The phase relations and thermal stabilities of phases in sputter deposited Be–Nb alloys (3–14% Nb) have been studied. An amorphous phase forms during deposition at ambient temperatures (30 °C) for compositions >5% Nb. Metastable crystalline phases form during deposition at 350–450 °C as well as during annealing of the amorphous phase. One metastable bcc phase designated as Be12Nb′ can be explained by an extremely high fault density in the Be12Nb structure and is a precursor phase to the formation of both Be12Nb and Be17Nb2. Another metastable bcc phase also forms during high temperature deposition. Transformation to the equilibrium phases occurs at temperatures >800 °C. A stoichiometric range of about 5.5–7.8% is indicated for the Be12Nb phase and is probably due to vacancies on the Nb sublattice. No evidence of a Be5Nb phase was found and the Be17Nb2 phase is stable to room temperature.

Using the all-electron full potential linearized augmented plane wave (FLAPW) total energy method, the influence of P impurity atoms on the cohesion of the Fe Σ3[1$\overline 1$10](111) grain boundary is studied through direct comparison of phosphorus/iron interactions in the grain boundary and free surface environments. The calculated nearest P–Fe distance in P/Fe(111) is 2.14 Å—amounting to a 5% contraction compared to that (2.26 Å) measured for the Fe3P compound and assumed for the P–Fe grain boundary. The polar-covalent P–Fe chemical bonding, which is a strong function of the P–Fe interatomic distance, is thus stronger on the Fe(111) surface, while P reduces the spin polarization of the surrounding Fe atoms more efficiently in the grain boundary environment. These effects are examined in terms of the relative segregation energies affecting the work of boundary fracture.

A review of the intermediate temperature creep properties of Ni3Al indicates that octahedral glide, the mechanism associated with the anomalous temperature dependence of yielding in this alloy, is exhausted during primary creep. Comparisons of this primary creep transient with the various models proposed to explain the anomalous yielding behavior suggest that additional transient experiments are needed to fully characterize octahedral glide in this alloy. Cottrell–Stokes type temperature change experiments, stress relaxation experiments, and deformation exhaustion/temperature drop tests have been conducted in an attempt to better characterize octahedral glide in Ni3Al. The results of these transient experiments indicate that octahedral glide is only partially a thermally reversible process and that the formation of dislocation substructure, KW locks, plays an important role in determining the flow strength of this alloy. These experiments also suggest that flow in Ni3Al should not be viewed as a viscous drag process, but can best be described as a “pure-metal-like” process involving the rapid motion of a small number of highly mobile dislocations. The stochastic nature of dislocation motion and the importance of substructure formation are emphasized and a description of octahedral glide that is consistent with the transient deformation experiments is proposed.

Oxygen incorporation in silicon crystals during Czochralski growth is dependent on many factors, of which the dissolution of the silica crucible is of great importance. In this paper the reactions between vitreous silica and molten silicon have been analyzed, both in sealed ampoules and in Czochralski crucibles. It was found that the vitreous silica crystallizes to cristobalite by lateral growth. For this reaction to occur it is necessary that liquid silicon is present. The vitreous silica dissolves and the cristobalite grows with a thin layer of liquid silicon between them. Different oxygen concentrations in the melt in equilibrium with the amorphous and crystallized silica are necessary for the reaction to proceed. The oxygen flux in the melt is dependent upon the dissolution of both vitreous silica and cristobalite as well as the reaction between these phases.

The phase constitution and the lattice parameter relationships in the rapidly solidified and heat-treated (Mn0.53Al0.47)100−xCx pseudo-binary alloys (x = 0–6) have been investigated by means of x-ray diffraction and transmission electron microscopy. The melt-spun alloys contained a single ∊ phase (cph) with 0.63–4.0 at. % C, and below and beyond this carbon composition range small traces of γ2-MnAl and Al4C3 compounds were formed, respectively. The heat treatment of the melt-spun alloys at 823 K produced a single τ phase (ordered bct, CuAu type I, L10) with 0.63–3.6 at.% C. The c lattice parameter of the ∊ unit cell was observed to increase pronouncedly with the carbon content whereas that of the a-axis revealed no apparent change; the corresponding increase of the unit cell volume was taken to indicate an interstitial dissolution of the carbon atoms in the ∊ lattice. On the other hand, for the τ phase, the c lattice parameter increased markedly with the carbon content while the a parameter decreased slightly, so that a large increase of c/a ratio was produced. The lattice parameter data for the τ phase thus indicated an increase of the unit cell volume with the carbon content, providing new evidence that the carbon atoms dissolve interstitially in the bct lattice. In addition, it was deduced that the higher c/a ratio with increasing carbon content may arise from a preferential site occupation of the carbon atoms at a specific type of octahedral interstitial site lying in the manganese atom layers.

