bluuebunny/crossref_metadata_2025_split huggingface dataset:
Continuous High Temperature Lubrication of Ceramics by Carbon Generated Catalytically
Authors: Lauer James L. , Dwyer Scott R. 
Published: March 2011

AbstractA system for the continuous lubrication of ceramic surfaces at high temperatures by a carbon formed exclusively at the wear surfaces is described. Thelubricant is delivered as a simple gas, ethylene, which is catalytically transformed. No reaction products are left which contain bearing surface material and the only non-volatile product is lubricating carbon. One of the wearing surfaces must contain or have an overlay of nickel (about 1000 A thick in this work) and, preferably, a coating of nickel oxide on top to reducenickel wear during startup. Since the carbon is formed only on nickel and the oxide is worn only in the weartrack, only the wear track is lubricated. The laboratory system consisted of a sapphire pin on a nickel-coated rotating alumina disc. Ethylene was delivered only to the conjunction region, which was surrounded by air. Contact pressures were about 200 MPa, linear speeds between 3 and 9cm/sec. Friction coefficients dropped from 0.6 to 0.06 when ethylene was delivered to the contact at 500°C. Wear rateswere not measureable under operating conditions. Cases other than ethylene and catalysts other than nickel will be explored in further work.
The Binding of Lubricating Films to Ceramic and Refractory Materials
Authors: Bums R. P. , Pierce D. E. , Gabriel K. A. 
Published: March 2011

AbstractIn order to better understand the chemical bonding forces which control lubricating film stability and adhesion, the binding of lead and tin atoms on the ceramics alumina and silica was investigated by laser induced thermal evaporation combined with mass spectrometric detection of the evaporated species. The interaction between lead or tin and alumina and silica was studied as a function of coverage. The sticking probability for the interaction was measured and found to be temperature and coverage dependent. At low coverage the binding energy of lead to alumina and silica was determined as 237and 246 KJ mol1 respectively, while the binding energy of tin to alumina and silica is 313 and 331 kJ mol1, respectively. A binding energy model based on thermochemical and crystallographic data was used to predict corresponding values which agree with the experimental values.In addition, temperature programmed desorption and\or decomposition (TPD) was used to investigate the thermal and\or chemical stability of MoS2 films on molybdenum supports. The TPD spectra for S2 from MoS 2 were analyzed, and activation energies were found to be dependent on the film application technique. The binding energy model also provided a useful approximation to the experimental activation energies for the S2 production from MoS2 films. Water and carbon impurities were shown to contribute to the decomposition of MoS2 producing SO2 and CS2. The TPD spectra of S2, SO2, and CS2 provide a measure of the onset of lubricant decomposition.
Broad Bandwidth Study of the Topography of the Fracture Surface of Energetic Materials
Authors: Lanzerotti M. Yvonne D. , Pinto James J. , Wolfe Allan 
Published: March 2011

AbstractThe Z,X coordinates of the fracture surfaces of TNT have been measured witha stylus profilometer. The fracture surfaces of the material under study are obtained by accelerating prepared samples in anultracentrifuge. When the tensile or shear strength is exceeded a fracture surface is obtained. Usingdiamond and sapphire styli the topography of the fracture surface has been studied from a wavelength of 1.0 micron to nearly 1.0 centimeter. The powerspectra have been calculated from the data using a prolate spheroidal data window in the horizontal space domain prior to the employment of the fast Fourier transform algorithm. The power spectra are found to decrease with increasing spatial frequency. Peaks are observed in the low frequency region of the power spectra and indicate that much of the fracture is occurring atgrain boundaries.
Exploring Failure Mechanisms of Lubricated 52100 Steel Contacts in High Vacuum and Dry Air
Authors: Dugger Michael T. , Chung Yip-Wah 
Published: March 2011

