bluuebunny/crossref_metadata_2025_split huggingface dataset:
Future Application Trends - a Case for Mechanistic Approaches
Authors: Fehrenbacher Larry L. 
Published: March 2011

AbstractThis paper reviews moving mechanical assembly (MMA) and component technology shortfalls imposed by demanding ground, naval and aerospace system requirements of the future. The tribology development needs for specific harsh environment applications such as high temperature engines, chemical reactant turbopumps, precision acquisition, tracking and pointing MMAs surveillance systems and laser communications components are identified. Development goals for lightweight bearing and gear alloys and ceramics, ultra low friction and wide temperature range solid lubricants, self lubricating composites and real time health monitoring devices are translated into a rationale for mechanistic, more fundamental research approaches.
A Study of Subsurface Damage Generation by Single Scratches of Silicon
Authors: Ahn J.H. , Danyluk S. 
Published: March 2011

AbstractThis paper describes the use of electrical resistivity to quantify the damage produced asa result of the scratching of single crystal silicon.The change in resistivity was measured as a function of time as a scratching diamond passed between four electrical contacts of a specially designed printed circuit and while thesilicon was heated to temperatures up to 300ºC. The data shows that the resistivity increases during scratching and reaches a steady state value if the silicon temperatureis below 200ºC. The conductivity recovers when the silicon temperature is 200ºC.
Stick-Slip\Smooth Slip as a Function of Ambient Gases and Pressures Disproving Previous Models of Adhesive Wear
Authors: Gao Chao , Kuhlmann-Wilsdorf Doris , Makel David D. 
Published: March 2011

AbstractFive different slip modes have been identified for bundles of copper fiberssliding on a smooth copper substrate in atmospheric air, argon and nitrogenat pressures from atmospheric to 0.01 Torr. These are stick-slip, variable sliding, intermittent stick sliding and two kinds of smooth sliding, one apparently a basic property of clean surfaces and the other due to contaminants. These forms of sliding are rather persistent once established, and they follow some trends. Specifically, low-pressure smooth sliding is coordinated with a value of the coefficient of friction (μ) near 0.15 and is seen when the surface film is exceptionally thin, while intermittent stick sliding appears to be due to “pads” on the substrate surface,and variable sliding to small particles caught in between the fibers and the copper substrate. However, the five slip modes are erratic in that under the same conditions one or another or yet a third may be observed, even though the electrical contact resistance (R) depends rather reproducibly on time, load, velocity, ambient atmosphere and pressure. That dependence indicates an equilibrium between film destruction through sliding and film formation, overwhelmingly through the presence of oxygen. In the stick-slip mode the difference between pst tic and ųK itic appears to be roughly proportional to ų 0.15, i.e. tfiee xcess of e average value of the friction coefficient above 0.15, being about 20% for ų 0.3 andvanishing near ų =0.15. During slip episodes, R spikes roughly in proportion to their magnitude. Some tentative interpretations are offered, based on the concept that ų consists of three additive components, namely due to the bulk (ųBulk), due to debris (ųDebris), and dueto scoring of surface films (ųFilm).At any rate, the conclusion that the results contradict all previous models of “adhesive” wearis inescapable.
Selection of Scuffing-Resistant Materials Under Lubricated, High-Speed Sliding
Authors: Au J. J. , Corcoran M. W. , Yung J.-Y. 
Published: March 2011

AbstractThe scuffing resistance of materials under lubricated high-speed sliding was analyzed based on the thermalelastic instability (TEl) model. The model was used to select and rank scuffing-resistant materials.The scuffing resistance was also determined experimentally by the Falex 6 thrust washer wear tests. There was good agreement between the experimental results and the analytical predictions.
Gas Plasma Treatment of Sputtered Carbon Thin Film and Enhancement of its Properties
Authors: Sharma J.P. , Narayan P.B. , Brar A.S. 
Published: March 2011

