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The coating of nuclear fuel kernels with pyrolytic carbon (PyC) is a well-understood practice dating back over half a century. In spite of decades of studies related to these coatings, no s...

The effect of a discrete elastic element on the transverse vibration of a Bernoulli–Euler beam has been well-studied; however, the same cannot be said for a beam with a viscous damper. While the former can be analyzed via separation of variables and the solution of the eigenvalue problem, this article presents a method for computing the resonances of the latter case. The nature of a discrete viscous damper's effect on the fundamental frequency of a beam is revealed as the method is applied to the case of a cantilevered beam. In this process, it is shown that damping has the capacity to increase the fundamental frequency of the beam, and that there exists both a particular location and critical value of damping that maximize this frequency.

Organic-based hydrogen getter materials have been in use for many years. These materials are able to prevent the dangerous buildup of hydrogen gas in sealed containers, and are also used to protect surrounding materials from degradation caused by chemical reactions. This document describes these materials.

Amorphous alloys are a promising alternative to Pd alloy membranes for hydrogen separation because of their lower cost and comparable hydrogen permeability. A series of amorphous alloy membranes consisting of Ni 60 Nb 20 Zr 20 (at%), (Ni 0.6 Nb 0.4 ) 100− x Zr x and (Ni 0.6 Nb 0.3 Ta 0.1 ) 100− x Zr x (where x = 0, 10, 20 or 30) were prepared by melt spinning and then coating the foil surfaces with a thin (500 nm) layer of Pd using physical vapor deposition (PVD). A (Ni 0.6 Nb 0.4 ) 70 Zr 30 membrane exhibited the highest hydrogen permeability (1.4 × 10 −8 mol m −1 s −1 Pa −0.5 ) of any of the materials, measured in pure hydrogen at 450 °C. Membrane permeability increased with Zr content, but membranes higher in Zr were more susceptible to brittle failure and were more thermally unstable. Decreases in hydrogen permeability were almost always observed during long-term permeability tests at 400 and 450 °C. The addition of Ta slightly increased the thermal stability, but moderately lowered the hydrogen permeability. An AES depth profile of the membrane surface showed that metallic interdiffusion had taken place between the Pd coating and the bulk membrane, which probably accounts for the reduction in hydrogen permeability over time at 400–450 °C.

Opacity data are very important in high energy density physics experiments. Recent targets of alternating layers of either Al2Te3 or Mg/Sn with a CH tamper have been made for obtaining these data. These targets are geometrically simple in the half-moon configuration of the metal compound coating to the pure CH tamper but require stringent procedural requirements to fabricate to the purity requirements. These specific targets require mass ratios of elements that proved to be difficult to obtain while also having the requirement of being pinhole-free and oxygen-free.

The goals of this work have been two-fold. First, to perform an initial, quantitative, optimization of getter performance, with the primary variables being DEB/Pd ratio and UV power. Second, to simplify the deposition process to make it more compatible with the DOE production environment.

Compliance with environmental regulations is becoming more and more costly for manufacturers as government scrutiny and global trade agreements become more stringent. Metal-cutting fluid use and disposal is a major concern as these environmental issues become more prominent. Gaining a clear understanding of the costs associated with machining coolant/lubricant use can be difficult. Many factors impact this cost, such as the original purchase price, maintenance costs, disposal management and fees, and performance factors related to the particular fluid. This paper develops a detailed cost and performance-based methodology for machining coolant/lubricant selection. A model by which to evaluate the relative impacts of coolant/lubricant decisions on the unit workpiece cost of production is described. At present, a widely accepted methodology is not available for this purpose. The model presented here will assist manufacturing companies of all types in making this critical decision.

PurposeTo develop a decision framework for the planning and development of a flexible manufacturing system (FMS).Design/methodology/approachA systematic weighted property index approach for FMS development decisions is developed to evaluate various design options. This methodology converts design property values of differing orders of magnitude into a unitless system where an overall evaluation of the options can be made.FindingsMajor design choices related to the implementation of an educational FMS are identified, and considerations affecting each choice are discussed. A methodology for the selection of the appropriate FMS is then developed and demonstrated.Practical implicationsProvides a useful framework for evaluating various options in FMS development and selecting an appropriate system for a given environment and situation.Originality/valueIdentifies the major design choices related to the implementation of an educational FMS, provides practical examples taken from the development of FMSs at Southwest Missouri State University and the University of Missouri‐Rolla, and presents a systematic methodology for FMS design decision making.

