The mechanisms for fiber damage in single crystal Al2O3 fiber-reinforced composites were investigated. Both fiber fragmentation and fiber strength degradation were observed in composites with a variety of matrix compositions. Four mechanisms that may be contributing to the fiber strength loss have been proposed and include matrix reaction, reaction with binders, residual stress-induced damage, and pressure from hot pressing. The effect of matrix reaction was separated from the other three effects by sputter-coating the matrices on cleaned fibers and annealing with a temperature profile that simulates processing conditions. These experiments revealed that Y and Cr in FeCrAlY base alloys and Zr in NiAl alloys reacted with the fiber, and grooves and adherent particles were formed on the fiber surface which were responsible for the strength loss. The effects of the matrix reaction appeared to dominate over the other possible mechanisms, although evidence for reaction with binders was also found. Ridges on the fiber surface, which reflected the grain boundaries of the matrix, were also observed. In order for single-crystal Al2O3 to be used as a fiber in MMC's and IMC's, a matrix or protective coating which minimizes matrix reaction during processing will be necessary. Of the matrices investigated, the Thermo-spanTM alloy was the least damaging to fiber properties.

Several substitutions have been attempted in the Hg layer of the Hg 1212 and 1223 cuprate superconductors. A new series of (Hg,Bi)1212 superconducting compounds has been synthesized. The highest Tc of the series (92 K) is found for the composition (Hg0.67Bi0.33)Sr2(Y0.5Ca0.5)Cu2O7−δ, with lattice constants a = 3.811 Å and c = 12.002 Å. X-ray diffraction and SEM with EDX analysis confirm that Hg is indeed incorporated in the structure. High-pressure oxygenation at 250 bar and 400 °C changes the magnetization curve, adding a second transition at ∼42 K; the 92 K transition remains unchanged. High-pressure oxygenation of Pb-substituted composition of the 1223 system, (Hg0.67Pb0.33)Ba2Ca2Cu3O8 also leads to the formation of low temperature phase with Tc = 67 K. The low Tc phase is associated with the incorporation of extra oxygen, possibly in the Hg layer.

The effect of alumina on densification of the binary borosilicate glass composite, containing low-softening borosilicate glass (BSG) and high-softening high silica (HSG) glass, has been investigated. It is found that with a small amount of alumina, 2-10 vol. %, present as a dopant in the binary glass mixture of BSG and HSG, both densification and densification rate are significantly reduced, but the activation energy of densification at a given densification is dramatically increased. However, no significant change in densification behavior with increasing alumina content from 2 to 10 vol. % is observed. These results are attributed to a chemical reaction taking place at the interface of alumina/BSG, forming a reaction layer adjacent to alumina. Since the composition of the reaction layer is known to be rich in aluminum and alkali ions and poor in silicon, the alkali ions content in BSG is continuously decreased during sintering. Accordingly, the resultant loss of alkali ions from BSG causes a rise in viscosity of BSG, thus slowing down the densification kinetics and increasing the activation energy of densification.

The thermodynamic parameters of all stable phases in the Ni-Zr system are reported in this paper. The available experimental data are taken into account in deriving the interaction parameters of various phases. The Ni7Zr2, Ni21Zr8, Ni11Zr9, NiZr, and NiZr2 phases are treated as stoichiometric. The solid solubility of the Ni5Zr, Ni3Zr, and Ni10Zr7 phases are described using a two sublattice model. The calculated thermodynamic properties and the phase diagram are in good agreement with the experimental ones. The thermodynamic parameters, along with the classical nucleation and crystal growth theory, have been used to explain the formation of metastable noncrystalline and crystalline phases upon rapid quenching of the liquid alloys. It has been demonstrated that even without any prior knowledge of the physical property, such as glass transition or crystallization temperature and thermodynamic property, such as the enthalpy of amorphous → crystal transformation of the amorphous alloy, it is possible to make a reasonably good “first order prediction” of the glass-forming range in a binary system. The experimentally determined glass-forming range in the Ni-Zr system is found to be in good agreement with the predicted one.

