The thermal diffusivities (D) of porous α–Al2O3 specimens prepared from nano-size γ–Al2O3 powder and from conventional submicrometer-size alumina powders were measured at room temperature, and the thermal conductivity (κ) was calculated from D. Plots of κ versus the volume fraction of porosity (P) showed that the data from both sets of samples followed similar linear curves. Similarly, data of Vickers hardness versus P obtained from the same specimens also followed a single linear curve. The good correlation of thermal diffusivity with P suggests that grain boundaries have a lesser effect on thermal transport than porosity.

Strontium bismuth niobate vanadates, SrBi2 (VxNb1-x)2O9 (with 0 ≤ x ≤ 0.1), were prepared by reaction sintering of powder mixtures of constituent oxides. With partial substitution of niobium by vanadium cations (up to 10 at.%), the single-phase layered perovskite structure was preserved, and the sintering temperature of the system was significantly lowered (∼200 °C). The incorporation of vanadium into the layered perovskite structure resulted in a shift of the Curie point to higher temperatures from 435 to 457 °C, with 10 at.% vanadium doping, and an increase in dielectric constant from ∼700 to ∼1100, with 10 at.% vanadium doping, at their respective Curie points. The remanent polarization increased from ∼2.4 to ∼8 µC/cm2, while the coercive field decreased from ∼63 to ∼45 kV/cm with 10 at.% V5+ doping.

Elemental germanium was mechanically milled with magnesium oxide with the intention of forming disperse nanoparticulate germanium in a soluble matrix. The crystallite size was determined by x-ray diffraction (XRD) and Raman spectroscopy using a phonon confinement model. The crystallite size was found to decrease exponentially with milling time; however, the size determined by XRD was typically five to ten times greater than that by Raman. This was attributed to the presence of two separate crystallite sizes, which were averaged when using the Scherrer equation for the XRD data. Sonication of the powder resulted in the breakup of >20 μm aggregates into individual particles of approximately 40 nm. These particles are thought to compose a single crystal core with a crystallite size of approximately 28 nm surrounded by a layer of smaller crystallites (approximately 5 nm), which showed quantization during Raman spectroscopy. Separation of the germanium from the magnesium oxide was readily achieved using a simple acid leach, although some oxidation of germanium was evident when using an aqueous leach.

A novel and simple microwave-assisted combustion procedure for the synthesis of a number of technologically important metal nitrides was demonstrated. The method involves the combustion reaction of a porous metal powder compact with N2 gas in the microwave field and provides phase-pure metal nitride products (consisting of fine particles, fibers, and whiskers) within minutes. The ignition and combustion temperatures of the reaction were found to vary as a function of compaction pressure. The microwave-prepared nitrides were characterized using x-ray diffraction, scanning electron microscopy energy dispersive spectroscopy, thermogravimetric analysis, and infrared spectroscopy. The present microwave-assisted hybrid-heating procedure allows the preparation of nitrides with good crystallinity, structural uniformity, and phase purity, and appears to have general applicability for the preparation of metal nitrides (using the respective metals or even their oxides).

Aluminum-borate (AlBO) whisker-reinforced AA6061 composite fabricated by squeeze casting was subjected to both tensile and creep investigations. The whisker exhibited a significant reinforcing effect on as-extruded AA6061, but not for T6-treated specimen. The yield strength of the composite decreased slightly after T6 treatment. This was caused by the degradation of the whiskers and the microcrack initiation. The incorporation of the AlBO whisker into the AA6061 improved the creep resistance of the alloy by several orders of magnitude. Moreover, the composite exhibited higher values of apparent stress exponent and apparent activation energy for both the static and cyclic creep. Finally, cyclic creep retardation behavior was observed for both reinforced and unreinforced AA6061.