AbstractIn magnetic recording, the metallic magnetic media are protected from corrosion and wear by a thin sputtered carbon layer. The latter also acts as a self-lubricating film during the interaction of the media with the ceramic read \write head pad material. Since the surface energy of carbon is high, it tends to absorb and chemisorb environmental constituents such as oxygen, nitrogen, water vapor and hydrocarbons. These could then react with the head\media interface and form heterogeneous layers of “frictional polymers”. These changes in carbon lead to frictional instability and friction build-up. Low temperature gas plasma treatment of sputtered carbon layer was found to improve the surface properties and the frictional instability problems. Use of a mixture of argon and carbon tetrafluoride gases led to the formation of a very thin self-lubricating layer, probably a fluorocarbon. The surface also becomes smooth. This is because of thecombined reaction of chemical reaction, ion-diffusion, ion-penetration and plasma etching. This reaction product was found to be prominently present at the grain boundaries and other morphological inhomogeneities, thereby strengthening the weak areas and improving the tribo-performance of the media.
Effects of Grain Boundary Characteristics of Steel on Magnetoacoustic Emission Spectra
Authors: Namkung M. , Yost W. T. , Utrata D. , Grainger J. L. , Kushnick P. W. 
Published: March 2011

AbstractThe pulse height distribution of a magnetoacoustic emission (MAE) spectrum is expected to be generally Gaussian due to its random nature. The functional form of distribution depends on the microstructure of a ferromagnet since the domain wall-lattice defect interaction produces MAE. The present study investigated the effects of grain boundary characteristics on the properties of MAE spectra obtained by external AC magnetic field-driven domain wall motions. The results show the enhancement of domain wall-defect interaction as more grain boundary disorder is introduced to HY80 steel samples. This was confirmed by the growth of a non-Gaussian-like distribution in the tail section of histograms with increased population of impurities trapped at the grain boundaries causing embrittlement. It is found that the enhancement of domain wall-defect interaction, which is responsible for generation of high amplitude MAE pulses, also tends to reduce the rate of such MAE events by limiting domain wall motions. Application of a stronger AC magnetic field should increase the count rate of high amplitude MAE signals in more embrittled samples.
In-Situ NMR Study of Dislocation Jump Distance During Creep of Pure and Doped NACL Single Crystals
Authors: Murty K. Linga , Kanert O. 
Published: March 2011

AbstractNuclear magnetic resonance pulse techniques are used in-situ during creep of single crystals of NaCl to evaluate the contribution of mobile dislocations to spin relaxation. 23Na spin-lattice relaxation rates were measured in the rotating frame (T1ρ) during compression creep of single crystals of NaCl along [110] direction at 473K at an applied stress of 20 MPa. The relaxation rates are evaluated from the spin-echo height following π/2, locking and 67° pulse sequence. The height of the free induction decay decreased as soon as the load is applied followed by a gradual increase until the steady-state is reached, at which point a saturation value is observed corresponding to the constant steady-state creep-rate. The mean jump distance of the mobile dislocations, evaluated from the ratio of the signal heights without deformation and during creep, decreased with time/strain reaching a constant value during steady-state creep regime. The results are compared with the dislocation-dislocation spacing, subgrain size as well as the jump distance predicted from creep models. The effects of dilvalent Ca and solid solution with LiCl are examined.
The Use of Time-Temperature Superposition Techniques to Forecast Creep Behavior in Engineering Plastics
Authors: Overton B. J. , Taylor C. R. , Shea J. W. 
Published: March 2011

AbstractA complete understanding of the time-temperature dependent, viscoelastic mechanical properties of polymeric materials is essential for their successful application to engineering designs. We describe a computer-based system for acquiring, reducing and storing the mechanical properties of polymers, from which the useful forms of the mechanical characteristics may easily be reproduced and compared. We provide several examples illustrating the variety of ways in which these properties are utilized to forecast the performance of polymeric components of engineering designs under extreme field conditions.
Study of Spherulites in a Semi-Crystalline Polymer Using Acoustic Microscopy
Authors: Duquesne J. Y. , Yamanaka K. , Neron C. , Jen C. K. , Piche L. , Lessard G. 
Published: March 2011