The impression creep behavior of lead was investigated using a 100 μm diameter punch at ambient and elevated temperatures (433 K-563 K) under punching stresses of 6–70 MPa. The results were compared with the data obtained from conventional creep tests reported in the literature. Unlike the indentation creep test, the impression creep test showed a steady-state velocity after a short transient period when the flat-end cylindrical punch was pushed against the lead surface by a constant load. Both the temperature and stress dependences were comparable to those of the constant stress tensile creep tests under similar conditions. A master curve for lead was established by collecting data from the impression creep tests and the constant stress tensile creep tests. The indentation creep measurements for lead were included also. However, the indentation data depend on the load applied.

Electrochemical and high pressure oxygenation experiments are described which extend the range of intercalated oxygen content beyond that accessible in 1 atm O2 treatments for the triangular planar cuprate delafossites YCuO2+x and LaCuO2+x, with the intention of increasing the hole doping, and filling vacancies in the intercalated oxygen lattice to decrease electrical resistivities. Stabilization of the 2H polytype of YCuO2 through 1% Ca substitution for Y and oxidation conditions for obtaining the pure orthorhombic intercalated oxygen superlattice form of YCuO2.50 are also described. Temperature dependent resistivities for some of the superoxygenated compositions are reported; metallic behavior was not observed.

The creation of a giant magnetoresistance (GMR) effect in a spinodally decomposed and deformed Cu-20% Ni-20% Fe alloy is reported. The alloy is processed to contain a locally multilayered superlattice-like structure with alternating ferromagnetic and nonmagnetic layers with a size scale of 10-20 Å. The microstructural modification produced a dramatic improvement in room-temperature magnetoresistance ratio from ∼0.6 to ∼5%. The observed magnetoresistance is most likely related to the spin-dependent scattering at the two-phase interface and in the ferromagnetic phase, although the exact mechanism involved may be qualitatively different from the usual GMR picture. A rather unusual temperature-dependence of magnetoresistance ratio, i.e., the room-temperature value being greater than that at 4.2 K, was found.

The influence of the ambient atmosphere on the synthesis of diamond by chemical vapor deposition using an oxygen-acetylene torch is investigated experimentally. Diamond synthesis in an air atmosphere is compared to that in an inert atmosphere. It is found that the quality of diamond deposited on substrates positioned in the burnt gases near the premixed flame of the torch (within 1 mm) is independent of the composition of the ambient gas. Farther downstream from the premixed flame in the feather region, however, diamond deposition is controlled by the combustion of incomplete products from the premixed flame with oxygen from the atmosphere. In this region diamond grows in an annulus on the substrate with an air atmosphere, but no film is grown with an inert atmosphere.

Xenon and krypton have been implanted into muscovite mica at room temperature and at liquid nitrogen temperature. The behavior of the implanted Xe and Kr was followed by low-temperature transmission electron microscopy and energy dispersive x-ray analysis. An electron diffraction pattern of diffuse bands is observed at room temperature due to the presence of fluid rare gas and to noncrystalline mica. Visible cavities with diameters 10–300 nm formed in the Xe-implanted mica. Visible cavities in room-temperature Kr-implanted mica ranged from 5–50 nm in diameter. The gas pressures at room temperature in the cavities are estimated, assuming all of the implanted gas precipitated in cavities to be ∼10 MPa for Xe and ∼20 MPa for Kr. These pressures are considerably lower than found for rare gases implanted in metals and ceramics, but sufficient to liquefy the rare gases at room temperature. The Xe and Kr were observed by dark-field microscopy to form fcc crystalline solids within the cavities at temperatures below their triple points, with lattice parameters of a(xe) = 0.630 ± 0.0015 nm and a(Kr) = 0.565 ± 0.005 nm. The solid Xe within bubbles was unstable under the electron beam of the transmission electron microscope at temperatures above 80 K, while the solid Kr within bubbles was unstable at temperatures as low as 35 K. The crystalline mica matrix undergoes a transformation from a crystalline structure to an amorphous structure as a result of implantation.

