Interdiffusion coefficients (D) were determined in the temperature range 1373 K–1073 K (0.85 Tm−0.65 Tm) from concentration-distance profiles that were generated from Al66Ti25Mn9/Al67Ti25Cr8 diffusion couples. As both of these materials are completely soluble in one another, the couples were treated as pseudobinaries (particularly because the Ti and Al levels were similar), and the Matano approach was used to calculate diffusion coefficients. The variation in D with composition was determined and a minimum was noted at intermediate temperatures and a relative Mn concentration of 0.5. A maximum in activation energy for interdiffusion was also noted at this concentration where Q ≍ 350 kJ/mol.

Phase pure YBa2Cu3O7 high transition temperature superconductor powders were synthesized by a new precursor route. This new synthesis procedure is easy, leads to an atomic mixture of the relevant constituents, and is readily adaptable to many other systems or to the doping of existing systems. A gel of yttrium, barium, and copper salts was prepared using organic gelling agents. The gel was then dried and ground, leaving the xerogel precursor. These xerogels are perfectly stable even under high humidity atmospheric conditions and show an amorphous structure when characterized by x-ray diffraction, which is consistent with the existence of an atomic mixture of the three relevant metal salts. The organic gelling agent was selected after optimization studies focused on such issues as ash residue after calcination, solubility, and chemical interference with the metal salts. From a great variety of these gelling agents (agar, xanthan gum, gelatin, alginates, and others), gelatin was chosen as the ideal gelling agent for this specific application. The final product characterization shows very unexpected results. The crystalline phase purity of the YBa2Cu3O7 superconducting phase was about 99%, with no traces of barium carbonate, as expected from pseudo-organic precursors (xerogels). The product shows superconducting properties even before oxygen anneal (Tc ≍ 70 K), and after oxygen annealing of the powders the transition temperature was found to be 91 K, showing a linear behavior of the resistivity versus temperature before the drop at Tc, extrapolating to zero at 0 K. The particle size of these powders is smaller than 1 μm, as shown by SEM.

High-angle grain boundaries in YBa2Cu3O7−δ thin films are of technological interest because of the weak coupling observed between the grains; however, not all high-angle grain boundaries show this weak-link behavior. The microstructure of both these boundaries is not understood, nor is the reason for the differing electrical transport properties. High-angle grain boundaries in YBa2Cu3O7−δ thin films on MgO, where the angular misorientation between the grains is ∼45°, have been examined using high-resolution electron microscopy. The results show that the boundary structure can appear quite different even when the angular misorientation between the two grains is the same. The stability of the grain boundaries under the electron irradiation in the electron microscope was found to be a function of the accelerating voltage—400 kV leads to rapid disordering of the boundary region.

Observations of the Bi–O surface of superconductive Bi2212 single crystals were carried out using an ultrahigh-vacuum scanning tunneling microscope (UHV-STM). In the atomic resolution images, surface corrugations, which correspond to the superstructure of the Bi–O surface in addition to Bi atom deficiencies, were observed. There were hollow lines along the ridges of the corrugations, which may be due to missing atom rows.

Shock-induced chemical reactions between nickel and aluminum powders (mixed in Ni3Al stoichiometry) are used for the synthesis of nickel aluminides. It is shown that the extent of shock-induced chemical reactions and the nature of the shock-synthesized products are influenced by the morphology of the starting powders. Irregular (flaky type) and fine morphologies of the powders undergo complete reactions in contrast to partial reactions occurring in coarse and uniform morphology powders under identical shock loading conditions. Furthermore, irregular morphology powders result in the formation of the equiatomic (B2 phase) NiAl compound while the Ni3Al (L12 phase) compound is the reaction product with coarse and regular morphology powders. Shock-induced reaction synthesis can be characterized as a bulk reaction process involving an intense “mechanochemical” mechanism. It is a process in which shock compression induces fluid-like plastic flow and mixing, and enhances the reactivity due to the introduction of defects and cleansing of particle surfaces, which strongly influence the synthesis process.

Ternary Ni77Al23−yXy (X = Zr or Hf, y = 0.5 or 1) + 500 ppm boron compounds with various grain sizes were welded by a CO2 laser. Fractographic examinations of the heat-affected zone (HAZ) in the welds with or without postweld heat treatment (PWHT) were performed on the impact-fractured specimens. In laser welds, the fracture appearance of the HAZ was mixed transgranular/intergranular modes for fine-grained alloys and intergranular mode for coarse-grained materials. However, an entirely transgranular mode was observed in the base metal regardless of the grain size of the compounds. Boron desegregation at high temperatures during the thermal cycle of welding could be used to explain the fractographic change from originally ductile mode into less-ductile or even brittle fracture in the HAZ. Short-term PWHTs along with slow cooling provided sufficient time for boron segregation back to the grain boundary, resulting in a completely transgranular fracture mode in the fine-grained HAZ. Nevertheless, such a phenomenon was not observed in the HAZ of coarse-grained welds. Cracks in the HAZ of coarse-grained welds after long-term PWHT, if not so severe, could be healed by a sintering process.

