bluuebunny/crossref_metadata_2025 huggingface dataset:
Cadmium Sulfide Films Deposited by Cw Laser Evaporation Technique
Authors: Moss R. W. , Harris J. , Lee D. H. , Condrate R. A. , Wang X. W. , Stoltz S. M. , Petrou A.
Published: April 2011

Cadmium Sulfide (CdS) thin films had been fabricated by a laser deposition technique. Our previous results indicated that the hexagonal structured films could be formed at a substrate temperature of 400 C or higher. Reducing the temperature to 200 C or lower, cubic dominant films had been fabricated. To further understand the effects of other deposition parameters, CdS films were deposited at 30 C in this study. Crystal structures of the films were analyzed by Xray diffraction (XRD) and Transmission Electron Microscopy (TEM). It was found that the processing windows for the cubic films were very limited. As revealed by optical transmission measurements, the optical absorption edge of the cubic film was different from that of the hexagonal film.
Low Temperature Epitaxy of Si on Dihydride-Terminated Si (001): Energetic Versus Thermal Growth
Authors: Taylor M. E. , Atwater Harry A. , Murty M. V. Ramana
Published: April 2011

Pulsed laser deposition of Si on dihydride-terminated (l×1) Si (001) at low temperatures yields epitaxial layers, unlike molecular beam epitaxy. Si films were grown by ultrahigh vacuum pulsed laser deposition on the dihydride surface at substrate temperatures from 40 °C to 350 ° C. Epitaxial thickness and interface roughness were measured by high-resolution cross-sectional transmission electron microscopy and found to be comparable to known data for Si films grown by molecular beam epitaxy on monohydride-terminated (2×l) Si (001). Si films were grown at 200 °C by pulsed laser deposition on the dihydride surface at argon background pressures between 10− torr and 10−1 torr. Ion probe time of flight data was collected over the same pressure range. Comparison of the results suggests that loss of epitaxy is correlated with low incident energy. This, in conjunction with information on surface reconstruction obtained from reflection high-energy electron diffraction, suggests that the mechanism enabling epitaxy on the dihydride surface is Si subplantation, a mechanism only possible in growth with an energetic beam.
Control of the hydrogen content of diamond-like carbon films deposited using unbalanced magnetron sputtering
Authors: Seo S.-C. , Ingram D. C.
Published: April 2011

The possible sources of hydrogen contamination of Diamond-Like Carbon (DLC) films deposited using Unbalanced Magnetron (UBM) sputtering of carbon from a graphite target have been studied. Without deliberate introduction of hydrogen or hydrocarbon gas, magnetron sputtered DLC can contain significant amounts of hydrogen, from 4 to 23 %, by changing the base pressure (or residual gas pressure, rgp) of the deposition system from 3 × 10−6 to 4 × 10−5Torr. This hydrogen contamination contributes to a large change in the optical band gap (0.2 to 1.0 eV) and lowers the density of the films. The hydrogen content in the films comes from water vapor in the deposition system, mainly absorbed in the graphite target, which is dissociated and/or ionized in the plasma. Hydrogen gas has been introduced up to a pressure of 7 × 10−1Torr at a base pressure of˜1 × 10−1Torr in order to simulate high residual gas pressure conditions. The properties of the plasma and the films produced at high base pressures have been compared to those at a high partial pressure of hydrogen gas. For the plasma properties, the electron temperature, Te, and the ion density, ni, were measured by using a double Langmuir probe. The films were characterized by using Ultraviolet-Visible, Rutherford Backscattering/Elastic Recoil, and X-ray Photoelectron Spectroscopies (UV-VIS, RBS/ERS, and XPS).
Fast Soldering Reactions on Au Foils
Authors: Kim P.G. , TU K.N.
Published: April 2011

We have studied the wetting behaviors and interfacial reactions of Pb‐containing (63Sn‐37Pb, 95Pb‐5Sn) and Pb‐free solders (pure Sn, 96Sn‐4Ag, 57Bi‐43Sn, 77.2Sn‐20In‐2.8Ag) on Au foils in order to understand the role of Pb in Pb‐based solders. Surface morphology, wetting angle, and interfacial reaction of the solders were studied by Scanning Electron Microscopy (SEM) and Energy Dispersive X‐ray Analysis (EDX). Pb‐containing and Pb‐free solders (pure Sn, 96Sn‐4Ag, 77.2Sn‐20In‐2.8Ag) showed rough surfaces due to the precipitation of intermetallic compounds on the surface of the solder caps. The eutectic SnBi (57Bi‐43Sn) solder, however, showed a smoother surface. The wetting angle of the eutectic SnPb (63Sn‐37Pb), pure Sn, 96Sn‐4Ag, and 77.2Sn‐20In‐2.8Ag solders decreased significantly with reflow time, while the eutectic SnBi and 95Pb‐5Sn solders showed a much smaller decrease. A large amount of intermetallic compounds was formed throughout the entire region of the solder cap for the eutectic SnPb, 96Sn‐4Ag, 95Pb‐5Sn, and 77.2Sn‐20In‐2.8Ag, mainly due to the high solubility of Au in these solders. Slow intermetallic compound growth was observed for the eutectic SnBi solder.
High Reliability Underfill for Flip-Chip Application
Authors: Sumita K. , Kumagae K. , Dobashi K. , Shiobara T. , Kuroda M.
Published: April 2011

A new underfill was developed for a flip chip application with a large VLSI die. The new underfill is resistant to hydrolysis, exhibits a significantly lower moisture saturation level than widely used carboxylic anhydride cured underfills, demonstrates superb penetration capability between such a large die and an organic substrate without void formation, and delivers excellent adhesion characteristics and reliability performance during temperature cycling test and PCT (pressure cooker test).

