bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mass Spectrometric Studies of Ions Produced in Halofluorocarbon Plasma Etching of Silicon and Silicon Dioxide
Authors: Occhiello E. , Garbassi F. , Coburn J. W. 
Published: March 2011

AbstractThe distribution of ions present in halofluorocarbon (CF4, CF3Cl, CF3Br, CF2Cl2 ) plasmas has been studied by mass analysis of the ions extracted from the discharge. Silicon and silicon dioxide targets have been used to study the discharge chemistry in Reactive Ion Etching (RIE) conditions. In the case of silicon, both fluorine and chlorine participate in the etching; therefore, the discharge is enriched in halocarbon oligomers and etch products containing fluorine, chlorine and bromine. The higher reactivity of fluorine induces the formation of chlorine or bromine-enriched molecules and ions. Chlorine and bromine molecules are formed but their concentration in the discharge is not high due to consumption by etching. The situation is different with the silicon dioxide target. In this case, etching consumes both fluorine and fluorocarbon radicals, leading to the formation of silicon tetrafluoride and carbon oxides. The target, in this case, is “neutral”; the discharge is not enriched in oligomers as for silicon. The tendency to form chlorine and bromine-enriched species is still present and considerable amounts of molecular chlorine and bromine are present in the discharge because they do not participate efficiently in etching.
The Adhesion of Growing Oxides to Metallic Substrates
Authors: Stringer John , Wood Graham C. 
Published: March 2011

AbstractThere are several possible descriptions of the nature of the adhesion between an oxide and a metal substrate, some of which are formally equivalent. These include electrostatic interactions connected with the development of space charge regions, chemical bonding across the interface, van der Waals forces, and mechanical interactions associated with a nonplanar interface. However, the detailed mechanism must also be consistent with the growth process and the associated evolution of the interface for an oxide growing on a metal substrate. The problem is further complicated by the nature of the failure at or near the interface which leads to a phenomenological definition of adhesion which is not necessarily identical to the formal definition, and involves other parameters such as the growth stresses in the oxide, the plasticity of the oxide or the surface metal, and the effect of thermal cycling when the coefficients of thermal expansion of the two phases differ. In this paper, an attempt is made to describe these different aspects of the problem, and to refer to some of the more important ways of modifying the adhesion of an oxide, including the reactive element effect and the segregation of impurities to the interface and the modification of the morphology of the interface.
Plasma Treatment of Polymers for Improved Adhesion
Authors: Kelber Jeffry A. 
Published: March 2011

AbstractA variety of plasma treatments of polymer surfaces for improved adhesion are reviewed: noble and reactive gas treatment of fluoropolymers; noble and reactive treatment of polyolefins, and plasmainduced amination of polymer fibers. The plasma induced surface chemical and morphological changes are discussed, as are the mechanisms of adhesion to polymeric adhesives, particularly epoxy. Noble gas plasma etching of fluoropolymers produces a partially defluorinated, textured surface. The mechanical interlocking of this textured surface is the primary cause of improved adhesion to epoxy. Reactive gas plasmas also induce defluorination, but oxygen containing gases cause continual ablation of the fluoropolymer surface. Noble and reactive gas (except for hydrogen) etching of polyolefins results in surface oxidation and improved adhesion via hydrogen bonding of these oxygen containing groups across the interface. The introduction of amine groups to a polymer surface by ammonia or amine plasma treatment generally results in improved adhesion to epoxy. However, amine-epoxy ring interactions can be severely effected by steric factors due to chemical groups surrounding the amine.
Photolithography of Polytetrafluoroethylene for Tailored Adhesion
Authors: Rye R. R. , Martinez R. J. 
Published: March 2011