A series of iron-chromium-nickel alloys was melted under a nitrogen atmosphere at several different pressures. Nitrogen–high pressure melting (N–HPM) was conducted under pressures ranging from 0.1 to 200 MPa. The total nitrogen concentrations achieved in these alloys were proportional to the square root of the nitrogen pressure used during melting. Nitrogen took the form of soluble interstitial nitrogen and metal nitride precipitates, FexN and CrN. Tensile properties of N–HPM alloys were directly proportional to the nitrogen concentration in the alloy.

Al films deposited on Pt layers developed voids after annealing at 250 °C. The amount of Al in the area surrounding the voids increased relative to the as-deposited film. The addition of 1 or 4% Cu to the Al suppressed the void formation and lateral Al migration. The void formation is related to compound formation with the Pt. The addition of Cu to the Al did not modify the Pt2Al3 formation.

A pulsed glow discharge electron beam has been used for the production of metallic amorphous surfaces in MgZn alloys. Electron beam pulses of 20 μs pulse width produced by a 40 A, 22.5 kV glow discharge were found to provide sufficient energy for melting the metallic surfaces; that due to the rapid cooling to the substrate yielded amorphous phases. The system allows control of the energy density, penetration, and pulse width of the heating pulse.

A part of the Al–Cu–Co phase diagram adjacent to the Al13Co4 composition was studied at 800 °C by scanning electron microscopy and x-ray diffractometry. The homogeneity region of the Al13Co4 phase was found to extend up to 6 at. % Cu. At 800 °C this phase is in equilibrium with Al(Co, Cu), Al5Co2, Al9Co2, the decagonal phase, and a liquid phase. The existence of the Y-phase and Al3Co was not confirmed at this temperature.

Copper and lead powders were precipitated by laser-induced reduction of copper(II) formate, copper(II) acetate, and lead(II) acetate dispersed/dissolved in glycerine by exposure to 248 nm KrF pulsed laser radiation. The deposited powders consisted of pure copper and a mixture of pure lead and partially reduced metallo-organic complexes, respectively. The reduction of the metallo-organic complex of lead was completed thermally. Temperature, concentration, laser pulse repetition rate, and stirring influenced the deposition rate in both cases. The copper particles were predominantly hexagonal in shape and ranged in size from 0.01–0.04 μm. The lead particles were football shaped and had a very narrow size distribution, with an axial dimension of about 0.5 μm. It was shown from a spectroscopic analysis of the reaction products that the initial nucleation was caused by photochemical processes. However, exposure of the nonaqueous solutions to CO2 laser pulses at room temperature did not yield any particles.

The nucleation and growth of quasicrystalline thin films during sequential vapor deposition of aluminum and manganese on various substrates have been studied at temperatures between 530 and 650 K. The films were analyzed by transmission electron microscopy, electron diffraction, energy dispersive x-ray analysis, replica techniques, and Auger depth profiling. The quasicrystalline phase is identified as icosahedral. It nucleates on the surfaces of the Al films. There is no indication of substantial bulk Mn diffusion. The growth process is governed by diffusion of Al to the quasicrystal surface where it reacts with the incident Mn.

The adhesion of as-sputtered Pt thin films to NiO single crystals has been characterized by a continuous microscratch technique. In these experiments, a conical indenter was driven into a 1.2 μm thick Pt film at a rate of 15 nm/s, and across the sample surface at a rate of 0.5 μm/s, until a load drop was observed indicating that the film had delaminated. Using the width of the scratch track at the point at which the film delaminated from the substrate, the critical load required for delamination, and the area of the delaminated region, a model has been developed to determine the work of adhesion of the Pt/NiO system. This model uses an elastic contact mechanics approach to relate the stresses acting in a scratch experiment to the strain energy released during film delamination. Using this model, the work of adhesion and hence the interfacial fracture toughness have been determined to be 0.023–0.06 J/m2 and 0.07–0.11 MPa$\sqrt m$, respectively. These values are in reasonable agreement with those determined by other methods for metal-ceramic systems.

Stress-driven diffusive growth of voids in encapsulated interconnect lines is studied. By calculating the rate of growth of a single void in a passivated line subjected to an initial hydrostatic tension stress and by assuming that failure occurs when the void reaches a critical size, a model for failure of encapsulated interconnect lines by stress voiding can be developed. The model for the prediction of void growth and failure is based on two limiting kinds of void growth. In one limit, which applies at short times, radial displacements occur by diffusional flow processes around the growing void and relax the local hydrostatic tension stress. In the long time limit, vacancies flow to the void from distant parts of the line by diffusion along grain boundaries, thereby relaxing the stress in a growing section of the line. A model based on a combination of these behaviors leads to a failure law for aluminum lines of the form tfσ2/d = 1019.2 exp(Q/RT) where tf is the failure time in seconds, σ is the initial hydrostatic tension stress in the line in Pa, d is the grain size in meters, and the activation energy, Q = 80.9 kJ/mol, is close to that for grain boundary diffusion in aluminum. The model predictions appear to be in good agreement with the few experiments on stress voiding that have been conducted.

