parameters that govern the life of metallic materials under conditions of fretting fatigue may be divided into two broad categories. The first category concerns the material properties (e.g., yield strength, elastic modulus, and surface roughness) while the second concerns the externally imposed loading conditions and contact geometry. The two in-contact materials may either stick, slip, or stick-slip (i.e., there is a slip and a stick region on their interface) against each other. It has been shown that the fatigue life reduction is highest under partial slip. The objective of the present research effort is to develop a model that enables the prediction of the particular fretting fatigue regime (i.e., slip, stick, or mixed). The parameters that affect the fretting fatigue life of metallic components were identified and integrated into a model, which allows the prediction of the interfacial contact conditions. The model was first used to identify the sensitivity of the fretting fatigue regimes upon the materials and external, and geometrical parameters. Experimental results concerned with the fatigue life were plotted on the fretting maps; the fretting fatigue regimes indicated by the latter enabled the interpretation of the experimental data.

A polymer-coated glass fiber with a low-modulus coating at the ends is considered. The objective of the analysis is to find out if there is sufficient incentive to use such a dual coating system for lower interfacial thermally induced stresses. These are due to the different coefficients of thermal expansion (contraction) of the dissimilar materials in the trimaterial structure. The study is restricted to the evaluation of the shearing stresses only and is based on a simplified strength-of-materials model, rather than on a rigorous theory-of-elasticity method. Such a approach seems to be justified, since the most accurate predictions of the magnitude and the distribution of the induced stresses are beyond the scope of this analysis. On the basis of the calculated data, we conclude that there is a definite incentive for employing a bimaterial coating system, in which “conventional” (high modulus) polymeric material is used in the midportion of the fiber, while a low-modulus material (typically, with a higher coefficient of expansion) is applied at its ends. Such a system could be recommended, when there is a need to bring down the interfacial stresses, and the possible increase in the manufacturing cost is not viewed as an obstacle.

Open cell periodic metal truss structures can exhibit significantly higher stiffnesses and strengths than stochastic cellular metal structures of the same relative density while still providing high mechanical energy absorption and efficient heat exchange opportunities. Here, a potentially inexpensive textile-based approach to the synthesis of periodic metal microtruss laminates is reported. The process consists of selecting a wire weave, laying up the mesh and joining using a transient liquid phase. Example structures constructed from nichrome (Ni–24Fe–16Cr) wire cloth were made and tested. These exhibited a linear dependence of stiffness and strength upon relative density, absorbed large amounts of mechanical energy, and showed good potential for efficient heat exchange.

In this paper it is shown that the initial stages in the laser-induced roughening in silicon is independent of the atmosphere used, whether it is Ar, vacuum, or SF6. It is also shown that the morphology that results after a few hundred laser pulses strongly depends on the crystallographic orientation of the surface. The morphological features that appear in this first stage have been related to the nature of the solidification process that follows laser melting. A second stage in the roughening process with a dramatic change in morphology takes place when a surface with deep depressions and hills is further irradiated in SF6. Very deep etching occurs in the depressions promoting the formation of microholes that with further irradiation lead to cone formation. It is further shown that the distance between microholes is equal to the distance between the depressions that formed as the initial perturbations developed. Then the wavelength of the initial perturbation and by extension the distance between microholes has been estimated.

Controlled pyrolysis of polymer ceramic precursors provides a new way of obtaining silicon nitride ceramics with high creep resistance. In this study, crack-free bulk amorphous Si–N–C materials were produced by warm-pressing followed by pyrolysis or alternatively by prepyrolysis and binding followed by pyrolysis. Amorphous compacts were then heat-treated at different temperatures to promote crystallization. High-resolution electron microscopy revealed that, at about 1650 °C, silicon nitride/silicon carbide nanocomposites with a high degree crystallinity can be achieved with grain sizes of about 30 nm. Aside from heterogeneous crystallization, which is closely related to gaseous phase reactions that happen along outer or inner surfaces, homogenous crystallization is responsible for crystallization of the bulk material. Although a certain amount of amorphous Si–N–C usually remains in intergranular regions, clean boundaries free of amorphous interlayers can be observed between grains when they come into contact.

Sol-gel hybrid glass films doped with benzildimethylketal (BDK) were prepared from [(methacryloxy)propyl]trimethoxysilane, methacrylic acid, and zirconium n-propoxide. Polymerization of methacryl groups and polycondensation of alkoxides by UV illumination and baking were observed using Fourier-transformed infrared spectroscopy. Polymerization kinetics and refractive index increase depend on UV illumination time. The refractive index increase is sensitive to BDK concentration and agrees well with photodecomposition of BDK. Thus, it is found that the refractive index increase is made by incorporation of the radicals produced by photodecomposition of BDK in the network as well as polymerization of methacryl groups.

