Interatomic potentials of the embedded atom and embedded defect type were derived for the Co–Al system by empirical fitting to the properties of the B2 CoAl phase. The embedded atom potentials reproduced most of the properties needed, except that, in using this method, the elastic constants cannot be fitted exactly because CoAl has a negative Cauchy pressure. In order to overcome this limitation and fit the elastic constants correctly, angular forces were added using the embedded defect technique. The effects of angular forces to the embedded atom potentials were seen in the elastic constants, particularly C44. Planar fault energies changed up to 30% in the {110} and {112} γ surfaces and the vacancy formation energies were also very sensitive to the non-central forces. Dislocation core structures and Peierls stress values were computed for the 〈100〉 and 〈111〉 dislocations without angular forces. As a general result, the dislocations with a planar core moved for critical stress values below 250 MPa in contrast with the nonplanar cores for which the critical stress values were above 1500 MPa. The easiest dislocations to move were the 1/2〈111〉 edge superpartials, and the overall preferred slip plane was {110}. These results were compared with experimental observations in CoAl and previously simulated dislocations in NiAl.

Three-dimensional temperature (T)–pressure (P)–composition (X) phase diagrams of binary carbon-hydrogen (C–H) and carbon-oxygen (C–O) systems for activated low pressure diamond growth have been calculated. Based on an approximation of linear combination between C–H and C–O systems, a projective ternary carbonhydrogen-oxygen (C–H–O) phase diagram has also been obtained. There is always a diamond growth region in each of these phase diagrams. Once a supply of external activating energy stops, the diamond growth region will not exist. Nearly all of the reliable experimental data reported in the literature drop into the possible diamond growth region of the calculated projective ternary C–H–O phase diagram under the conditions of 0.01–100 kPa and above 700 K.

Epitaxial Tl2Ba2CaCu2O8 thin films with excellent electrical transport characteristics are grown in a two-step process involving metal-organic chemical vapor deposition (MOCVD) of a BaCaCuO(F) thin film followed by a postanneal in the presence of Tl2O vapor. Vapor pressure characteristics of the recently developed liquid metal-organic precursors Ba(hfa)2 • mep (hfa = hexafluoroacetylacetonate, mep = methylethylpentaglyme), Ca(hfa)2 • tet (tet = tetraglyme), and the solid precursor Cu(dpm)2 (dpm = dipivaloylmethanate) are characterized by low pressure thermogravimetric analysis. Under typical film growth conditions, transport is shown to be diffusion limited. The transport rate of Ba(hfa)2 • mep is demonstrated to be stable for over 85 h at typical MOCVD temperatures (120 °C). In contrast, the vapor pressure stability of the commonly used Ba precursor, Ba(dpm)2, deteriorates rapidly at typical growth temperatures, and the decrease in vapor pressure is approximately exponential with a half-life of ∼9.4 h. These precursors are employed in a low pressure (5 Torr) horizontal, hot-wall, film growth reactor for growth of BaCaCuO(F) thin films on (110) LaAlO3 substrates. From the dependence of film deposition rate on substrate temperature and precursor partial pressure, the kinetics of deposition are shown to be mass-transport limited over the temperature range 350–650 °C at a 20 nm/min deposition rate. A ligand exchange process which yields volatile Cu(hfa)2 and Cu(hfa) (dpm) is also observed under film growth conditions. The MOCVD-derived BaCaCuO(F) films are postannealed in the presence of bulk Tl2Ba2CaCu2O8 at temperatures of 720–890 °C in flowing atmospheres ranging from 0–100% O2. The resulting Tl2Ba2CaCu2O8 films are shown to be epitaxial by x-ray diffraction and transmission electron microscopic (TEM) analysis with the c-axis normal to the substrate surface, with in-plane alignment, and with abrupt film-substrate interfaces. The best films exhibit a Tc = 105 K, transport-measured Jc= 1.2 × 105 A/cm2 at 77 K, and surface resistances as low as 0.4 mΩ (40 K, 10 GHz).