An ongoing goal of multilayer capacitor research is to lower the firing temperature of the dielectric. This paper gives a detailed study of sintering BaTiO3 with LiF flux, which lowers the firing temperature through liquid-phase sintering. A detailed set of experiments is discussed concerning microstructural evolution and corresponding dielectric properties under a number of processing variables, including amount of LiF, sintering temperature, and particle size. Different scales of chemical inhomogeneity were observed in this system, which reflect two underlying mechanisms: solution reprecipitation with limited grain growth at low temperatures, which resulted in distinct core–shell structures, and flux volatility, which gave rise to microscopic chemical inhomogeneity at higher sintering temperatures.

Co90P10 amorphous microtubes with thickness ranging from 2 to 19 μm were electrodeposited onto Cu wire substrates. Samples exhibit radial magnetic anisotropy as deduced from hysteresis loops and magnetic force microscopy imaging. These microtubes show quite noticeable giant magnetoimpedance effect (GMI) with amplitude depending on layer thickness and frequency. The hysteresis in the GMI curves is small, which can be ascribed to the radial anisotropy. Such small hysteresis is of importance for technological applications.

Material damage caused by fretting wear is of significant concern in many engineering applications. This paper describes the design and performance of a new machine for the laboratory investigation of fretting wear under oscillating normal force (fretting mode II). The test machine uses an electromagnetic actuator to impose an oscillating normal force between the contacting bodies at a constant force amplitude over a wide range of frequencies. The principle of the actuation mechanism and the fretting wear induced with this particular wear test configuration are outlined in detail. Normal force and electrical contact resistance were measured on-line during fretting mode II wear tests. The performance of the wear test machine is illustrated by data obtained for different materials combinations, namely, hard materials, such as high-speed steel and (Ti,Al)N coatings oscillating against alumina ball counterbodies, and soft materials, such as a tin coating oscillating against the same. In general, wearing of the counterbodies was observed in the slip region. It has been observed that hard coatings and bulk ceramics are prone to fretting fatigue cracking. The evolution of electrical contact resistance in the case of the self-mated soft tin coatings tested under fretting mode II conditions is also reported.

We recently proposed a theory of mechanism-based strain gradient (MSG) plasticity to account for the size dependence of plastic deformation at micron- and submicronlength scales. The MSG plasticity theory connects micron-scale plasticity to dislocation theories via a multiscale, hierarchical framework linking Taylor's dislocation hardening model to strain gradient plasticity. Here we show that the theory of MSG plasticity, when used to study micro-indentation, indeed reproduces the linear dependence observed in experiments, thus providing an important self-consistent check of the theory. The effects of pileup, sink-in, and the radius of indenter tip have been taken into account in the indentation model. In accomplishing this objective, we have generalized the MSG plasticity theory to include the elastic deformation in the hierarchical framework.

The effect of poling field on the photocurrent was investigated in (Pb0.85La0.15)TiO3 and BaTiO3 ceramics. Non-steady-state photovoltaic current and no pyrocurrent on cooling were observed in both poled ceramics. The maximum behaviors were obtained at the poling field of 1.5 kV/mm. They were explained in terms of the photoinduced reversible and irreversible increases in the remanent polarization resulting from the space charge field, which was established by electrons trapped at grain boundary during illumination. No pyrocurrent on cooling was responsible for the reversible increase of the remanent polarization. The photoinduced irreversible increase of the remanent polarization, i.e., photodomain effect, was confirmed using the acoustic emission technique.