AbstractA vacuum chamber was designed for studying tribological properties of materials under pressures of 5xlO8 Torr to one atmosphere. The chamber is equipped with a pin-on-disk tribometer, in-situ Auger\X-ray photoelectron spectroscopies, a sputter-ion gun and a windowless solid-state X-ray detector. In this paper, we present results of a study using 52100 steel balls sliding on flat disks of the same material in vacuum and in dry air as a function of normal load. The contacts were lubricated with a synthetic hydrocarbon oil (poly-a-olefin). Failure is defined as the point at which the coefficient of friction increases rapidly above the steady state value.As expected, failure occurs much sooner in vacuum than in dry air. Surface analysis (Auger and XPS) shows direct evidence of the occurrence of high temperature flashes on the surface, which allows the formation and maintenance of a thick oxide in the presence of an adequate supply of oxygen. In addition, a brown film is formed in the vicinity of the wear track for tests performed in dry air, while this film is absent in vacuum. The brown film appears to be a combination of iron oxide and oxidized hydrocarbon from XPS measurements. Results of these studies suggest that the maintenance of an oxide is associated with extended contact life in these studies.
Tribology in Slow Rolling Bearings
Authors: Kingsbury E. 
Published: March 2011

AbstractWear has been found in the Hertz tracks of fluid lubricated, high quality angular contact ball bearings which spin too slowly to generate an elastohydrodynamic lubricating film. Often a taper section or profile of the track shows a “W” or a “U” shaped groove. A mechanism is proposed to account for these shapes.This wear has been detected by destructive long term life tests in expensive bearings. A bench test is described which gives accelerated results on easily rejuvenated plates. Connections between the ball on plate tester and any angular contact bearing are outlined.Ball on plate tests using two perfluorinated and one synthetic hydrocarbon lubricant are interpreted in terms of a slow buildup of an electrically insulating, chemically derived film on the Hertz track. Details of the film buildup and its wear protection ability are specific to each lubricant.
Surface Modification for Tribology with Pvd Processes: Problems and Prospects
Authors: Ramalingam S. 
Published: March 2011

AbstractThe last two decades have seen substantial progress in the development of physical vapor deposition processes and in ion implantation technologies to modify the surface properties of engineering materials. Surface modification to engineer surfaces for tribological applications has become possible. Hard coatings are now in wide commercial use in tooling applications both to reduce wear and to extend the product life. However, the use of wear resistant coatings in engineered parts and components is yet to become significant. Some of the problems inhibiting wider use of surface modification in tribological applications are discussed in this paper. Recent developments in arc coating to overcome the discrete interface problem associated with low temperature PVD are described. It is shown that the creation of graded interfaces is now feasible. Results from a study involving the multi-layer deposition of titanium and nickel from a single, composite cathode are presented and discussed. It is shown that the prospects for increased use of surface modification to improve the characteristics of tribological components have been enhanced.
Energetics of Bcc-Fcc Lattice Deformation in Iron
Authors: Krasko Genrich L , Olson G. B. 
Published: March 2011

AbstractThe lattice deformation of the BCC-FCC martensitic transformation in iron can be described as a continuous change of the c/a parameter of the body-centered tetragonal (BCT) lattice from c/a=1 (BCC) to c/a=√2 (FCC). Along this deformation path, the total energy (as a function of volume), the enthalpy (as a function of pressure), the pressure-volume relations--both for nonmagnetic (NM) and ferromagnetic (FM) states--were calculated using the ab initio LMTO method. The ground-state magnetic properties: ferromagnetic contributions to the total energy and magnetic moments, were found by making use of the Stoner theory of itinerant ferromagnetism, rather than spin-polarized calculations. This circumvents the difficulties of using the traditional local spin-density approximation which failes to describe correctly the energetics of iron phases. The Stoner exchange parameter, I, was calculated from the linear response theory for each c/a as a function of volume. Then a constant enhancement factor, β, was introduced and the new Stoner parameter, βl, as used in all the calculations. The factor β was found by fitting the equilibrium atomic volume of the FM BCC phase to its experimental value. No other adjustments of any quantities were performed. The calculations revealed a somewhat unusual behavior of enthalpy along the deformation path. Instead of a double-well curve with a barrier maximum somewhere at 1 < c/a < √2, the enthalpy of the NM phase exhibits a monotonic decrease with c/a, the BCC modification being unstable with respect to the shear deformation. Moreover, up to a certain c/a (depending on pressure), the nonmagnetic BCT phase is also unstable with respect to spontaneous magnetization. Ferromagnetism stabilizes the BCT phases. However, the FM FCC phase is unstable with respect to shear deformation. The enthalpy curve along the deformation path then has a cusp corresponding to a first-order phase transition between ferromagnetic and nonmagnetic states accompanied by an appreciable volume discontinuity. The bulk modulus, the magnetic moments and the BCC-FCC enthalpy differences are in good agreement with the available experimental data.
Electron-Phonon Coupling Strength of Specific Phonons from First Principles Lapw Calculations
Authors: Krakauer H. , Cohen R. E. , Pickett W. E. 
Published: March 2011

