bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reduction in Wear Rate of α-Alumina and Silicon Nitride by Diffusional Surface Modification
Authors: Gangopadhyay A.K. , Fine M.E. , Cheng H.S. 
Published: March 2011

AbstractThe surface regions of α-alumina and hot pressed silicon nitride were modified by suitable alloying in order to improve their wear resistance. The surface modification in polycrystalline α-alumina was done by diffusing chromia into the surface region which resulted in the formation of a thin layer of A12O3 - Cr9O3 solid solution which has a lower thermal expansion coefficient than pure α-alumina. Also Cr2O3 has a larger lattice parameter than α-alumina thus during cooling the surface was put into compression. The surface region of hot pressed silicon nitride was modified by diffusing α-alumina into the surface which resulted in the formation of a thin sialon layer. A surface compressive stress was again introduced due to the lower thermal expansion coefficient and larger latticeparameter of sialon compared to silicon nitride.Wear tests were conducted against 52100 steel under both lubricated and unlubricated sliding contact using a block on ring apparatus. The wear resistance of chromia surface alloyed α-alumina was improved considerably over unalloyed α-alumina under both lubricated and unlubricated conditions. The wear resistance of alumina surface alloyed silicon nitride was also improved over unalloyed silicon nitride under both lubricated and unlubricated conditions.Different wear modes were identified by examining the worn surfaces under the scanning electron microscope.
Surface and Bulk Oxidizing Species for Self Lubricating Ceramics
Authors: Blanchard-Ardid C. R. , Lankford J. , Page R. A. 
Published: March 2011

AbstractThe use of ceramic materials for high temperature engine applications has prompted interest in the friction and wear characteristics of ceramicceramic pairs in mating contact. This interest has led to both surface and bulk material modifications aimed at improving the lubricity and wear resistance of these materials. This paper will discuss two basic systems developed to allow self-lubrication at high temperatures in ceramic materials through the formation of a lubricious oxide film. Both methods operate under the assumption that the oxide chemistry of the system controls the lubricity and wear properties. Relevant issues for each system will be presented and discussed.
Fluorinated Diamond Films, Slabs, and Grit
Authors: Patterson Donald E. , Hauge Robert H. , Margrave John L. 
Published: March 2011

AbstractDiamond powders, single crystal diamonds (slabs and naturally occurring stones), and CVD diamond films have been fluorinated via direct fluorination and plasma techniques at a variety of temperatures and reaction times. Infrared, ESCA, and mass spectrometric studies verify that the diamond surfaces are altered by fluorination and that fluorine is attached to the surface to some degree in most instances. Based on spectra obtained using the FT-IR techniques of DRIFTS and ATR, the fluorine appears to have an effect on the diamond surfaces at relatively low temperatures in short reaction times by the removal of surface contaminants. A relatively high temperature (600ºC) or long reaction time at slightly lower temperatures is needed to attach a significant number of fluorine atoms onto the diamond surface. Once fluorinated, the diamonds show enhanced resistance to further oxidation. The outward appearance of the diamonds remains unchanged even at fluorination temperatures nearing 800ºC.
Thin Diamond Films for Tribological Applications
Authors: Wong M.S. , Meilunas R. , Ong T.P. , Chang R.P.H. 
Published: March 2011

AbstractDiamond films have been deposited on Si, Mo and many other substrates by microwave and radio frequency plasma enhanced chemical vapor deposition. Although the adhesion between the diamond film and most of the metal substrates is poor due to residual thermal stress from the mismatch of thermal expansion coefficients, we have developed processes to promote the growth of uniform and continuous diamond films with enhanced adhesion to metal substratesfor tribological applications. The tribological properties of these films are measured using a ring-on-block tribotester. The coefficients of friction of diamond films sliding against a 52100 steel ring under the same experimental conditions are found to be significantly different depending on the morphology, grain size and roughness of the diamond films. However, under all cases tested, it is found that for uniform and continuous diamond films with small grain size of 1-3 micrometers, the coefficient of friction of thediamond film sliding against a steel ring under lubrication of a jet of mineral oil is about 0.04.
Comparative Wear Tests of Different Types of Coatings on Steels
Authors: Habig Karl-Heinz 
Published: March 2011

