Chemical reactions and morphological stability at the Cu/Al2O3 interface

The microstructures of diffusion‐bonded Cu/(0001)Al₂O₃ bicrystals annealed at 1000 °C at oxygen partial pressures of 0.02 or 32 Pa have been studied with various microscopy techniques ranging from optical microscopy to high‐resolution transmission electron microscopy. The studies revealed that for both oxygen partial pressures a 20–35 nm thick interfacial CuAlO₂ layer formed, which crystallises in the rhombohedral structure. However, the CuAlO₂ layer is not continuous, but interrupted by many pores. In the samples annealed in the higher oxygen partial pressure an additional reaction phase with a needle‐like structure was observed. The needles are several millimetres long, ～10 µm wide and ～1 µm thick. They consist of CuAlO₂ with alternating rhombohedral and hexagonal structures. Solid‐state contact angle measurements were performed to derive values for the work of adhesion. The results show that the adhesion is twice as good for the annealed specimen compared to the as‐bonded sample.     

Study of seizure of coated and treated titanium alloy under fretting conditions

Titanium alloys are well known to present poor sliding behaviour and high wear values. Various coatings (soft thick coatings and thin hard coatings) and treatments have been tested to prevent such an occurrence under fretting conditions at high frequency of displacement (100 Hz). An original test apparatus, using an open-loop system, has been performed to directly display the phenomenon of seizure. No seizure was recorded at low load (6 N), while, at higher load (10 N), all samples undergo a more or less early seizure. The total sliding distance D₀ proved to be a pertinent parameter to study the seizure resistance. Furthermore, the results highlight that D₀ is linked to the total energy dissipated in the contact, E_dt, and reveal two distinct behaviours at low load, which suggest two distinct dissipating mechanisms of energy. The first trend can be connected with the plastic deformation and the trapping process of debris within the contact zone occurring on soft coatings. The second trend can be related to the higher debris ejection observed on hard samples. So, soft thick coating satisfies most of the chosen criteria except those of wear. In contrast, thin and hard coatings are not sufficient to totally protect the substrate but they are already able to efficiently reduce wear.     

High-resolution electron microscopy image simulation on a Cray 1S/2300 computer

High-resolution electron microscopy (HREM) image simulation by the multislice method has been implemented on a Cray 1S/2300 computer, allowing accurate full nonlinear image intensity calculations with possible sampling up to 2ⁿ × 2^m samples of the transmission function (n + m = 20). As examples of applications, images have been obtained from an interface in PbTiO₃ and of a small gold aggregate. HREM image simulation of perfect or faulted crystals can now be applied with reasonable computing times to problems involving a large number of atoms and thick or large supercells.     

Investigation on the impact behavior of Al2O3-SiC-MgO nanoceramic/metal laminated composite

Lightweight laminated composites containing a ceramic front layer and a metallic backing layer were used in order to protect people, moving equipment, and mobile vehicles from high velocity impact and the increased mobility of mobile vehicles. In this study, by adding10 vol% SiC and 500 ppm MgO nanoscale particles on the microstructure of Al ₂ O ₃ matrix and applying optimum sintering conditions, ceramic performance against high-speed projectile impact was improved. To perform this investigation, a number of target samples with two different types of front layers (alumina and Al ₂ O ₃-SiC-MgO nanocomposite ceramic) were produced. Impact tests were conducted on these samples using 7.62 mm projectiles with a velocity of 820 ± 15 m/s. The amount of bulge and bending of the backing layer caused by impact tests was measured. The results of the impact tests on the samples made of Al ₂ O ₃-SiC-MgO nanocomposite ceramics and alumina were also compared and analyzed. The results indicate that the substitution of Al ₂ O ₃-SiC-MgO ceramic layer — which is proffered in this paper — instead of pure alumina ceramic layer, decreases the areal-density of the samples by at least 30% and improves mechanical properties by about a 60% increase in flexural strength and 100% growth of the energy distribution factor, which impressively increases impact energy absorption.     