Over the past quarter century, much effort has been devoted to the design and development of simulation modeling languages, and to methods for the development of simulation models themselves. Less effort, however, has been expended on the design of the experimental models upon which simulation studies are based. This paper describes a methodology for the determination of near optimal solutions considering experimental design and simulation modeling. Using this methodology, simulation scenarios are created and analyzed using an analysis of variance (ANOVA)-based experimental design. This paper also presents an application of this method in analyzing a manufacturing system design problem.

The purpose of this study was to identify and correlate the microstructural and luminescence properties of europium-doped Y 2 O 3 (Y 1-x Eu x ) 2 O 3 thin films deposited by metallorganic chemical vapor deposition (MOCVD), as a function of deposition time and temperature. The influence of deposition parameters on the crystallite size and microstructural morphology were examined, as well as the influence of these parameters on the photoluminescence emission spectra. (Y 1-x -Eu x ) 2 O 3 thin films were deposited onto (111) silicon and (001) sapphire substrates by MOCVD. The films were grown by reacting yttrium and europium tris(2,2,6,6-tetramethyl-3,5-heptanedionate) precursors with an oxygen atmosphere at low pressures (5 torr (1.7 x 10 3 Pa)) and low substrate temperatures (500°-700°C). The films deposited at 500°C were smooth and composed of nanocrystalline regions of cubic Y 2 O 3 , grown in a textured [100] or [110] orientation to the substrate surface. Films deposited at 600°C developed, with increasing deposition time, from a flat, nanocrystalline morphology into a platelike growth morphology with [111] orientation. Monoclinic (Y 1-x -Eu x ) 2 O 3 was observed in the photoluminescence emission spectra for all deposition temperatures. The increase in photoluminescence emission intensity with increasing postdeposition annealing temperature was attributed to the surface/grain boundary area-reduction effect.

Here, we compare the aging behaviors of cross-linked ethylene/vinyl acetate/vinyl alcohol terpolymers, also referred to as EVA-OH, when they are either immersed in nitroplasticizer (NP) liquid or exposed to NP vapor at different temperatures. And while thermogravimetric analysis and differential scanning calorimetry are used to probe the thermal stability of aged NP and polymers, Fourier transform infrared, gel permeation chromatography, ultra-violet/vis, and nuclear magnetic resonance are used to probe their structural changes over the aging process. Our study confirms that NP degrades through C[BOND]N cleavage, and releases HONO molecules at a slightly elevated temperature (

To study the aging behavior of cured vinyl copolymer elastomer (VCE) under thermal and nitroplasticizer (NP) environ- ment, we investigated the sorption and diffusion of NP in VCE and its composites. The sorption kinetics of NP into VCE and its composites with respect to filler concentration (0-80%) and temperature (18-70 � C) were investigated by conventional gravimetric method. The NP sorption process is endothermic. Kinetic studies show that Fickian diffusion can describe the NP sorption in the VCE polymer. The samples with a high filler concentration show more complicated behavior at low temperature than that at high temperature. The present article discusses the dependences of diffusion coefficient and other related parameters on the polymer con- centration and morphological structures of the samples. V C 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40729.

An organometallic chemical vapor deposition (OMCVD) process was developed for the preparation of protective erbium oxide coatings resistant to corrosion by liquid plutonium. The coatings were deposited from the precursor compound Er(tmhd) 3 using a standard hot-wall reactor. The substrates used for process development were 304 stainless-steel flats; coatings were subsequently deposited on the internal surfaces of high-aspect-ratio tubular parts, as well as a variety of curved samples. The coatings have the correct oxygen/erbium ratio, and small concentrations of carbon and hydrogen impurities. The impurities are present in the form of unreacted or partially-reacted precursor molecules, presumably concentrated at the grain boundaries of the material. The films are polycrystalline with a grain size of 40–50 nm, and exhibit excellent adhesion and mechanical toughness. The small grain size and the resultant favorable mechanical properties may be attributable in part to the presence of the organic fragments at the grain boundaries. Coatings deposited on stainless-steel flats are resistant to corrosion by liquid plutonium, although an erbia-thickness threshold is observed. The failure mechanism for samples with thicknesses below the threshold value is most likely related to flaws in the film morphology, for example large pinholes, rather than grain-boundary attack.