AbstractDifferent coatings were formed by galvanical deposition, thermochemical treatment, CVD, PVD or plasma spraying. Their wear behaviour was tested under various conditions so that adhesive and abrasive wear mechanisms predominated. The resistance of the coatings to adhesive failure and wear was examined with the pin and disc system under conditions of boundary lubrication. The discs were protected by different coatings while the pins were made of tool steel or alumina. For abrasive wear tests a grinding apparatus with grinding papers of flint, alumina or silicon carbide was used. From the resultsthe following conclusions can be drawn: -Thermochemically treated steels and nickel-phosphorus coatings have a high resistance to galling if the counterbody consists of steel or alumina. The couples plasma sprayed molybdenum against steel and tungsten carbide against alumina also have a high resistance against galling.-The wear of most coatings is low if the counterbody is made of steel. By analumina counterbody the wear of the coatings isincreased. Alumina is worn less by the coatings than steel.-The hard CVD- and PVD-coatings, the thermochemically formed iron boride andvanadium carbide coatings and the electroless nickel-phosphorus-diamond coatings have a high abrasive wear resistance.
What Part do Adhesion and Deformation Play in Fine-Scale Static and Sliding Contact?
Authors: Guo Q. , Ross J.D.J. , Pollock H.M. 
Published: March 2011

AbstractWe describe experiments involving the static or sliding contact of a 'single asperity' and a flat surface. Plastic deformation and possibly junction growth can occur even at zero applied load, as a consequence of surface forces. The conditions for this to occur, and the different modes of separation of an adhesive contact, are clarified with the help of 'maps': use of the macroscopic concepts involved, such as yield stress and work of adhesion, is sometimes questionable and evidence of the importance of nanometre-scale stepped topography is presented. Strong adhesion between hard non-metals can required thermal activation. Sliding contacts at the sub-micrometre level have shown behaviour ranging from 'unstable ploughing' to adhesive peeling, but the frictional mechanisms involved are often unclear.
Measurements of Static and Dynamic Interactions of Molecularly Thin Liquid Films Between Solid Surfaces
Authors: McGuiggan Patricia M. , Israelachvili Jacob N. , Gee Michelle L. , Homola Andrew M. 
Published: March 2011

AbstractNew experimental techniques are described for measuring both the static and dynamic interactions of very thin liquid films between two molecularly smooth surfaces as they are moved normally or laterally relative to each other. Film thickness can be measured and controlled to IA. Results are presented of how the properties of liquid films only one, two, or three molecular layers thick differ from those of bulk liquids. When close together, two molecularly smooth surfaces slide (shear) past each other while separated by a discrete number of liquid layers. The critical shear stress required to initiate motion for simple spherical molecules is “quantized” with the number of layers. Another important characteristic of molecular thin liquid films undergoing shear is the phenomenon of “stick-slip” or “intermit-tent” motion. Both of these phenomena have been studied as a function of driving velocity, area of contact, and number of molecular layers.
Assessment of the Tribological Requirements of Advanced Spacecraft Mechanisms
Authors: Fleischauer Paul D. , Hilton Michael R. 
Published: March 2011

AbstractA survey was conducted of existing technologies for moving mechanical assemblies used in spacecraft applications. The purpose was to identify areas where future requirements for lifetimes in excess of ten years with anticipated speeds, loads, and temperatures might not be satisfied. Some specific mechanisms, such as momentum/reaction wheels, high-speed turbines, pointing and tracking mechanisms, despin mechanisms, and gimbal mechanisms, were identified as areas for potential application of existing but unused technologies. Two major problem areas identified involve boundary-regime lubrication and lubricant supply (active or passive) for long life. Areas where substantial, near-term improvements appear practical include the use of hybrid bearings, new synthetic fluid lubricants, new bearing retainer materials, and properly designed solid-film lubricants.
NDT-Techniques for Monitoring Material Degradation
Authors: Höller Paul , Dobmann Gerd 
Published: March 2011