Adsorption of Water on Lubricated and Non Lubricated TiC Surfaces for Data Storage Applications

In this work we have studied the adsorption of water on TiC-coated quartz crystals to evaluate the use of TiC as a potential candidate for overcoats on magnetic media. It was observed that at room temperature the amount of adsorbed water onto thick sputtered TiC films, up to 20 nm in thickness, was similar to the amount of water adsorbed on standard amorphous 1.0–5.0 nm thick CHx films, which are currently used as protective overcoats on magnetic media. The sputtered TiC lubricated with Fomblin ZO3 in Vertrel XF solution also shows similar amounts of water adsorption as compared to unlubricated CH _x films. The amount of water adsorbed on TiC and CH _x films was measured in-situ by a quartz-crystal microbalance apparatus in an ultra-high vacuum chamber.     

Formation of tangential pre-stress as a residual stress and its influence on the tribological performance of nodular cast irons

Since any state of residual stress influences the service behavior of a material, it is of particular interest for engineers and designers to know its benefits to machine parts, and where it can be utilized successfully. From this point of view, mechanical tangential pre-stress as circumferential compressive residual stress has been investigated for wear performance. For this purpose, a thick walled cylinder specimen model was established as a tribo-element, and the force, which will form the desired tangential pre-stress representing residual stress, has been calculated by the rules of elasticity theory. In order to compare the effect of residual stress on the wear performance under dry and lubricated conditions, 0.8 R_e (R_e: unidirectional yield strength) were applied to the nodular cast iron (DDK-40, DDK-60) specimens. Wear test results have been evaluated in terms of two different stress levels, 0 R_e and 0.8 R_e, formed on the specimen.     

Elasticity solution for an axially compressed and encased cylindrical specimen

We present the solution of the linear elasticity equations governing the deformation of an elastic cylinder encased in a tube and subjected to uniform compression on the flat ends. The solutions for the stresses, strains, and displacements in the encased and compressed cylinder are all systematically determined from the basic solution of Lamé's classical elasticity problem of the long tube subjected to internal and external pressures. We first derive the general elastostatic analysis for an encased hollow cylinder, stress-free at the cavity, and later particularize the solution to a solid cylindrical specimen. The effective modulus E_eff of the encased sample is found to be a function of the bulk modulus k and Poisson's ratio ν of the material. E_eff differs from k except for nearly incompressible materials, where E_eff approaches the bulk modulus value. In the incompressible case, we also show how a load applied on the cylinder's flat ends is equivalent to, and can be replaced by, the same load acting on the curved surface. For compressible materials, a more general expression for E_eff is found that also accounts for the case deformation. These results explain the deformation of an axially compressed and encased cylindrical specimen tested in compressibility measuring devices such as those described by Matsuoka and Maxwell [Response of linear high polymers to hydrostatic pressure. Journal of Polymer Science 1958; 32:131–59]. The present analysis thus contributes to a better understanding of how this device works and to the interpretation of measurements taken with it.     

Study of the heating rate effect on the glass transition properties of (60 − x)V2O5–xSb2O3–40TeO2 oxide glasses using differential scanning calorimetry (DSC)

The glass-transition temperature (T_g) and crystallization temperature (T_Cr) have been determined for the system (60 − x)V₂O₅–xSb₂O₃–40TeO₂ with 0 < x < 10 (in mol%) using differential scanning calorimetry (DSC) at heating rates φ = 3, 6, 9 and 13 K/min. The effect of the heating rate and the Sb₂O₃ content on T_g is discussed. It was observed that the transition region shifts to higher temperatures when the measuring time is reduced (or, conversely, when the applied temperature rate is increased). Using differential scanning calorimetry, the compositional dependence of T_g has been determined and so, an empirical equation has been deduced which relates the glass-transition temperature with the Sb₂O₃ content.     