The new underfill utilizes amine catalyzed ring opening polymerization of epoxides, forms ether linkages during cure rather than ester linkages which anhydride cured underfills form, and strongly resists to hydrolysis. The underfill is less sensitive to moisture contamination and provides improved floor life as well as storage life in contrast to anhydride cured underfills as well. Unique low stress performance and penetration capability of the underfill are attributed to the use of proprietary silicone modified epoxy resin as well as highly loaded filler of optimized size, shape and size distribution in reference to the gap between a die and an organic substrate.

An optimum cure schedule and a desirable viscosity range have also been identified for the new underfill to minimize filler segregation. Proper preheating of a die‐substrate has effectively reduced void formation while facilitating the removal of volatile from an organic substrate.
Development of New High-Mounting Density Packages
Authors: Kasai J. , Tsuji K. , Yoneda Y.
Published: April 2011

In low pin-count packages mounted with a device for portable electronics equipment, we have developed the CSP(Chip Size Package), which guarantees the reliability similar to the former SSOP (Shrink Small Outline Package) despite its drastic miniaturization in size than SSOP. The BCC (Bump Chip Carrier) we developed this time, as the name suggests, is a package with bumps, having the following structure: resin bumps covered with metal film are laid out in the base peripherally as mounted terminals. This resin bump can be formed by molding monolithically with resin sealing, and the connection between the bump and metal film has been implemented using lead frame manufacturing technology and etching technology we have developed. In this paper, we outline the structure and manufacturing technology of BCC as well as the results of reliability evaluation for BCC.
InN-Based Ohmic Contacts to AlInN
Authors: Donovan S. M. , Ren F. , MacKenzie J. D. , Abernathy C. R. , Pearton S. J. , Jones K.
Published: April 2011

In order to maximize the performance of III-Nitride devices, it is necessary to develop thermally stable low resistance Ohmic contacts to III-N based electronic structures. This paper reports on the utility of InN as an aid to contact formation on widegap materials such as InAIN. For n-type materials, several questions relating to the growth conditions have been explored. Specifically, the impact of substrate type (GaAs vs. Sapphire), cap layer growth temperature and V/III ratio on contact resistance has been investigated. It was found that the use of sapphire substrates combined with high growth temperatures (575°C) and high V/III ratios produced acceptable contact resistances (∼10−6Ohm-cm2) to InAIN.
Nitride-Based Thin-Film Cold Cathode Emitters
Authors: Christman James A , Sowers Andrew T , Bremser Michael D , Ward Brandon L , Davis Robert F , Nemanich Robert J
Published: April 2011

Cold cathodes have been fabricated using two different nitride structures as a thin film emitting layer. The A1N and graded AlGaN structures are prepared by metalorganic chemical vapor deposition (MOCVD) on an n-type 6H-SiC substrate. Individual aluminum grids are perforated with an array of either 1, 3, or 5μm holes through which the emitting surface is exposed. After device fabrication, a hydrogen plasma exposure was found to be necessary to activate the cathode. The devices have displayed a limited lifetime and a small percentage of the devices operate, although half of the devices with 5μm holes functioned. The highest measured collector currents are 0.1μA for A1N and l0nA for AlGaN at grid voltages of 110V and 20V, respectively. The grid currents are typically 10 to 104 times the collector currents.
A Microstructural Analysis of Orientation Variation in Epitaxial AlN on Si, Its Probable Origin, and Effect on Subsequent GaN Growth
Authors: Beye R. , George T. , Yang J. W. , Khan M. A.
Published: April 2011

A structural examination of aluminum nitride growth on [111 ] silicon was carried out using transmission electron microscopy. Electron diffraction indicates that the basal planes of the wurtzitic overlayer mimic the orientation of the close-packed planes of the substrate. However, considerable, random rotation in the basal plane and random out of plane tilts of about ±3–4$ are evident. The orientation variations were traced to the Si interface, where crystallites and an amorphous-like background were present. A strong relationship between these phenomena and substrates containing Si is established by comparing the present growth results with those reported elsewhere. Crystalline quality of the overgrown GaN on the AIN layer is described, with suggestions for the relation between surface pyramids or peaks and the mis-oriented buffer layer.
In Situ Reflection High-Energy Electron Diffraction Study of Structure and Morphology Evolution of AlN Thin Films During Growth
Authors: Jin F. , Auner G. W. , Naik R. , Zatyko P. , Rao U.
Published: April 2011

AIN films were grown on Si (111) substrates using a PSMBE deposition system. Two types of growth methods were used: (i) a continuous growth at one temperature and (ii) a two stage growth where a buffer layer at low temperature is followed by deposition at higher temperature. The structure and morphology of the films grown at different temperatures are compared. The evolution of surface structure and morphology of the film during the growth were studied using in-situ RHEED, X-ray diffraction, and AFM.
High Resolution X-ray Diffraction from Epitaxial Gallium Nitride Films
Authors: Lafford T. , Loxley N. , Tanner BK
Published: April 2011

