Amorphous powders in the Cs2O–Al2O3−SiO2 system were prepared by sol-gel processing. Gels made from TEOS, Al-chelate, and Cs-acetate were dried and calcined to obtain molecularly mixed powders of analyzed compositions in the range useful for conversion to pollucite (CsAlSi2O6) glass-ceramics. X-ray diffraction (XRD), differential thermal analysis (DTA), thermogravimetry (TG), and scanning electron microscopy (SEM) were used to characterize the powders. A typical amorphous powder of analyzed chemical composition (in wt.%) = 28.05Cs2O, 37.77SiO2, and 37.96Al2O3 was found to have a glass transition temperature of 945 °C and a glass crystallization temperature of 1026 °C. Preliminary experimental results of densification and crystallization of the amorphous powders show pollucite/mullite phases to be present.

The effect of different drying and calcination methods on the ultimate particle size of YBa2Cu3O7 (Y-123) has been investigated. The starting material was a tetramethylammonium (TMA) carbonate-precipitated slurry. Spray-drying the slurry after filtering and reslurrying (to remove residual TMA) was most effective in the ultimate formation of finely divided Y-123. The morphology of the spray-dried powder could be preserved by calcining in very low total pressures of flowing oxygen. When a slurry with 0.16% solids content was spray dried, and this powder calcined at 750 °C in 2 Torr of flowing oxygen, a Y-123 powder of mean particle size 0.74 μm (66% submicron) was obtained.

In sintering and annealing of ceramic superconductors, diffusion of oxygen and sample weight changes are two important parameters to understand. In this work, we have undertaken to make weight loss measurements at different temperatures. At 400–600 °C, the weight loss data can be simply interpreted via one diffusion process. The Arrhenius activation energy is found to be ca. 23 kcal/mole. At 500 °C, the isotropic diffusion constant was found to be 9.5 × 10−12 cm2/s. Above 600 °C, the weight loss curves become complex and indicate the occurrence of two diffusion processes. The oxygen loss and the oxygen uptake data are interpreted via our present knowledge of this system.

YBa2Cu3O7−δ has an internal friction peak near 210 °C measured at 1.18 Hz. The shift in the temperature of this peak with frequency as measured with different internal friction techniques indicates that the relaxation process has an average activation energy of 1.14 ± 0.05 eV and a pre-exponential factor, τ0 = 1.5 × 10−13s (log τ0 = −12.82 ± 0.23). The peak height decreases during annealing at above 375 °C in helium and increases when annealed in oxygen. The mechanism for the relaxation is believed to be the stress-induced motion of oxygen atoms in the Cu–O plane. Detailed analysis shows that the internal friction peak is determined by a spectrum of activation energies; this spectrum is a symmetrical single peak 0.12 eV wide at half-height. Models for the relaxation are considered and the resulting diffusivities are compared to tracer diffusion results.

By controlling the pH of mixed nitrate solutions, we have produced single-phase YBa2Cu3O7−x platelet particles with an average size of 2.5 μm. The kinetics of superconducting phase formation and the thermal properties of the related phases were systematically studied. Through this understanding, we have developed sintering techniques which produce YBa2Cu3O7−x with wide areas of highly aligned grains at 1010 °C. By incorporating aligned microsized particles into the matrix of this reactive precursor powder as nucleation sites, samples with large randomly oriented domains can be formed at 980 °C.

Thin films of Y1Ba2Cu3O7−x have been prepared on MgO, SrTiO3/Al2O3, and Al2O3 substrates by rf magnetron sputtering. A buffer layer of SrTiO3 was deposited on Al2O3 by flash evaporation. The as-deposited films on MgO and SrTiO

Submicron YBa2Cu3O7−δ particles have been produced in an aerosol flame reactor by a spray pyrolysis method in which an aerosol composed of an aqueous solution of Y, Ba, and Cu nitrate salts was introduced into a flame. It was observed that the configuration of the flame is particularly important for the successful application of the method. A premixed flame gave particles with an x-ray diffraction pattern resembling the XRD spectra of materials exposed to high concentrations of water vapor. An over-ventilated diffusion flame configuration produced the desired result: submicron unagglomerated, solid crystalline particles with Tc = 92 K.