The knowledge of tribological properties of silicon is important due to its potential application for micromechanical devices. The present work focuses on the friction and wear studies of single crystal silicon (100) implanted with carbon and nitrogen at 60 keV. These tests were performed using a pin-on-disc (POD) apparatus with a 52100 pin, under contact stress of 225 MPa and at 35% relative humidity. Changes in surface roughness before and after the wear tests were studied using atomic force microscopy (AFM). Transmission electron microscopy (TEM) investigations and ion-channeling measurements revealed amorphous phases for all the implanted species at all doses. Although the surface hardness measurements performed by nano-indentation indicated no improvement in surface hardness for samples implanted with carbon, the tribological studies indicated an improvement in wear and frictional properties. We relate this improved wear behavior to the formation of amorphous SiC.

As part of a larger study to investigate atomic-diffusion behavior in both elemental boron and refractory transition-metal borides, neutron reflectometry was used to examine the temperature-induced self-diffusion of isotopically enriched thin films of amorphous $^{11}\mathrm{B}$ on $^{10}\mathrm{B}$ deposited by electron-beam evaporation. The reflectometry studies were performed and model boron density profiles for samples annealed at various times and temperatures of 360 and 400 \ifmmode^\circ\else\textdegree\fi{}C were fit to the reflectivity data. Although the $^{10}\mathrm{/}^{11}$B interface did not move relative to the air/boron interface upon annealing, the expected standard Fickian diffusion for the annealed samples was not observed. A pinned Fickian diffusion model, which imposes the boundary conditions of a fixed composition of $^{10}\mathrm{B}$ to $^{11}\mathrm{B}$ at the interface, fit the reflectivity data accurately and consistently. A typical equilibrium diffusion constant was determined to be \ensuremath{\sim}${10}^{\mathrm{\ensuremath{-}}17}$ ${\mathrm{cm}}^{2}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$, measured at an annealing temperature of 360 \ifmmode^\circ\else\textdegree\fi{}C. The measured diffusion constants are inconsistent with the high melting temperature of elemental boron, but are consistent with measured boron diffusion constants in other amorphous thin films. The presence of clusters in the boron film is proposed to explain the observed results.

Carbon films with up to 32 at. % of nitrogen have been prepared with ion beam assisted magnetron, using a N2+/N+ beam at energies between 50 and 300 eV. The composition and density of the films vary strongly with the deposition parameters. EELS, SXS, XPS, and IR studies show that these a-C: N films are mostly graphitic and have up to 20% sp3 bonding. Nitrogen is mostly combined with carbon in nitrile (C ≡ N) and imine (C=N) groups. It is shown by RBS and NDP that density goes through a maximum as the average damage energy per incoming ion increases. Positron annihilation spectroscopy shows that the void concentration in the films goes through a minimum with average damage energy. These results are consistent with a densification induced by the collisions at low average damage energy values and induced graphitization at higher damage energy values. These results are similar to what is observed for Ar ion assisted deposition of a-C films. The mechanical properties of these films have been studied with a nanoindenter, and it was found that the hardness and Young's modulus go through a maximum as the average damage energy is increased. The maximum of mechanical properties corresponds to the minimum in the void concentration in the film. Tribological studies of the a-C: N show that the friction coefficient obtained against diamond under dynamic loading decreases strongly as the nitrogen composition increases, this effect being more pronounced at low loads.

