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Experiments were conducted to determine the effect of various implanted species on the hardness of single crystal Ni3Al (Ta, Al, B) and polycrystalline TiAl (Ta, N, B). Implantations were conducted to yield about 7 at. % Ta under the peak and ∼30% Al, N, or B under the peak in the respective targets. Hardness was measured using the Nanoindenter. Results showed that Ta+-implanted Ni3Al softens due to disordering, and subsequent heat treating results in strengthening due to preferential occupation of Al lattice sites. However, B+ and Al+ implantations result in increases in the hardness, while heat treating returns the surface hardness to bulk values. Ta+, N+, and B+ implantations into TiAl all result in hardening with N+ implantation producing the greatest hardening by a factor of ∼1.9. The probable mechanism is solid solution strengthening.
Some peculiar positive charge carriers are thermally generated in fused silica above 500 °C. These charge carriers appear to be positive holes, chemically O− states, probably arising from dissociation of peroxy defects. The charge carriers give rise to a pronounced positive surface charge which disappears upon cooling but can be quenched by rapid quenching from ≍800 °C. Reheating to ≍200 °C remobilizes these charge carriers and causes them to anneal below 400 °C. The generation of positive holes charge carriers may be important to understand failure mechanisms of SiO2 insulators.
An aqueous sol-gel procedure to obtain fine Y–Ba–Cu particles with an approximately 1-2-3 stoichiometric ratio is described. This involves precipitating an aqueous solution of the oxides in HC1 by neutralization with Ba(OH)2, and precipitation of BaCO3 from solution with CO2. A novel treatment with H2O2 decreased the weight loss while sintering. The average particle size and shape was characterized by rheology, light scattering, and scanning electron microscope. Particle composition was studied with x-ray diffraction, electron microprobe, and infrared spectroscopy. The suspension was formed into a fiber and sintered, and measurements were made indicating a superconducting transition temperature near 60 K.
Superconducting YBa2Cu3O7−x fibers were fabricated by the sol-gel method using modified metal alkoxides. To prepare a heterometallic alkoxide as a precursor of a homogeneous and viscous sol, Y and Cu alkoxides were modified with ethyl acetoacetate (EAA) and ethylenediamine (en), respectively. Their structures were determined by FT-IR and EXAFS. The heterometallic alkoxide was synthesized by partial hydrolysis of the modified alkoxides and was further hydrolyzed and concentrated to obtain a viscous sol. This sol had good spinability and was spun into gel fibers by a spinning apparatus. The gel fibers had a high oxide content of 61 wt.%. The fiber, fired at 950 °C for 10 h in O2, had only closed pores and a dense structure. Tc (onset) of this fiber was 94 K.
Electron spectroscopies were used to study the reaction of Si and SiO2 layers with high-Tc superconductors at room temperature and under annealing conditions. The superconductor samples include YBa2Cu3O7 ceramic and thin film samples as well as GdBa2Cu3O7 ceramic samples. The results show that the Si overlayers withdraw oxygen from the superconductor and form an interfacial layer of Si oxide at room temperature. Annealing increases the reaction rate so that films as thick as 30 Å become completely oxidized following annealing above approximately 100 °C. Ba segregates to the surface from the bulk after Si oxidation when annealed at temperatures higher than 200 °C, while the rare earth element (Gd) does not segregate.
A 1/1-type approximant to the AlCuCr icosahedral phase and approximants to a decagonal phase have been found in an as-cast Al65Cu20Cr15 ingot. Selected area electron diffraction indicates that the 1/1-type approximant consists of Mackay icosahedra arranged on a bcc lattice, similar to the α-AlMnSi cubic phase. Ordering of the glue atoms produces a base-centered orthorhombic superstructure, making the overall structure monoclinic P2/m, with lattice parameters a = 12.6 Å, c = 17.92 Å, and α = 90°.
Several samples of type 316 stainless steels, which were treated differently and modified with minor elements (such as Ti, Nb, etc.), were irradiated by 1 MeV electrons in HVEM at temperatures ranging from 823 K to 883 K. Void swelling behavior of the steels was investigated, and three parameters, i.e., swelling, void density, and void size, were measured. The results show that prior cold work improves the swelling resistance of type 316 stainless steels more effectively than solid-solution treatment. It is also shown that Ti is the best alloying element studied that can suppress void nucleation and its growth drastically by acting as sinks and impeding dislocation climb, resulting in the reduction of void swelling.
