In this brazing technique, at least one of the metal surfaces to be joined is coated with a powder-mixture of silicon and a potassium fluoroaluminate flux. Brazing of aluminum is carried out by heating at ∼600 °C in nitrogen gas. During heating, the flux melts and dissolves the oxide layers on the contacting surfaces, thus allowing the silicon to come into intimate contact with bare aluminum. At a temperature exceeding the Al–Si eutectic temperature of 577 °C, the silicon diffuses rapidly into the aluminum and generates in situ a layer of Al–Si liquid alloy of near-eutectic composition. The filler material then flows into the joint and forms a fillet. This brazing technique may be exploited with aluminum using intermediary elements other than Si, and may be used for joining a variety of metals.

Single-crystal epitaxial films of cubic β(3C)–SiC(111) have been deposited on hexagonal α(6H)–SiC(0001) substrates oriented 3–4° toward [1120] at 1050–1250 °C via gas-source molecular beam epitaxy using disilane (Si2H6) and ethylene (C2H4). High-resolution transmission electron microscopy revealed that the nucleation and growth of the β(3C)–SiC regions occurred primarily on terraces between closely spaced steps because of reduced rates of surface migration at the low growth temperatures. Double positioning boundaries were observed at the intersections of these regions.

Zirconia-toughened MgO was manufactured and examined by scanning and transmission electron microscopes. It was found that ZrO2 particles that are present on the MgO grain boundary limit the grain growth of MgO. The cooling rate has an effect on the ZrO2 phase in zirconia-toughened MgO fired in a cubic ZrO2–MgO field, but it does not have an effect on the ZrO2 phase in specimens fired in a tetragonal ZrO2–MgO field. Tetragonal ZrO2 was retained at room temperature in zirconia-toughened MgO.

A simple and convenient method for the synthesis of YBa2Cu3O7−x powder is described. The technique involves autoignition of a citrate-nitrate gel resulting from a thermally induced oxidation-reduction reaction to yield an ash that upon calcination produces the desired compound. The resulting powder is pure, homogeneous, and possesses a reasonably fine particle size. The autoignition is restricted to a particular range of citrate-nitrate ratio in the gel. Attempts have been made to understand the ignition process with the help of Thermogravimetry (TG) and Differential Thermal Analysis (DTA) of the samples. The process appears to have a higher degree of reproducibility and a good potential for large-scale production.

TEM studies have been conducted on melt-textured YBa2Cu3Ox samples that were uniaxially and isostatically deformed at high temperatures and compared with those of undeformed samples. Dislocation pile-ups along [100] and [010] are found to be the common feature between undeformed samples with the best Jc and the uniaxially deformed samples, and are suggested to be responsible for enhanced pinning when the magnetic field (H) is applied parallel to the a-b plane. Dislocation loops, tangles, and arrays are also observed, and are considered to contribute to pinning in field orientations other than H ‖ a-b. In addition to these dislocations, 〈301〉 type partial dislocations are found to be present in isostatically deformed samples. The strain field around these dislocations is considered to be an additional source of pinning in the intermediate field orientations.

Modifications of a recent model by Izumi et al.1 on diffusion controlled growth of YBa2Cu3O7−x (123) superconductors are proposed, taking into account especially the engulfment process of the Y2BaCuO5 (211) particles into the solidifying 123 interface. The proposed modifications are evidenced by experimental results and applied to explain microstructural features of the 123 superconducting material. In particular, the 1:1 correlation between 123 platelet thickness (planar defect spacing) and 211 particle size as described by Jin et al.2 is explained by an observed bridge growth resulting in a zipper-like mechanism. By this mechanism the platelets grow together in an oriented way leading to a quasi single crystalline material.