AbstractElectron-phonon matrix elements, phonon linewidths and mode coupling strengths are being calculated for La2-xMxCuO4 (M-divalent cation, for paramagnetic x-0.0 and for x-0.15 in a rigid band picture) from first principles local density calculations. The change in potential due to a particular phonon mode is calculated from the difference of self-consistent one-electron potentials, and appropriate Fermi surface averages are carried out for selected modes, allowing us to obtain the phonon linewidth due to the electron-phonon interaction, and the corresponding coupling strength λQ. Here we establish the numerical accuracy within the dual representation of the potential used in the Linearized Augmented Plane Wave (LAPW) method. Evaluations of phonon linewidths and mode coupling strengths are presented for Al and Nb and compared with previous information on these modes. We present preliminary results for the full matrix elements and coupling of the La2CuO4 oxygen planar X-point breathing mode, and compare with a simpler approximation.
Theory and Calculation of the Thermal Conductivity of Amorphous Si
Authors: Feldman Joseph L. , Allen Philip B. 
Published: March 2011

AbstractVibrations of amorphous Si are represented by three available 216 atom models and the forces of Stillinger and Weber. It is shown how the Kubo formula for thermal conductivity can be evaluated “exactly” assuming harmonic vibrations, making only finite system-size errors. The results are rather insensitive to the particular model for the coordinates of the atoms and support a “shunt resistor model” for the thermal conductivity which fits data for glasses very well.
Enhanced and Retarded Diffusion of Shallow Impurities in Silicon
Authors: Nichols C.S. , Walle C. G. Van De , Pantelides S.T. 
Published: March 2011

AbstractWe have carried out systematic state-of-the-art calculations using density-functional theory, norm-conserving pseudopotentials, and large supercells in order to investigate the diffusion mechanisms of B, P, As, and Sb in Si under both equilibrium and non-equilibrium concentrations of intrinsic point defects. In addition, we have developed a theory for the non-equilibrium concentrations of the relevant diffusing species from which expressions for the activation energies may be derived. In equilibrium, we find that vacancies and self-interstitials mediate the diffusion of B, P, and As with comparable activation energies, but we show from our non-equilibrium diffusion calculations that these impurities have a dominant interstitial component. Sb diffusion, on the other hand, is mediated primarily by vacancies. We also find that the direct exchange mechanism plays only a minor role in all cases.
Growth Kinetics of Grain-Boundary Induced Melting: A Molecular-Dynamics Study
Authors: Phillpot S. R. , Lutsko J. F. , Wolf D. , Yip S. 
Published: March 2011

AbstractThe growth kinetics of melting nucleated at a high-angle twist boundary in silicon are investigated using molecular dynamics. Melting is found to be a two-stage process. In the first stage order is lost within a single plane at the interface and the density of the solid increases to that of the liquid. In the second stage the atomic coordination changes and an isotropic liquid is formed.
High-Temperature Behavior of Grain Boundaries from Embedded Atom Method Molecular Dynamics Simulation
Authors: Lutsko J. F. , Wolf D. , Phillpot S. R. 
Published: March 2011