Electrical and structural properties of coevaporated Fe–Si thin alloy films as a function of annealing temperature have been studied by in situ electrical resistivity measurements and structural analysis including 2 MeV 4He+ ion backscattering, x-ray diffraction, scanning microscopy, and roughness measurements. In the as-deposited state the coevaporated alloy film was amorphous. Upon annealing a sharp increase in resistivity occurred near 400 °C and the increase was determined to be amorphous-to-crystalline β–FeSi2 phase transformation. In cooling, the resistivity increased monotonically with decreasing temperature. Surface roughness is well pronounced for films heat treated at temperatures higher than 700 °C and is due to the difference in thermal expansion coefficients of substrate and β–FeSi2. The crystalline β–FeSi2 was determined to be a semiconductor with an energy gap of 0.80 eV. It is p-type, having a hole concentration and a Hall mobility of 1.4 × 1018 cm−3 and 4 cm2/V s, respectively, at room temperature. The kinetics of the transformation was determined by isothermal heat treatment over the temperature range of 362 °C to 390 °C, and an activation energy of 2.3 eV was measured. The nucleation and growth kinetics in the crystallization process show a change in the power of time dependence from 2.1 to 3.4.
Reaction of Ni–Al alloys within the β-NiAl phase with CrB2 was studied at 1473 K as a function of Al concentration in the alloy. Reaction of 49–50 at. % Al alloys with CrB2 occurred by interdiffusion of Ni into CrB2 and Cr into the alloy without forming a new product phase. On the other hand, a new product phase, rich in Ni and B, formed by the reaction of alloys having Al concentrations 48 at. % or lower with CrB2. The reaction product was observed both at the CrB2/alloy interface and along the alloy grain boundaries.
Continuous-fiber reinforced metal-matrix composites consisting of Ni3Al alloys and Saphikon Al2O3 single crystal fibers were fabricated by hot-pressing of fiber-foil lay-ups. Two matrix compositions were employed, namely, IC50 (Ni–22.5Al–0.5Zr–0.1B, at. %) and IC396M (Ni–15.9Al–8.0Cr–0.5Zr–1.7Mo–0.02B, at. %). Etching of the foils in aqueous FeCl3 solution prior to lay-up and hot-pressing tended to improve fiber-matrix bonding and the density-normalized room temperature yield stress. Whereas strength improvements for the IC50 matrix were only moderate, significant improvements were found for an IC396M composite reinforced with 10 vol. % of Saphikon fibers.
This work presents the first experimental evidence of the formation of a fractal network of crystalline clusters in the first stage of the amorphous-crystal transformation. Although this transformation has been extensively studied, such an intermediate stage between amorphous and crystalline phases has never been experimentally revealed before. This fractal network was obtained by laser irradiation of an amorphous Te–Se–Br alloy. The irradiation conditions have been determined in order to be in a regime of limited diffusion, which is the basis of fractal formation. Moreover, the fractal dimension has been determined to be 1.55, which corresponds to the theoretical value obtained for fractal growth by a process of cluster-cluster aggregation with some structural readjustment.
The atomic structure and roughness on the surface of a carbon fiber have a great effect on the degree of bonding of that fiber in a carbon fiber composite. Although there have been many studies on the bulk structure of these fibers, this is the first study dealing with the atomic surface structure of several carbon fibers. With the advent of the scanning tunneling microscope (STM), it is now possible to study both the roughness and structure of these fibers on the atomic scale. Type II PAN based fibers were found to have a rougher surface than type II pitch-based fibers. Similar to what has been observed in the interior of pitch fibers, the percentage of graphitic structure on the surface increased with the degree of heat treatment and with the modulus of the fiber.
Formation of End-of-Range (EOR) disorder was studied in (100)-oriented silicon, when subjected to amorphization by implantation of Ge+ ions, followed by a 10 s Rapid Thermal Annealing (RTA) at 1050 °C. XTEM, RBS/channeling, and SIMS were used to analyze Czochralski grown (CZ) silicon wafers with oxygen concentrations of 6.5, 7.0, and 8.0 × 1017/cm3 and Float Zone (FZ) silicon, as “low oxygen” wafers. Amorphization on neighboring parts of the 4″ wafers was made either by 60 keV Ge+ implantation or by 110 keV Ge+ implantation and by sequential (60 keV + 110 keV) Ge+ implantation. Parts of each wafer were additionally implanted with 13 keV boron. In FZ silicon, no defects were found for 60 keV Ge+ implantation and RTA at 1050 °C. For 110 keV Ge+ and sequential (60 keV + 110 keV) Ge+ implantation in FZ-silicon the majority of the samples showed perfect annealing. Two wafers, however, subjected to sequential implantation still contained defects but with a defect density that was one order of magnitude lower than for CZ wafers. For one of them, not even a continuous layer of defects was formed. In contrast, CZ wafers contained defect bands, except for the 60 keV Ge+ implantation [in accord with the findings of Ozturk et al., IEEE Trans. on Electronic Dev. 35, 659 (1988)]. The presence of boron had no visible effect on the defect structure.