The width of double axis X-ray rocking curves of epitaxial GaN layers is shown to be critically dependent on the width of the detector aperture. We show that triple axis diffraction measurements using a crystal analyser before the detector enables the instrument function to be defined and the tilt and dilation distributions separated. All GaN samples examined showed a mosaic structure of misoriented sub-grains with little dilation within the mosaic blocks. In reciprocal space maps this was revealed as a wide distribution of intensity in a direction perpendicular to the reciprocal lattice vector.
Deep Levels in GaN Studied by Extrinsic Photoconductivity Measurement
Authors: Zhang Rong , Huang Zhenchun , Guo Bo , Chen J. C. , Yan Li , Zheng Youdou , Kuech T. F.
Published: April 2011

Modulation Extrinsic photoconductivity spectra between 1.44eV and 1.75eV of unintentionally n-doped high resistance GaN film grown by MOCVD are measured at room temperature by using wavelength adjustable Ti:Sapphire laser. We find that there are two major deep levels in the GaN material in the used photon energy range. The relaxation time of excess carriers controlled by those levels are in the order of 10−4sec. The concentration of localized states are determined as 1.8×108cm−3 and 2.5×109cm−3, respectively. A physical model is developed to explain the results and process the data. Using a new method we have determined the optical absorption cross section of deep levels are 1.5×10−17cm2 and 2.7×10−18cm2, respectively.
Analytical Theory of Electron Mobility and Drift Velocity in GaN
Authors: Gelmont B. L. , Shur M. S. , Stroscio M.
Published: April 2011

We derive balance transport equations for the electron mobility and drift velocity, which are applicable at any degeneracy of the electron gas. These equations account for the polar optical phonon scattering and ionized impurity scattering and include the effects of screening. These equations are valid only for very high concentrations (above 1019 cm-3 for GaN). However, the comparison with the results of Monte Carlo simulations shows that they fairly accurately reproduce the field-velocity curves in GaN in moderate electric fields (up to 100 kV/cm). The comparison with the electron mobility calculated using the two-step model [1] shows a much larger difference but allows us to illustrate the trends in mobility dependencies caused by electron-electron collisions. We also derive the balance transport equations accounting for the polar optical phonon scattering in a two-dimensional electron gas. The calculations based on these equations, show that the unscreened polar optical scattering mobility is smaller in the two-dimensional gas than in the bulk intrinsic semiconductor and that the mobility decreases with the decrease of the quantum well thickness.
Study of Traps in GaN by Thermally-Stimulated Current
Authors: Zhang Rong , Huang Zhenchun , Chen J. C. , Zheng Youdou , Kuech T. F.
Published: April 2011

In this paper we employed the TSC method to investigate the traps in GaN. The measured sample was a M-S-M UV-detector of high-resistance GaN on sapphire grown by LP-MOCVD. The relation of dark conductance to temperature clearly showed three major donor levels at 0.019, 0.13 and 0.74eV respectively. TSC measurements from 60 to 380K indicated that there were at least 11 traps in the GaN material. The active energy of those traps were 0.15, 0.19, 0.25, 0.28, 0.33, 0.39, 0.47, 0.55, 0.60, 0.63 and 0.67eV. The range of trap density is from 6 × l014cm-3 to 2 × l018cm-3. By comparing TSC spectrum to dark current, we consider there are at least 4 hole traps in the measured range with energy of 0.25, 0.28, 0.33 and 0.39eV. The illumination time effect was studied and discussed.
Relaxations at GaN (1010) and (110) Surfaces
Authors: Filipetti Alessio , Menchi Manuela , Bosin Andrea , Cappellini Giancarlo
Published: April 2011

We present anab-initiocalculation of GaN wurtzite (1010) and zinc-blende (110) surface structures and formation energies. Our method employs ultrasoft pseudopotentials and plane-wave basis. These features enable us to obtain accurate results using small energy cut-off and large supercells. The (110) surface shows a Ga-N surface dimer rotation of ∼ 14°, i.e. about one half that of the ordinary III–V non-nitride compounds, and a 5% contraction of the surface bond-length (more than the double that occurring in GaAs). For the (1010) surface, a layer rotation angle of about 11° and a bond-length contraction of 6% has been found. Zinc-blende GaAs (110) and wurtzite ZnO (1010) surfaces have been studied as well, for the sake of comparison. GaAs results are in good agreement with the experimental findings. For ZnO a large bond contraction and a rotation angle of around 11% result. Thus, our findings place GaN closer in behaviour to the highly ionic II–VI compounds than to the non-nitride III–V semiconductors.
Characterization of SiGe Alloy Nanocrystallites Prepared by Pulsed Laser Ablation in Inert Gas Ambient
Authors: Yamada Yuka , Orii Takaaki , Yoshjda Takehito
Published: April 2011

We report nanometer-sized silicon germanium (SiGe) alloy crystallites prepared by excimer laser ablation in constant-pressure inert gas. Size distribution of the SixGelxultrafine particles decreases with decreasing x under fixed conditions of deposition such as ambient gas pressure. Raman scattering spectra of the deposited SiGe ultrafine particles show three peaks intrinsic to crystalline SiGe alloys, and the linewidths of these peaks broaden due to the reduced size of the crystallites. Furthermore, a visible photoluminescence (PL) band with a peak at around 2.2 eV is obtained at room temperature after an annealing process.
Luminescence Properties of Silicon Nanocrystals
Authors: Li Shoutian , Silvers Stuart J. , Samy El-Shall M.
Published: April 2011

Weblike aggregates of coalesced Si nanocrystals are produced by a laser vaporization -controlled condensation technique. SEM micrographs show particles with ∼ 10 nm diameters but the Raman shift suggests the presence of particles as small as ∼ 4 nm. FTIR of the freshly prepared particles shows weak peaks due to the stretching, bending and rocking vibrations of the Si-O-Si bonds indicating the presence of a surface oxidized layer SiOx (x<2).