Artificial multilayers, or microlaminates, composed of alternating layers of Nb and MoSi2 of equal thickness were synthesized by d.c., magnetron sputtering. Four different modulation wavelengths, λ, were studied: 7, 11, 20, and 100 nm. The compositions, periodicities, and microstructures of the microlaminates were characterized by Auger electron spectroscopy and transmission electron microscopy. Structural characterization revealed that the as-deposited Nb layers are polycrystalline, while the MoSi2 layers are amorphous. The hardnesses and elastic moduli of the films were measured using nanoindentation techniques. Neither a supermodulus nor a superhardness effect could be identified in the range of wavelengths investigated; for each of the microlaminates, both the hardness and modulus were found to fall between the bounds set by the properties of the monolithic Nb and MoSi2 films. Nevertheless, a modest but a measurable increase in both hardness and modulus with decreasing wavelength was observed, thus indicating that behavior cannot be entirely described by a simple rule-of-mixtures. The hardness was found to vary linearly with Δ−1/2 in a manner similar to the Hall–Petch relationship. Annealing the microlaminates at 800 °C for 90 min produces significant increases in hardness and modulus due to chemical interaction of the layers.

BaZrO3 and BaHfO3 modified polycrystalline BaTiO3 are candidate materials for transverse mode and pyroelectric charge coupled device (CCD) arrays. Addition of 3–4% barium zirconate and barium hafnate to barium titanate alters the temperature of phase transformations and with it, dielectric and pyroelectric properties. These additions create a temperature range close to room temperature where the pyroelectric coefficient is extremely high relative to the dielectric permittivity. These materials show a very high figure of merit for dielectric bolometer applications that is competitive with existing materials, while being relatively easy to prepare.

An equilibrium precipitation of Al2Ti is shown to occur within a Cu-modified Al2Ti alloy having the L12 structure. This precipitation is analyzed by conventional and high resolution electron microscopy and some insights are given concerning the mechanisms of nucleation and growth of Al2Ti within the L12 matrix. In the meantime, Vickers microhardness tests have been performed as a first approach to the mechanical behavior of this alloy and the results are compared to measurements obtained in an actual single-phased L12 compound. The Al2Ti precipitation seems to have an important hardening effect.

Constant load creep experiments were conducted using a depth-sensing indentation instrument with indentation depths in the submicron range. Experiments were conducted on polycrystalline Sn and sputtered Al films on Si substrates. The results show that the plastic depth versus time curves and the strain rate versus stress plots from these experiments are analogous to those obtained from conventional creep experiments using bulk specimens. The value of the stress exponent for Sn is close to the reported values from uniaxial creep tests. Tests on Al films showed that the stress exponent is dependent on the indentation depth and is governed by the proximity to the film/substrate interface. Load change experiments were also performed and the data from these tests were analyzed. It is concluded that indentation creep experiments may be useful in elucidating the deformation properties of materials and in identifying deformation mechanisms.

Deposition rates are predicted in a cylindrical upflow reactor designed for chemical vapor deposition (CVD) on monofilaments. Deposition of silicon from silane in a hydrogen carrier gas is chosen as a relevant example. The effects of gas and surface chemistry are studied in a two-dimensional axisymmetric flow field for this chemically well-studied system. Model predictions are compared to experimental CVD rate measurements. The differences in some physical and chemical phenomena between such small diameter (∼150 μm) fiber substrates and other typical CVD substrates are highlighted. The influence of the Soret mass transport mechanism is determined to be extraordinarily significant. The difficulties associated with the accurate measurement and control of the fiber temperature are discussed. Model prediction sensitivities are investigated with respect to fiber temperatures, fiber radii, Soret transport, and chemical kinetic parameters. The implications of the predicted instantaneous rates are discussed relative to the desired fiber properties for both batch and continuous processes.

It was found that the modulation wavelength and average composition of multilayers are related to the position, intensity, and diffraction order of x-ray modulation peaks for multilayers. The relation between the characteristics of the modulation peaks in different as-deposited multilayers and their interdiffusion capability is also discussed.

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).

Experiments are described that provide evidence for the formation of an excited condensed state of matter in the form of μm to mm size particles. The particles are formed at a high temperature diffusion source, which has been shown to give field ionizable clusters of cesium in previous experiments (Åman et al., 1990). The excited matter formed by cesium, hydrogen, or ethylene in the source is in the present experiments collected on a surface, which is cooled to liquid nitrogen temperature. Subsequently, the excited particles emit their excitation energy in the form of visible “microflashes”, either spontaneously or triggered by impact of low energy ions. An estimate of the visible energy in the microflashes agrees well with the energy contained in an excited state of matter that was predicted by Manykin et al. (1981, 1982). We conclude that our results agree with their predictions.