AbstractThe behavior of a metallic grain boundary at high temperatures is studied using an embedded atom potential. A recently developed molecular dynamics code is used which allows the simulation of an isolated grain boundary at temperatures as high as the bulk melting point. The stability of the boundary below the melting point is studied and compared with earlier investigations which have suggested the existence of a “premelting“ transition. It is found that the boundary migrates at high temperature but remains well defined up to the bulk melting point. In contrast to simulations of ideal crystals, it was not possible to superheat the grain boundary due to the nucleation of bulk melting at the boundary.
Electrostatic Models of Relaxation at Metal Surfaces
Authors: Marcus P. M. , Jiang P. , Jona F. 
Published: March 2011

AbstractThe physical basis for electrostatic models of relaxation at metal surfaces, including the meaning of the two parameters of the modified point-ion or α model, is discussed. The empirical α parameter is shown to produce agreement with experiment and to arise from the non-uniformity of the fixed background of electronic charge around the ions. An explicit non-uniform model of the background charge is defined which is shown to be equivalent to the successful α model and provides an example of a pure electrostatic model without empirical parameters.
The Self Energy Approach for Calculation of Quasiparticle Energies in Materials Systems
Authors: Hybertsen Mark S. 
Published: March 2011

AbstractA self energy approach directly taking into account the many-body nature of the electron-electron interaction is described which gives an excellent account of the quasiparticle band energies in semiconductors and insulators. The self energy approach provides a crucial link between structural models and spectroscopic probes of materials systems. Applications to bulk semiconductors, semiconductor surfaces and short period superlattices are described. A model for the screened Coulomb interaction can reduce the amount of computation required. Applicability of bulk self energy results to more complex systems, e.g. surfaces, is discussed.
Applications of Positron Annihilation to the Monitoring of Fatigue Damage and Creep in Technological Components
Authors: Allen A J , Coleman C F , Conchie S J , Smith F A 
Published: March 2011

AbstractThis paper reviews the use of positron annihilation methods for technological applications, particularly the use of positron annihilation gamma ray lineshape analysis for the non-destructive assessment of static deformation, machining processes, high cycle fatigue and creep in metal and alloy componen:s. The paper includes description of a transportable lineshape analysis system recently developed for field applications.
NDE Observations of Hydrogen Effects in 4340 Steel
Authors: Shim In-Ok , Byrne J. G. 
Published: March 2011

AbstractCathodic charging of hydrogen into 4340 steel produces drastic deterioration of mechanical properties such as the notch tensile strength, depending on current density, charging time, and the poison used as an inhibitor of hydrogen recombination and bubble formation at the specimen surface. Fusion of charged samples permitted hydrogen content to be measured and revealed a linear increase in the latter with charging current density. The change in the Doppler spectrum sharpness parameter Δ(P/W) deviates negatively with cathodic charging time but inversely with the charging current density (fugacity). Thus a low-fugacity hydrogen charging appears merely to screen existing positron trap sites, whereas a high-fugacity charge also creates new defect traps. This would result in a lesser net screeninig effect which would be seen as a smaller negative deviation in Δ(P/W) as observed. For cumulative charging, however, one finds oscillatory behavior in (P/W) as in earlier cumulative charging experiments with Ni. This behavior indicates that hydrogen screening of positron traps was followed by new positron trap site creation and that this sequence of events occurred repeatedly and in that order.
Assessment of Creep Damage by NDT
Authors: Willems Herbert H. 
Published: March 2011

AbstractResidual lifetime analysis of power plant components requires information on the degree of degradation of the material. In case of hightemperature creep, material damage can be related to cavity formation or to the accumulated creep strain. At present, only metallographic replication technique is widely used for in-service inspection to detect creep cavitation. Other NDT-techniques like ultrasonic velocity and electrical resistivity, which have potential for detection of low pore concentrations, are being developed for practical application. The use of capacitive strain gages yields encouraging results for the long-time monitoring of creep deformation. Potential and limits of these NDT-techniques together with industrial needs for creep damage assessment are reviewed.
X-Ray Diffraction Determination of Metallurgical Damage in Turbo Blower Rotor Shafts
Authors: Porter John F. , Morehouse Dan O. , Brauss Mike , Hosbons Robert R. , Root John H. , Holden Thomas 
Published: March 2011