The particles show luminescence properties that are similar to those of porous Si and Si nanoparticles produced by other techniques. The nanoparticles do not luminesce unless, by exposure to air, they acquire the SiOx passivated coating. They show a short-lived blue emission characteristic of the SiO2 coating and a biexponential longer-lived red emission. The short lifetime component of the red emission, about 12 μs, does not depend on emission wavelength. The longer-lived component has a lifetime that ranges from 90 to over 130 μs (at 300 K), increasing with emission wavelength. The results are consistent with the quantum confinement mechanism as the source of the red photoluminescence.
Deposition of Polypyrrole into Porous Silicon
Authors: Moreno J. D. , Agullo-Rueda F. , Guerrero-Lemus R. , Martinpalma R. J. , Martinez-Duart J. M. , Marcos M. L. , Gonzalez-Velasco J.
Published: April 2011

Polypyrrole has been electrocleposited in the interior of the pores that form the Porous Silicon structure, and a very significant increase of the electrical conductivity of the samples has been observed. The degree of filling by the polymer has been found to be highly dependent on the electropolymerization conditions. Micro-Raman Spectroscopy experiments have allowed us to measure the amount of polymer as a function to the distance from the outer PS surface.
Growth of Thin
 μc-Si:H on Intrinsic a-Si:H for  Solar Cells Application
Authors: Pemet P. , Goetz M. , Keppner H. , Shah A.
Published: April 2011

The
 μc-SiC:H /  a-Si:H junction can be considered to be a sub-system of a n/i/p solar cell. Optimised performance of this junction can be assumed to be a key feature for obtaining high efficiency solar cells.

In this paper the authors present results on the conductivity of boron doped microcrystalline hydrogenated silicon (
 μc-Si:H) thin films deposited on amorphous substrates (e.g. glass or glass/ a-Si:H). It is shown that, without any treatment of the substrate or of the underlying surface, the
 layers showed a strongly reduced conductivity. This indicates either a bad nucleation or a poor microcrystalline behaviour. By using an appropriate surface treatment of the substrate, a gain in photoconductivity of about three orders of magnitude could be obtained (σ > 3 S/cm at a layer thickness of 400Å). We conclude from this, that for thin
 type μc-Si:H layers the nucleation conditions are essential for obtaining best electric properties of the film w.r.t. solar cell performance.

Based on these results, interface treatment was successfully implemented in n/i/p solar cells deposited on TCO coated glass and stainless steel. The results of these experiments are also presented.
Epitaxy-Like Growth of Polycrystalline Silicon on the Seed Crystallites Grown on Glass
Authors: Miyamoto Y. , Miida A. , Shimizu I.
Published: April 2011

Polycrystalline silicon thin films were grown on glass by two-steps, i.e., deposition of seeds on glass (1) and growth epitaxy-like on the seeds (2). For the growth of seeds, the surface reaction was intentionally enhanced by impingment of atomic hydrogen at rather high temperature (450 °C). Strongly textured polycrystalline Si exhibiting (220) preferential orientation was grown epitaxy-like on the seeds.
Nanocomposite Thin Films of Transition Metal Carbides Fabricated Using Pulsed Laser Deposition
Authors: Brock W. F. , Krzanowski J. E. , Leuchtner R. E.
Published: April 2011

A study has been conducted on the pulsed laser deposition (PLD) of transition metal carbides in order to examine alloying and phase formation in binary systems. Alternating layers of TiC/ZrC and ZrC/VC were deposited at 400 C and 5 mTorr Ar with nominal period thicknesses of 0.6 nm, 10.0 nm, and 50.0 nm. ZrC/VC x-ray diffraction analysis showed that the alloys were amorphous and the TiC/ZrC alloys were crystalline. The thicker films showed a higher degree of phase separation of the two compounds. Transmission electron microscopy confirmed the amorphous structure in the 0.6 nm ZrC/VC film, while the 50.0 nm film showed a layered structure and extremely fine grain size.
Preparation and Characterization of Nanocomposite Composed of TiO2 as Active Matrix
Authors: Sasaki T. , Rozbicki R. , Matsumoto Y. , Koshizaki N. , Terauchi S. , Umehara H.
Published: April 2011

Pt/TiO2 nanocomposite films were deposited on quartz glass and ITO glass substrates by the co-sputtering method. As-deposited composite films were amorphous and content of Pt in the films could be easily controlled by the amount Pt wire placed on the TiO2 target. Pt/Ti atomic ratio in the nanocomposite increased as the length of Pt wire on the TiO2 target increased. It was determined by XPS that the chemical states of Pt in as-deposited nanocomposites were Pt metal, Pt-O-Ti and PtO2, which were dependent on the Pt/Ti atomic ratio in the nanocomposite. The size of Pt nanoparticles in the composite films increased as the temperature of heat-treatment and Pt/Ti atomic ratio in the composite films increased. Pt nanoparticles in the nanocomposite films inhibited grain growth of TiO2 during heat-treatment.
Synthesis and Characterization of Aerogel-derived Cation-substituted Hexaaluminates
Authors: Yan Lin-chiuan , Thompson Levi T.
Published: April 2011