A multiphase oxidation resistant composition (Nb–67Al–7Cr–0.5Y–0.25W) based on NbAl3 was prepared by both induction melting and rapid solidification processing (RSP), followed by grinding to 75 μm powder and consolidating by powder metallurgy techniques (hot pressing, hot isostatic pressing, and Ceracon pressing). Constant strain rate compression tests conducted on consolidated materials in the temperature range 300–1300 K indicated that the RSP material exhibited significantly higher strength and ductility than the induction melted alloy up to 1200 K. Bend strengths measured on induction melted material were significantly lower than the corresponding compressive strengths, suggesting the brittle, flaw-sensitive nature of this alloy. The NbAlCrYW alloy exhibits a brittle-to-ductile transition around 1000 K. The constant load creep tests conducted on the induction melted alloy in the 1200–1300 K temperature range indicated that this alloy shows a power law creep dependency with a stress exponent, n, of 3.2. It was found that the specific strength of this alloy is competitive with other aluminide intermetallics.

Diamond films were grown by microwave plasma assisted chemical vapor deposition using mixtures of 1% 13CH4 and 0.5% 12C2H2 in H2, and stable gaseous products were analyzed by mass spectrometry. The major gaseous products are methane and acetylene, and scrambling of the 13C label can be controlled at relatively high gas flow rates. At the highest flow rate studied a diamond film was grown with 77% 13C incorporation, while the methane in the reactor exhaust gas at this flow rate contained 83% 13C. By comparing gaseous 13C compositions with that of the films, the efficiency of diamond growth from methane (possibly via the methyl radical) is estimated to be about ten times higher than that for acetylene.

Relationships between embedded-atom method parameters and the energies of fcc-hcp stability and intrinsic and extrinsic fcc stacking-faults were studied for Cu, Ag, Au, Ni, Pd, and Pt. It was found that the relative magnitudes of these energies for different metals are determined primarily by the physical input data and are almost independent of the cutoff distance and the functions used in the model. These energies increase with increasing vacancy formation energy, decrease with increasing atomic volume and shear modulus, and are almost independent of variations in the cohesive energy and the bulk modulus. However, the shape of the energy versus cutoff distance curve is almost the same for all six metals and is determined primarily by the cutoff distance and the functions used in the model. The shape for a given model is almost independent of the physical input parameters used for fitting to specific metals, can yield either positive or negative values (determined primarily by the cutoff distance), and is similar for all three energies.

Johnson and Oh have recently developed Embedded Atom Method potentials for bcc metals (Na, Li, K, V, Nb, Ta, Mo, W, Fe). The predictive power of these potentials was first tested by calculating vacancy formation and migration energies. Due to the results of these calculations, some of the functions were slightly modified to improve their fit to vacancy properties. The modified potentials were then used to calculate phonon dispersion curves, surface relaxations, surface energies, and thermal expansion. In addition, Johnson's alloy model, which works well for fcc metals, was applied to the bcc metals to predict dilute heats of solution.

Synthetic multilayers consisting of periodic layers of the refractory metal Mo and the oxide ceramic Al2O3 have been produced by alternating d.c. and r.f. reactive sputter deposition. Microlaminates with four different modulation wavelength—5, 20, 30, and 100 nm—were investigated in this study. The compositions, periodicities, and microstructures of the microlaminates were characterized by Auger electron spectroscopy, low-angle x-ray diffraction, and transmission electron microscopy, including high resolution lattice imaging and microdiffraction. Transmission electron microscopy from the microlaminates indicated that the as-deposited Mo layers are polycrystalline, while the as-deposited Al2O3 layers are primarily amorphous. The Mo and Al2O3 layers are thermally compatible at 800 °C for 6 h, showing no evidence of atomic interdiffusion between the layers. The mechanical properties of the microlaminates, as well as those of monolithic films of Mo and Al2O3 (i.e., the baseline materials), were investigated using nanoindentation methods. A higher than expected modulus and hardness were observed for the microlaminate with the longest wavelength (100 nm); otherwise the mechanical properties are explainable by a rule-of-mixtures. The enhanced mechanical properties of the 100 nm microlaminate may be attributed to crystallization of the amorphous Al2O3 layers and the evolution of a structural texture within this phase.

The structural transition between the metastable fcc and hcp crystalline solid solutions in the Ni–Ru system has been studied as a function of composition using the mechanical alloying technique. At the transition point, the spacings between the close-packed planes of the metastable fcc and hcp phases are the same. No amorphization is observed at the interfaces. This mechanically induced phase transition has been studied by x-ray diffraction, transmission electron microscopy, and differential thermal analysis.

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.