AbstractStudies have been ongoing at Defence Research Establishment Atlantic on the evaluation of non-destructive techniques for residual stress determination in structures. These techniques have included neutron diffraction, x-ray diffraction and blind-hole drilling. In conjunction with these studies, the applicability of these procedures to aid in metallurgical and failure analysis investigations has been explored. The x-ray diffraction technique was applied to investigate the failure mechanism in several bent turbo blower rotor shafts. All examinations had to be non-destructive in nature as the shafts were considered repairable. It was determined that residual stress profiles existed in the distorted shafts which strongly indicated the presence of martensitic microstuctures. These microstructures are considered unacceptable for these shafts due to the potential for cracking or in-service residual stress relaxation which could lead to future shaft distortion.
Quantitative NDE Applied to Composites and Metals
Authors: Heyman Joseph S. , Winfree William P. , Parker F. Raymond , Heath D. Michele , Welch Christopher S. 
Published: March 2011

AbstractThis paper reviews recent advances at LaRC in quantitative measurement science applied to characterizing materials in a nondestructive environment. Recent demands on NDE have resulted in new thrusts to achieve measurements that represent material properties rather than indications or anomalies in a background measurement. Good physical models must be developed of the geometry, material properties, and the interaction of the probing energy with the material to interpret the results quantitatively.In this paper are presented NDE models that were used to develop measurement technologies for characterizing the curing of a polymer system for composite materials. The procedure uses the changes in ultrasonic properties of the material to determine the glass transition temperature, the degree of cure, and the cure rate. A practical application of this technology is a closed feedback system for controlling autoclave processing of composite materials.An additional example is in the area of thermal NDE. Thermal diffusion models combined with controlled thermal input/measurement have been used to determine the thermal diffusivity of materials. These measurements are remote, require no contact with the material under test and thus have interesting promise for NDE applications.
Application of Ultrasonic Techniques to Study the Properties of Silicone Elastomers in High Pressure Gas Media
Authors: Briscoe Brian J. , Zakaria Salman 
Published: March 2011

AbstractPolymers absorb large quantities of gas under high pressure. This process is usually accompanied by a significant volumetric strain and also by changes in the mechanical properties of the sample. We will describe how these properties may be studied by using an ultrasonic technique. The sorption and volumetric changes are progressive in nature following the application of an incremental increase or decrease in ambient pneumatic stress. These techniques are also used to follow the time dependent changes in both the linear strain and the mechanical properties of the system. Data will be cited for a range of nitrogen gas pressures up to 27 MPa at 20°C for a virgin Poly-dimethylsiloxane (PDMS) elastomer and for its composite with glass filler to exemplify the experimental and analytical procedures. The final section of the paper shows how the same techniques may be used to monitor the inception and progressive development of internal cracks during certain ambient gas decompression profiles.The information obtained provides a basis for better material selection and for the specification of the service life of particular materials in hostile environments.
Microfocus Radiographic Characterization of Materials and Components for High Performance Applications
Authors: Cotter D J. , Koenigsberg W. D. , Dunn E. M. , Abdollahian M. 
Published: March 2011

AbstractResults are presented from several studies where microfocus radiography has been applied to provide feedback necessary to improve reliability and performance of materials and components. Improving the reliability of advanced silicon nitride ceramics through the use of NDE was studied by exploring the relationship between process-related defects, radiography results, and fracture of test samples. Research in the areas of structural and electronic ceramic joining has been aided by monitoring the effects of process modifications with real-time microfocus radiography and computer- based image processing.Microfocus projection radiography was used to nondestructively examine a large quantity of silicon nitride modulus of rupture test bars for internal defects. Failure stress prediction was attempted using a fracture mechanics model and quantitative NDE data, and compared to actual failure stress.In-process NDE of silicon nitride ceramic to Incoloy 909 metal brazed test samples was performed. Correlation between NDE results, optical microscopy, and destructive mechanical strength levels of samples is discussed.Microfocus x-ray imaging was used to monitor the process of bonding microwave power transistors to metallized BeO ceramic substrates. Nonuniform distribution of the eutectic bond was readily detectable, thereby providing feedback for process improvement. Comparison is made between x-ray, optical, and infrared images.