The microstructure of gas-atomized Al-20 wt. % Si-1 wt. % Ni powders was investigated by electron microscopy. Primary Si crystals about 2 μm in size are homogeneously distributed in the Al matrix. Eutectic Si crystals about 50 nm in size are precipitated with the definite crystallographic relationship of 〈110〉Si ‖ 〈110〉Al. Most of the interfaces between Al and Si are semicoherently bonded with close-packed planes of {111}Si and {111}Al. The special crystallographic relationship and interfaces are interpreted by matching between Si and Al lattice spacings.

Metastable k–Al2O3 often occurs as islands in thin α–Al2O3 coatings produced by CVD. In this investigation a thick single-phased K–Al2O3 coating was produced in order to determine the mechanical properties of the K-phase. As a comparison, a CVD coating as well as a sintered bulk specimen of α–Al2O3 were studied. The mechanical behavior was probed by a depth-sensing indentation (nanoindentation) system on polished taper and cross sections at several applied loads. Hardness and elastic modulus were derived and are discussed in conjunction with the crystal structure and the microstructure of the two materials. K–Al2O3 shows a marked microstructural and structural anisotropy, which is also reflected in anisotropic mechanical properties. Parallel to the c-axis, which, in this study, closely coincided with the growth direction, both the hardness and the elastic modulus are significantly higher than in the perpendicular direction. α–Al2O3 has the same hardness and elastic modulus in the coating and in the bulk form and shows no clear anisotropy in microstructure. If the two alumina materials are compared, K–Al2O3 is significantly harder than α–Al2O3 in the growth direction (on the taper section), whereas it is significantly softer in the perpendicular direction. In either of the loading directions, the elastic modulus of K–Al2O3 is significantly lower than in α–Al2O3.

Barium hexa-aluminate (BaO · 6Al2O3) aerogels were prepared using a supercritical drying method and their properties examined. A barium hexa-aluminate aerogel prepared from a double alkoxide of barium and aluminum showed a high specific surface area of 421 m2/g. Monolithic barium hexa-aluminate formed. No BaO · Al2O3 or alumina was observed, as is often the case in powder processing. The specific surface area of the monolithic barium hexa-aluminate fired at 1400 °C for 2 h was 12 m2/g, while that of the barium hexa-aluminate xerogel was only 0.8 m2/g. A barium hexa-aluminate aerogel was also prepared using barium by using a chelating agent. This aerogel showed a specific surface area of 454 m2/g as-dried. In the case of the chelating agent, BaO · Al2O3 was also detected along with barium hexa-aluminate after firing.

Using conventional and high resolution TEM, we have studied the microstructure of C70 polycrystalline films, prepared by sublimation of C70 powder onto glass, carbon holey film, and sapphire substrates held at 200 °C. An fcc structure with lattice parameter 1.50 nm is observed for the films on glass and amorphous carbon. A different structure and stronger adherence to the substrate was observed for the thin film grown on sapphire, suggesting a stronger molecule-substrate interaction in this case. Thicker films on sapphire, however, did have fcc structure. In all cases, the film grows in large grains about 100 nm in size, indicating high effective surface mobility of the C70 molecules. Further analysis of the films on carbon holey substrates indicates a preferred [011] film growth orientation, the existence of twins, and a high density of stacking faults. Extended exposure of the films to oxygen did not result in visible structural changes, but strong illumination for several hours in atmosphere led to partial annealing of planar defects and higher sensitivity to the electron beam, with film amorphization taking place at much shorter times under the electron beam.

Improvement of copper to graphite adhesion by thin interfacial films of titanium and chromium was investigated. Graphite fibers and highly oriented pyrolytic graphite flats were sputter-coated first with 10 nm of titanium or chromium and then with 50 nm of copper. After annealing to 970 °C in argon/5%-hydrogen at atmospheric pressure for 5 min, copper without an interfacial bond layer agglomerated into nearly spherical particles, copper with the chromium bond layer agglomerated into particles with a contact angle less than 90°, indicating improvement in adhesion, and copper with the titanium bond layer exhibited a continuous metal film. In the latter case, most of the interfacial titanium was observed to have migrated into the copper and to the free surface, where the titanium reacted with contaminants in the annealing ambient.