Epitaxial TiN/V0.3Nb0.7N superlattices with a 1.7% lattice mismatch between the layers were grown by reactive magnetron sputtering on MgO(001) substrates. Superlattice structure, crystalline perfection, composition modulation amplitudes, and coherency strains were studied using transmission electron microscopy and x-ray diffraction. Hardness H and elastic modulus were measured by nanoindentation. H increased rapidly with increasing Λ, peaking at H values ≍75% greater than rule-of-mixtures values at Λ ≍ 6 nm, before decreasing slightly with further increases in Λ. A comparison with previously studied lattice-matched TiN/V0.6Nb0.4N superlattices, which had nearly identical composition modulation amplitudes, showed a similar H variation, but a smaller H enhancement of ≍50%. The results suggest that coherency strains, which were larger for the mismatched TiN/V0.3Nb0.7N superlattices, were responsible for the larger hardness enhancement. The results are discussed in terms of coherency strain theories developed for spinodally decomposed materials. Nanoindenter elastic modulus results showed no significant anomalies.

Hydroxypropyl cellulose (HPC) of degree of substitution three and average molecular weight of 100,000 was processed in a magnetic field of 1.2T. Films of HPC were cast from water, methanol, ethyl methyl ketone, and 1,1,2,2-tetrachloroethane solutions in a magnetic field using static and dynamic casting techniques. The processed films were evaluated for tensile strength, elastic modulus, microhardness, and molecular chain alignment by wide angle x-ray diffraction and polarized infrared. The best alignment and hence the greatest improvement in properties was obtained using a combined magnetic field and flow alignment procedure. These samples showed no increase in the elastic modulus, a 106% increase in the tensile strength, a 21% increase in the microhardness, and were dichroic. © 1994 John Wiley & Sons, Inc.1

Surface modification of ceramics has proved to be of benefit in a number of applications. Excimer laser light provides a rapid and efficient means for surface alloying and modification of ceramic materials. The laser pulse can melt the surface of the ceramic as well as a deposited metal layer. This results in diffusional mixing in the liquid state, which is followed by rapid resolidification. The high temperatures involved can overcome kinetic barriers to mixing found in ion beam experiments. Tribological measurements on surface treated materials show reduced friction and increased surface toughness. Increased fracture toughness in laser surface alloyed ceramics has also been observed. Excimer laser processes therefore may enable the use of ceramic materials in applications for which they are not now suitable.

The critical current density {ital J}{sub {ital c}} in Y{sub 0.9}Gd{sub 0.1}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}} was found to increase relative to the unirradiated value following neutron irradiations in a mixed-spectrum reactor (total neutron fluences ranged between 1{times}10{sup 17} and 2{times}10{sup 18} {ital n}/cm{sup 2}). Additional neutron irradiations of structurally similar GdBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}} were carried out in either a highly thermalized or a pure fast-neutron environment (in the same reactor). This was done to determine whether enhancements in {ital J}{sub {ital c}} are to be attributed to defects arising from interactions with thermal neutrons ({ital E}{sub {ital n}}{similar to}0.025 eV) or with fast neutrons ({ital E}{sub {ital n}}{gt}0.1 MeV). Magnetic-hysteresis measurements on these samples indicate that flux pinning (and thereby {ital J}{sub {ital c}}) is enhanced by fast-neutron irradition, but not by thermal-neutron irradiation. On the other hand, the critical temperature {ital T}{sub {ital c}} is significantly altered by exposure both to thermal and fast neutrons. It is proposed that thermal neutrons induce the formation of Frenkel pair defects on the rare-earth sublattice, but that these point defects do not serve as effective flux-pinning centers.

A hybrid process, aerosol-assisted chemical vapor deposotion (AACVD), is described for reproducible preparation of superconducting thin films of YBa 2 Cu 3 O 7−χ . The process consists of atomizing a toluene solution of the Y, Ba, and Cu tetramethylheptanedionato complexes using an aerosol generator. The aerosol is transported into a CVD reactor where solvent and precursor evaporation and deposition occur at atmospheric pressure on heated substrates. The process provides stable evaporation rates for all three precursors, yielding constant film stoichiometry throughout the deposition period and from film to film. Superconducting films may be deposited in-situ at substrate heater temperatures above 825°C, or may be formed at lower temperatures by deposition followed by post-deposition annealing at higher temperatures. The microstructure and quality of films are highly dependent on the conditions employed in deposition and in the case of films deposited below 825°C, the post-deposition annealing conditions. Superconducting films prepared by the AACVD/post-annealing process have a metallic normal state resistivity signature with a zero resistance temperature typically above 88K, and are highly c -axis oriented. Transport critical current densities measured at 75 K on polycrystalline films prepared by the AACVD process are 220 000 A/cm 2 and 84 000 A/cm 2 at self-field and 0.1 T, respectively.