Layered MnPS3 and CdPS3 powders were used to prepare M1−xK2xPS3/poly(ethylene glycol) (PEG) and M1−xK2xPS3/poly(vinyl pyrrolidone) (PVP) (M = Cd, Mn) intercalation nanocomposites. The structure of these compounds was studied by x-ray diffraction. The host layers in Cd0.8K0.4PS3 (PEG)2.0 and Mn0.8K0.4PS3(PEG)2.0 nanocomposites were 3-dimensional crystals with a monoclinic unit cell. The in-plane spacings were slightly expanded from original monoclinic MPS3 (0.2% for CdPS3 and 0.5% for MnPS3), while the inter-layer spacing was expanded by 8.87 Å for Cd0.8K0.4PS3(PEG)2.0 and 8.86 Å for Mn0.8K0.4PS3(PEG)2.0. The Cd0.8K0.4PS3(PVP)1.1 and Mn0.8K0.4PS3(PVP)1.1 nanocomposites, on the other hand, had an expanded interlayer spacing of about 30 Å and the diffraction patterns contained only (00l) and (hk0) peaks, and no mixed (hkl) peaks were observed. The (hk0) peaks were 2-dimensional, with strongly asymmetric line shapes, and there was excellent agreement with pattern calculations for single molecular layers. This demonstrated that the host layers in Cd0.8K0.4PS3(PVP)1.1 and Mn0.8K0.4PS3(PVP)1.1 nanocomposites were tubostratically stacked layered systems.

This paper describes experimental measurements of the linear viscoelastic behavior of the surface of low-density (LD) polyethylene in contact with a pyramidal Berkovich diamond indenter. The experiments were carried out at two different temperatures, 15.9 and 27.2 °C, between frequencies of 0.1 and 800 Hz. Using the shift of the loss tangent between the two temperatures at frequencies lower than 20 Hz and an Arrhenius equation, an activation energy of 105 ± 2 kJ/mol was obtained. This value is in good agreement with the bulk value of the a relaxation of LD polyethylene reported in the literature.

The microstructures of β-SiC nanorods synthesized by hot-filament chemical vapor deposition were studied in detail by high-resolution electron microscopy. Two distinct types of nanorods were identified. The longer nanorods (lengths > 0.1 mm) contained globules at their tips and a relatively low density of stacking faults perpendicular to their [111] growth direction. It was also observed that SiC nanorods that grew along [100] direction contained no planar defects. Meanwhile, Ni was found to be an effective catalyst for SiC nanorod growth. The short nanorods (lengths < 50 nm), which contained no globules at their ends, can grow along [111], [100], or [112] direction. The growth of these nanorods was interpreted by a two-dimensional vapor–solid mechanism.

A refractory silicon nitride joint, which contains β–Si3N4 grains and grain boundary amorphous phase in the joined layer, was developed with the aid of a ceramic adhesive based on the system Si3N4–Y2O3–SiO2–Al2O3. The similarity in chemistry and microstructure between the parent ceramic and the joint zone indicates that the joining mechanism is the same as that involved in the sintering of Si3N4. The resultant joint exhibits a high bond strength of 550 MPa at 25 °C and retains a strength of 332 MPa at 1000 °C. Post-joining hot-isostatic pressing was applied to strengthen the joint, resulting in increased strengths of 668 MPa at room temperature and 464 MPa at 1000 °C.

The crystallization mode of the Zr–Al–Ni–Cu amorphous alloys changed from a single stage to become two stages by the addition of Ag or Pd, and the first-stage exothermic reaction was found to result from the precipitation of nanoscale icosahedral particles with a size of 20 to 50 nm. The precipitation took place by high nucleation and low growth rates in a polymorphous mode for the Ag-containing alloys, and a diffusioncontrolled mode for the Pd-containing alloys. The nanoscale mixed structure alloys exhibited improved strength and ductility as compared with the corresponding amorphous single-phase alloys. The findings of the dispersion strengthening as well as the dispersion ductilization gave a future opportunity to fabricate a new bulk nonequilibrium phase alloy by use of the new phenomenon.