AbstractThe early detection of material degradation by NDT is of basic importance for safe and economic operation of many industrial components. Depending on the type of component as well as on service exposure conditions, NDT-techniques, which are sensitive to deformation, erosion, wear, porosity, microcracks and so on, are required. At present, only very few techniques are available for monitoring early stages of degradation. An overview of NDT-techniques already in use as well as under development in Germany for this problem is given. Special emphasis will be laid on the presentation of recent advances towards better detectability and objectivity.
Nondestructive Detection of Material Degradation Caused by Creep and Hydrogen Attack
Authors: Birring A. S. 
Published: March 2011

AbstractHydrogen attack and creep damage may reduce the fracture toughness as well as the strength of steels. This reduction is caused partially by the presence of cavities and microcracks at the grain boundaries. A large reduction in fracture toughness can make some components unsafe for operation. Ultrasonic tests performed on damaged samples showed a decrease in wave velocity and an increase in backscatter. The longitudinal-wave velocity decreased more than shear-wave velocity. Where the fracture toughness was reduced by 43 percent, samples with hydrogen attack showed a tenfold increase in backscatter. Such results demonstrate the potential for ultrasonic nondestructive testing to quantify damage and assess the component's remaining life.
Ultrasonic Non Destructive Evaluation of Microstructural Changes and Degradation of Ceramics at High Temperature
Authors: Gault Christian 
Published: March 2011

AbstractThis paper deals with the use of pulsed ultrasonic waves to monitor microstructural changes and degradation of ceramics in the field of high temperature. Two types of devices are described. One is a low frequency system for the measurement of Young's modulus at temperatures up to 1800°C. The second is an ultrasonic spectroscopy system for the evaluation of damage in structural ceramics during thermal fatigue experiments. Applications concern phase changes, porosity evolution or microcracking induced by thermal stresses when heating monolithic or composite ceramics.
Ultrasonic Characterization of SOL/GEL Processing
Authors: Chiou S. , Hahna H. T. 
Published: March 2011

AbstractThe sol/gel process has recently received attention because it enables the production of pure and homogeneous glass without external heating, eliminating the high processing temperatures needed in conventional methods. A disadvantage of the process is that if the rate of evaporation during syneresis is too high, cracking due to mechanical shrinkage can be extensive. A slower evaporation rate produces less cracking, but results in a longer processing time. The key to decreasing processing time while simultaneously eliminating shrinkage cracks lies in monitoring the change of the mechanical properties during the evaporation process. Ultrasonic techniques are ideal for this purpose.To monitor the process, an ultrasonic signal was passed through the material. Spectrum changes were measured and then converted to changes in modulus and viscosity, while shrinkage and density changes were monitored using an air-type transducer and an electronic balance. The results show no observable change up to the beginning of the gelation process, followed by rapid increase in the modulus and viscosity after the onset of shrinkage. This finding was confirmed using a viscometer and laser light scattering measurements. Because of the effectiveness of this ultrasonic technique in detecting changes in the material, such as the onset of cracking, it may be used in controlling and improving the process.
Anomalous Scattering of Polarized X-Rays
Authors: Templeton David H. , Templeton Lieselotte K. 
Published: March 2011

AbstractSome elements in some chemical states exhibit strong dichroism and birefringence near x-ray absorption edges. The atomic scattering factor is a complex tensor. This polarization anisotropy has profound effects on the transmission and scattering of x-rays even when the incident radiation is unpolarized. The linear polarization of synchrotron radiation makes it easier to study the effects and to use them for new methods of structure determination. Several of these anomalous scattering tensors have been measured by absorption spectroscopy and in diffraction experiments. New polarization terms enter the calculation of diffraction intensities, with interesting consequences. Reflections forbidden by a screw-axis rule are observed in sodium bromate near the Br K edge and permit direct observation of the structure factor phases of their second order reflections. This technique is a method of selective diffraction in which atoms of single element in a single chemical state contribute to the signal, and it can reveal their positions with precision. These effects can be a handicap for some applications of near-edge anomalous scattering in the study structures of crystals and amorphous materials.
Polycrystalline Diffraction and Synchrotron Radiation
Authors: Hart Michael , Parrish William 
Published: March 2011

