-situ composites during the last five years. For example, fracture-toughness values in excess of 20 MPa √m have been reported in silicide-based composites toughened by niobium-based metallic solid solutions. These composites also have oxidation resistances and rupture lives comparable to those of single-crystal superalloys for temperatures up to 1,150°C. In this article, fracture toughness, oxidation characteristics, high-temperature mechanical behavior, and low-temperature fatigue properties of refractory metal-intermetallic composites (RMICs) are described and compared to air-craft-engine fundamental material property goals for the next millennium. Further avenues toward the pursuit of these goals are outlined.

Instant Notes is divided by the major sections of inorganic chemistry (atomic structure; introduction to inorganic substances; structure and bonding in molecules; structure and bonding in solids; chemistry in solution; chemistry of nonmetals, non-transition metals, and transition metals; lanthanides and actinides; and environmental, biological and industrial aspects).

A wafer prebonding treatment by ammonium hydroxide (NH 4 OH) leading to a high bonding strength at low temperatures is presented in three material systems. After 200°C annealing, a surface energy of about 700 mJ/m 2 for thermal silicon-oxide bonding and of 1300 mJ/m 2 for plasma-enhanced chemical vapor deposition oxide bonding is realized. It is suggested that the lower ability of ammonia, the by-product of a polymerization reaction, to break the siloxane (Si-O-Si) bridging bonds appears to be responsible for the increase in surface energy in both silicon oxide bonding cases. NH 4 OH treatment is also effective on bare germanium/ silicon-oxide bonding with a surface energy of 800 mJ/m 2 . A highly hydrophilic germanium surface obtained by this treatment accounts for the high bonding energy.

Calculated ionic charges show that BF3 and SiF4 are predominately ionic molecules yet in contrast to BeF2 and AlF3 they exist as gases at room temperature and form molecular solids rather than infi...

Using the electron-hopping model (analogous to people sitting in chairs) to explain electron movement and conductivity in insulators, semiconductors, and metals.

Temperature, pressure and time are parameters in the solid-state bonding of metals to oxide materials. The role of these parameters in the bonding of metals with low melting point to glass and ceramic and their interrelationship is experimentally investigated in relation to the adherence of the bonds. The influence of the surface structure and the unevenness of the bonding surfaces is also considered.

Present-day treatments of diffusion in metallic solid solutions require an accurate, convenient analysis that takes account of the actual variations of atomic size with concentration. Recent research by the author has produced such an analysis, which employs ordinary Cartesian coordinates. The first and second Fick equations are essentially the same as the usual forms (for constant, equal atomic size), differing only in the addition of the factor ¯V, the total molar volume of the solid solution. The prevalent erroneous concept of an “invariant” for diffusion demonstrates the need for a clearer understanding of the role of reference planes in treatments of diffusion. Reference systems of two types are dicussed: conventional reference systems (Fick and molecular), and the lattice (Kirkendall) reference system. The diffusion velocity,v, of a given component is used as the basis for defining the diffusion flux. Absolute values ofv can be determined from data on the Kirkendall shift, but only relative values (v−Ω) can be employed if only a conventional reference system is used in the analysis.

Structural transformations in non-metallic solids induced by energetic heavy ions at intermediate (∼1013−1016 ions/cm2) and high (∼ 1017 ions/cm2) doses normally take the form of amorphization, crystallization, or stoichiometry changes. Using the results of 72 substances both a temperature-ratio and a bond-type criterion are shown to be successful in predicting the occurrence of amorphization or crystallization. The former, based on a physical model involving thermal spikes, states that amorphization should occur whenever the ratio (crystallization temperature)/(melting point) exceeds 0.30. The latter, of more or less empirical origin, states that amorphization should occur whenever the ionicity is ≤0.47. Stoichiometry changes are basically different from amorphization and crystallization and this is reflected in the criterion. It is shown that whether or not a substance (such as AgBr or TiO2) loses a component (such as Br or O) during bombardment correlates with the heat of atomization showing a...

The recent advances in calculational schemes involving density functional theory permit numerically accurate determinations of the electronic structure in ordered and disordered alloys. In order to establish the validity of the calculations and to investigate the electronic mechanism responsible for phase stability, for example, an experimental technique is required which probes the electronic spectral density in k-dependent detail. We demonstrate that angle-resolved photoemission measurements in association with photo-current calculations based on a realistic model can provide such a technique.

Amorphous or non-crystalline materials can be produced by a variety of techniques including rapid quenching from the melt, vapour deposition, sputtering and ion implantation. The amorphous metallic solids produced by melt quenching, popularly known as metallic glasses, have been found to have a good combination of physical, chemical and mechanical properties and can also be produced in bulk quantities. Metallic glasses are metastable with respect to their crystalline counterparts and thus undergo transformations when subjected to annealing. A knowledge of the 'stability' of the glasses is important before applications fpr these novel materials are thought of. The present paper discusses the thermodynamics, kinetics and mechanisms of crystalization of metallic glasses. Effect of external factors such as high pressure, deformation and irradiation have also been discussed.