Silicon wafers have been implanted with As+ ions at an energy of 100 keV and a dose of 1 × 1017 cm−2 and subsequently annealed at 1050°for 15 min. This results in a peak As concentration of 7 × 1021 cm−3, which is far beyond the solid solubility value of arsenic in silicon at this annealing temperature. Rod-like precipitates, dislocations, and small precipitate-like defects have been observed by transmission electron microscopy. From the analysis of several diffraction patterns taken on a number of rod-like particles at different tilt angles, it has been unambiguously found that they have the structure of the monoclinic SiAs compound previously reported in literature. The stoichiometry of the precipitates has been confirmed by x-ray microanalysis. To our knowledge, this is the first time that this SiAs phase is detected in As+-implanted silicon.
Thermal diffusivity of the sintered semiconductors was measured by the photopyroelectric (PPE) method. The measurement based on the phase-modulation frequency characteristics was shown to give superior results, eliminating errors expected in the conventional signal amplitude-distance characteristics measurements. Thermal diffusivities of the melt-grown and hot-pressed samples were found to be αmelt(c⊥) = 0.014 cm2/s, αmelt(c//) = 0.011 cm2/s, αhot(c⊥) = 0.012 cm2/s, and αhot(c//) = 0.008 cm2/s, depending on the relation between the c-axis direction of grain and thermal flow direction. The thermal diffusivity of the hot-pressed samples shows a strong dependence on the hot-press pressure through the orientation factor.
Films of NiOxHy were made by reactive dc magnetron sputtering of Ni followed by electrochemical treatment in KOH. Infrared reflectance spectroscopy with obliquely incident p-polarized light documented a unique topochemical reaction with the bleached state being β–Ni(OH)2 and the colored state being β–NiOOH. The same technique yielded clear, though not yet fully understood, data on the evolution of electrochromism during potentiodynamic cycling.
Transmission electron microscopy (TEM) has been used to explore details of the structural phase transitions and corresponding microstructural features in the solid solution of Pb1−xBaxNb2O6 (PBN) tungsten bronze ferroelectrics at compositions embracing the morphotropic phase boundary between orthorhombic and tetragonal ferroelectric phases. In addition to the ferroelectric domain structures that were consistent with the expected symmetries, incommensurate ferroelastic phases were observed. The “onset” and “lock-in” transition temperatures are a function of the Pb/Ba ratio, and for lead-rich compositions it appears that the incommensurate distortion may occur above the ferroelectric Curie temperature in the paraelectric phase.
Electrical conduction in thick film resistors has been studied, and microstructures, especially around conducting RuO2 phases in a lead-borosilicate glass matrix in as-fired and high-voltage-surged thick film resistors, have been observed in detail using transmission electron microscopy. Lattice images of as-fired thick film resistors have suggested the presence of subtle structural modifications in the very thin area across the RuO2/glass interface, whereas in the glass matrix very small dot-like contrasts on the order of 1 nm were occasionally observed and were interpreted as being small crystallites or Ru clusters. Heavy electrical loadings of thick film resistors were found to induce the local formation of plate-like crystals in glass, which were identified by electron diffraction to be a slightly modified anorthite. The significance of these observations in terms of the conduction network and the degradation due to the electrical overloading of thick film resistors are discussed.
Oxide thin films on Si substrates were prepared from carboxylate precursors by the reaction of the metal nitrates and ammonium trimethylacetate. Precursor salts were characterized with respect to purity, structure, thermal pyrolysis, and phase development during calcination. A solvent system, based on carboxylic acid/amine mixture, was developed to dissolve the synthesized precursors, resulting in increased solubility, viscosity, and stability. Smooth, fine-grained ZrO2, Y2O3, and YSZ films were obtained on Si wafers by spin-coating and subsequent heat treatment above 500 °C. Films heat treated below 700 °C were generally adherent, amorphous, or microcrystalline, while YSZ and ZrO2 showed (111) preferred orientation above 700 °C. These oxide films show promise as protective or buffer layers on Si wafers.
Mg–Ti–spinel formation along the interface of epitaxial TiN(100) films to MgO(100) substrates has recently been investigated by transmission electron microscopy (TEM) in the diffraction-contrast mode in samples grown at substrate temperatures higher than 800 °C and in such post-annealed at 850 °C. This phenomenon has now been investigated by high resolution electron microscopy of cross-sectional samples, at an acceleration voltage of 300 kV. Emphasis is given to the TiN/spinel and the spinel/MgO interfaces with respect to their structure and morphology. The results obtained confirm the previously drawn conclusions on the atomic mechanism of the solid state reaction during the spinel-forming process: The spinel, which most likely is of the composition Mg2TiO4, forms by counterdiffusion of the cations Ti4+ and Mg2+ in the rigid oxygen frame provided by the fcc oxygen sublattice of MgO. The latter is completely taken over by the spinel lattice. This “host” character of the MgO substrate lattice for the topotaxial growth of the spinel lattice and the coherency of the solid state reaction with respect to the lattices of all the phases involved are demonstrated. Misfit dislocations at the TiN/MgO, TiN/spinel, and the spinel/MgO interfaces, as well as antiphase boundaries of the cation sublattice of the spinel phase, have also been observed.