Nanocrystalline Inconel 625 alloy, with a uniform distribution of grains, was synthesized using cryogenic mechanical milling. Microstructures of the powder, cryomilled for different times, were investigated using transmission electron microscopy (TEM), scanning electron microscopy, and x-ray diffraction. The results indicated that both the average powder particle size and average grain size approached constant values as cryomilling time increased to 8 h. The TEM observations indicated that grains in the cryomilled powder were deformed into elongated grains with a high density of deformation faults and then fractured via cyclic impact loading in random directions. The fractured fragments from the elongated coarse grains formed nanoscale grains. The occurrence of the elongated grains, from development to disappearance during intermediate stages of milling, suggested that repeated strain fatigue and fracture, caused by the cyclic impact loading in random directions, and cold welding were responsible for the formation of a nanocrystalline structure. A high density of mechanical nanotwins on {111} planes was observed in as-cryomilled Inconel 625 powders cryomilled, as well as in Inconel 625 powder milled at room temperature, Ni20Cr powder milled at room temperature, and cryomilled pure Al.

Potassium lithium niobate (KLN) powders and thin films were prepared from metalorganic compounds through the sol-gel process. A homogeneous and stable KLN precursor was synthesized by mixing the metal ethoxides. Powder gels were obtained through the hydrolysis of the solution by exposing it to the ambient atmosphere. Thin films were deposited on Si, SiO2/Si, and fused quartz by a spin coating technique. The pyrolysis and crystallization of KLN powders and films were investigated through the methods of differential thermal analysis, thermogravimetric analysis, x-ray diffraction, and Raman scattering spectroscopy. The results revealed that both KLN powders and films could crystallize into a tetragonal tungsten–bronze-type phase with appropriate annealing. Optical studies indicated that the films were highly transparent in the visible–near-infrared wavelength range and could support optical modes.

c-Axis-oriented (Hg0.9Re0.1)Ba2CaCu2Oy thin films were grown on the (100) plane of SrTiO3 substrates by a so-called two-step process. Transmission electron microscopic observation revealed that, in the film annealed under a higher temperature, some steplike regions appeared at the top layer of SrTiO3 substrate. High-resolution transmission electron microscopic images showed that the lattice parameters in these regions are about 4.05–4.15 Å, being longer than the lattice parameter of SrTiO3. It is supposed that a chemical reaction occurred in these regions, and a phase of (Bax,Sr1−x)(Cuy,Ti1−y)O3δs was formed by partially substituted Ba for Sr and Cu for Ti.

Lead zirconate titanate (PZT) thin films were deposited in a reactive argon/oxygen gas mixture by radio-frequency-magnetron sputtering. The use of a metallic target allows us to control the oxygen incorporation in the PZT thin film and also, using oxygen 18 as a tracer, to study the oxygen diffusion in the thin films. Electrical properties and crystallization were optimized with a 90-nm PZT thin film grown on RuO2 electrodes. These PZT films, annealed with a very modest thermal budget (550 °C) show very low leakage current densities (J = 2 × 10−8 A/cm2 at 1 V). In this article we show that a strong correlation exists between the oxygen composition in the PZT film and the leakage current density.

A Hf69.5Al7.5Ni11Cu12 metallic glass was prepared by a single roller melt-spinning method, and the crystallization process was studied by x-ray diffraction, differential scanning calorimetry, and transmission electron microscopy. The metallic glass crystallizes through three exothermic reactions. The low-temperature exothermic reaction corresponded to the precipitation of an icosahedral quasicrystalline phase. Further annealing at higher temperature led to the decomposition of the icosahedral quasicrystalline phase to other stable crystalline phases, indicating that the precipitated icosahedral quasicrystalline phase was in a metastable state. The crystallization process of the present alloy was compared with that of other Hf–Al–Ni–Cu alloys, and the reason for the precipitation of the icosahedral quasicrystalline phase was discussed.

Pulsed heating experiments that measure high-temperature thermophysical properties using pyrometric measurement of the temperature–time history of metal specimens rapidly heated by passage of electric current have a 30-year history at the National Institute of Standards and Technology. In recent years, efforts have been made to move beyond the limitations of the standard technique of using costly, black-body geometry specimens. Specifically, simultaneous polarimetry measurement of the spectral emissivity has permitted study of sheet and wire specimens. This paper presents the results of two efforts to expand beyond the macroscopically monolithic, single-phase materials of all previous studies. In the first study the melting temperatures of coatings, including Ti and Ti(Al) alloys, deposited on higher melting Mo substrates are measured. In the second study the melting temperatures of substrates, Ti and Cr, covered by higher melting W and Mo coatings are measured.

Y0.25Zr0.75O2−x and Y0.5Zr0.5O2−y phases, with L12- and L10- like cation-ordered structures, respectively, have been found in ZrO2–Y2O3 ceramics in both the sintered and annealed states. High-resolution electron microscopy, energy-dispersive x-ray spectroscopy and computer simulation have been used to reveal the presence of the phases. The formation of Y0.25Zr0.75O2−x and Y0.5Zr0.5O2−y phases was initiated during the sintering procedure and developed with the increase in annealing temperature and time. Segregation of yttrium, which was prevalent in different regions even within one grain, induced the formation of Y0.25Zr0.75O2−x and Y0.5Zr0.5O2−y phases.