The recovery of lattice damage in ion implanted 6H-SiC single crystals by thermal annealing has been investigated in the temperature range 200–1000 °C by Rutherford backscattering spectrometry-channeling and by optical measurements in the UV-visible wavelength. The damage was produced by implantation at room temperature of 60 keV N+ at fluences between 1014 and 5 × 1015 ions/cm2. At low fluences a partially damaged layer with defects distributed over a depth comparable to the projected ion range was obtained. At higher fluences a continuous amorphous layer was formed. The defect annealing behavior depended on the initial damage morphology: an almost total defect recovery occurred in partially damaged layers with kinetics depending on the initial damage degree. If the defect concentration is smaller than 20 at.% the annealing rate is independent of temperature. Amorphous layers were stable in the investigated temperature range and no epitaxial regrowth occurred. After annealing, a strong change in the optical properties of the amorphous phase was observed indicating a recovery of the electronic properties of the material, suggesting the existence of several amorphous states and the relaxation of the amorphous that evolves toward thermodynamic states characterized by lower free energy values.

Microstructures of two-phase Ti–Cr alloys (Ti-rich bcc + TiCr2 and Cr-rich bcc + TiCr2) are analyzed. A variety of TiCr2 precipitate morphologies is encountered with different nominal alloy compositions and annealing temperatures. Lattice constants and crystal structures are determined by x-ray diffraction (XRD) and transmission electron microscopy (TEM). Orientation relationships between the beta bcc solid solution and C15 TiCr2 Laves phase are understood in terms of geometrical packing, and are consistent with a Laves phase growth mechanism involving twinning.

Furnace brazing is commonly used in the electronic industry to attach I/O pins, lid-seal rings, and heat spreaders to cofired multilayer ceramic packages. Despite the widespread industry usage of electrolytic and electroless Ni coatings to render base metal surfaces wettable by braze fillers, there is no fundamental treatment of “brazeability” in the published literature that can be used by the materials technologist to design coatings for a given application. In this study, dynamic hot stage microscopy is used to establish the parameters that control the spreading of eutectic Ag–Cu braze on surfaces plated with electrolytic Ni. The effects of plating thickness, substrate type, plating annealing, and the braze thermal cycle are considered. A braze spreading mechanism developed for polycrystalline Ni foil in Part I of this study is linked to Ni-plated surfaces through consideration of differences in microstructure. Eventual extension of this improved understanding to surfaces plated with electroless Ni–B and Ni–P deposits will result in shortened product design time and improved manufacturing process control.

Fourier transform infrared (FTIR) spectroscopy analysis of SCS-6 silicon carbide fibers was performed to detect the presence of oxygen in the form of SiO2. The results showed infrared peaks corresponding to SiC fundamental lattice absorption as well as reflection. No absorption peak due to SiO2 was observed. These results are in agreement with previously reported data indicating low levels of oxygen in this fiber.

Carbon nanotubes can be produced by the catalytic decomposition of hydrocarbons on small metal particles. However, nanotubes are generally produced together with non-tubular filaments and tubes coated by pyrolytic carbon. We propose a novel catalyst method for the in situ production, in a composite powder, of a huge amount of single- and multiwalled carbon nanotubes, having a diameter between 1.5 and 15 nm and arranged in bundles up to 100 μm long. We anticipate that dense materials prepared from such composite powders could have interesting mechanical and physical properties.

The energetics of a simple model of void nucleation on a contaminated patch between the sidewall and metal in an integrated circuit interconnect are examined to determine void nucleation behavior. The conditions under which there is no void nucleation barrier are represented by a simple relationship between the volume driving force, the equilibrium contact angle, the surface energy of the metal, and the contaminated patch radius. The void nucleation barrier, when it exists, is a strong function of these same parameters, and increases sharply as the driving force decreases, and under some conditions, increases with increasing equilibrium contact angle.

Deformation of HfN thin films deposited by the reactive sputtering method on silicon and alumina substrates has been investigated using depth-sensing indentation. The experiments performed in a low load range (2−50 mN) revealed that even extremely shallow indentations were affected by the elastic/plastic response of the substrate. The analysis of the shape of the indentation load-depth hysteresis loops and of conventional hardness data was supplemented by considerations based on the recently proposed energy principle of indentation.