On the collapse of dented cylinders under external pressure

In this paper the reduction in the collapse pressure of long cylinders which have local dents is evaluated through a combination of experiment and analysis. A number of stainless steel tubes, with diameter-to-thickness ratios of approximately 33,24 and 19, were indented to various degrees with spherical indentors of two diameters. The geometry of each dent was recorded using an imperfection scanning system and the cylinders were subsequently collapsed under external pressure. Denting reduces the local collapse resistance of the cylinder. For larger dents the collapse pressure was found to approach the propagation pressure of the tube. Collapse was found to be relatively insensitive to the detailed geometry of a dent but to be critically dependent on the maximum ovalization of its most deformed cross section (Δ_0d). The collapse pressures of tubes with dents produced by indentors of different diameters could be well correlated through this measure of the dent geometry.The denting and collapse processes were simulated numerically using appropriately nonlinear elastoplastic shell analyses. Both steps of such simulations were shown to be in good agreement with experimental results for a broad variation of the parameters of the problem. The key role of the geometric parameter Δ_0d was exploited in order to generate a Universal Collapse Resistance Curve for dented cylinders. It was possible to show that the post-limit load response (P — Δ) of a cylinder, with a small but axially uniform initial ovality, provides a very good lower bound to the collapse pressures of the dented cylinders plotted against the dent parameter Δ_0d. The significance of this curve is that it can be used to estimate the reduction in the collapse pressure of a cylinder with any dent geometry from only one relatively simple measurement of the geometry of the dented section.     

Numerical investigation of cross-flow around a circular cylinder at a low-reynolds number flow under an electromagnetic force

The effect of the electromagnetic force (or Lorentz force) on the flow behavior around a circular cylinder is investigated by computation. Two-dimensional unsteady flow computation forR _e =10² is carried out using a numerical method of finite difference approximation in a curvilinear body-fitted coordinate system by solving the momentum equations including the Lorentz force as a body force. The effect of spatial variations of the Lorentz forcing region and forcing direction along the cylinder circumference is investigated. The numerical results show that the Lorentz force can effectively suppress the flow separation and oscillation of the lift force of circular cylinder cross-flow, leading to reduction of drag.     

Soft X-ray contact microscopy with nanosecond exposure times

High resolution (better than 20 nm) contact micrographs have been produced with exposure times of about a nanosecond. The illuminating source was a short-lived carbon plasma produced by focusing a single short (～1 ns) 100 J pulse from the Vulcan laser at the Rutherford Appleton Laboratory (RAL) to a 300 μm spot on a graphite target. This plasma emits strongly in the soft X-ray region, particularly at the CVI (3.37 nm) and CV (4.03 nm) lines. The specimens were behind a 100 nm thick Si₃N₄ window, at atmospheric pressure in an environmental cell. The images of diatoms recorded on X-ray resist showed features down to the limit of resolution of the SEM used to view the developed resist, which was about 20 nm.     

A Tribological Model for Chocolate in the Mouth: General Implications for Slurry-Lubricated Hard/Soft Sliding Counterfaces

We have investigated the rheological and lubrication properties of molten chocolate samples. To this end, a series of chocolate samples having various textural/compositional features have been prepared. The rheological properties of the chocolate samples are discussed in terms of the Casson model. The lubrication properties of the molten chocolate samples have been characterized by means of pin-on-disk tribometry. For the tribo-pairs, zirconia (ZrO₂) and poly(tetrafluoroethylene) (PTFE) have been used in all permutations for both slider (pin) and track (disk), providing the four tribo-pair combinations; ZrO₂/ZrO₂, PTFE/ZrO₂, ZrO₂/PTFE, and PTFE/PTFE. The results showed that both the rheological and lubrication properties of the chocolate samples are strongly influenced by the textural and compositional characteristics. The lubrication properties are further influenced by the choice of the tribo-pair. The different lubrication properties of the chocolate samples at different tribo-pairs are discussed in terms of particle behavior in the surrounding region of the inlet of the sliding tribo-pairs.     

