The surface of Zr41.25Ti13.75Cu12.5Ni10.0Be22.5, a bulk metallic glass prepared by RF induction melting, has been imaged using atomic force microscopy. The untreated surfaces were very smooth; features were no higher than 3 nm over a 10 × 10 μm region, comparable to many polished surfaces. Two types of microstructure were also observed; periodic striations forming either a striped or a checkered structure were present, with wavelengths between 1 and 2 μm, and amplitude of approximately 2 nm; in other cases, “cracked mud”-like patterns were observed. These microstructures could be related to strain-induced surface roughening; preliminary calculations are presented that are consistent with this hypothesis.

Competitive gas-solid reactions have been observed during high-energy ball milling of zirconium metal powder under an ammonia atmosphere at room temperature. The milling processes were investigated by monitoring pressure changes and subsequently analyzing milled powders with x-ray diffraction, thermal analysis, and elemental composition analysis. It is shown that during an early stage of milling, while the pressure is decreasing, a hydridation reaction predominates and leads to the formation of ZrH2 phase. During further milling the pressure increases again, and corresponds to a nitridation reaction between ZrH2 and available nitrogen (either excess NH3 or incorporated nitrogen in the powder) to form ZrN. Hydrogen gas is liberated and complete conversion to ZrN occurs after prolonged milling. The above reaction sequence was confirmed by the nitridation reaction of ZrH2 ball milled in NH3 atmosphere.

A new corrosion resistant coating, being designed for possible replacement of chromate conversion coatings on aluminum alloys, was investigated for composition, structure, and solubility using a variety of techniques. The stoichiometry of the material, prepared by immersion of 1100 Al alloy into a lithium carbonate-lithium hydroxide solution, was approximately Li2Al4CO3(OH)12 · 3H2O. Processing time was shown to be dependent upon the bath pH, and consistent coating formation required supersaturation of the coating bath with aluminum. The exact crystal structure of this hydrotalcite material, hexagonal or monoclinic, was not determined. It was shown that both the bulk material and coatings with the same nominal composition and crystal structure could be formed by precipitation from an aluminum supersatured solution of lithium carbonate.

La0.5Sr0.5CoO3 (LSCO) thin films have been deposited on (100) MgO substrates using pulsed laser ablation-deposition (PLAD). The crystallographic orientation of LSCO was found to be dependent on the surface treatment of (100) MgO prior to deposition. PLAD deposition parameters were optimized to yield LSCO films with an RMS surface roughness of 40–50 Å. A smooth surface morphology was reproduced as long as the oxygen content of the LSCO target was preserved. Otherwise, “splashing” occurred which resulted in the transfer of condensed particles from molten spherical globules of LSCO from the target to the substrate. Splashing was subsequently eliminated and smooth surface quality was restored after annealing the LSCO target at 550 °C in oxygen for 3 h. Optical emission spectroscopy (OES) of the LSCO's plume identified excited atomic cobalt neutrals, excited singly ionized strontium and lanthanum, and excited molecular LaO species. Oxygen interaction with the plume produced no new species. Furthermore, the OES data suggest that the observed LaO molecules were not created by the chemical reaction between La and O2 during ablation, but were ejected directly from the target during the PLAD process.

The effect of a second-phase particle size distribution on grain boundary pinning was studied using a Monte Carlo simulation technique. Simulations were run using a constant number density of both whisker and rhombohedral particles, and the effect of size distribution was studied by varying the standard deviation of the distribution around a constant mean particle size. The results of present simulations indicate that, in accordance with the stereological assumption of the topological pinning model, changes in distribution width had no effect on the pinned grain size. The effect of induced unpinning of particles on microstructure was also studied. In contrast to predictions of the topological pinning model, a power law dependence of pinned grain size on particle size was observed at T = 0.0. Based on this, a systematic deviation to the stereological predictions of the topological pinning model is observed. The results of simulations at higher temperatures indicate an increasing power law dependence of pinned grain size on particle size, with the slopes of the power law dependencies fitting an Arrhenius relation. The effect of induced unpinning of particles was also studied in order to obtain a correlation between particle/boundary concentration and equilibrium grain size. The results of simulations containing a constant number density of monosized rhombohedral particles suggest a strong power law correlation between the two parameters.

Using a cylindrical indenter (or punch), the impression creep behavior of MoSi2-SiC composites containing 0–40% SiC by volume, was characterized at 1000–1200 °C, 258–362 MPa punch pressure. Through finite element modeling, an equation that depends on the material stress exponent was derived that converts the stress distribution beneath the punch to an effective compressive stress. Using this relationship, direct comparisons were made between impression and compressive creep studies. Under certain conditions, compressive creep and impression creep measurements yield comparable results after correcting for effective stresses and strain rates beneath the punch. However, rate-controlling mechanisms may be quite different under the two stressing conditions, in which case impression creep data should not be used to predict compressive creep behavior. The addition of SiC affects the impression creep behavior of MoSi2 in a complex manner by pinning grain boundaries during pressing, thus leading to smaller MoSi2 grains and by obstructing or altering both dislocation motion and grain boundary sliding.