AbstractsThe local elastic properties of a semi-crystalline polymer (isotactic polypropylene) have been investigated with the use of scanning acoustic microscopy (SAM) techniques. The operating frequency was 775 MHz and the temperatures ranged between 25 and 60°C. A new and effective signal processing method was developed to process the material signature V(z) curve. This method avoids complicated calibration procedures involved with operating the SAM lens at different temperatures. Longitudinal velocities VL(α) and VL(β) in individual α and β-type spherulites of isothermally crystalized samples have been measured. Acoustic velocity of a quenched sample was also obtained. It was found that vL(α) and VL(β) were nearly equal but the acoustic impedances of α and β-spherulites were unexpectedly very different.
Elastic Properties of Porous Ceramics
Authors: Ledbetter H. M. , Lei M. , Datta S. K. 
Published: March 2011

AbstractUsing theoretical models, we consider the sound velocities and elastic constants of ceramics containing pores. As an example, we consider alumina. However, the approach applies to all ceramics. As a point of departure, we consider spherical pores. For all the usual elastic constants–Young modulus, shear modulus, bulk modulus, Poisson ratio–we give relationships for both the forward and inverse cases: predicting the porous ceramic properties and estimating the pore-free ceramic properties. Following a suggestion by Hasselman and Fulrath that sintering or hot pressing can produce cylindrical pores, we derive a relationship for the elastic constants of a distribution of randomly oriented long cylinders (c/a + ∞, the prolate-spheroid limit). This model predicts elastic constants lower than for spherical pores, but well above measurement. We obtain agreement with observation by assuming the pores are oblate spheroids. For alumina, the necessary aspect ratio equals oneninth. Besides pore aspect ratio, the model requires only the pore-free alumina elastic constants. It contains no adjustable parameters.
Thermal Properties of Non-Metallic Films by Means of Thermal Wave Techniques
Authors: Frederikse H. P. R. , Ying X. T. , Feldman A. 
Published: March 2011

AbstractThe propagation of a thermal wave into a thin film or coating depends on the thermal properties of the material. Consequently, thermal wave generation and detection can be used to obtain the heat conductivity of the material. The method is also useful because thermal wave propagation is sensitive to inhomogeneity, porosity, inclusions, voids, and delaminations. The results of two specific applications of the thermal wave technique are presented, the heat resistance of oxide coatings and of diamond films.
Detecting Areas of High Chloride Concentration in Bridge Decks
Authors: Lim K. , Gress D. L. , Maser K. 
Published: March 2011

AbstractThe presence of chloride ions in New England bridge decks has caused severe damage and has contributed greatly in reducing service life. The source of the chloride ions is mainly from deicing salts applied for snow and ice removal to enable safer driving during the winter. The chloride ion acts as an accelerator in the corrosion of reinforcing bars causing expansion and therefore deterioration of the bridge deck concrete.At present the method of determining the percentage of chloride present in bridge decks is a very time consuming, expensive and destructive process. The need for a fast nondestructive procedure to determine the amount of chloride in a concrete bridge deck is apparent. This paper introduces a means of utilizing ground penetrating radar as a viable nondestructive means of detecting areas of high chloride concentration in concrete bridge decks. The technique is based on the attenuation of a radar signal emitted from a radar unit in the presence of chloride.
Correlating Microstructure with Backscattered Ultrasonic Energy
Authors: Mittleman John , Mohr David W. 
Published: March 2011

AbstractHigh frequency ultrasonic energy interacts with metallurgical microstructure to produce scattered energy fields that are useful in characterizing the material. By using a focused transducer whose focal spot size and ultrasonic wavelength are both comparable to the scale of grain structure in high purity copper specimens, the authors have shown a strong correlation between microstructure and the pattern of backscattered ultrasonic signals. A systematic series of experiments logged the ultrasonic returns from cold-rolled copper with the direction of the ultrasonic beam both parallel to and transverse to the rolling direction. Fourteen samples were annealed to various degrees, capturing several stages of recovery and recrystallization. Use of backscattered ultrasonic energy rather than specularly reflected energy allows isolation of grain boundary scattering in an otherwise quiet acoustic environment. Clear differences between returns of backscattered shear waves from parallel and transverse beam orientations relative to the rolling direction gradually disappear as the annealing process re-establishes a field of equiaxial crystals. Backscattered surface waves also show variations that appear to correspond with the relaxation of residual stresses before the onset of recrystallization, and preferred orientation after recrystallization.
Ultrasonic Characterization of Texture
Authors: Li Y. , Thompson R. B. 
Published: March 2011