Effect of laser textured dimples on the lubrication performance of cylinder liner in diesel engine

Laser surface texturing (LST) technique was utilised on a cylinder liner in a diesel engine. In order to analyse the effect of LST micro‐dimples on the lubrication and friction properties of cylinder liner–piston ring (CL–PR), we developed a new mixed lubrication model on the basis of the average Reynolds equation and asperity contacts equation. The model can consider the coupling effects between the surface roughness of non‐texturing regions and micro‐dimples and the synergistic effects of multi‐micro‐dimples. The results show that cylinder liner surface by LST can form effective hydrodynamic lubrication effect in most regions of the strokes, only near the dead points, the friction pair is in mixed lubrication state, asperity contact plays a major role in balancing the external load and the asperity friction force is obvious. The micro‐dimple parameters were optimised to obtain a better lubrication effect with the following optimised results: r_p = 30–60 µm, S_p = 0.2–0.4 and e = 0.03–0.1. Copyright © 2012 John Wiley & Sons, Ltd.     

Scanning Electron Microscopy (SEM) and Light Microscopy (LM)‐based Palyno‐morphological views of Solanaceae in Western Himalaya

In this study, plants belonging to family Solanaceae growing in Western Himalaya region have been observed palynologically under Light Microscope and Scanning electron microscope. Present investigation comprises of 10 genera and 23 species, namely, Atropa acuminata, Capsicum decoraticus, Capsicum frutescens, Cestrum aurantiacum, Cestrum diurnum, Cestrum nocturnum, Datura alba, Datura innoxia, Datura stramonium, Hyoscymus niger, Lycopersicon esculentum, Nicotiana rustica, Nicotiana tabacum, Petunia alba, Petunia hybrida, Solanum erianthum, Solanum melongena, Solanum miniatum, Solanum pseudocapsicum, Solanum surratense, Solanum tuberosum, Withania coagulans, Withania somnifera. Solanaceae is a eurypalynous family. Grains are usually Tricolporate and Tetracolporate, radially symmetrical, isopolar, prolate‐spheroidal to oblate‐spheroidal to oblate‐spheroidal to subprolate to per prolate or suboblate to oblate, size range: 8.55–72 μm, amb circular, semi‐angular or subangular, aperture drop‐type, labrum common‐type, exine usually 2 μm thick, nexine 1–1.5 μm thick. Tectum usually psilate, sexine reticulate, granulate or striato‐reticulate, with obscure pattern, sexine 1–2 μm thick, nexine 1–1.5 μm thick, and intine 0.5–1 μm thick. Most striking variation has been found in the shape class, aperture‐type, and tectal surface. Based on these characters, taxonomic keys have been made for correct identification of members in Solanaceae. However, the grains of this family are usually tricolporate and have direct relationship with certain members of the family Scrophulariaceae. Palyno‐morphological characters of family Solanaceae have been studied for the first time in Western Himalayan region of Pakistan. These palyno‐morphological characters are significant for identification of the members of family Solanaceae.     

Microstructure and electrical properties of NaNbO3-BaTiO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x) NaNbO3-xBaTiO₃ have been fabricated by a traditional ceramic sintering technique. The effects of BaTiO₃ (BT) synthesized by hydrothermal method on crystal structure, density, dielectric, piezoelectric, and electromechanical properties were investigated. Results show that the phase structure transforms from the orthorhombic phase to the tetragonal phase with the increase of the content of BT, and the two phases co-exist when 0.08<×⩽0.10. However, the optimum composition for (1 − x)NaNbO₃-xBaTiO₃ ceramics is 0.90NaNbO₃-0.10BaTiO₃. The 0.90NaNbO₃-0.10BaTiO₃ ceramics sintered at 1250°C have higher properties: piezoelectric constant d ₃₃ of 120 pC/N, dielectric constant ε_τ of 718, planar electromechanical coupling factor k _p of 24%, planar frequency N _d of 3 MHz·mm, and the mechanical quality factor Q _m of 138, respectively. The results show that the (1−x)NaNbO₃-xBaTiO₃ ceramics is one of the promising lead-free materials for high-frequency applications.     