AbstractSynchrotron radiation sources allow a new generation of parallel beam instruments to be developed for polycrystalline xray diffraction. Spectroscopy can be combined with diffraction in either angle or energy scanning modes. The high intensity narrow instrument profile and freedom from aberrations make possible a wide range of measurements; of anomalous dispersion, of peak-shape analysis to determine particle size and strain, of preferred orientation and structure as a function of depth and of lattice parameters with a precision approaching 1 part per million. The parallel beam instrument which we have developed is now to be installed on a regular basis at SSRL and at Daresbury.
Near Surface Structure of Ion Implanted Si Studied by Grazing Incidence X-Ray Scattering
Authors: Wallner G. , Burkel E. , Metzger H. , Peisl J. , Rugel S. 
Published: March 2011

AbstractX-rays incident on a surface under grazing angle may undergo total external reflection and excite an interior wave field damped exponentially into the bulk. These evanescent waves are a sensitive probe for the study the real structure in the near surface region. We report results on the influence of implantation defects on Bragg diffracted and on diffuse intensities. By detailed comparison of Bragg intensities with predictions of dynamical scattering theory we detect the presence of amorphous layers and determine their thickness. For the first time defect induced diffuse scattering underconditions of grazing incidence andexit is observed and compared to recent theoretical results. Strength and symmetry of implantation induced defects can be determined as well as their depth distribution which is compared to results of a TRIM simulation: the defect distribution is found to agree with that of the deposited collisional energy.
Time-Resolved Small Angle X-Ray Scattering and Dynamic Light Scattering Studies of Sol-Gel Transition in Gelatin
Authors: Wu Dan Q. , Chu Benjamin 
Published: March 2011

AbstractStructural and dynamical properties of an aqueous gelatin solution (5 wt%, 0.1M NaCi, pH=7) in a sol-gel transition were studied by time-resolved small angle x-ray scattering (SAXS) and dynamic light scattering (DLS) after quenching the gelatin sol at ∼45”C to 11°C. SAXS intensity measurements suggested the presence of gel fibrils which grew initially in cross-section. The average cross-section of the gel fibrils reached a constant value after an initial growth period of ∼800 sec. Further increase in SAXS intensity could be attributed to the increase in the length of the gel fibrils. Photon correlation, on the other hand, clearly showed two relaxation modes in both the sol and the gel (∼1 hr after the quenching process) states: a fast cooperative diffusion mode which remained constant from the sol to the gel state after correction for the temperature dependence of solvent viscosity; and a slow mode that could be attributed to the self-diffusion of the “free” gelatin chains and aggregates. The slow mode contribution to the time correlation function was reduced from ∼40% in sol to ∼20% in gel signaling a decrease but not the elimination of “free” particles in the gel network. The decrease in the intensity contribution by the slow mode is, however, accompanied by a large increase in the characteristic line-width distribution.
Investigation of Grain Boundary Migration in Situ by Synchrotron X-Ray Topography
Authors: Bauer C. L. , Gastaldi J. , Jourdan C. , Grange G. 
Published: March 2011

AbstractGrain boundary migration has been investigated in prestrained monocrystalline specimens of aluminum in situ, continuously and at temperatures ranging from 415 to 610°C by synchrotron (polychromatic) x-ray topography (SXRT). In general, new (recrystallized) grains nucleate at prepositioned surface indentations and expand into the prestrained matrix, revealing complex evolution of crystallographic facets and occasional generation of (screw) dislocations in the wake of the moving boundaries. Analysis of corresponding migration rates for several faceted grain boundaries yields activation energies ranging from 56 to 125 kCal/mole, depending on grain boundary character. it is concluded that grain boundary mobility is a sensitive function of grain boundary inclination, resulting in ultimate survival of low-mobility (faceted) inclinations as a natural consequence of growth selection. Advantages and disadvantages associated with measurement of grain boundary migration by SXRT are enumerated and corresponding results are interpreted in terms of fundamental relationships between grain boundary structure and corresponding migration kinetics.
Synchrotron Microtomography of Composites
Authors: Stock S. R. , Kinney J. H. , Breunig T. M. , Bonse U. , Antolovich S. D. , Johnson Q. C. , Nichols M. C. 
Published: March 2011