AbstractIrradiation of polytetrafluoroethylene (PTFE) with Mg(Ka) X-rays is shown to protect the surface against the chemical etching steps used to prepare PTFE for adhesion. Pre-irradiated etched samples of PTFE have adhesion strengths of less than 3% of that for non-irradiated etched samples. The major portion of this decrease in adhesion strength occurs for X-ray exposures of less than 10 min (∼4.8×103 mrads) and failure in every case occurs in PTFE and not in the bonded transition region. XPS measurements (20 Å sampling depth) show little difference in F content between irradiated and non-irradiated samples, but thermal desorption shows increasing fluorocarbon desorption with irradiation time. These results are consistent with the known radiation chemistry of PTFE. Irradiation produced free radicals lead to branching and/or cross-linking, and a surface rich in low molecular weight fluorocarbons. The more rigid cross-linked surface is resistant to deep (10,000 Å) chemical attack and the bond formed is with a surface rich in short chain fluorocarbons. Both a thin boundary region and bonding to short chain species is expected to lead to weak adhesive bonding. Electron irradiation is shown to lead to protection against chemical etching comparable to that obtained with X-rays. With electrons one has the capability of rastering the electron beam and drawing low adhesion strength patterns with resolution limited by the beam diameter.
Oxygen Reactive Ion Beam Etching on Polyimide to Enhance Copper Film Adhesion
Authors: Paik Kyung W. , Ruoff Arthur L. 
Published: March 2011

AbstractPolyimide(PI) films were modified by O2 reactive ion beam etching(RIBE) to make special surface features which enhance the adhesion of copper films. The top plane and the cross-sectional plane of PI films were changed to a grass-like structure and a plate-like structure, respectively. The reason for these surface morphological changes is presumably due to the structural inhomogeniety of PI. XPS studies show that the O2 RIBE oxygenates the PI, resulting in an increase in oxygen and a decrease in carbon and nitrogen. The adhesion of evaporated copper on the O2 RIBE modified PI was substantially increased. In this study, the maximum peel strength of modified PI, 70 grams/mm, is more than 25 times larger than that of the unmodified PI, 2.5 grams/mm. Two types of failure mechanisms were observed with various ion doses:adhesive failure at the Cu/PI interface and at very large doses cohesive failure at the roots of the thin and long grass blades of PI.
The Elastic Behavior of Partially-Sintered Materials
Authors: Green David. J. , Brezny Rasto , Nader Chris 
Published: March 2011

AbstractA simple model is presented for the elastic behavior of a powder compact that has undergone small amounts of sintering. The analysis shows that the elastic constants are sensitive to small changes in the interparticle contact areas. The elastic constants are also shown to be dependent on factors relating to the structure of the powder compact, such as the particle coordination number. It is concluded that such elastic constant measurements are a valuable tool in studying adhesion within compacts, the mechanisms involved in the initial stages of sintering and the characterization of powders.
Density Functional Theory for Thin Film Adhesion
Authors: Senbetu L. , Pronko J. G. , Bardin T. T. 
Published: March 2011

AbstractA theoretical formalism to describe interface adhesion phenomena between materials has been developed. In this model electron densities, potentials, and adhesion energies of thin metal films at metal–semiconductor and metal–insulator interfaces are derived through a partially self–consistent calculation. The theory is based on a density–functional formalism applied to a simple model of the system in which the metal is replaced by a uniform positive background and the semiconductor by a continuum with a static dielectric constant. Numerical results of the metal electron density distribution and effective potential of Au–vacuum and Au–GaAs system, and the adhesion energy at Au–GaAs interface are presented. The interface energies are then used to estimate the adhesion strength and compare with experiment.
Direct Observation of Friction at the Atomic Scale
Authors: McClelland Gary M. , Mate C. Mathew , Erlandsson Ragnar , Chiang Shirley 
Published: March 2011

AbstractAn atomic force microscope has been used to measure the frictional force on a tungsten tip sliding across the basal plane of graphite at low loads < 10-4 N. The frictional force displays the 2.5 Å periodicity of the graphite surface.
Liquid Mediated Adhesion of Ultra-Flat Solid Surfaces
Authors: Matthewson M. J. , Mamin H. J. 
Published: March 2011

AbstractThe presence of a liquid film between contacting ultra-flat surfaces can produce high levels of adhesion. The liquid film may be a pre-existing film of lubricant or may be a capillary condensate. This paper considers the meniscus and viscous components to the adhesion. Different regimes are identified which are distinguished by differing quantities of liquid in the gap between the surfaces. The role of surface roughness is also evaluated. The force required to separate the surfaces in the tangential direction is considered. The magnitude of this force is dependent not only on the adhesion but also on the separation rate and loading conditions.
Growth and Thermal Stability of γ/γ'-α Eutectic Composite
Authors: Nakagawa Y. G. , Nemoto M. 
Published: March 2011

