The structure of nanocrystalline palladium and copper, made by inert gas condensation and compaction, was studied using small angle neutron scattering (SANS), optical microscopy, and scanning electron microscopy. The effects of annealing and warm compaction were also examined with these techniques. The SANS results were interpreted using a maximum entropy routine, combined with knowledge of the Archimedes density and hydrogen concentration determined by prompt gamma activation analysis (PGAA). Similar hydrogen concentrations were detected by SANS and PGAA. This hydrogen content, which was approximately 5 at. % in samples compacted at room temperature, was reduced by both annealing and warm compaction. Defects in several size classes were observed, including missing grain pores (≈1−50 nm diameter) and defects of micrometer size. Warm compaction produced a lower number density of pores in nanocrystalline palladium, which led to increased density. The observed structure was correlated with Vickers microhardness and fracture surface morphology.

Dispersions of nanometer-sized In particles embedded in an Al matrix (10 wt. % In) have been synthesized by ball milling of a mixture of Al and In powders. The as-milled product was characterized by using x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x-ray spectrometer (EDX), transmission electron microscopy (TEM), and high resolution transmission electron microscopy (HREM), respectively. It was found that In and Al are pure components immiscible with each other, with nanometer-sized In particles dispersively embedded in the Al matrix. The melting behavior of In particles was investigated by means of differential scanning calorimeter (DSC). The calorimetric measurements indicate that both the melting point and the melting enthalpy of the In nanoparticles decrease with increasing milling time, or refinement of the In particles. Compared to its bulk melting temperature, a melting point depression of 13.4 K was observed when the mean grain size of In is 15 nm, and the melting point depression of In nanoparticles is proportional to the reciprocal of the mean grain size. The melting enthalpy depression was interpreted according to the two-state concept for the nanoparticles. Melting of the interface was deduced to be an exothermal process due to its large excess energy/volume.

Sol-gel-derived films containing BaTiO3 crystallites have been grown on suitable substrates using a precursor composition in the system Li2O-BaO-TiO2. Silver particles of diameters in the range 4.9 to 16.2 nm have been synthesized within these films by ion exchange and reduction technique. Electrical resistivities are found to vary from ∼102 to 105 ohm-cm, depending on the silver particle diameter. A low activation energy, approximately a few millielectron volts, is found to characterize the electrical properties of most of the samples. A quantum size effect is invoked to explain the results.

The oxidation of ZrC single crystals having (100) faces was performed at a temperature of 600 °C at an oxygen pressure of 2.6 kPa. A polished cross section of oxide scale was observed by backscattered electron imaging (BEI) in a scanning electron microscope (SEM). The oxide scale was observed to consist of two subscales, zones 1 and 2; zone 1 is adjacent to the ZrC. The thickness of zone 1 was kept constant (about 2 μm), independent of oxidation time. The interfacial microstructure between ZrC and cubic ZrO2 (c-ZrO2) phase in zone 1 was observed by high resolution transmission electron microscopy, by using an extremely thin foil of an oxidized crystal. The c-ZrO2 crystallites of 2 to 10 nm in size showing the (111), (200), and (220) lattice fringes were aggregated and distributed in an area about 10 to 20 nm away from the interface, with an amorphous layer observed adjacent to the ZrC. Electron dispersive x-ray analysis (EDX) indicated that carbon is concentrated at the interface; a decreasing oxygen concentration gradient in the oxide phase and away from the interface in the ZrC suggests the formation of oxygen-deficient ZrO2–x and oxycarbide on the respective sides of the interface. A black coating layer appeared, resulting from detachment or dissolution of zone 2, when a crystal oxidized for 1 h was treated in a HF solution. The layer was shown by the Raman spectrum to be amorphous carbon.

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.

Thermal waves are used to image damage accumulation digitally beneath Hertzian contacts in ceramics. Alumina ceramics over a range of grain size 3–48 μm are used in a case study. The nature of the images changes with increasing alumina grain size, reflecting a transition in damage mode from well-defined cone fracture in the finer-grain materials to distributed subsurface microfracture in the coarser-grain materials. Quantitative determinations of microcrack densities are evaluated in the latter case by deconvoluting thermal diffusivities from the image data. These determinations confirm the grain-size dependence of degree of damage predicted by fracture mechanics models. Potential advantages and disadvantages of thermal waves as a route to damage characterization in ceramic systems are discussed.

Silicon carbide fiber (SCS-6) reinforced-reaction-formed silicon carbide matrix composites were fabricated using a reaction-forming process. Silicon-2 at. % niobium alloy was used as an infiltrant instead of pure silicon to reduce the amount of free silicon in the matrix after reaction forming. The matrix primarily consists of silicon carbide with a bimodal grain size distribution. Minority phases dispersed within the matrix are niobium disilicide (NbSi2), carbon, and silicon. Fiber pushout tests on these composites determined a debond stress of ∼67 MPa and a frictional stress of ∼60 MPa. A typical four-point flexural strength of the composite is 297 MPa (43.1 KSi). This composite shows tough behavior through fiber pullout.