We discuss the results obtained for SrTiO3/YBa2Cu3O7 layers deposited on (001) MgO substrates by UV pulsed laser ablation. Different samples were prepared to study both the growth of a thin (55 nm) layer of SrTiO3 on MgO and the successive epitaxy of a 220 nm YBa2Cu3O7 (YBCO) film on the SrTiO3 layer. An x-ray diffraction (XRD) texture analysis is reported for the bilayers together with resistivity versus temperature and critical current density (Jc) measurements of the superconducting films. The results show that YBCO grains grow with c-axis normal to the surface; the main in-plane orientations are [100] MgO // [100] SrTiO3 // [100] YBCO ([010] YBCO). The XRD line broadening analysis suggests that YBCO columnar grains grow along the whole thickness of the film, also evidencing dislocations and/or faulting separated by a mean distance of 80 nm. The values obtained for the critical current of the superconductor demonstrate the effectiveness of the SrTiO3 intermediate layer in improving the structural quality of the YBCO film.

Thick film (1.2 μm) YBCO superconductors grown by pulsed laser deposition on unbuffered and CeO2-buffered single crystal (001)-oriented yttria-stabilized zirconia (YSZ) substrates have been investigated. YBCO and YSZ react to form BaZrO3 (BZO), whereas YBCO and CeO2 react to form BaCeO3. Reaction phases were examined by θ-2θ and four-circle x-ray diffraction and high resolution electron microscopy. Three orientation relationships identified for the unbuffered films were (i) (001)YBCO ‖ (011)BZO ‖ (001)YSZ with [110]YBCO ‖ [100]BZO ‖ [100]YSZ, (ii) (001)YBCO ‖ (001)BZO ‖ (001)YSZ with [110]YBCO ‖ [100]BZO ‖ [100]YSZ, and (iii) (001)YBCO ‖ (001)BZO ‖ (001)YSZ with [100]YBCO ‖ [100]BZO ‖ [100]YSZ. The results suggest that for films grown at typical deposition temperatures, YBCO epitaxy is established before the interfacial reaction occurs. The presence of BaCeO3 in buffered films grown at high temperatures (790 °C) was confirmed by θ-2θ scans and selected area diffraction patterns.

We have developed a novel approach for quantifying the microstructure of granular thin films using digital image processing and analysis. In the past, conventional scanning electron microscopy of thin films has generated qualitative information on the surface topography and film microstructure. However, when coupled to digital image analysis, the amount or degree of surface contours (i.e., granularity) in SEM micrographs can be quantified in a rapid and reproducible manner. Briefly, SEM micrographs are digitized and the edge boundaries on the film surface are enhanced by a gradient filter; granularity is then quantified by calculating the %AREA covered by the edges with respect to the entire field. Objects of a particular shape, such as phase impurity particles, can be selectively deleted from the image using a specific sequence of shape analysis algorithms and parameter values. In this manner, the contributions of edges from the phase impurity particles is minimized in the final measurement of real surface contours. Statistical analysis of the data yields quantitative information concerning variations in microdomains within single thin films and can detect statistically significant differences among samples. This method is being used in the characterization of the microstructure of superconducting thin films for optimization of their electrical and magnetic properties.

A submicrometer-grained (SMG) Al−3% Mg solid solution alloy, with an initial grain size of ∼0.2 μm, was produced by intense plastic straining. Experiments show that tensile specimens of the SMG alloy exhibit high elongations to failure at low testing strain rates at the relatively low temperature of 403 K. The stress exponent is high (∼7–8) and calculations show deformation is within the region of power-law breakdown. The initial microstructure of the alloy consists of diffuse boundaries between highly deformed grains. At strain rates of ∼10−4 s−1 and lower, plastic deformation leads to dynamic recrystallization and the formation of highly nonequilibrium grain boundaries that gradually evolve into a more equilibrated configuration.

Elemental Ti–Al powder blends were mechanically alloyed in order to study phase formation during the alloying process. In addition, the stability of intermetallic phases upon milling was investigated separately in order to determine the origins of phase selection during the milling process. It was found that by mechanical alloying of powder blends, as well as by ball milling of Ti-aluminides for long milling times, the same metastable phases were formed for corresponding compositions, i.e., the hep solid solution for Al concentrations up to 60 at. % and the fcc solid solution for 75 at. % Al. X-ray diffraction (XRD) analyses indicated that the process of mechanical alloying occurred via the diffusion of Al into Ti. By lowering the milling intensity, a two-phase mixture of the hcp solid solution and the amorphous phase was observed for Ti50Al50 and confirmed by transmission electron microscopy (TEM). The results show that phase selection in the final state during mechanical alloying of Ti–Al powder blends and milling of intermetallic compounds is mainly determined by the energetic destabilization of the competing phases caused by the milling process. The destabilization is most pronounced in the case of intermetallic compounds due to the decrease in long-range order upon milling. For the final milling stage, phase formation can be predicted by considering the relative stabilities of the respective phases calculated by the CALPHAD method using the available thermodynamic data for the Ti–Al system.