New methods have been developed for the synthesis of high surface area cation-substituted hexaaluminates. These materials were prepared by calcining high temperature (ethanol extraction) or low temperature (CO2 extraction) aerogels at temperatures up to 1600°C. Cation-substituted hexaaluminates have emerged as promising catalysts for use in high temperature catalytic combustion. In comparing unsubstituted and cation-substituted hexaaluminates, we found that the phase transformations were much cleaner for the cation-substituted materials. BaCO3 and BaAl2O4 were intermediates during transformation of the unsubstituted materials, while the cation-substituted materials transformed directly from an amorphous phase to crystalline hexaaluminate. Moreover, the presence of substitution cations caused the transformation to occur at lower temperatures. Mn seems to be a better substitution cation than Co since the Mn-substituted materials exhibited higher surface areas and better heat resistances than the Co-substituted materials. The low temperature aerogel-derived materials possessed quite different characteristics from the high temperature aerogel-derived materials. For example, phase transformation pathways were different.
Electrical Conductivity of Pure and Doped Nanocrystalline Cerium Oxide
Authors: Lavik E. B. , Chiang Y.-M.
Published: April 2011

We have previously shown that dense nanocrystalline CeO2−x of approximately 10 nm grain size exhibits enhanced electrical conductivity and an enthalpy of reduction that is more than 2.4 eV lower than that for conventional ceria [1, 2]. These effects were attributed to preferential interface reduction. In this work, we investigated the relationship between interfacial area, heat treatment conditions, and conductivity by varying the grain size of dense samples through annealing at various temperatures. It is shown that the conductivity does not scale in direct proportion to interfacial area. Moderate temperature (700 °C) anneals which change the grain size by only a few nanometers reduce the conductivity by three orders of magnitude. It is suggested that atomistic relaxation occurs at the interfaces, and eliminates many low energy defect sites.
Monotonic and Transient Creep Experiments for Single Phase Gamma TiAl at Intermediate Temperatures
Authors: Lu Min , Hemker K. J.
Published: April 2011

Monotonie creep experiments (constant stress and constant temperature) of a single phase γ Ti47Al51Mn2 were conducted within a temperature region where the yield stress anomaly is observed (500°C - 600°C). The creep strength was found to have a normal temperature dependence. In addition to the monotonie creep experiments, temperature change experiments were performed. The creep activation energy obtained by the transient experiments was found to be significantly lower than that obtained from the monotonie experiments. TEM observations indicate that the microstructure evolves throughout creep, and no evidence of the formation of subgrains was observed. Instead, the mobility and the multiplication of ordinary dislocations were found to play a dominant role in intermediate temperature creep of single phase γ TiAl.
Effect of Stress on Creep of Lamellar Near γ-TiAl
Authors: Beddoes J. , Triantafillou J. , Zhao L.
Published: April 2011

The creep behaviour of a binary Ti-48%A1 intermetallic is presented as a function of stress for two fully lamellar microstructures. The two lamellar conditions differ in terms of the lamellar interface spacing and grain boundary morphology. Air cooling (AC) from the single phase a region causes planar grain boundaries and lamellar spacing of 90 to 130 nm, while furnace cooling (FC) causes interlocked lamellae along grain boundaries and 350 to 550 nm lamellar spacing. Monotonie and stress increment creep tests at 760°C indicate that the AC condition exhibits a lower mimimum creep strain rate at stresses between 105 MPa and 290 MPa. The stress exponent increases from ∼ 1 at low stress to ∼ 10 at high stress. Consecutive stress reduction creep tests indicate that the internal stress required for dislocation glide is higher for the AC condition. The results suggest that at low stress the creep rate is controlled by recovery mechanisms, while at high stress the creep rate is predominantly controlled by dislocation glide. It is postulated that at high stresses the lower creep rate of the AC condition, compared to the FC condition, results from the reduced lamellar interface spacing, which increases the internal stress required for dislocation glide.
Microstructure Control in Iron Aluminides by Phase Decomposition or by Mechanical Alloying for Improved Strength and Ductility
Authors: Morris D. G. , Gunther S.
Published: April 2011

The iron aluminides based on Fe3Al or FeAl being developed for intermediate temperature applications suffer from mediocre room temperature strength and ductility and poor high temperature tensile and creep strength. Attempts to overcome these problems have been restricted by the limited possibilities of structure modification by, for example, precipitation of stable strengthening particles. The present study examines two approaches to obtaining two-phase mixtures for improved strength and ductility: by adjusting chemical compositions such that two-phase order-disorder (α-α″) mixtures are obtained, and by mechanical alloying. Two-phase α-α″ mixtures are obtained by heat treatment of Fe-Al alloys with Al content near 20–24% and in ternary Fe-Al-Si alloys with suitably adjusted Al and Si contents. Microstructures of such alloys can be modified during heat treatments by ordering, precipitation or decomposition, and two-phase mixtures similar to those in the γ-γ superalloys obtained. Such two-phase alloys show good high temperature tensile and creep strength with some indication of reasonable ductility and reduced environmental sensitivity. Mechanical alloying can easily produce FeAl alloys of fine grain size reinforced with stable oxide particles. These structures lead to high room temperature strength with some ductility: controlled recrystallization can significantly modify both strength and ductility.
Primary Creep of Ni3(Al, Ta) Single Crystals at Room Temperature
Authors: Uchic M. D. , Nix W. D.
Published: April 2011