Interfaces formed by condensing Ni atoms onto YBa2Cu3O7−x (Y-123) and Bi2Sr2Ca0.8Y0.2Cu2Ox (Bi-2212) have been studied with x-ray photoelectron spectroscopy. For both Y-123 and Bi-2212, the Ni 2p3/2 and O 1s core level features indicate Ni–O reactions and changes in the Cu 2p3/2 emission that reflect reduction from nominal Cu2+ to Cu1+ oxidation states. Ni deposition onto Bi-2212 also reduces Bi–O bonding and releases Bi atoms. For Ni/Y-123, analysis of emission intensities as a function of coverage shows that O and Ba intermix in the growing metal overlayer but that Cu is trapped at the buried interface. For Ni/Bi-2212, similar analysis shows O and Bi intermixing but less effective Cu trapping.

The structural evolution and cationic stoichiometry of Bi(Pb)–Sr–Ca–Cu–O superconductors have been studied using transmission electron microscopy and x-ray microanalysis. The nature of the incommensurate modulation changes systematically as increasing amounts of lead are added. X-ray microanalysis studies reveal that lead replaces Bi in the structure. Pb addition improves the microstructural homogeneity leading to the formation of a nearly homogeneous sample consisting of the “2223” phase. Based upon all the experimental results, it is inferred that the role of Pb substitution is related to the thermodynamics and kinetics of the formation of the n = 3 phase.

Cu films with a thickness around 3.5 μm have been deposited on rough Al2O3 ceramic substrates by the partially ionized beam deposition technique. While the ion bombardment parameters are similar for all depositions, the substrate temperature during deposition is varied from 50 °C to 300 °C. Physical structure of the films is studied by SEM in cross-sectional and surface geometries. X-ray diffraction 2θ scan is performed to obtain information on the microstructure of the films, such as (111) fiber texture and average crystallite size. Resistivity of the films is also measured. It has been found that the physical structure of the films varies from a typical columnar structure at 50 °C to a completely noncolumnar structure at 300 °C. The XRD results show that the films are polycrystalline and have different degrees of 〈111〉 preferred orientation, depending on the substrate temperature. The average crystallite size increases with the increase of substrate temperature. No correlation between the physical structure and microstructure of the films is observed. The resistivity of the films was also seen to change as a function of the substrate temperature. This can be explained by quantitative models in which grain and columnar boundaries in the films are responsible for the decrease in electric conductivity of the films.

The Embedded Atom Method (EAM) is used to compute density, internal energy, and structure factor for bulk liquids of the fcc metals at several temperatures above and below the melting temperature. The calculated values are found to be in generally good agreement with experiment, although the volume expansion upon melting does differ by up to 50% from the expected result for some of the elements studied. The total energy of a liquid system with surfaces is calculated, and the results are compared with the bulk liquid results to determine the enthalpy and thickness of the liquid-vapor interface. Also, the surface tension is found for Cu near the melting temperature. The EAM values for surface enthalpy and surface tension are found to be smaller than experimental values, which is consistent with results for EAM calculations of the surface energy of crystalline solids.

Severe microstructural damage has been observed in polycrystalline OFHC copper specimens thermally exposed to high pressure tritium gas at temperatures ⋚200 °C, but not at 300 °C. No such damage occurs in single crystal specimens exposed under identical conditions, regardless of temperature. In the polycrystals, the damage takes the form of very flat, crack-like intergranular cavities. It is found that the cavitation evolves slowly with time. For short exposure times, cavities as small as 0.1 μm are observed. In specimens subjected to the longest aging times, the cavities grow and link until entire grain boundary facets fail. The driving force for the growth of these cavities is attributed to the internal gas pressure of helium-3 generated by the decay of tritium. The growth kinetics of the cavity microstructure are described by a coupled grain boundary, surface self-diffusion process. The tritium exposure profoundly affects the mechanical properties of the polycrystalline material, inducing a severe loss in ductility. In concert with the observed ductility loss is a change in fracture morphology from transgranular ductile rupture to intergranular fracture. Examination of the resulting grain boundary facets reveals a dimple structure. The spacing of these dimples can be correlated with the spacing of the exposure-induced grain boundary cavities.