AbstractThis paper will propose a new technique to characterize texture of rolled plates of cubic crystallites. This technique uses information from ultrasonic velocities of high order plate mode to improve the estimation of orientation distribution coefficients (ODC's), especially W400. Also discussed will be the generalization of this technique to the case of hexagonal crystallites.
Interaction of Thin Ga Overlayer with InP(110): a Photoemission Study
Authors: Cao R. , Miyano K. , Kendelewicz T. , Lindau I. , Spicer W. E. 
Published: March 2011

AbstractPhotoemission study of the Ga/InP(110) interface, in particular at the In 4d cooper minimum (CM) reveals that the growth of the deposited Ga on InP(110) at room temperature (RT) has two modes: chemisorption at low coverage and metallic island formation at high coverage, whereas the Ga overlayer is much more uniform at 80K low temperature (LT). A replacement reaction between Ga and InP is found to take place only underneath the Ga islands. Metal screening from the Ga islands is suggested to weaken the substrate bonds and enhance the replacement reaction. Distinct behavior of Fermi level pinning has been observed at different temperatures. This is correlated with the temperature dependence of the overlayer morphology as well as the interfacial reaction.
Exafs Studies of Multilayer Interfaces
Authors: Heald S. M. , Lamble G. M. 
Published: March 2011

AbstractImportant for the understanding of multilayer materials is a determination of their interface structure. The extended x-ray absorption fine structure (EXAFS) technique can be useful, particularly for interfaces with a high degree of structural disorder. This paper reviews the application of EXAFS to multilayers, and describes the standing wave enhancement of the EXAFS from multilayer interfaces. Examples are given for W-C and Ni- Ti multilayers.
Fluorescence Yield Near Edge Spectroscopy (Fynes) for Ultra Low Z Materials: an In-Situ Probe of Reaction Rates and Local Structure
Authors: Fischer D. A. , Gland J. L. , Meitzner G. 
Published: March 2011

AbstractFluorescence Yield Near Edge Spectroscopy (FYNES) of ultra low Z materials represents a synchrotron radiation milestone for in-situ determination of local structure for a range of materials problems from monolayers to bulk samples even in the presence of a reactive atmosphere. Two examples will be presented highlighting the broad range of materials problems addressed by the FYNES technique. First a study of the kinetics of CO displacement on Ni(100) by hydrogen at pressures up to.1 torr. These kinetic results highlight the unique capabilities of FYNES to directly characterize surface reaction rates in the presence of reactive gases. Second, a pioneering fluorescence EXAFS study characterizing low concentration fluorine materials will be discussed. Finally new opportunities in FYNES presented by increased photon flux from insertion-device- based sources will be explored.
Exafs Studies of Cobalt Silicide Formation Produced by High Dose Ion Implantation
Authors: Tan Z. , Budnick J. I. , Sanchez F. , Tourillon G. , Namavar F. , Hayden H. , Fasihuddin A. F. 
Published: March 2011

AbstractThe early stages of cobalt silicide formation in high dose (1.0 to 8.0× 1017Co/cm2) cobalt implanted Si(100) are studied by extended X-ray absorption fine structure (EXAFS), X-ray diffraction (XRD) and Rutherford backscattering spectroscopy (RBS). Locally ordered silicide that is not detectable in XRD has been observed with EXAFS in the as-implanted samples. Long-range ordered phases are observed in the 3 × 1017Co/cm2 samples. After thermal annealing at 700–750°C, single phase CoSi2 with (400) orientation is formed in all implants.
Structural Changes in Ag,Fe,Mn, and Ge Microclusters
Authors: Zhao J. , Ramanathanl M. , Montano P. A. , Shenoy G. K. , Schulze W. 
Published: March 2011