This study examines the time-dependent deformation of Ni3(Al, Ta) at room temperature. Tension creep experiments have been performed on single crystals with one {111}<101> slip system active at the start of the test, where the applied stress ranged from 66.4 MPa (the measured 0.01% flow stress) to 143 MPa (which produced approximately 9% plastic strain). All creep curves displayed primary creep leading to eventual exhaustion, where the measured creep strain declined at a rate faster than predicted for logarithmic creep. However, no correlation between the applied stress and the form of the declining creep rate can be made at this rime. Many creep curves can be obtained from one sample, as the creep curves from both virgin samples and samples with prior deformation history (at the same test stress) were indistinguishable. At the beginning of an incremental creep test, where the stress is increased by a small amount to reinitiate plastic flow in an exhausted sample, a significant retardation of the plastic response of the sample occurred when the stress increment was below 4 MPa. Preliminary TEM studies of a sample strained to 6% suggest that room temperature creep tests may not be ideal for examining the flow of Anti-Phase-Boundary (APB) dissociated dislocations.
Microstructural Stability of Directionally Solidified Eutectic NiAl-Mo Under Static and Thermal Cycling Conditions
Authors: Kush M. T. , Holmes J. W. , Gibala R.
Published: April 2011

The quasi-binary eutectic NiAl-9% Mo with faceted molybdenum fibers was subjected to both thermal annealing conditions and to annealing under thermal cycling conditions to determine the microstructural stability of this alloy. The static temperature tests were run at 0.85TM- 0.97TMin an argon gas atmosphere. The thermal cycling tests were performed between temperatures of 700°C and 1200°C by induction heating disk-shaped specimens in an argon gas atmosphere using time-temperature heating and cooling profiles to approximate potential engine applications. To quantify microstructural changes, the fiber size and size distribution and number of fibers per unit area were measured as a function of time at temperature. The overall results demonstrate that the directionally solidified eutectic NiAl-9Mo subjected to thermal fatigue conditions exhibits cell boundary coarsening and large shape changes, whereas the microstructure under static stress-free annealing is stable.
TEM In-Situ Study of Dislocation Motion in B2 NiAl Single Crystals
Authors: Ghosh B. , Crimp M. A.
Published: April 2011

In an effort to understand dislocation mobility in stoichiometric NiAl single crystals, in-situ tensile deformation experiments have been performed in a transmission electron microscope. Commercially pure and high purity single crystals with <001> and <110> orientations have been examined. Two different thermal treatments were adopted in order to effect the mechanical response. Dislocation motion was observed in all samples. Pre-existing dislocations, either isolated or tangled, were not observed to move at any point leading up to sample failure. Cross-slip of the mobile dislocations was observed in some cases. In commercially pure single crystals, dislocations were found to move at a much slower rate and uniform manner in contrast to motion in high purity single crystals which occurs by rapid jumps.
Slip Transition and Dislocation Structures in Off-Stoichiometric NiAl Single Crystals
Authors: Srinivasan R. , Savage M. F. , Daw M. S. , Noebe R. D. , Mills M. J.
Published: April 2011

Compression tests have been performed on hard-oriented Ni-44A1 single crystals for several temperatures and strain levels. There is a slip transition from a<111> type slip to non-a<111> type slip which corresponds with the observation of yield points. Transmission electron microscopy studies provide evidence for decomposition of a<111> dislocations into a<101> and a<010> dislocations near the “knee” of the yield strength curve. The mechanism of this slip transition and the nature of the dislocation processes both below and above the “knee” are described.
Deformation of Diffusion-Bonded Bi-Pst and Directionally Solidified Crystals of TiAl
Authors: Kishida K. , Johnson D. R. , Shimada Y. , Masuda Y. , Inui H. , Yamaguchi M.
Published: April 2011

With a data base now available on the microstructural characteristics and the deformation, fracture and macroscopic flow behavior of polysynthetically twinned (PST) crystals of γ/α2 TiAl-base alloys, an approach to achieve a good combination of strength, ductility and toughness in γ/α2 TiAl-base alloys was proposed using directional solidification (DS) techniques to produce a columnar grain material with the lamellar orientation aligned parallel to the growth direction. Such alignment of the lamellar microstructure was recently accomplished in γ/α2 TiAl-base alloys of near equiatomic compositions using an appropriately oriented seed crystal from the Ti-Al-Si system.

At the same time, bi-PST crystals, each containing a planar boundary parallel to the loading axis were prepared by directional solidification and diffusion bonding of two PST crystals. Such bi-PST crystals were deformed in tension at room temperature and their deformation behavior was examined in terms of the compatibility requirements imposed at the grain boundary and the interaction of the two component PST crystals.