In this paper, the possibilities of preparing TiC-reinforced Ni3Al-matrix composites by SM (self-propagating high temperature synthesis and melting process) were examined. Two kinds of composites, namely, commercial TiC-reinforcement and synthesized TiC-reinforcement Ni3Al-matrix composites, were fabricated. The effects of particle size of the commercial TiC on the mechanical properties of the Ni3Al-matrix composites were studied. The results show that the mechanical properties of the composites decrease with increasing particle size of the commercial TiC. The microstructures of 35 wt. % TiC + 65 wt. % Ni3Al composites produced by SM technology from the four elements Ti, C, Ni, and Al were examined. The results show that in these composites, the particle size of TiC synthesized in situ is fine and that the materials have considerable high-temperature bending strength and fracture toughness.

Space groups and atomic coordinates for the 4H, 6H, 8H, 10H, 15R, and 21R polytypes of diamond are presented. The systematic method used to determine the highest symmetry space group for diamond polytypes is described.

The deposition of diamond phase carbon films on stainless steel substrates by an ionized deposition technique has been studied. A molybdenum grid used during argon ion sputtering had a decisive role in improving the morphology and adhesion ability of the substrate surface. The chemical composition of the surface was obtained by x-ray photoelectron spectroscopy, indicating the reduction of oxygen, carbon, and other contamination, while the surface morphology of the substrate obtained by scanning electron microscopy showed less roughness with a partially smooth surface. Attempts to extract the deposited films from the pretreated substrate surface by a superadhesive agent with an adhesion of 250 kg/cm2 failed, yielding a much stronger adhesion for the pretreated surface. This fact was also supported by examining the surface morphology, hardness, and the resistivity of the films deposited on the same substrates. As for the crystal structure of diamond phase carbon films on stainless steel, selected area diffraction patterns obtained from transmission electron microscopy suggested a mixture of amorphous carbon and polycrystalline diamond components.

B-doped diamond films were synthesized by microwave plasma chemical vapor deposition using a mixture of methane (0.5% or 1.2%) and diborane (B2H6) below 50 ppm on either Si substrates or undoped diamond films that had been synthesized using 0.5% or 1.2% methane. The surface morphologies of the synthesized films were observed by Secondary Electron Microscopy, and the infrared absorption and Raman spectra were measured. It was found that when diborane concentration was low, B-doped films preferred (111) facets. On the other hand, high diborane concentrations resulted in a deposition of needle-like material that was identified as graphite by x-ray diffraction.

Diamond crystallites and continuous films were deposited on (100) silicon with various surface treatments by microwave plasma assisted CVD at times varying from 2 min to 1600 min. In each experiment, the average diameter of the crystallites increased linearly with time, while the density of crystallites was essentially constant. Thus, nucleation of the diamond occurred within a short time interval early in the deposition process. After the nucleation event, only growth occurred. Various surface treatments were used: untreated, polished with 1 μm diamond, scratched with 350 mesh SiC, scratched with 1 μm alumina, wiped with 350 mesh graphite powder, and spin coated with polymethyl methacrylate. Only the diamond polishing affected the crystallite density, and none of the surface treatments had any effect on crystallite morphology or growth rate. Growth rates were determined by least squares fits to average diameter versus time for crystals and average thickness versus time for films. The growth rate data extrapolate to zero size at zero deposition time. Applying the Volmer–Weber model, an activation energy for nucleation of diamond on silicon was calculated to be 52 kcal/mole.