Composed of sp3 bonded nodules of carbon, nanophase diamond films are deposited in vacuum onto almost any substrate by condensing carbon ions carrying keV energies. These multiply charged ions are obtained from the laser ablation of graphite at intensities in excess of 1011 W cm−2. The high energy of condensation provides both the chemical bonding of such films to a wide variety of substrates and low values of residual compressive stress. Coatings of 2–5 μm thickness have extended lifetimes of materials such as Si, Ti, ZnS, ZnSe, and Ge against the erosive wear from high-speed particles by factors of tens to thousands. In this research emphasis has been placed on studies of the bonding and properties realized by the direct deposition of nanophase diamond films on stainless steel substrates. Examinations of interfacial layers showed deep penetrations of carbon atoms into steel substrates. Resistances to low and high impact wear estimated by a tumbler device and a modified sand blaster, respectively, and results indicated significant increases in the lifetime of stainless steel samples. The characterization studies in this work demonstrated nanophase diamond as an attractive material for use as a protective coating in current industrial applications.

Modeling of TiC powder behavior in Ar–H2 and Ar–N2 RF thermal plasmas has been performed as well as the numerical analysis of the plasma fields to investigate the plasma/powders interaction. The heat transfer rate from the plasma to the powders decreases with increasing the powder feed rate and with decreasing the plasma pressure, because of the significant local cooling owing to the presence of the injected powders. These results agree fairly well with the experimental results of our following paper. The modeling herein gives guidance for the rational design of new material processing using thermal plasmas.

We have investigated the near-interface characterization of diamond films grown on Si(100) substrates by means of a hot-filament chemical-vapor-deposition (HFCVD) method using high-resolution-electron microscopy (HREM). Atomic scale study of the diamond/Si interface reveals that on the top of the amorphous intermediate layer, there exists a precursor phase which seems to be a diamond-like structure, which provides a suitable site for subsequent diamond nucleation. High density crystal defects directly originate from the precursor phase. HREM images also reveal that during the deposition Si recrystallizes in some damaged areas left by pretreatment, such as scratching grooves. In the recrystallization process twins and microtwins can be formed, and amorphous solid is left in the Si crystals.

Two techniques are described for synthesizing nanometer-sized TiB2 particles by gas-phase combustion reactions of sodium vapor with TiCl4 and BCl3: a low-pressure, low-temperature burner and a high-temperature flow reactor. Both methods produce TiB2 particles that are less than 15 nm in diameter. The combustion by-product, NaCl, is efficiently removed from the TiB2 by water washing or vacuum sublimation. Material collected from the low-temperature burner and annealed at 1000 °C consists of loosely agglomerated particles 20 to 100 nm in size. Washed material from the high-temperature flow reactor consists of necked agglomerates of 3 to 15 nm particles. A thermodynamic analysis of the Ti/B/Cl/Na system indicates that near 100% yields of TiB2 are possible with appropriate reactant concentrations, pressures, and temperatures.

The influence of applied stress on the measurement of hardness and elastic modulus using nanoindentation methods has been experimentally investigated using special specimens of aluminum alloy 8009 to which controlled stresses could be applied by bending. When analyzed according to standard methods, the nanoindentation data reveal changes in hardness with stress similar to those observed in conventional hardness tests. However, the same analysis shows that the elastic modulus changes with stress by as much as 10%, thus suggesting that the analysis procedure is somehow deficient. Comparison of the real indentation contact areas measured optically to those determined from the nanoindentation data shows that the apparent stress dependence of the modulus results from an underestimation of the contact area by the nanoindentation analysis procedures.

The synthesis of uniform colloidal crystalline particles of Zr- and Sr-doped barium titanates at a low temperature of 85 °C by the controlled double-jet precipitation (CDJP) technique is described. The stoichiometry of the powders can be precisely controlled by adjusting the compositions of the starting reactant solutions. Barium titanate with 20% Zr substitution, sintered at 1275 °C, satisfied the requirements for the Y5V multilayer capacitors application. The grain sizes are uniform and small, ranging from 1 to 3 μm. Solids with an extremely sharp change in the dielectric constant as a function of temperature, which are suitable for thermal IR detectors application, can be obtained when both Sr and Zr are incorporated as dopants.

Fiber optic modulators were fabricated by coating optical fibers with electrode and piezoelectric ZnO layers. The techniques of piezoelectric fiber optic modulator (PFOM) fabrication are presented, and the microstructure and crystallographic texture of the coatings are analyzed. In order to produce thick (approximately 5 μm) ZnO coatings, it was necessary to study the reactive dc magnetron sputtering process in O2/Ar gas mixtures under conditions close to the transition between an oxidized and nonoxidized Zn target surface. In situ quartz crystal microbalance measurements of the deposition rate revealed thee distinct regions in the deposition rate (R) vs oxygen partial pressure behavior, at constant total pressure, for sputtering under conditions that provided an oxidized Zn target surface. Additionally, a transition between oxygen and argon dominated sputtering as observed by varying the sputtering pressure while maintaining a constant The transition between oxygen and argon dominated sputtering influences R to varying extents within the three R vs regions for an oxidized target surface. Correlations among the cathode current and voltage, deposition rate, and gas flow rate are presented to give a better understanding of the reactive sputtering processes occurring at the oxidized Zn target surface. Sputtering conditions optimized for a high ZnO deposition rate were used to produce 〈001〉 radially oriented ZnO fiber coatings for PFOM devices that can produce optical phase shifts as large as 0.38 rad/V.