The elastic interactions of dislocations and intergranular cracks in isotropic materials have been studied. In the first part of the paper, a model based on the Rice–Thomson theory is established under which the conditions for dislocation emission and crack propagation can be described in terms of an emission surface, cleavage surface, and loading line in the local k-space associated with a mixed mode intergranular crack. For a given crack, the local k-field changes with the emission of dislocations from the crack tip, which alters the balance of cleavage and emission. In the second part, we present experimental results of in situ TEM observations of intergranular cracks in molybdenum. Alternating brittle crack propagation and dislocation emission is observed. The number of emitted dislocations corresponding to each crack propagation is in good agreement with the calculated values.

We report first principles local density calculations for the metastable Al3Li intermetallic compound with cubic L12 crystal structure using the full-potential linearized augmented plane wave method. From the second derivative of the total energy as a function of volume, and generated tetragonal and trigonal lattice distortions, the elastic constants C11, C12, and C44 were derived yielding C11 = 158 GPa, C12 = 29.4 GPa, and C44 = 57.7 GPa. Because of the very high Young's modulus (E = 141 GPa) compared, for example, to pure Al (E = 66 GPa), it is suggested that Al3Li plays an important role in strengthening the Al–Li alloys. The calculated Young's modulus appears in good agreement with experimental estimates when the experimental values are extrapolated to 0 K. Although the Young's modulus of Al3Li is increased in comparison to Al, the calculated bulk modulus is decreased to a value of 72 GPa as compared to pure Al (82 GPa), in agreement with experiment. As a result, the Poisson ratio is reduced to ŝ = 0.173 as compared to the value 1/3 for an isotropic medium. Because of this and the high Young's modulus, the calculated Debye temperature ΘD at 0 K amounts to 672 K, which is substantially larger than ΘD for Al, which is about 400 K.

The effects of substituting Cu for either Ti or Al in Al3Ti were studied by the first-principles local density self-consistent linear muffin tin orbital method. The Cu atoms are found to strongly favor Al sites and to promote the stability of the L12 phase, in agreement with experiment. Surprisingly, the rigid band model is closely followed when Cu substitutes for Al. However, the structure of the density of states undergoes remarkable changes if Cu substitutes for Ti; a much weaker hybridization occurs in both L12- and DO22-like structures, giving rise to weaker binding effects. The modification of bond directionality upon Cu addition is determined by comparing the charge density for the structures calculated with those of pure Al3Ti. The effect of tetragonal distortion is also examined. By comparing with the bonding characteristics of pure Al3Ti in the L12 and DO22 structures, the addition of Cu to Al3Ti is found to be equivalent to the tetragonal distortion in DO22 Al3Ti as far as bonding is concerned, resulting in the stabilized L12-like structure for (AlCu)3Ti. The semi-empirical inverse relation between the structural stability and the density of states at Fermi energy is well established.

The relative variations of the intensities of the superlattice peaks in the x-ray scattering of Ti50−xMnxAl50 alloys (x = 0, 0.77, 1.85, and 3.30) are used to determine the site occupancy by Mn atoms. It is concluded that up to x = 1.85, Mn occupies the Ti sites whereas for x = 3.30, some Al sites may also be occupied in the L10 structure of γ–TiAl alloys.