A nonplanar X-band cavity amenable to coating with high-temperature superconducting films by conventional physical vapor deposition processes has been designed, fabricated, and tested. The cavity geometry resembles a symmetric clamshell configuration. It consists of two truncated cones joined at their bases. The specific dimensions of the cavity were calculated using the SUPERFISH computer code. Cavities were constructed using a silver-based alloy, Consil 995. The separate cavity sections were coated with Tl-based high-temperature superconducting material using a two-step deposition and annealing process. The unloaded Q values for this coated clamshell cavity are 66,000 and 105,000 at 77 and 20 K, respectively.

Bozoian et al. have developed an analytical theory which predicts the incident ion energy at which elastic-scattering cross sections begin to deviate from their Rutherford values as the result of nuclear perturbations. The predictions are in good agreement with experimental data for proton and helium-ion beams, and should be applicable to heavier projectiles. The theory has also been extended to account for isotopic variation of the incident beam. As a further test of the theory, we have performed a series of backscattering measurements using both 6Li and 7Li ion beams. Lithium-ion backscattering is of importance to thin-film analysis because it offers improved depth sensitivity and kinematic mass resolution as compared to helium. Elastic-backscattering cross sections for O, F, Al, and Ti were measured relative to those ofhigh-Z reference elements over an energy range of 2.5–9.25 MeV, and the energies at which they began to deviate from their Rutherford values were determined. The experimental results are compared to predictions from the analytical theory, and from optical-model calculations.

Films of Ba-Ca-Cu-O have been RF-magnetron-sputtered onto Consil 995 substrates. A postdeposition anneal in an overpressure of Tl produces the superconducting 1212 and 2212 phases. Varying the annealing procedures changes the electrical properties of the final films dramatically. Dynamic impedance, a novel approach to the electrical characterization of these films on a conductive substrate, is discussed and compared with SEM (scanning electron microscope), XRD (X-ray diffraction) and RBS (Rutherford backscattering) measurements as a function of differing annealing protocols. The improvement in the superconducting responses as a function of annealing procedures correlates well with the improved morphology observed in the SEM photographs. Also, the XRD data show increased c-axis material with the C annealing protocol.

We have investigated the fabrication of thin‐film superconductors by Cu‐ion implantation into initially Cu‐deficient Y(BaF2)Cu thin films. The precursor films were co‐evaporated on SrTiO3 substrates, and subsequently implanted to various doses with 400 keV 63Cu2+. Implantations were performed at both LN2 temperature, and at 380 °C. The films were post‐annealed in oxygen, and characterized as a function of dose by four‐point probe analysis, x‐ray diffraction, ion‐beam backscattering and channeling, and scanning electron microscopy. It was found that a significant improvement in film quality could be achieved by heating the films to 380 °C during the implantation. The best films made became fully superconducting at 60–70 K, and exhibited good metallic R vs T behavior in the normal state.

Recent experiments have demonstrated the utility of high-energy backscattering for thin-film analysis, often exploiting elastic-scattering resonances to increase sensitivity to low-Z elements. However, higher-Z elements may also exhibit deviations from Rutherford scattering, and it is desirable to examine the problem theoretically so that such deviations can be predicted and corrected for. We have used the optical-model computer code SCAT86 to calculate the projectile energy Enr at which the scattering cross section begins to deviate from its Rutherford value. The results agree well with data for both alpha particle and proton projectiles, but the interaction potentials are complicated, and the program does not provide an analytical predictive formula. We have therefore developed a simple classical model which treats the interaction as a sum of Coulomb and Yukawa-like potentials. For small deviations from Coulomb scattering, the problem can be solved analytically, providing a simple expression for Enr which agrees well with both experimental data and SCAT86. The classical approach is valid for all but small-angle forward scattering and can easily be extended to heavier projectiles such as Li.