Lead-based relaxor ferroelectrics such as Pb(Mg1/3Nb2/3)O3 (PMN), Pb(Zn1/3Nb2/3)O3 (PZN), and their solid solutions with BaTiO3 and PbTiO3 have been prepared by a solution combustion process which involves metal nitrates/oxalate and tetraformal trisazine (TFTA) at 350 °C. Thermal evolution of perovskite relaxors has been investigated at different temperatures of calcination using the powder x-ray diffraction method. Particles are fine and sinter-active at low temperature (1050 °C). Both particulate and dielectric properties are compared.

A new philosophy for tailoring layer composites for damage resistance is developed, specifically for alumina-based ceramics. The underlying key to the approach is microstructural control in the adjacent layers, alternating a traditional homogeneous fine-grain alumina (layer A) for hardness and wear resistance with a heterogeneous alumina : calcium-hexaluminate composite (layer C) for toughness and crack dispersion, with strong bonding between the interlayers. Two trilayer sequences, ACA and CAC, are investigated. Hertzian indentation tests are used to demonstrate the capacity of the trilayers to absorb damage. In the constituent materials, the indentation responses are fundamentally different: ideally brittle in material A, with classical cone cracking outside the contact; quasi-plastic in material C, with distributed microdamage beneath the contact. In the ACA laminates, shallow cone cracks form in the outer A layer, together with a partial microdamage zone in the inner C layer. A feature of the cone cracking is that it is substantially shallower than in the bulk A specimens and does not penetrate to the underlayer, even when the applied load is increased. This indicates that the subsurface microdamage absorbs significant energy from the applied loads, and thereby “shields” the surface cone crack. Comparative tests on CAC laminates show a constrained microdamage zone in the outer C layer, with no cone crack, again indicating some kind of shielding. Importantly, interlayer delamination plays no role in either layer configuration; the mechanism of damage control is by crack suppression rather than by deflection. Implications for the design of synergistic microstructures for damage-resistant laminates are considered.

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.

A new method was developed to determine the eutectoid temperature, Ac1, of carbon steel during laser surface hardening. In the method a three-dimensional heat flow model with temperature-dependent physical properties was set up and solved for the temperature distribution employing a finite element method (FEM). Workpieces were heat-treated to produce a melted and hardened zone by a single pass of a continuous-wave TEM00 CO2 laser beam. The depth profile of the melted zone was used as a calibrator to solve the uncertainty imposed by the unknown surface absorptivity. Obtained was an Ac1 of, on average, 770 °C, a superheat of 47 °C compared to the equilibrium Ac1 of 723 °C. Furthermore, the numerical model was also employed to predict the hardened depth, and the results show that, for a depth of more than 100 μm, the eutectoid temperature 770 °C leads to a depth about 10% smaller than that predicted at 723 °C. The use of the temperature-dependent physical properties is critical; an error up to 80% could result if constant physical properties are used.

Microwave plasma chemical vapor deposition (MWPCVD) process has been used to grow diamond thin films on silicon substrates from CH4–H2 gas mixture. Bias-enhanced nucleation (BEN) pretreatment has been used to increase the density of diamond nuclei. Various species in the CH4–H2 plasma have been identified using optical emission spectroscopy (OES), and their effect on the film microstructure has been studied. During the pretreatment process the emission intensities of CH, CH+, C2, H, and H2* species have been found to increase significantly for a negative dc bias voltage |VB| > 60 V. The higher concentration of excited species and the associated effects play a significant role in the growth process. A very thin layer of a-C containing predominant sp3 bonded carbon species in the initial stages of the growth is found to be present in these films. The microstructure of the films has been found to be very sensitive to the biasing conditions.

The domain structure and dielectric properties as a function of lanthanum concentration and Zr/Ti ratio have been investigated in rhombohedral and tetragonal lead lanthanum zirconate titanate (PLZT) ceramics. Transmission electron microscopy revealed that, with increasing lanthanum concentration and Zr/Ti ratio, the long-range-ordered domains (macrodomains) reduced in width, initially being fine scale (20 nm) striations, but eventually forming a “mottled” contrast (5 nm), characteristic of a relaxor. Relative permittivity measurements as a function of temperature revealed a correlation between broadening of the dielectric maxima and the onset of relaxor-type behavior with the appearance of the striations and mottled (relaxor) contrast, respectively.