In this paper, (i) the current status of our DS processing efforts, (ii) some results of microscopic characterization of grain boundaries in diffusion bonded bi-PST crystals and (iii) results of deformation experiments of bi-PST crystals prepared by DS processing and diffusion bonding, will be reported.
Notch-TIP Deformation of Ni3Ai Single Crystals
Authors: Schulson E. M. , Xu Y.
Published: April 2011

The notch-tip deformation field of Ni3AI single crystals doped with boron is characterized by fan-shaped sectors within which one slip system dominates. Cracks initiate and propagate along slip planes on both sides of the notch plane.
Recent Work on Environmental Embrittlement in Silicides
Authors: Chen Guoliang , Peng Jihua , Wang Xitao
Published: April 2011

This paper reviewed the recent progress in the environmental embrittlement of suicide. On the surface of suicides, the Si in the suicides such as Fe3(Si,Al) alloy reacts with both oxygen and water vapor more easy than with iron. A molecular hydrogen machanism of surface reaction, i. e. Si + 2H2O = SiO2 + 2H2, can be derived. The moisture-induced embrittlement of suicides can be considered to be an embrittlement in a localized high pressure molecular hydrogen condition. It is a kinetic hydrogen gas embrittlement. Suicides may have more severely intrinsic brittleness than iron aluminides due to their special electronic structure and bonding mechanism, leading to elucidate the role of environment on ductility with difficulty. The improvement of both the intrinsic brittleness and moisture-induced embrittlement are critical for the development of suicides.
Effects of Rhenium Alloying on the Microstructures and Mechanical Properties of Directionally Solidified NiAl-Mo Eutectic Alloy
Authors: Misra A. , Wu Z. L. , Gibala R.
Published: April 2011

Low ductility of the reinforcing bcc metal phase at room temperature and weak interfaces can limit the intrinsic toughness and ductility of NiAl-bcc metal eutectic composites. The potential of rhenium (Re) addition, which is known to solid solution soften and lower the ductile-to-brittle transition temperature of various bcc metals, to enhance the ductility and toughness of a directionally solidified NiAl-9 at.% Mo eutectic alloy was investigated. Re partitioned to the bcc metal phase and formed a substitutional solid solution. The interface morphology was changed from a faceted to a non-faceted one. Re alloying caused softening of the Mo fibers, and as a result NiAl-Mo(Re) alloys were softer in compression and flexure and had ∼20% higher fracture toughness values as compared to the transverse orientation toughness of NiAl-9Mo alloy. The toughness of the NiAl-Mo(Re) alloys was lower man the longitudinal orientation toughness of the NiAl-9Mo alloy due to the poor alignment of the Mo(Re) phase with the growth direction. The toughening mechanisms have been evaluated and schemes for processing NiAl-Mo(Re) alloys for higher toughness in the longitudinal orientation are suggested. The role of the residual interstitial impurities and partitioning of Ni and Al to Mo fibers on the mechanical properties are highlighted.
Al2O3 Composites Containing Fe, Nb and Zr Aluminides
Authors: García D. E. , Schicker S. , Bruhn J. , Krupp A. , Janssen R. , Claussen N.
Published: April 2011

A reactive powder-processing technique involving controlled exothermic solid-state reactions between Al and oxides has been used to produce nearly fully dense composites with interpenetrating networks of aluminides and Al2O3. The process consists of the in situ formation of aluminides and Al2O3 from compacts of intensively milled oxide-Al powder mixtures followed by pressureless sintering. The reactions take place usually at temperatures below the melting point of Al. At temperatures >1000°C, the reaction products start to sinter yielding microstructures with very fine and uniform phase distribution. The present paper discuses processing parameters such as attrition milling, heating cycle and atmosphere controlling microstructural development and mechanical properties of Al2O3 composites containing Fe, Nb and Zr aluminides.
Strengthening Epoxy/High Impact Polystyrene Interfaces Using End Grafting Polymer Chains
Authors: Sha Y. , Hui C. Y. , Kramer E. J. , Hahn S. F. , Berglund C. A.
Published: April 2011

The fracture toughness Gc of epoxy/high impact polystyrene (HIPS) interfaces was measured as a function of grafting chain density Σ of dPS-COOH chains of various degrees of polymerization N. For short chains, no effective entanglements can be formed between the dPS chains and the PS matrix of the HIPS, thus no enhancement in Gc over that of a bare interface. For very long chains, even though each chain is well entangled with the HIPS, the maximum grafting density achievable is very low and such an interface fails by scission of the grafting chains so that the interface fracture toughness is also low. Large values of Gc are observed at intermediate chain lengths where both effective entanglements can be formed and a large Σ can be achieved. Under these conditions the interface fails initially due to the formation of crazes and the subsequent break down of one of these crazes at the interface. The transition areal chain density from chain scission to crazing, Σc,is independent of N.
Effect Of Drying on Permeability of Multilayer Polymeric Films
Authors: Nagarkar P. V. , Ko C. S.
Published: April 2011

Photographic applications rely greatly on the permeability and swelling behavior of multilayer thin films. This behavior is, at least, a function of (I) material properties such as particle size, percent solids and solubility, and (II) processing conditions that affect film formation, such as rate of drying, maximum web temperature and nature of underlying layers.

In order to test permeability of multilayer structures, an alkaline medium is allowed to permeate sample. In the structure under test, the bottom most layer is acidic in nature. This acid neutralizes the alkali as it permeates through the layers. Neutralization causes a change in ionic concentration in the sample and this is measured using a high frequency cavity sensor (commercially available as the conductivity Puntex technique) that changes its resonant frequency in response to change in conductivity of the sysytem. This frequency change can be monitored to to give a time transient for permeability. In the event that frequency changes even before neutralization has occured, it can be correlated to capacitance changes within the layers produced by swelling and water uptake.