The aging of the NC 19 Fe Nb alloy (Inconel 718), previously quenched from 990 °C, is characterized by a hardness peak at 650 °C, then a maximum in hardness at about 750 °C. Over this temperature, the hardness progressively decreases. In the 550–650 °C temperature range, TEM observations have revealed that β (Ni3Nb) precipitates are formed as long platelets parallel between them within the same grain, as well as extremely fine γ′[Ni3(Ti, Al)] particles responsible for the observed improvement in hardness. For a tempering temperature higher than 650 °C, a first hardening occurs after a 4 h treatment, which has been associated with the γ′ phase precipitation, with a more or less spherical shape. Beyond this time, a second hardening takes place linked to the γ″ phase precipitation (Ni3Nb, bct D022 structure), as thin platelet shaped, perfectly coherent with the matrix. The misfit between the γ and γ″ phases is about 3% in the 〈001〉γ″ direction and lower than 1% in the 〈100〉γ″ and 〈010〉γ″ directions. During a longer aging at 750 °C, the γ″ platelets progressively dissolve while β precipitates grow.

To investigate potential limits to the rate at which high-quality YBa2Cu3O7–δ can be deposited, we have produced a series of 1 μm thick films by pulsed laser deposition on single-crystal SrTiO3 substrates at average rates ranging from 2 Å/s to 240 Å/s. The critical current density of low-rate films was over 2 MA/cm2 at 75 K, self field, but dropped linearly with rate to about 1 MA/cm2 at the upper end of the range. In addition, the superconducting transition temperature, resistivity above the transition, and performance in an applied magnetic field were all degraded by increasing the deposition rate. A change in c-axis lattice parameter suggests that possible causes for this degradation are oxygen deficiency or cation disorder with the latter being the more likely. Annealing high-rate films at 790 °C for as little as 20 min improved critical current density to within 20% of low-rate values, and resulted in dramatic improvements in other film properties as well.

Micropyretic synthesis technique employs self-sustaining exothermic (combustion) reactions for the preparation of various ceramic, intermetallic, and composite materials. In the present work, the combustion reactions of Mo and Si with Al additions have been systematically studied. The atomic mixtures of the reactant powders are chosen to be Mo + (2 − x)Si + xAl with x = 0−0.4. In comparison with the Mo + 2Si reaction which leads to the formation of MoSi2, the substitution of Al for Si decreases the sample ignition temperature, but increases the intensity of the combustion reactions. In addition, the substitution of Al for Si results in the formation of a ternary intermetallic phase, called molybdenum alumino-silicide Mo(Si, Al)2, in the synthesized product. When the content of Al in the reactant mixtures reaches 0.4, nearly single phase Mo(Si, Al)2 is obtained and no MoSi2 is detected in the reaction product. These influences are analyzed by using x-ray diffraction (XRD), scanning electron microscopy (SEM), and differential thermal analysis (DTA). The effect of Al additions on the reaction mechanism is also discussed.

Fluorine doping of silicon dioxide films in tetraethylorthosilicate (TEOS)-based plasma enhanced chemical vapor deposition (PECVD) processes was investigated using two fluorine dopant sources, C2F6 and 1,2 bis[methyldifluorosilyl]ethane (FASi-4). Much as TEOS-based undoped silica glass (USG) films display improved step coverage over silane-based USG films, it was suspected that fluorinated silica glass (FSG) films deposited using the relatively new TEOS-based fluorine source FASi-4 might have improved gap fill capabilities as compared to FSG films deposited using gas-based C2F6 fluorine sources. The physical properties and intermetal gap filling capabilities of FSG films deposited using FASi-4 as a fluorine dopant source were compared with the properties of FSG films deposited using C2F6 as a fluorine source. Fluorine dopant levels in the films were found to be linear functions of C2F6TEOS and FASi-4yTEOS ratios. The RI, film stress, and gap fill capability were found to be strongly dependent on the Si–F content in the film regardless of dopant source reagents. Improved gap fill characteristics were observed in films doped with FASi-4 at a given Si–F/Si–O% as compared to C2F6-based FSG films. Dopant source dependence of doping characteristics, physical properties, and gap filling capability of FSG films is reported.