Polycrystalline diamond thin films have been selectively grown on silicon, silicon dioxide, silicon nitride, tantalum, molybdenum, alumina, and sapphire substrates using selective damaging by ultrasonic agitation. Processes were developed to selectively damage the substrates by ultrasonic agitation in methanol containing diamond particles of typical size 90 μm. Optical and scanning electron microscopy is used to study selectivity and morphology of as-grown diamond thin films.

The XeCl laser ablation of a polyetheretherketone (PEEK)-carbon fiber composite (APC-2) is reported. Etch rates and measurements of the ablation products have been carried out, together with scanning electron microscope evaluation of the etch craters. Selective removal of the PEEK matrix occurs for fluences ∼70–400 mJ cm−2. Net composite etching commences at ∼420 mJ cm−2, with an etch rate above this value that is determined by the carbon fibers and is consistent with thermal vaporization at high temperature (≥4000 K).

Kapton films, 25 μm thick, were carbonized and then graphitized at various temperatures up to 3000 °C. They were studied by optical microscopy and transmission electron microscopy and were prepared by thin-sectioning for transmission electron microscopy. The residual embedded blocks were used as polished sections for optical microscopy. Kapton thin film heat-treated at 650 °C showed thin areas of preferred orientation at its two opposite faces. This orientation extends all over the film thickness between 800 °C and 1000 °C. It corresponds to a statistical orientation of small aromatic layer stacks, parallel to the film plane. From 1000 °C up to 2475 °C flattened pores develop everywhere. At 2475 °C, they suddenly collapse and partial graphitization occurs. The Kapton film is completely graphitized between 2820 °C and 3000 °C. The mechanism of graphitization is similar to that of anthracites and also to that of nongraphitizing carbons heat-treated under pressure.

Structural and textural changes in carbon films prepared from the polyimide Kapton with heat-treatment temperatures up to 3000 °C were followed by measuring the magnetoresistance at 77 K, the ratio of electrical resistivity at room temperature to that at 77 K, and x-ray powder patterns. The maximum magnetoresistance (Δρ/ρ)max as a measure of graphitization changed its sign from negative to positive around 2500 °C and then increased its value abruptly. The resistivity ratio ρR.T./ρ77 K increased above 2500 °C treatment. The values of (Δρ/ρ)max and ρR.T./ρ77 K after 3000 °C treatment reached 275% and 0.93, respectively. The average interlayer spacing d002 after the 3000 °C treatment was 0.3354 nm, the same as natural graphite. The changes in structure and texture in the film were consistent with the model proposed in the previous paper from observation by transmission electron microscopy.

The preferred orientation of pitch precursor fibers and carbon fibers from an isotropic pitch was studied using x-ray diffraction techniques. The φ scan profile of a pitch precursor fiber was divided into two parts: φ scan-dependent (anisotropic) and φ scan-independent (isotropic) profiles. The half width at half maximum (HWHM) intensity of the anisotropic part became smaller as the pitch viscosity increased during spinning and as the filament diameter decreased. The area ratio of the anisotropic part to the total area increased when spinning at higher pitch viscosities and when making the diameter thinner; no preferred orientation existed for pitch precursor fibers with very large diameters. A thermodynamic model is proposed for the preferred orientation formation when spinning an isotropic pitch. The carbon fiber exhibited no skin-core difference in preferred orientation. A crystallite with a larger crystallite size Lc(002) in the carbon fiber was shown to be better aligned along the fiber axis than that with a smaller Lc(002). Furthermore, a well-aligned crystallite possessed a larger Lc(002) than one that was misaligned. The pitch precursor fiber also exhibited such a correlation between Lc(002) and the preferred orientation, but the correlation was weak.

Diamond crystals have been selectively grown on the apex of anisotropically chemically etched silicon pyramids. A novel process sequence is developed which exposes a patterned sharp apex of silicon pyramids surrounded by thermally grown silicon dioxide to a high pressure microwave plasma-assisted chemical vapor deposition (HPMACVD) process where the reactant feed gases are methane and hydrogen. The nucleation rate of diamond is very high on the sharp edge of a silicon mesa structure or an apex of a silicon pyramid, as anticipated. Selective growth of diamond particles on the apex of silicon pyramids fabricated using various approaches was analyzed by scanning electron microscopy.