ABSTRACTThe paper summarizes the results of a series of investigations carried out for a γ/γ'-α(Ni-Al-Mo) eutectic. The subjects include a thermal analysis of the composite growth in a high temperature gradient provided by a fluidized bed cooling, a study of defect formation such as the banding structure at unstable thermal conditions, Tem observation and phase identification for micro-phases existed in an as-growth state as well as phases produced after various quench and aging treatments, and an evaluation of the composite thermal stability in terms of the microstructures and the high temperature strength. The fluidized bed placed beneath a melting furnace was proved to establish a temperature gradient equivalent to the liquid metal cooling, and to promote a stable steady growth of the composites without bandings. Quenching the eutectic above a peritectoid temperature diminished the blocky γ'. The subsequent aging treatments induced small Mo platelets above 830°C and blow the temperature a metastable Ni2Mo particle precipitation in the γ phase causing appreciable composite hardening. The creep rupture strength, however, was reduced by the heat treatment due to δ-NiMo phases precipitated during the test in consumption of the Mo fibers.
Development of The γ-γ'-Cr3C2 In-Situ Composite
Authors: Mclean M. , Quested P.N. , Henderson P.J. , Menzies K. 
Published: March 2011

ABSTRACTThe effects of various alloy additions to the microstructures and properties of the γ-γ'-Cr3C2 in-situ composite have been investigated. Combinations of platinum and Yttrium prevent the formation of an additional phase that occurs when Yttrium alone is added; the phase morphology is unaffected by rhenium and ruthenium dopants.Combined quenching studies and differential thermal analysis show that phase alignment at high growth rates in this alloy is not due to plane front solidification but to highly branched carbide growth ahead of the melt/ matrix interface. This mechanism allows good phase alignment to be achieved over a wide composition range. Tests on six alloy casts to commercial specifications indicate retention of, and often improvement to, the microstructures and properties obtained with laboratory control.
In Situ Composites Prepared By Solidification And Mechanical Techniques
Authors: Verhoeven J. D. 
Published: March 2011

ABSTRACTAn alternate in situ technique is presented for preparation of aligned microstructures which has been successfully applied to the preparation of copper alloys. In this technique, a two phase alloy is first prepared by conventional casting techniques to produce a random array of dendrites of phase 1 in a matrix of phase 2. The casting is then reduced to wire size by mechanical reductions. It is demonstrated that the alignment of the dendritic phase produced by the mechanical reduction is surprisingly good, and that one can achieve a wide range of microstructural control over the filament size and morphology by utilization of controlled coarsening anneals followed by additional wire drawing. Examples are presented of Cu-Nb alloys which are converted to Nb3 Sn-Cu superconducting wires possessing excellent critical current values, and of Fe-Cu alloys which produce wires having quite high strength to resistivity ratios.
The High Temperature Degradation of Cd-Zn and Pb-Cd Eutectic Alloys
Authors: van de Merwe R. H. , Smith R. W. 
Published: March 2011

ABSTRACTVarious thermal treatments have been applied to Cd-Zn and Pb-Cd eutectic alloys in an attempt to better understand the thermal stability of eutectics close to their melting temperatures. Specimens of each system were grown at 40, 400 and 4000 mm/hr to obtain microstructures which were either lamellar, lamellar/cellular, or cellular. These specimens were thermally treated by either: (1) isothermal annealing at 0.95 Tm (up to 192 hrs), (2) thermal cycling between room temperature and 0.95 Tm (up to 64 cycles), (3) exposing to thermal gradients parallel to the growth direction and maintaining one end of the specimen at 0.95 Tm and the opposite end at room temperature (up to 48 hrs). It was found in all cases that some microstructural changes occurred but that the two alloy systems displayed marked differences in degradation sequence. An explanation and interpretation of these decay sequences is attempted. The mechanical properties of the variouslytreated alloy specimens were determined and are correlated with the observed microstructural features. The Cd-Zn specimens coarsened more rapidly than equivalent Pb-Cd specimens, as might be expected since the interphase boundary energies have been reported as 86 and 67 erg/cm2respectively.
The Response of Mnsb-Sb Composites to Isothermal Aging
Authors: Marinis T. F. , Sekerka R. F. 
Published: March 2011