Central pairwise empirical interatomic potential functions have been extensively used to calculate various properties of metallic solids. Although enough useful information could be gathered from these calculations, they are inadequate to reflect the true behaviour of a metal. In the present work we have computed the binding energy using a first-principles quantum-mechanical interaction model under Ashcroft's local pseudopotential formalism. The binding energy contains non-central terms and the stability conditions have been accordingly worked out. A perfect lattice of fcc aluminium subjected to tensile and compressive stresses in the [100] direction, has been investigated for mechanical stability under the above model. Two phases of stable structure were found. A tensile strength of 0.405 GPa and a maximum strain of 5.18% were calculated which are a little lower compared to their experimental values.

The problem of melting of ordinary (nonmetallic) and metallic solids in enclosures has received considerable research attention due to its importance, for example, in materials processing and latent heat energy storage. It is well known that natural convection in the melt, as well as heat condition in the solid, considerably influence the solid/liquid interface shape and motion. However, attempts to correlate the average heat transfer and melting rates have been relatively unsuccessful, except for a few special cases. Consequently, the objective of this study is to demonstrate that a more general melt fraction correlation can be obtained covering the entire time domain as well as the additional effect of heat conduction in the solid. The present analysis is based on the assumptions that (1) the melting proceeds through the three heat transfer regimes described above and (2) the liquid and solid Stefan numbers are small so that the heat transfer is quasi-steady (i.e., negligible thermal inertia of the liquid and solid). The latter assumption is supported by the fact that in virtually all previous numerical and experimental studies the Stefan numbers were less than about 0.3. For conciseness, this study concentrates on melting in rectangular enclosures. However, the methods presentedmore » can easily be applied to other geometries (e.g., cylinders, etc.). The melt fraction correlation derived in this study is validated using the example of melting of metals in vertical cavities.« less

This paper fulfils the need for a unified description of interfacial segregation in metallic solids. A model is developed which accounts for equilibrium and non-equilibrium segregation in a combined fashion. As a result it is possible to predict the amount of segregation to grain boundaries and other interfaces as a function of heat treatment variables like cooling rates and solution, ageing or tempering temperatures. The model's application to grain boundary segregation in ferritic/martensitic steel is described, and reasonable agreement between model predictions and observed segregation-based behaviour is demonstrated. The model is used to provide a set of rules which should be followed to alleviate harmful segregation for various elements in the steel.

Clustering and ordering processes often occur concomitantly or synergistically during the decomposition of supersaturated solid solutions. However, the occurrence of spinodal decomposition in conjunction with an order → disorder transformation thermodynamically of first order under equilibrium conditions is generally not well understood. In this paper a simple graphical approach using free energy-composition diagrams and loci of thermodynamic instability delineating regions of continuous transformation is used to develop a framework for understanding the interplay between clustering and ordering occurring in metallic solid solutions where the ordered precipitate stems from a phase diagram configuration in which the ordered and disordered states are connected by a first-order phase transition. The approach is applied to the NiAl, NiTi and AlLi binary alloy systems in which the interaction of clustering and ordering appears to play an important role.

We have previously demonstrated that the enthalpy of alloy formation can be described in terms of a cellular atomic model. Energy effects are expressed as contact interactions that take place at the interface shared by pieces of dissimilar metals having the size of atoms. In this paper the consequences of the contact interaction approach are discussed at osme length. Examples are: (i) the regular solution approach for the heat of liquid alloys and the pair interaction model for treating ordering in metallic solid solutions are basically inadequate if the two types of atoms differ appreciably in size: and (ii) an important quantity is ƒ A B , the degree to which A atoms are surrounded by B-type neighbours. This quantity determines the concentration dependence of the formation enthalpies of ordered phases in a binary system and makes it possible to rationalize their occurrence.

(1987). Diffusion bonding of glass to metals with reference to quartz-aluminium bonding. Welding International: Vol. 1, No. 6, pp. 544-547.

The formation and resulting mechanical strength of solid state metal-ceramic reaction bonds of alumina to platinum are investigated in terms of the effects of three main parameters — bonding temperature, time at temperature and contact pressure. Also the effect of the subsequent operating temperature on the bond strength is examined. An optimum bonding regime can be devised to create platinum-alumina bonds of optimum strength and durability, suitable for use in practical bonding applications.