Ball milling has been used as a solid-state mechanical alloying technique in two binary systems of plastic crystals: neopentylglycol/pentaglycerin (NPG/PG), showing a partial solubility in the ordered phase, and 2-amino-2-methyl-1,3-propanediol/tris(hydroxymethyl) (AMP/TRIS) whose immiscibility in this ordered solid phase is almost total. For the AMP/TRIS system the stable state at room temperature was reached by milling. Contrarily, for NPG/PG, DSC measurements reveal that an annealing period is required after milling. These results have been compared with those of the pentaglycerin/pentaerythritol (PG/PE) binary system, previously studied, whose miscibility is total at room temperature.

The deformation characteristics of icosahedral Al–Cu–Fe quasicrystals were determined by high temperature creep experiments between 680 and 720 °C and 15 and 41 MPa. The deformation process was determined to be controlled by grain boundary mechanisms. Both the stress and grain size sensitivity exponents were found to be 2, suggesting that grain boundary sliding was the rate-controlling deformation mechanism. Microstructural analysis supported this conclusion, as no intragranular defects were produced during the deformation experiments.

For high temperature superconducting multichip modules and other related electronic applications, it is necessary to be able to fabricate several Y1Ba2Cu3O7–x (YBCO) layers separated by thick low dielectric constant dielectric layers. In this work, we report the successful fabrication of YBCO/YSZ/SiO2 (1–2 μm)/YSZ/YBCO multilayer structures on single crystal yttria stabilized zirconia (YSZ) substrates. In contrast to previously reported work, the top YBCO layer did not show any cracking. This is due to a technique that allows for stress relief in the SiO2 layer before the second YBCO layer is deposited. The top YBCO layer in our multilayer structure had Tc = 87 K and Jc = 105 A/cm2 (at 77 K), whereas the bottom YBCO layer had Tc = 90 K and Jc = 1.2 × 106 A/cm2 (at 77 K). We also showed that the quality of the bottom YBCO layer was preserved during the fabrication of the multilayer due to the annealing process during which O2 diffused into the YBCO, replacing the O2 lost during the deposition of the top YBCO layer.

The combustion reaction while mechanical alloying (MA) the Al–Ti–C system has been detected by in situ thermal analysis and the results of x-ray diffraction (XRD). Based on the information provided by in situ thermal analysis, the reaction temperature is estimated to be 1677 K, which is in good agreement with the value of the adiabatic temperature of 1700 K. It is considered that the formation reaction of Ti–C, which ignited by the heavy collisions of milling balls, induced the following reaction between Ti and Al at high temperature.

Scanning electron microscopy (SEM) and surface replica method have been employed to study the micromechanism of fatigue crack initiation at Nd-rich phase particles in a high temperature titanium (Ti-55) alloy. It was found that the microcrack initiates near the equator of Nd-rich particles in the matrix. The microcrack grows first at an angle of about 45° with respect to the tensile axis, and then its growth direction becomes approximately normal to the tensile axis. The experimental results are analyzed in terms of the elastic stress distribution around soft particles imbedded in the matrix to account for the experimental findings of particle cracking and the associated surface microcrack initiation near the particle “equator.” A model of fatigue crack initiation at a soft surface particle is proposed.

Fine-grained kappa carbide (Fe3AlCx) materials, containing 12.5 and 14% Al, and 3.5% C, were prepared by powder processing and hipping procedures. The creep behavior of the kappa materials was shown to be identical to that observed in superplastic iron carbide, and was shown to follow a grain boundary–diffusioncontrolled grain boundary sliding relation. The tensile fracture strains in kappa, however, were shown to be considerably less than in iron carbide with a maximum elongation of 92% noted. This difference is attributed to either a low stress intensity factor or to contamination of the powder surface in the kappa material. The compression creep strength, at a given strain rate, was shown to be about two times higher than the tension creep strength.