Early studies showed that the two-phase ordered alloy of semi-coherent β–Ni2AlTi (L21) and β–Ni(Al, Ti) (B2) exhibits excellent elevated-temperature creep strength, and the precipitation of the “rod-like” γ'–Ni3(Al, Ti) (L12) from either the β or the β' phase improves the room-temperature ductility of the phases concerned. In the present investigation an attempt is being made to combine the above microstructural features in β'–β–γ' three-phase alloys and for this purpose the composition Ni63Al22Ti15, near the β'–γ' edge of the three-phase region in the recently estimated Ni–Al–Ti isotherm at 900 °C, has been selected for detailed study. The expected precipitation of both the β and the γ' phases occurs in the dendritically solidified β' phase after a 1100 °C/3 h homogenization and a 900 °C/115 h anneal, although the original interdendritic γ' phase remains. The morphology of the two types of precipitates and their orientation relationships with the β' parent phase have been examined using transmission electron microscopy and diffraction, and the experimentally obtained data compared with those predicted by Khachaturyan's elastic strain energy theory. The β precipitates are nearly cuboidal in shape and are bounded by interface dislocations of aβ〈100〉 edge type. For the β precipitates, both morphology and orientation relation agree with those predicted by the theory. The γ' precipitates were found to obey the Nishiyama–Wassermann orientation relationship with the parent phase. These precipitates are about 0.5 μm thick and elongated along their 〈211〉 directions, and in all cases consist of two twin-related variants, giving a sword-like morphology. The {11} twin planes, parallel to the {10} of the parent phase, have been identified as the habits of the precipitation. The theory, however, predicts a habit of {0.732, 0, 0.681}γ' type and a Baker–Nutting orientation relationship. This discrepancy has been attributed to the inapplicability of some assumptions made in the theory: equal elastic moduli between parent and product phases and a tetragonal transformation strain based on Bain's model of the bcc → fcc transformation. The presence of diffuse streaks in the diffraction patterns of the parent phase, which can be correlated with the 〈110〉〈10〉 shear waves, suggests high elastic anisotropy and lends credit to Zener's model. Crystallographic consideration shows that this model is feasible for the L21 → L12 transformation and explains the observed morphological features of the γ' precipitates. Some earlier studies are also discussed.

An alumina (Al2O3) diffusion barrier coating to inhibit the interfacial reactions between boron-carbide-coated boron (B4C/B) fibers and a nickel-aluminide (Ni3Al) (IC-221) matrix was investigated. The alumina diffusion barrier was deposited on the B4C/B fibers using chemical vapor deposition. Also, Saphikon single-crystal Al2O3 fibers were used to demonstrate the compatibility between Al2O3 and Ni3Al. The detailed microstructures and chemical compositions of the fibers, coating, and matrix before and after various thermal exposures were analyzed using scanning electron microscopy, energy dispersive x-ray analysis, and ion microprobe mass analysis. The interfacial reaction products present after 6 h at 980 °C were characterized, and Ni was found to be the dominant diffusion species. The alumina diffusion barrier shows promise for effectively inhibiting the deleterious reactions between B4C/B fibers and the Ni3Al matrix. The uncoated B4C/B fibers were consumed by the matrix after fabrication alone, whereas the Al2O3 coated fibers demonstrated resistance to the matrix for 25 h at 880 °C and 6 h at 980 °C. The Saphikon fiber-reinforced Ni3Al composites demonstrated excellent compatibility after 50 h at 1000 °C. Zirconium (Zr)-rich precipitates on the order of 2 μm in diameter formed at the fiber interface after this exposure, but no gross reaction was indicated between the fiber and the matrix.

A Ni3Al-based alloy containing Cr is examined after preparation by Osprey deposition. The microstructure consists of solidified spherical regions showing cellular segregation interspersed with regions of finer, equiaxed segregation morphology. The segregation structure is characterized by cell interiors rich in aluminum and poor in chromium, while the cell walls are poor in aluminum and rich in chromium. This segregation pattern is the inverse of that expected, based on earlier melt spinning experience, and is explained in terms of the undercooling of the melt prior to solidification. Very high temperature annealing is required to homogenize the material, despite the use of this rapid solidification process for material fabrication.

A quasicrystalline transition state was found in an Al65Cu20Fe15 alloy after heat treatment at 700 °C and subsequent slow cooling of samples originally containing the icosahedral quasicrystalline phase. The transition state is characterized by the simultaneous presence of two types of quasicrystalline domains. Their structure can be obtained by the introduction of one-dimensional periodicity along one of the fivefold axes of the original icosahedral quasicrystal. The two types of domains differ in their period lengths which are obtained by multiplying a fundamental length of the icosahedral structure by the Fibonacci numbers 5 and 8.