An important, rather novel procedure for the synthesis of submicron crystalline multicomponent oxide ceramic powders has been studied. The synthesis of CuFe2O4 powder, a ferrite material, has been used as a model system for understanding the synthesis process. The effect of the fuel content, powder packing, and surface heat loss has been investigated in terms of the maximum reaction temperature and reaction period, phase formation, and particle size and morphology. It has been shown that the maximum temperature and reaction period can be tailored to produce different phases. The submicron features of the synthesized powders are indicated by the large surface area values obtained from BET measurement.

Epitaxial films of single-layer SnO2 and PbTiO3/SnO2 heterostructures were obtained on (0001) sapphire (α-Al2O3) substrates by metal-organic chemical vapor deposition. X-ray diffraction and transmission electron microscopy were used to characterize the structural properties of these films. The epitaxial relationship for the heterostructure PbTiO3/SnO2/sapphire was found to be (111) [011]PbTiO3 ‖ (100) [001]SnO2 ‖ (0001) [1100]α-Al2O3. The fact that epitaxial ferroelectric films were obtainable in such a structurally highly heterogeneous system suggests that a wide range of material selection is possible in exploring the kind of applications that need to utilize epitaxial ferroelectric films in a multilayered heterostructure.

The reaction of n-butyl amine adsorbed on the ternary oxide La2CuO4 has been studied by x-ray photoelectron spectroscopy (XPS), paying special attention to the surface composition. We suggest that n-butyl amine reacting with La2CuO4 reduces CuO to Cu2O. The reaction is confined to the surface because the original composition of the material could be restored after in situ scraping with a stainless steel blade.

Theoretical and empirical considerations of the work-of-fracture, γwof, of brittle materials are reviewed. The energy principle of the work-of-fracture provides a modified Irwin similarity relationship in the nonlinear fracture mechanics regime. Various microscopic deformation and fracture processes in the crack wake and the crack-face contact regions contribute to the rising R-curve behavior of brittle materials, and then significantly affect the work-of-fracture, resulting in the work-of-fracture that is dependent on the dimension and geometry of test specimens as well as test methods. The requisite for the work-of-fracture to be a material characteristic resistance to failure is discussed in relation to the R-curve behavior. Some examples of the work-of-fracture test results demonstrate the usefulness of the work-of-fracture for designing brittle materials with improved toughness.

The influence of finely dispersed, stable particles on the mechanical strength and microstructure of Al films on Si substrates has been studied. Aluminum oxide particles were produced in Al films by oxygen ion implantation, and the grain size was increased by a laser reflow treatment. Transmission electron microscopy (TEM) was employed to observe the oxide particles and the grain structure in the films after subsequent annealing, and the wafer curvature technique was used to study the deformation properties of the films as a function of temperature. Significant particle strengthening was obtained in the coarse-grained films in tension as well as in compression. In the as-deposited and ion-implanted films a very fine grain size of only 0.35 μm is stabilized after annealing which causes considerable softening of the film in compression at higher temperature because of the enhancement of grain boundary and volume diffusion controlled relaxation mechanisms. However, in tension at low temperature these films show high stresses comparable to those of the laser reflowed and ion-implanted films. The results are discussed in the light of TEM observations.

Barium metazirconate (BaZrO3) fine powder has been produced by thermally decomposing a molecular precursor, barium bis(citrato)oxozirconate(IV) tetrahydrate at about 700 °C. The precursor, Ba[ZrO(C6H6O7)2] · 4H2O (BZO) has been synthesized and characterized by employing a combination of spectroscopic and thermoanalytical techniques. The precursor undergoes thermal decomposition in three major stages: (i) dehydration to give an anhydrous barium zirconyl citrate, (ii) decomposition of the anhydrous citrate in a multistep process to form an ionic oxycarbonate intermediate, Ba2Zr2O5CO3, and (iii) decomposition of the oxycarbonate to produce BaZrO3 fine powder. The particle size of the resultant BaZrO3 is about 0.2 μm, and the surface area is found to be 4.0 m2 g−1.