ABSTRACTAn eutectic alloy of antimony and manganese was directionally solidified to produce a composite of cylindrical fibers of MnSb aligned in a Sb matrix. The fibers were about 3 microns in diameter by 1 millimeter long and occupied 30% of the composite volume. Isothermal aging caused the fibers to develop undulations that had an average wavelength of 1.74 + 0.45 times the fiber circumference. The Nichols' and Mullins' model of fiber spheroidization predicts an undulation wavelength of √2 times the fiber circumference, for interface diffusion control. The Coine model, for volume diffusion control, predicts a wavelength that approaches infinity for this fiber volume fraction. Our modeling efforts have shown that the predicted wavelength is quite sensitive to the assumed spatial correlation between nodes on adjacent fibers. We also found that the undulation growth rate achieves a broad maximum as a function of wavelength, which may account for the large standard deviation associated with our measurements.
The Elevated Temperature Response of Silicon Carbide and Boron Reinforced Aluminum and Titanium Metal Matrix Composites
Authors: Madhukar M. S. , Fareed A. , Awerbuch J. , Koczak M. J. 
Published: March 2011

AbstractThe elevated temperature modulus and strength of aluminum, titanium, and hybrid aluminum/titanium metal matrix composites were investigated. Aluminum (6061-F) and titanium (Ti-6AI-4V) metal matrix composites reinforced with AVCO silicon carbide or boron fibers were vacuum hot pressed and their tensile properties evaluated to temperatures in excess of 300°C. Microstructure, fracture modes and mechanical properties were characterized to assess the effect of fibers and matrix on composite strength and modulus as a function of temperature. Finally, a comparison of specific strength and modulus is provided as a function of temperature. In general, the metal matrix composites exhibited low density (<2.8 g/cm3), high modulus (200 GPa), and strengths equivalent to 1250 MPa at 250–300°C. The effect of fiber orientation on axial stiffness was investigated using boron fiber reinforced aluminum (6061-F).
Enhanced Plasticity of Mechanically Alloyed Aluminum IN90211
Authors: Bieler T. R. , Nieh T. G. , Wadsworth J. , Mukherjee A. K. 
Published: March 2011

AbstractThe tensile behavior of IN90211 was characterized at strain rates between 0.0001/sec and 340/sec at temperatures between 425 and 475 °C. At strain rates below 0.1/sec, the strain rate sensitivity m is about 0.027, with corresponding low elongation (<100%). At strain rates above 0.1/sec, the strain rate sensitivity increases to 0.26. A maximum elongation of 500% was obtained at 475 °C at a strain rate of 2.5/sec. Grain boundary sliding and rotation was observed on the highly elongated specimens and fracture surfaces exhibited intergranular fracture. Experimental data in the high strain rate regime (superplastic) revealed the existence of a temperature dependent threshold stress that seemed unrelated to the low stress deformation regime. This result is consistent with stress relaxation experiments. These threshold stresses are generally lower than those typically observed in other oxide dispersion strengthened (ODS) alloys. This observation is not expected from conventional superplastic creep theory.
Microstructural characterization of a SiC Whisker-Reinforced HIPped Reaction-Bonded Si3N4
Authors: Farmer S. C. , Pirouz P. , Heuer A. H. 
Published: March 2011

AbstractA SiC whisker reinforced HIPped RBSN material fabricated with a Y2O3 sintering aid was characterized using TEM. The matrix is > 90% β-Si3 N4 with a Y-Si-O-N glassy phase at the Si3 N4 grain boundaries and about the SiC whiskers. The SiC whisiers are heavily faulted and have a well defined core. Si3 N4 precipitates are observed in the core region after composite fabrication. A preliminary mechanism for the growth of the SiC whisker, based on the VLS mechanism is proposed.
The Frictional Resistance to Sliding of a SiC Fiber in a Brittle Matix
Authors: Weihs T. P. , Dick C. M. , Nix W. D. 
Published: March 2011

AbstractThe frictional resistance to sliding of a SiC fiber in a brittle, ceramic matrix has been measured with two different experimental techniques. Both techniques utilize a load-controlled indentation instrument. In the first technique, the ends of individual fibers are displaced down into the matrix. The frictional resistance to sliding, τ, was calculated using the elastic model of Marshall and Oliver and the load-displacement data. Alternatively, fibers have been displaced along their complete lengths through thin sections of the matrix. The critical force for complete slip and the sample geometry determined τ for a given fiber. For this technique slip over the complete length of a fiber was verified by the protrusion of that fiber from the bottom of the sample. By inverting the sample and loading the protruding fiber, the frictional resistance to reverse sliding was also measured. The results obtained from the two complementary techniques are in general agreement.
Creep Behavior of an Al2O3-Sic Composite
Authors: Lipetzky P. , Nutt S. R. , Becher P. F. 
Published: March 2011