AbstractX-ray computed tomography (CT) uses absorption profiles from many different viewing directions to reconstruct the two-dimensional distribution of x-ray absorptivity within a slice of the sample. The tunability, high brightness and parallelism of synchrotron radiation are critical to high resolution (0.001mm), high contrast (1%) CT or microtomography. In situ study of samples multiple times during the course of an experiment is exciting to consider.Continuous fiber SiC/Al composites were deformed under three-point bending, and the resulting damage and fiber arrangement were revealed with synchrotron microtomography. Several hundred slices of 0.012 mm thickness were recorded simultaneously using 25 key radiation and a phosphor screen/charge coupled device (CCD) detector. Reconstruction was with the filtered back projection method. Low density regions were observed in the matrix in regions of highest stress where cracking is expected.
X-Ray Fluorescence Microprobe Imaging with Undulator Radiation
Authors: Rivers Mark L. , Sutton Stephen R. , Gordon Barry M. 
Published: March 2011

AbstractSynchrotron x-ray fluorescence experiments were performed using a prototype undulator for the Advanced Photon Source installed on the CESR storage ring at Cornell University during a run in May, 1988. Fluorescence spectra were collected from a number of standard references and unknowns. Thick target minimum detectable limits (MDL) were about a factor of two higher than those obtained using white bending magnet radiation at the NSLS. The higher MDLs could be due to lower polarization and/or imperfect alignment of the Si(Li) detector. Thin target MDLs were about 10 times lower than the NSLS since the undulator produced a usable spot size which was also 10 times smaller. Several one dimensional multi-elemental scans and two dimensional images were made with 10 μm resolution and 30 ppm MDL. These experiments demonstrate that undulators on the proposed Advanced Photon Source will be ideal for a trace element x-ray fluorescence microprobe with excellent elemental sensitivity and spatial resolution.
Synchrotron Radiation Studies of Magnetic Materials
Authors: Erskine J. L. , Ballentine C. A. , Araya-Pochet Jose , Fink Richard 
Published: March 2011

AbstractNew opportunities for research on magnetic materials are emerging as a result of quiet revolutions in several areas including: materials synthesis techniques, surface characterization capabilities, new magnetic sensitive detectors and spectroscopic techniques, improved synchrotron radiation instrumentation, and predictive modeling based on first principals calculations. This paper describes some of the more recent advances and assesses some of the new opportunities that are emerging in the field of magnetic materials research.
Reflectance-Difference Spectroscopy: a New Real-Time, In-Situ Analysis of MBE and OMCVD Growth Surfaces.
Authors: Colas E. , Aspnes D.E. , Bhat R. , Studna A.A. , Koza M.A. , Keramidas V.G. 
Published: March 2011

ABSTRACTReflectance-difference spectroscopy (RDS) is a recently developed optical technique that allows to monitor chemical and structural changes at a growing semiconductor surface, in-situ and in real-time. This technique was applied recently to organometallic chemical vapor deposition (OMCVD) on a [100] GaAs growth surface. The results show that submonolayer coverage of reacted species can be followed by this technique, which provided unique insights into the microscopic growth mechanisms. The time, temperature and pressure dependences of surface coverage show that OMCVD growth is controlled by two basic processes with distinct activation energies, i.e. reversible chemisorption (at -26 kcal/mole), and decomposition (at 39 kcal/mole) of trimethylgallium (TMG) at surface lattice sites. The importance of reversible chemisorption, which is of an excluded-volume type, due to the large size of the TMG molecule, had been overlooked until now in the literature, where only one activation energy was used to describe growth kinetics.
Vertical Bridgman Growth of GaAs
Authors: Kremer R. E. , Francomano D. , Beckhart G. H. , Burke K. M. , Miller T. 
Published: March 2011

ABSTRACTWe have developed a process to grow both undoped, semi-insulating (SI) and silicon-doped, semiconducting (SC) GaAs using a vertical Bridgman method. The technique combines advantages of both liquid encapsulated Czochralski (LEC) and horizontal Bridgman (HB) processes. SI ingots, grown in pBN boats, and SC ingots, grown in quartz boats, are passed through a relatively shallow temperature gradient. Properties of the resulting material are highly uniform across the surface of a wafer. Because of the small temperature gradient, dislocation densities are very low (typically under 4000/cm∩2).