A quantitative texture analysis, including calculations of the orientation distribution function, is applied to investigate the preferred orientation of β–Si3N4 in a fine-grained material containing almost equiaxed grains that has been hot-pressed, annealed, and plane-strain compressed. The results show that (i) plane strain compression can produce relatively strong textures that were dependent on the compressive strain; (ii) the basal plane of hexagonal β–Si3N4 was normal to the hot-pressing direction for the hot-pressed and annealed samples, whereas it was parallel to the stress axis for deformed samples; and (iii) the mechanisms for texture development were preferred grain growth for the annealed sample and grain rotation for the hot-pressed and deformed samples, respectively.

A preceding study of contact damage in a bilayer system consisting of a porcelain coating on a stiff Pd-alloy substrate is here expanded to investigate the role of substrate modulus and hardness. Bilayers are made by fusing the same dental porcelain onto Co-, Pd-, and Au-alloy metal bases. Indentations are made on the porcelain surfaces using spheres of radii 2.38 and 3.98 mm. Critical loads to initiate cone fracture at the top surface of the porcelain and yield in the substrate below the contact are measured as a function of porcelain thickness. Radial cracks form at the lower surface of the coating once the substrate yield is well developed. By virtue of its controlling role in the metal yield process, substrate hardness is revealed to be a key material parameter—substrate modulus plays a secondary role. A simple elasticitybased analysis for predetermining critical loads for a given brittle/plastic bilayer system is presented.

There is ample experimental evidence demonstrating space charge segregation in acceptor-doped BaTiO3. However there is still some controversy regarding donor-doped BaTiO3. Considering the space charge segregation theory in BaTiO3, the calculated driving force for space charge segregation is larger in acceptor-doped cases than in donor-doped cases. This result explains why acceptor segregation can be easily detected. However, a significant concentration of donors can also cause donor segregation. In donor and acceptor codoped BaTiO3, the grain sizes are very small, and donor segregation can be detected for compositions inducing a large space charge potential. In addition, in compositions that induced a small space charge potential, the grain sizes are very large, and donor segregation is not detected, although the total doping concentration is larger. This phenomenon means that donor segregation is caused by the space charge potential rather than misfit strain energy.

The modified Pechini method using ethylenediaminetetraacetic acid as a chelating agent to prepare Ba2Ti9O20 is reported. The resin precursors were prepared and heated at 700 to 1200 °C in air, and x-ray diffraction was used to determine the phase transformations as a function of temperature. Single-phase Ba2Ti9O20 was obtained at 1200 °C for 2–6 h, without the need of prolonged heat treatment time. The process was simple and easy to control: low-temperature conditions or a protective atmosphere was not needed. Differential thermal analysis, thermogravimetric analysis, and Raman spectroscopy were used to characterize the precursors and derived oxide powders. Details of the synthesis and characterization of the resultant products were given.

Microscale sandwich beams with cell diameters and wall widths down to 150 and 15 μm, respectively, and having both metallic and polymer/metal cores were produced through fabrication methods that combined photolithography and electrodeposition. Various core structures were used, including some with negative Poisson's ratio. The bending response was investigated and compared with beam-theory predictions. Most of the cores evaluated had sufficient shear stiffness that the bending compliance was relatively high and dominated by the face sheets. Two of the core configurations were “soft” and exhibited behavior governed by core shear. The relative dimensions of the cores evaluated in this study were far from those that minimize the weight, because of fabrication constraints. The development of an ability to make high-aspect ratio cores is an essential next step toward producing structurally efficient, lightweight microscale beams and panels.

Interface structure and solute-segregation behavior in the high-strain-rate superplastic SiCp/2124 and SiCp/6061 Al composites were investigated. Evidence for interfacial reaction between reinforcement and Al matrix, which was evident in the superplastic Si3N4p,w/2124 Al and Si3N4p,w/6061 Al composites, could not be detected in the current SiC-reinforced Al composites. Instead, strong solute segregation was observed at SiC/Al interfaces. Extensive formation of whiskerlike fibers was observed at the fractured surface of tensile samples above the critical temperature where particle weakening began to be seen. These results suggest that partial melting occurs at the solute-enriched region near SiC interfaces and is responsible for the particle weakening. The absence of reaction phase in the SiC-reinforced composite may explain why no endothermic peak for partial melting appears in its differential scanning calorimetry curve and why its optimum temperature for superplasticity is generally higher than that of the Si3N4-reinforced composite.

The present work is concerned with the methods of simulation of data obtained from depth-sensing submicron indentation testing. Details of analysis methods for both spherical and Berkovich indenters using multiple or single unload points are presented followed by a detailed treatment of a method for simulating an experimental load–displacement response where the material properties such as elastic modulus and hardness are given as inputs. A comparison between simulated and experimental data is given.