AbstractThe addition of SiC whiskers to Al2O3 causes significant improvement in mechanical properties, including fracture toughness, thermal shock resistance, and creep resistance. The creep response of a whisker-reinforced alumina composite has been measured using four-point flexural loading at temperatures of 1200 and 1300C. Composites were fabricated by hot-pressing a blend of alumina powder with 33 volume percent SiC whiskers. The creep data showed a stress-dependent stress exponent equal to 1 at low stress levels and ranging from 4–6 at higher stresses. The applied stress at which the transition occurred was temperature dependent and ranged from 50–125 MPa. Mechanisms of creep deformation were determined from TEM observations of specimens prepared from interrupted creep tests. Voids were observed at grain boundary-interface junctions in tensile regions and whiskers within the composite were sometimes oxidized where voids had formed. TEM observations from specific stages of steady state creep reached under different applied loads are presented, and the relative contributions of different deformation mechanisms are discussed.
Interfacial Chemistry-Structure and Fracture of Ceramic Composites
Authors: Schoenlein L. H. , Jones R. H. , Henager C. H. , Schilling C. H. , Gac F. 
Published: March 2011

AbstractThe interfacial chemistry and phases of SiC-reinforced Si3N4 composites have been evaluated by transmission electron microscopy (TEM) with associated x-ray energy dispersive spectroscopy (EDS) microanalysis, and Auger electron spectroscopy (AES). Hot-pressed Si3N4 (HPSN) composites reinforced with Nicalon™ SiC fibers or Tateho SiC wiskers and reaction-bonded Si3N4 (RBSN) composites reinforced with uncoated or coated VLS SiC whiskers have been evaluated. In the Nicalon™ fiber-reinforced HPSN, an interfacial phase composed of a layer of amorphous carbon and an adjacent layer of graphitic carbon was observed and is believed to assist fiber pullout during fracture of the composite. However, the fracture strength and toughness of these composites were considerably less than those of unreinforced HPSN. HPSN composites reinforced with Tateho SiC whiskers contained an interfacial phase believed to be similar to the intergranular phase found in the HPSN matrix. In RBSN composites fabricated with an Fe2O3 sintering aid, the VLS SiC whiskers were severely faceted by a reactive iron silicide phase despite C, BN, or SiO2 coatings on the whiskers. When no sintering aid was used, the uncoated whiskers were not degraded and appeared to be strongly bonded to the RBSN matrix. The composites reinforced with SiO2-coated whiskers possessed the highest fracture strength and toughness, and the composites reinforced with the BN-coated whiskers possessed the lowest fracture strength and toughness.
Thermal Oxidation of Al2O3-SiC Whisker Composites: Mechanisms and Kinetics
Authors: Lin F. , Marieb T. , Morrone A. , Nutt S. 
Published: March 2011

AbstractIt has been shown that SiC whisker-reinforced Al2O3 is susceptible to thermal oxidation because of a series of reactions in which SiC is oxidized and then reacts with Al2O3 to form a whisker-free layer of mullite and silica glass. In this paper, the kinetics of the reaction are analyzed as a function of the composition and whisker content of the composite. The mechanism of the reaction is described in terms of the evolution of phases within the reaction layer on the basis of transmission electron microscope observations and concentration profiles determined by electron microprobe analyses. The reaction is initiated by oxidation of SiC, forming silica glass and graphitic carbon. The silica glass penetrates the Al2O3 matrix along grain boundaries, and reacts to form mullite. As the reaction proceeds, Al2O3 is consumed, leaving residual intragranular Al2O3 islands, and a population of transgranular microcracks in the mullite. It has also been shown that Al2O3-SiC composites are susceptible to crack nucleation and growth under cyclic compressive loads. The presence of the mullite reaction layer on the surface of the composite reduces its resistance to crack initiation under these conditions. The threshold for crack initiation in cyclic compression is measured as a function of reaction layer thickness.