Determination of diffusion controlled reaction rates at a solid/liquid interface using scanning electron microscopy

A high‐resolution method has been developed for the determination of localized values of interfacial reaction rate and mass transfer coefficient in aqueous solution. Scanning electron microscopy has been successfully applied to this problem through the measurement of electroplated film thickness formed under limiting current conditions. The method involves the calculation of local values of reaction rate via Faraday's laws and subsequent conversion of the data to absolute values of mass transfer coefficient. The technique has been verified in an undisturbed, turbulent flow regime (rotating cylinder electrode) through the use of Sherwood group dimensionless analysis. The resulting relationship shows comparable accuracy relative to electrochemical measurements. Favourable comparison has also been made with the generally accepted rotating cylinder correlation of Eisenberg, Tobias and Wilke. Differential rates of mass transfer to a single surface under conditions of disturbed flow have also been examined at a high spatial resolution using the stepped rotating cylinder electrode geometry. In this case, reaction rates have been measured as a function of circumferential distance within a recirculation zone situated immediately downstream of a backward‐facing step.     

Wear behavior of adaptive nano-multilayered AlTiN/MexN PVD coatings during machining of aerospace alloys

Machining of aerospace materials is one of the major challenges of modern manufacturing. Application of nano-multilayered AlTiN/Me_xN PVD coatings (where Me_x is a transition metal of V-VI groups of periodic table) to cemented carbide tooling results in a significant tool life improvement under conditions of cutting hard to machine alloys such as Ni-based Inconel 718 superalloy and Ti-based TiAl6V4 alloy. Microhardness and coefficient of friction of the coatings were measured during this experiment. Investigations of the coated tool life, wear behavior, chip formation (chip type and undersurface morphology) for cutting tools with nano-multilayered PVD coating were also performed. Morphology of worn tools has been studied using SEM and EDX. This study will show that metallurgical design of the nano-multilayered coating should be tailored to its application. To achieve better tool life when machining Inconel 781, adaptive nano-multilayered AlTiN/MoN coating is recommended, whereas a AlTiN/VN coating is better suited to machining TiAl6V4 alloy. A driving force behind selecting these coatings was a noticeably lower coefficient of friction at elevated temperatures.     

Features of Electromagnetic-to-Acoustic Conversion in Thermally Processed 30KhGSA Steel

The paper reports on an experimental investigation of EMAC parameters characterizing the 30KhGSA steel as functions of temperature in samples processed at various tempering temperatures T _tem. The EMAC efficiency varies with temperature in a different manner in samples processed at different tempering temperatures. The character of correlations among EMAC parameters as functions of T _tem remains largely the same over the temperature range between the room temperature and 200°C. Features of EMAC have been studied in the regions of domain wall displacement and domain rotation. We have found a parameter that is a derivative of the E-effect and correlates with the impact toughness.     

Automatic discontinuous 2 × 1 transmission lines with sections of different productivity (q1 > q2), in the case of simultaneous failures of the sections and the bunker

An analytical solution is derived for automatic discontinuous 2 × 1 transmission lines with sections of different productivity (q ₁ > q ₂), in the case where simultaneous failures of the sections and the bunker are taken into account. The solution provides the basis for improvements in the design of such lines. The mathematical principles that have been developed evidently permit the analysis of any 2 × 1 transmission lines.     

Design of interference fits via finite element method

Studies of interference fits in ring gear-wheel connections show that the traditional design method based on thick-wall cylinder theory has some limitations. Application of the finite element method (FEM) for the three-dimensional stress analysis of interference fitted connections gives more complete and accurate results than the traditional method. An improved design method utilizes two safety factors, λ_s and λ_p, providing a new approach for evaluating the quality of interference fits. A tolerancing method utilizing the I_max and I_min curves provides a quantitative guideline for interference fit design. The selective assembly method combined with the FEM-based method for interference fit design provides an effective approach to achieve more reliable interference-fitted connections and more precise assembly with lower manufacturing cost.