We have used nanoindentation to measure the mechanical properties of epitaxial TiN/(V0.6Nb0.4)N superlattices, grown on MgO(100), as a function of the wavelength λ. The V/Nb ratio within the VNbN layers was chosen to provide a lattice match with TiN, minimizing effects resulting from coherency strains. For λ≥4 nm, the hardness was found to be significantly enhanced relative to a homogeneous reference film of the same average composition. For λ

A multi-step process is used to fabricate Tl2Ba2Ca1Cu2O8 films on (100) LaA103 substrates. Submicron thick precursor films of Ba-Ca-Cu-O are rf magnetron sputter deposited from a single target. Film stoichiometry is measured by ion beam backscattering spectroscopy. Deficiencies of the alkaline earths that are found in the precursor films are then compensated for by the addition of appropriate CaF2 and/or BaF2 films onto the surface of the precursor film. Post deposition annealing of the films is then done in an atmosphere of thallium oxide and oxygen in order to form the superconducting phases. The annealed films are examined using x-ray diffraction (XRD), an ac inductance technique, and critical current in an external magnetic field. XRD shows the c-axis length of the superconducting phase to increase as the overall film stoichiometry approaches 2212. The transition widths measured by inductive coupling weakly correlate with 77 K critical current measurements. Our best critical current results are 1.5*106 amps/ cm2 for a film measured at 4 K in an 8 T magnetic field (parallel to the films' c-axis).

We have used pulsed excimer laser radiation at 248 nm to mix Ti layers into Si3N4 substrates. Mixed layers show formation of small grain TiN in a Si3N4 but no evidence of Ti‐Si compounds or free Si. Low fluence (∼1.0 J cm−2) processing results in minimal mixing as TiN formation at the interface impedes further diffusion. At higher fluence (≳2 J cm−2) complete and quite uniform mixing occurs. The mixed layer is of the order of 0.5 μm thick.

Under conditions used for pulsed laser deposition (308 nm, 20 ns, 2–8 J/cm2) of Y‐Ba‐Cu‐O superconducting thin films, we have measured a pronounced decrease in deposition rate with cumulative laser exposure of the target. This decay in rate is accompanied by evolution on the target surface of microscopic columnar structures, having yttrium‐enriched surfaces, which are aligned in the direction of the incident laser beam (45°). Neither the vapor plume direction nor film stoichiometry is affected by the presence of these oriented, chemically altered surface features.

Superconducting Tl2Ba2CaCu2Ox films were fabricated using a three‐step process. Amorphous BaCaCuOF films were deposited on MgO(100) single‐crystal substrates by metalorganic chemical vapor deposition at 500 °C using fluorinated β‐diketonate complexes of Ba, Ca, and Cu. The fluorine was stripped in wet oxygen at 785 °C and c‐axis oriented Tl2Ba2CaCu2Ox films were then formed by annealing in dry at 870 °C in the presence of Tl2O3/Ba2Ca2CuN3Ox pellets. The best films showed onsets of superconductivity at 125 K and zero resistivity was achieved by 108 K. Critical current densities as high as 104 A/cm2 were obtained at 90 K.

Broad angular distributions have been observed for XeCl laser ablation plumes used in the deposition of YBa2Cu3O7−δ thin films. Distributions (inferred from film thickness) and film stoichiometry were measured as a function of laser fluence, beam shape, and oxygen pressure. Parallel to the long axis of the laser spot, plumes exhibited a cos3.5(θ) spread and composition varied with angle; in the perpendicular direction, more diffuse [cos1.5(θ)] plume distributions were associated with stoichiometric deposition. The observed phenomena are consistent with formation of a Knudsen layer near the target surface.