Al2O3 powders with four different particle sizes were densified using a spark plasma sintering (SPS) apparatus under three different sintering conditions: holding time, heating rate, and mechanical pressure. The Al2O3 powder compact sintered at a higher heating rate produced a sample with a higher density and a fine-grained microstructure, while abnormal grain growth and a lower density resulted when a lower heating rate was applied, though the sintering temperature and holding time were the same in both cases. This revealed that rapid sintering by SPS was effective for promoting the densification of the powder. However, the powder with a coarse particle size was hard to sinter at a higher heating rate. Microstructural observation revealed that the edge part was denser than the inside of the sample when the holding time was short. Increasing the holding time made it possible for the inside to be sintered almost as dense as the edge part. Mechanical pressure was found to enhance densification of the Al2O3 powder. On the basis of these results, the SPS process is discussed.

Composite ceramics with compositions within the ZnO–NiO–TiO2, ZnO–MgO, and ZnO–Ln2O3 (Ln = Nd, Sm) systems were found to exhibit an anomalous positive temperature coefficient of electrical resistivity (PTCR) effect. The investigations revealed, that in all cases when the PTCR effect was identified, the composite ceramics were found to be composed of phases with different electrical resistivities and linear thermal expansion coefficients. Thermal mismatch between the phases in the composites leads to a disconnection of the grains of the low resistivity constituent phase on account of the high thermal expansion of the other high resistivity constituent phase, resulting in a PTCR effect.

Residual stresses in sputter-deposited Cu/Cr multilayers and Cu and Cr single-layered polycrystalline thin films were evaluated by the substrate curvature method. The stresses in the multilayers were found to be tensile and to increase in magnitude with increasing layer thickness (h) to a peak value of ∼1 GPa for h = 50 nm. For h > 50 nm, the residual stress decreased with increasing h but remained tensile. The same trends were observed in single-layered Cu and Cr thin films, except that the maximum stress in Cu films is 1 order of magnitude lower than that in Cr. Transmission electron microscopy was used to study the microstructural evolution as a function of layer thickness. The evolution of tensile growth stresses in Cr films is explained by island coalescence and subsequent growth with increasing thickness. Estimates of the Cr film yield strength indicated that, for h ≥ 50 nm, the residual stress may be limited by the yield strength. Substrate curvature measurements on bilayer films of different thicknesses were used to demonstrate that a non-negligible contribution to the total stress in the multilayers arises from the interface stress.

Nanopowders of amorphous silicon nitride were densified and sintered without additives under ultrahigh pressure (1.0–5.0 GPa) between room temperature and 1600 °C. The powders had a mean diameter of 18 nm and contained ∼5.0 wt% oxygen that came from air-exposure oxidation. Sintering results at different temperatures were characterized in terms of sintering density, hardness, phase structure, and grain size. It was observed that the nanopowders can be pressed to a high density (87%) even at room temperature under the high pressure. Bulk Si3N4 amorphous and crystalline ceramics (relative density: 95–98%) were obtained at temperatures slightly below the onset of crystallization (1000–1100 °C) and above 1420 °C, respectively. Rapid grain growth occurred during the crystallization leading to a grain size (>160 nm) almost 1 order of magnitude greater than the starting particulate diameters. With the rise of sintering temperature, a final density was reached between 1350 and 1420 °C, which seemed to be independent of the pressure applied (1.0–5.0 GPa). The densification temperature observed under the high pressure is lower by 580 °C than that by hot isostatic pressing sintering, suggesting a significantly enhanced low-temperature sintering of the nanopowders under a high external pressure.

Mullite-based composites can be made by an in situ reaction process using silica-coated alumina (SCA) powder as a mullite precursor. In this paper we present the combined effects of zirconia and premullite seeds on the crystallization process and microstructure development. When zirconia is added without seeding, mullite formation proceeds through the formation of transient zircon. This phase provides a lower energy barrier for mullite nucleation and thus lowers the mullitization temperature. The presence of yttria as a stabilizer in zirconia reduces the activation energy for zircon formation and thus promotes the transient reaction. The addition of premullite seeds results in the nucleation of mullite from alumina and silica, and zircon does not form. At low seeding levels mullitization remains nucleation-controlled; however, once the seeding level exceeds 1–2%, this is no longer the case.