AbstractThe structures of Ag,Fe,Mn, and Ge microclusters were determined using EXAFS. The measurements were performed over a wide range of clusters sizes.The clusters were prepared using the gas aggregation technique and isolated in solid argon at 4.2 K. A strong contraction of the interatomic distances was observed for Ag dimers and multimers. Silver clusters larger than 17 A mean diameter show a small contraction of the nn distance and a structure consistent with an fcc lattice. By contrast smaller clusters show the presence of a small expansion and a strong reduction or absence of nnn in the EXAFS signal. This points towards a different crystallographic structure for Ag microclusters. In iron clusters we observed a gradual reduction of the nn distance as the cluster size decreases. The interatomic distance for iron dimers was determined to be 1.94 A, in good agreement with earlier measurements. The iron microclusters show a bcc structure down to a mean diameter of 9 A. Iron clusters with 9 A mean diameter show a structure consistent with an fcc or hcp lattice.Mn microclusters show a simpler crystallographic structure than α-Mn. The measurements on Ge clusters show the presence of only nearest neighbors. There was clear evidence of temporal annealing as determined by variations in the near edge structure of the K-absorption edge. Absorption edge measurements were also performed on free Ge clusters traveling perpendicular to the direction of the synchrotron radiation beam.
Application of Multilayer Structures to the Determination of Optical Constants in the X-Ray, Soft X-Ray and Extreme Ultra Violet Spectral Ranges
Authors: Barbee Troy W. 
Published: March 2011

AbstractThe dispersion of x-rays (XR), soft x-rays (SXR) and extreme ultraviolet (EUV) light by multilayer structures is dependent on the scattering and absorption cross-sections of the elements used to synthesize the multilayer. In this paper it will be shown that this dependence provides a means for the accurate experimental determination of the optical constants of the multilayer constituents. Two specific approaches will be presented and discussed. First, it will be shown that detailed analysis of the energy dependence of the reflectivity of a simple depth periodic multilayer allows the unfolding of the optical constants. Secondly a new optic structure, the multilayer diffraction grating, will be described and it will be demonstrated that such combined microstructure optics allow the scattering cross-sections of the multilayer constituents to be accurately determined over broad spectral ranges.
Automatic Orientation Mapping with Synchrotron Radiation
Authors: Gottstein G. 
Published: March 2011

AbstractSynchrotron radiation can be utilized to obtain Laue back reflection patterns of microscopic areas with very short exposure time. A method is presented to fully automatically evaluate Laue patterns. The experimental setup and procedure are outlined to determine the orientations of a large number of contiguous grains, and consequently to enable orientation mapping. Preliminary experimental results are presented.
Surface Lattice Strain and the Electronic Structure of Thin Mercury Overlayers
Authors: Varma Shikha , Kime Y. J. , Dowben P. A. , Onelliont M. 
Published: March 2011

AbstractThe stress in the surface of a thin (0–10 monolayer) film of mercury can be relieved by either changing the substrate and consequently changing adlayer lattice constants or by growing thicker films. An empirical relationship between strain and the valence electronic structure of mercury overlayers can be demonstrated, though we present evidence that this relationship can be altered and destroyed by crystallography changes.
Growth of CdTe Thin Films on Polar and Nonpolar Semiconductor Substrates by Metalorganic Chemical Vapor Deposition.
Authors: Grodzinski P. , Mazur J.H. , Nouhi A. , Stirn R.J. , Sudharsananu R. 
Published: March 2011

ABSTRACTElectron diffraction and high resolution electron microscopy (HREM) have been used to investigate the origin of multiple orientation-relationships and defect structure of CdTe thin films grown on (100) GaAs and Si substrates by metal- organic chemical vapor deposition (MOCVD). It has been determined that growth at 370°C with pre-exposure of the GaAs surface to Te following oxide desorption treatment at 600°C resulted in non-parallel epitaxy ((111)CdTe // (100)GaAs), while growth at 300°C following oxide desorption at 500°C with no exposure to Te resulted in parallel epitaxy ((100)CdTe // (100)GaAs). Both epitaxial orientation-relationships were observed on the same substrate for growth at 300°C temperature after 600°C oxide desorption treatment, but with no pre-exposure of the GaAs surface to Te. Preliminary results of growth of CdTe on Si are also reported.