Neutron reflectometry (NR) studies1 of thin films of amorphous 11B/l0B on silicon indicate that a non-standard form of Fickian diffusion occurs across the boron interface upon annealing. In order to verify this observation, the samples were examined by neutron depth profiling (NDP). Comparison of the results from models of a step function, standard Fickian diffusion and Fickian diffusion with a fixed composition at the interface were made and compared to the previous NR results. The diffusion constant resulting from the non-standard Fickian model for the NDP data differs slightly from that obtained from the commonly used Fickian diffusion model and is not inconsistent with the NR results. This finding suggests that more information regarding diffusion at interfaces can be gained from these higher resolution neutron scattering techniques.

Multilayers of Ru-Cu and Ru-Ti have been prepared by electron beam evaporation technique. One set of composites has Ru thickness varying from 250 to 2500Å alternating with Cu or Ti of 15Å. The other set has 250Å of Ru and the Cu or Ti layer varies between 15 and 200Å. Nanoindentation measurements show that there is no significant change in hardness as either Ru or Cu/Ti thickness varies. However, the Ru-Cu multilayer has twice the hardness of the Ru-Ti system. High resolution transmission electron microscopy discloses that there is an epitaxial orientation relationship between Ru and Ti in Ru-Ti while no such relationship exists in Ru-Cu.The strengthening mechanism proposed by Koehler [1] predicts that Ru-Ti composites should have a higher strength than Ru-Cu due to the larger modulus difference between Ru and Ti. The discrepancy between the prediction and the experimental results suggests that other strengthening mechanism(s) may be operating. We have proposed two models based on a "shear" mechanism to explain the differences observed between these two systems. The effects of these mechanisms in controlling the deformation process in nanolayer composites are discussed.

Excimer laser processing enables both thermally-driven transformations and the incorporation of solutes into the surface of materials through melting and diffusional mixing. We have examined the effect of excimer laser processing on the microstructure and surface mechanical properties of titanium alloys. Changes in the surface hardness due to laser processing were studied using a Nanoindenter™. Alloying experiments using both mixing of evaporated surface layers of boron and laser gas alloying in air and in nitrogen all result in changes in the surface hardness of the material. Alloying with boron results in an amorphous surface which is somewhat harder than the as polished surface. Laser processing in air and pure nitrogen results in incorporation of oxygen and nitrogen and the development of fine precipitates of TiO and TiN respectively. Substantial increases in surface hardness result due to solution and precipitation mechanisms. Nanoindenter™ data from several depths in the material are correlated with microstructure and solute concentration to illuminate the strengthening mechanisms involved.

We have begun a series of neutron reflectometry studies to investigate atomic diffusion behavior in both elemental boron and refractory transition-metal borides. In this paper, we report on the results for boron-atom self-diffusion in amorphous elemental boron. The samples used for the measurements were thin-film bilayer structures consisting of alternating layers of isotopically enriched 10B and 11B, deposited by electron-beam evaporation. The reflectometry studies were performed with a beam of pulsed neutrons having a broad thermal spectrum incident on the samples at an angle of approximately 1.00 degree(s). Specularly reflected neutrons were detected as a function of their time-of-flight with a position-sensitive detector. This data was reduced to obtain a plot of the reflectivity vs. the perpendicular wavevector. Because of the different nuclear potentials for the two boron isotopes, an interference pattern was observed, analogous to those obtained by X-ray measurements on samples with a modulated index of refraction. Reflectivity profiles were measured and analyzed as a function of annealing time for temperatures of 360 degree(s)C and 400 degree(s)C. Variations in the interference patterns were then used to determine the diffusion coefficient, D, at 360 degree(s)C, and hence the intrinsic diffusion parameters. A typical equilibrium result was determined to be D approximately 10-1 angstroms2s, measured at an annealing temperature of 360 degree(s)C. The measured diffusion constants are inconsistent with the high melting temperature of elemental boron, but are consistent with measured diffusion constants in other amorphous thin films.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Excimer laser surface processing of Ti-6A1-4V results in substantial surface oxygen incorporation as measured by the narrow resonance in the elastic scattering of a particles at 3.05 MeV. Single pulse processing at 1.0 J-cm−2 results in transformation from the original a + β grain structure to a martensite structure. Multiple pulse processing results in oxygen incorporation proportional to the number of pulses during processing, but this is primarily reflected in the depth of the oxygen containing layer. A maximum oxygen to titanium ratio of 1.0 was observed in the surface layer. This was confirmed by transmission electron microscopy (TEM) which showed the development of a fine-grained equiaxed TiO surface layer from a phase mixture of Ti alloy with TiO precipitates. Concentration vs. depth profiles show that this layer is approximately 400 nm thick after 40 pulses. Further processing with a total of 60 pulses results in coarsening of the grains and an increase in the thickness of the layer. The TiO precipitate concentration increases gradually, becoming apparent in electron diffraction patterns after 30 pulses. No other oxide phases are observed, the TiO developing directly from the metallic phases. In particular, we do not observe the formation of Ti2O prior to the formation of the TiO, or the formation of TiO2.