The kinetics of reaction between chemical vapor deposited diamond films (prepared by the hot filament method) and oxygen gas was studied by thermogravimetry. The reactions were carried out at atmospheric pressure in gas mixtures containing between 25 and 100 vol. % oxygen (balance argon), and in the temperature range of 973–1073 K. The apparent order of the reaction is close to 0.6, and the apparent activation energy is 232 kJ/mole. The kinetic data are explained by assuming no mass transfer limitations, direct reaction between CVD diamond and oxygen to form CO and CO2, and thermodynamic equilibrium between CVD diamond, CO, and CO2. The dominant chemical reaction involves the formation of CO, while the formation of CO2 is not significant. Three stage mechanistic schemes are developed involving adsorption of oxygen on CVD diamond surface, surface chemical reaction, and desorption of adsorbed species to CO or CO2. The experimental rate data conform to the reaction rate expressions developed for the mechanistic schemes leading to the formation of CO and CO2, assuming adsorption as the rate-controlling step. The adsorption rate constants for the formation of CO and CO2 are determined. The activation energy of the adsorption step leading to the formation of CO is 213 kJ/mole.

A combination of in situ transmission electron microscopy and thermogravimetric techniques has been used to follow the manner by which phosphorus addition to graphite influences its interaction with oxygen. Direct observation of the process shows that the additive completely inhibits the reaction at temperatures below 830 °C. At higher temperatures phosphorus species are found to bond preferentially to the graphite “armchair”{1120} faces leaving the “zigzag” {100} faces vulnerable to attack by oxygen. In situ electron diffraction analysis indicates the formation of a chemical bond between the phosphorus and graphite edge atoms at high temperatures, which involves the formation of a complex believed to become an integral part of the structure. This unique type of chemical bonding is believed to be responsible for the observed thermal stability of P–O species on the graphite atoms at temperatures up to 1050 °C. In a further series of experiments, phosphorus was found to poison the catalytic activity of cobalt, which in its unadulterated state is a very effective promoter of the graphite-oxygen reaction.

When NB is moles of oxygen atoms dissolved into an Si wafer of NA moles, the concentration of oxygen atoms in the Si wafer is given by mole fraction as XB = NB/(NA + NB), and the degree of supersaturation is defined by σ = (XB/XBS,T) – 1 where XBS,T is the mole fraction of the saturated state at temperature T. We have proved that σ is equal to the chemical potential difference of oxygen atoms in between saturated and supersaturated states if σ ≪ 1. Here the spontaneous generation rate is proportional to σγ, where γ is the number of the oxygen atoms in the critical oxide particles in the Si wafers. Duration time of a low temperature heating (at about 700 °C) will determine the number of nuclei for oxide precipitates, and a treatment near 950 °C is very effective on growth of oxide particles, because growth of the oxide particles is determined by diffusion of the atoms. Before the low temperature treatments, preheating at a temperature higher than 1000 °C is effective in dissolving Si–O pairs and making interstitial oxygen atoms, where the Si–O pairs have been generated by the cooling stage after the crystal growth.

The nanostructure and chemical distribution in semi-insulating polycrystalline oxygen-doped silicon (SIPOS) deposited on (001) Si and its isothermal transformation behavior at 900 °C were investigated by high resolution electron microscopy (HREM) and electron energy loss nanospectroscopy (EELS). The structure of the as-deposited film, which contained 15 at. % oxygen, was amorphous. No evidence for nanocrystalline second phases was found. It was similar in appearance to amorphous silicon. After annealing for 30 min at 900 °C in an inert environment (N2), a dispersion of small nanocrystals, identified as silicon by imaging, diffraction and EELS, formed in the amorphous SIPOS matrix, with a thin precipitate free zone (PFZ) adjacent to the Si substrate. The SIPOS matrix oxygen concentration increased to 36 at. % and the matrix remained amorphous after annealing. No other phases were observed in annealed specimens. Changes in Si–L near edge fine structure and low loss peaks in EELS spectra from SIPOS with increasing oxygen concentration indicated that it is a solid solution supersaturated with silicon. Microstructures indicated that the Si nanocrystals formed during a homogeneous precipitation reaction.