For a porous layer within the sample, the permeation proceeds along two paths. One through the porosity and the other through the bulk. In this case the bulk signal is superimposed over the signal from porous component. For such a system, a transient of the time derivative of resonant frequency proved to be a useful tool to study interfacial interactions between the acid layer and the layer above it. Impact of drying was also inferred from similar measurements. Data indicate that the higher temperature of drying of constituent layers resulted in a microstructurally tighter film, that took longer time for the alkali to permeate.
Polymer Blends made from Ionomer and Ionomer Precursor Polymer
Authors: Bellinger M. A. , Ma X. , Tsou L. , Sauer J. A. , Hara M.
Published: April 2011

Rigid-rigid blends made of an ionomer and an ionomer precursor polymer, based on either polystyrene (PS) or poly(methyl methacrylate)(PMMA), were studied. A positive deviation from the rule of mixtures in both strength and toughness was observed over the entire composition range; and an especially significant enhancement was observed at low ionomer composition (e.g., 10 wt.%). This is attributed to a fine dispersion of the rigid ionomer phase in the matrix polymer together with good interfacial adhesion between the phases. The adhesion arises from entanglements due to athermal interactions between the same monomeric units of both the ionomer and the ionomer precursor. In addition, all the blend samples are found to be transparent due to similar refractive indices of the two components.
Laser Induced Decohesion Spectroscopy: A New Technique for Measuring Polymer Interfacial Adhesion
Authors: Meth J. S. , Sanderson D. , Mutchler C. , Bennison S. J.
Published: April 2011

We present a new technique, laser induced decohesion spectroscopy (LIDS), which is capable of measuring the practical work of adhesion G between a transparent polymer film and an opaque substrate. In LIDS, a laser pulse directed onto the sample creates a blister at the film/substrate interface. The blister's internal pressure depends on the laser pulse energy, and at a critical pressure the sample fractures. We have derived a theoretical analysis of this experiment based on elasticity theory and fracture mechanics, and present the results. By measuring physical variables such as the thickness of the transparent polymer, the blister radius, and the blister curvature, it is possible to deduce G between the two coatings. Here we report G for a matrix of automotive finish systems consisting of four opaque basecoats of various colors (black, white, red, green) coated with a clearcoat of various thicknesses. We expect G to be a system parameter for each basecoat independent of clearcoat thickness. The values of G for the different basecoats yield the relative adhesion of the various pigmented paint formulations.
Production of Crucible Steel by Co-Fusion: Archaeometallurgical Evidence from the Ninth-Early Tenth Century at the Site of Merv, Turkmenistan
Authors: Feuerbach Ann , Merkel John F. , Griffiths Dafydd R.
Published: April 2011

Various methods were used to produce steel in early Islamic times. According to early Islamic texts, three methods are described for indirect production of steel (fuladh). The methods are solid-state carburization of wrought iron, partial decarburization of cast iron or a high carbon steel, and co-fusion of cast iron with wrought iron. Evidence from a metallurgical workshop at Merv, dated to the ninth-early tenth century A.D., provides an illustration of the co-fusion method of steel production in crucibles. The primary investigations of the crucibles are presented. The crucible slag was found to contain droplets of cast iron and steel and the crucible fabric contains mullite.
European White Glass Trade Beads as Chronological and Trade Markers
Authors: Hancock R.G.V. , Aufreiter S. , Kenyon I.
Published: April 2011

European explorers and traders, on their arrival in North America, found the aboriginal peoples willing to exchange furs and other goods for European-made metal objects and glass beads, the remains of which may be found at archaeological sites. Specific trade goods, including multi-coloured or curiously shaped glass beads that are visually distinctive, are used as chronological markers by archaeologists. Most of the single coloured, mainly blue or opaque white beads are very common and cannot be visually, chronologically differentiated. Non-destructive analysis (INAA) of turquoise blue or white beads from known-age archaeological sites in Ontario has revealed chemical changes in glass manufacturing compositions over time. This allows these otherwise nondescript, single coloured beads to be used as chronological and trade markers. Although the turquoise beads were always coloured by Cu, the white beads employed different opacifiers over time. First came Sn-rich beads (early to late 17th century); then Sb-rich beads (late 17th century to mid-19th century); finally As-rich beads (very late 18th century to early 20th century) and even F-whitened beads (19th century to 20th century). Within each major group, it appears that changes in glass making recipes may be found using the Na, K, Ca, Al and Cl contents. Therefore, chemical analysis of white glass trade beads may be as profitable as chemical analysis of turquoise blue trade beads in establishing chemical chronologies.
An Investigation of the Sources of Bronze Age Pottery from Göltepe and Kestel, Turkey by Neutron Activation
Authors: De Sena E.C. , Friedman E.S.
Published: April 2011

As part of a broader research scheme intended to examine the relationship between the ceramic and metal industries of Bronze Age Anatolia, a program of compositional analysis by neutron activation was performed on ceramic material dated to the third millennium BC from Göltepe and Kestel, Turkey, the earliest known tin mining and processing sites in the Near East. Fifty-one archaeological samples representing five classes of pottery (crucibles, burnished ware, micaceous ware, fine-slipped ware, and metallic ware) and three local clay samples were analyzed in order to clarify problems related to the sources of the archaeological ceramics. Evidence provided by these experiments indicates that the four classes of domestic pottery and the crucibles derive from at least two distinct sources. One of these sources, the alluvial clay outcrops in the vicinity of Göltepe, was exploited for the manufacture of two types of domestic pottery (burnished ware and micaceous ware), as well as the “industrial” crucible refractories. Metallic ware appears to represent a distinct source group; however, the specific location of the source remains unclear. The geochemical relationship between fine-slipped ware and the other ceramics remains unclear.