Solid state bonding is genrally applied to joint of a dissimilar metal which is very difficult to bond by fusion welding techniques.In this paper a diffusion bonding of aluminum bronze containing Si to austenitic stainless steel has been investigated. The investigations were performed by both method of a direct bonding without insert metal and bonding with insert metals of Cu, phosphor bronze and Ni foils under a restrained condition or a constant bonding pressure, 0.94 MPa. The results obtained as follows; (1) The bonding strength in the insert metal bonding was higher than that in the direct bonding and it was the highest in case of using Ni insert metal among others in the bonding temperature below 890°C. A maximum strength of 410 MPa was obtained at 710°C. (2) In case of using Cu insert metal, the bonding sterngth was much lower comparing to other cases, especially lower than the case of using Ni in the low temperature below 950°C, however, in the temperature of 960°C both bonding strength became almost the same. (3) At the temperature of 960°C and higher than that, the optimum results were obtained with melted down phosphor bronze, it is considered that a liquid phase bonding occurred then. (4) In case of using Ni insert metal, the effect of thickness differences of insert metals ranging between 10 and 60μm on the bonding strength was not recognized extending over all of the bonding temperature used. On the other hand, in the Cu insert metal bonding, the bonding strength in the case of 10μm foil was higher than that of 100μm foil and the strength difference in both foils was from 50 to 100 MPa. (5) The tensile fracture occurred at the boundary interface between the two base metals in the case of the direct bonding, it occurred too in the case of insert metal bonding between aluminum bronze and the insert metals such as Ni or Cu. For phosphor bronze insert metal bonding fracture occurred respectively at three places which are the interfaces between aluminum bronze and the insert metal, between the insert metal and a diffusion layer produced in stainless steel side and between the diffusion layer and stainless steel.

One of the contributions to the enthalpy of formation ΔH of substitutional metallic solid solutions is the elastic energy due to atomic size mismatch between solute and solvent. Starting with a formula due to Eshelby and valid in the dilute regime, a multi-step process is derived which permits to generalize Eshelby's formula to the concentrated alloy regime. Miedema's chemical (liquid-like) contribution to ΔH is then added, and the final expression for δH is used to compute the free energy of formation of binary substitutional solid solutions of transition metals. L'energie elastique, due a la difference de grandeurs atomiques entre le solute et le solvant, est une des contributions a l'enthalpie de formation des solutions substitutionelles solides des metaux. A partir d'une formule de Eshelby, valable pour le regime dilue, nous presentom un processus en plusieurs etapes, lequel nous permet de generaliser la formule de Eshelby pour les alliages en regime concentre. Nous ajoutons alors a ΔH la contribution chimique (de type liquide) de Miedema; ainsi l'expression finale de ΔH est utilisee pour la computation des energies de formation des solutions solides substitutionelles binaires pour des metaux de transition.

A new model is developed to account for the anisotropy of the equilibrium surface composition of dilute alloys. The anisotropy is assumed to result from the existence of a distribution of different surface sites, each of which may possess a unique enthalpy of segregation. The model relies on the hypothesis that any given surface, with an orientation parallel to a plane having Miller indices (hkl), may be synthesized from atoms distributed among terrace, step, and kink sites. The types and densities of surface sites in a given (hkl) surface are evaluated by means of an existing microfacet notation An enthalpy of segregation for each type of site is then computed by the embedded atom method. Finally, a scheme is developed to evaluate an effective enthalpy of segregation for a surface composed of specified fractions of terrace, step, and kink sites. Model calculations of the effective enthalpy of segregation for a dilute nickel-gold alloy are presented in two limits, either in the regular solution approximation or with the inclusion of an empirical entropy of segregation. The results obtained are compared with those of other approaches which have been used to evaluate the anisotropy of surface composition.

The Coulomb-capture ratios of muons in the metallic solid solutions Au-Ag, Te-Se, Cd-Mg, Nb-V, and Cu-Ni have been measured via the muonic Lyman series intensities. In the case of Nb-V, targets of three stoichiometric ratios were investigated. The results do not agree with the per-atom ratiosA(Z/Z′) assumed to be equal toZ/Z′ (“Fermi-Teller law”) or (Z/Z′)7/6. They are better, but also not in general well, reproduced byA(Z/Z′)=Z1/3 ln(0.57Z)/[(Z′)1/3 ln(0.57 Z′)], deviations occuring in cases of different metallic radii.

A steady creep rate together with a review of the literature on diffusion measurements in beta phases of the alloys Ag-50 at.% Zn, Cu-25 at.% Al, Cu-14.4 at.% Sn and Cu-42.7 to 52 at.% Zn are incorporated in the Dorn equation in order to choose the effective diffusion coefficient D. The thermodynamic approach to the vacancy mechanism allows the introduction of a new 'segregation coefficient', in addition to the stationary, homogeneous and interdiffusion coefficients. This analysis is reinforced by the work of Menon and Copley (1975) on segregation in binary metallic solid solutions due to diffusional creep.

The planar bonding in graphite is interpreted in terms of the deformation density approach. The calculated ratio of the 100 and 110 structure factors is in good agreement with experimental results. This suggests possibly a general means of comparing bonding effects in structures where either the strength of the bonding or the atomic environment is similar and where the bonding parameters in one of the structures are known.