Prior to considering crack-face bridging, the stress/strain-field ahead of the crack tip in the compact tension (CT) geometry is numerically assessed by means of finite element method (FEM). The stress field along the crack line which has a decreasing profile of tensile stresses from the crack tip converts to monotonically increasing compressive stresses toward the back face of the CT specimen via a rotational center. Based on these stress-field analyses, a novel crack-face bridging model for fiber-reinforced brittle matrix composites is presented. The application of the model to the experimental result of a 2D-C/C composite enables one to estimate the crack-face fiber bridging stresses and their distribution profile.

The microstructure and mechanical properties of hot-pressed zirconia-toughened alumina (ZTA), fabricated from the ZTA powders containing (Zr, Ti)O2 in Ar gas were investigated. In hot-pressed ZTA, the presence of Ti concentration in the grains of Al2O3 or (Zr, Ti)O2 was analyzed by the energy dispersive spectroscopy (EDS) attached to the analytical electron microscope (AEM) apparatus. Experimental results showed that some Ti ions diffused to the grain boundary and into the Al2O3 grains, thereby enhancing the densification of hot-pressed ZTA. It was possible to retain tetragonal ZrO2 at room temperature in the ZTA specimens containing ≥5.5 mol% TiO2 and hot pressed at 1350 °C for 1 h. The bending strength and toughness of hot-pressed ZTA were enhanced by the addition of TiO2.

Planar laser-based imaging measurements of fluorescence and particle scattering have been obtained during flame synthesis of iron-oxide/silica superparamagnetic nanocomposites. The theory and application of laser-induced fluorescence, the spectroscopy of FeO(g), and the experimental approach for measurement of gas phase precursors to particle formation are discussed. The results show that the vapor phase FeO concentration rapidly rises at the primary reaction front of the flame and is very sensitive to the amount of precursor added, suggesting nucleation-controlled particle growth. The FeO vapor concentration in the main nucleation zone was found to be insensitive to the amount of silicon precursor injected, indicating that nucleation occurred independently for the iron and silicon components. Light scattering measurements indicate that nanocomposite particles sinter faster than single component silica, in agreement with TEM measurements.

The development of a novel Al matrix composite is described based on a simple displacement reaction when an SiO2 particulate preform is brought into contact with liquid Al at temperatures between 1273 and 1373 K. This interaction leads to the wetting of the SiO2 particles by Al and its eventual transformation to a composite with Al2O3/Al particles in an Al matrix. Infiltration of the preform as induced by this reaction takes place with the simultaneous formation of the Al2O3/Al particles in situ. Synthesis of engineered multiphase composites, wherein reinforcements of other materials incorporated into the preform and reacted with liquid Al, is also presented.

Surface modification of emeraldine (EM) and nigraniline (NA) base films by argon plasma treatment was investigated by x-ray photoelectron spectroscopy (XPS). Argon plasma treatment, followed by atmospheric exposure, results in the oxidation of some carbon atoms, first to C–O species and then to C = O and COOH species for samples with extended plasma treatment time. Most important of all, Ar plasma treatment and the accompanied carbon oxidation readily cause a decrease in the intrinsic oxidation state ([=N— ]/[—NH—] ratio) of the aniline polymers.

Stick-slip process occurred during the scratch test of styrene-acrylonitrile copolymer. For the first time, a bamboo-like morphology of the scratch track corresponding to the stick-slip phenomenon was observed. A “joint” was formed during the stick stage and during slip a uniform “stem” was made. The period and amplitude of the stick-slip both increase with the vertical load and decrease with the driving speed. A theoretical model is constructed based on the stiffness of the system and the plastic deformation of polymer both in the vertical and horizontal directions. The model assumes no distinction between the coefficients of static and kinetic friction and gives quantitatively consistent results with experiments.

Organic and polymeric materzials have seen a tremendous growth in research in the last five years as potential electroactive elements in thin-film-transistor (TFT) applications. These are driven by the increasing interest in flat-panel-display applications, for which organic and polymeric materials offer strong promise in terms of properties, processability, cost, and compatibility with eventual lightweight, flexible plastic displays. In this review we summarize the current status of our knowledge on the science of these organic and polymeric semiconducting materials. Most of these are based on linear thiophenes, especially a-hexathienyl, which has elicited by far the most attention. Mobility values in the 10−2–10−1 cm2/Vs and especially source-drain current on/off ratios of up to 106 make this a highly promising potential alternative to amorphous silicon. Other thienyl compounds are also discussed, as are polymeric analogues. A brief discussion of technological potential, limitations, and problems that need to be overcome is given at the end.