We have investigated the fabrication of thin-film superconductors by Cu-ion implantation into initially Cu-deficient Y(BaF2)Cu thin films. The precursor films were co-evaporated on SrTiO3 substrates, and subsequently implanted to various doses with 400 keV 63Cu2+. Implantations were preformed at both LN2 temperature and at 380°C. The films were post-annealed in oxygen, and characterized as a function of dose by four-point probe analysis, X-ray diffraction, ion-beam backscattering and channeling, and scanning electron microscopy. It was found that a significant improvement in film quality could be achieved by heating the films to 380°C during the implantation. The best films became fully superconducting at 60–70 K, and exhibited good metallic R vs. T. behavior in the normal state.

Target modification by excimer laser exposure has been investigated. Under conditions typical in the fabrication of superconducting thin films, deposition rate decreases with exposure and significant physical and chemical modifications occur on the target surface. These modifications do not inhibit congruent evaporation.

Thick (8 to 10 µm) Ba-Ca-Cu-O films have been rf magnetron sputtered onto Ag alloy (Consil 995) substrates. The films were given a post-deposition anneal in an over pressure of Ti in order to form the superconducting phases. Annealing protocols were done which result in predominantly the 1212 and 2212 phases. The substrate orientation was varied to determine its effect on film orientation. Material properties of the films were characterized by x-ray diffraction (XRD), ion beam backscattering spectroscopy, energy dispersive x-ray analysis (EDAX), and scanning electron microscopy (SEM). Electrical characterization of the films was done using dynamic impedance (DI) at 10 kHz and rf surface resistance (Rs) at 18 GHz in a TE011 fundamental mode cavity.

The Interfacial stability of a high strength TiB2/Cu multilayer structure was examined by subjecting the layers to ion irradiation by 400 keV Ne++ ions up to a maximum dose of 12×1015 ions/cm2. Even at the highest dose, with a maximum dpa value of 4.92, the TiB2/Cu interface did not show any mixing. This stability of the multilayers has been explained by examining the maximum thermodynamic driving force for Interfacial reactions in this system.

Angular distributions of sputtered atoms have been obtained for 3, 25, and 50 keV Ar+ bombardment of a liquid Ga-In eutectic alloy target. Sputtered material was collected on graphite foils which were subsequently analyzed by Rutherford backscattering spectroscopy, and the resulting distributions were fit by a functional form, N (θ) α. cos^nθ. For each energy, the angular distribution of sputtered In atoms was overcosine, with n_(In) ≈ 1.8 ±0.1. The distributions of the sputtered Ga atoms were sharper, varying from n_(Ga) ≈ 3.2 ± 0.2 at 25 and 50 keV, to n_(Ga) = 4.9 ± 0.3 at 3 keV. A comparison of the sputtered flux composition with the alloy surface composition profile gives F_1, the fraction of sputtered atoms originating from the first atomic layer. The fraction was found to be f_1 = 0.87 ± 0.01 for 25 and 50 keV bombardment, and increased to 0.94 ± 0.01 at 3 keV. The variations of n_(ga), and F_1 with projectile energy may be the result of a decrease in the average recoil-atom energy for the 3 keV bombardment. The large values found for F_1 support a prediction that the sputtered-atom escape depth is determined by the elastic-collision mean free path of recoil atoms.