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Ultrahard Multilayer Coatings

Description: We have developed a new multilayer a-tC material that is thick stress-free, adherent, low friction, and with hardness and stiffness near that of diamond. The new a-tC material is deposited by J pulsed-laser deposition (PLD) at room temperature, and fully stress-relieved by a short thermal anneal at 600°C. A thick multilayer is built up by repeated deposition and annealing steps. We measured 88 GPa hardness, 1100 GPa Young's modulus, and 0.1 friction coefficient (under high load). Significantly, these results are all well within the range reported for crystalline diamond. In fact, this material, if considered separate from crystalline diamond, is the 2nd hardest material known to man. Stress-free a-tC also has important advantages over thin film diamond; namely, it is smooth, processed at lower temperature, and can be grown on a much broader range of substrates. This breakthrough will enable a host of applications that we are actively pursuing in MEMs, sensors, LIGA, etc.
Date: May 1, 1999
Creator: Chrzan, D.C.; Dugger, M.; Follstaedt, D.M.; Friedman, Lawrence H.; Friedmann, T.A.; Knapp, J.A. et al.
Partner: UNT Libraries Government Documents Department

Electrical characterization of irradiated prototype silicon pixel sensors for BTeV

Description: The pixel detector in the BteV experiment at the Tevatron (Fermi Laboratory) is an important detector component for high-resolution tracking and vertex identification. For this task the hybrid pixel detector has to work in a very harsh radiation environment with up to 10{sup 14} minimum ionizing particles/cm{sup 2}/year. Radiation hardness of prototype n{sup +}/n/p{sup +} silicon pixel sensors has been investigated. We present Electrical characterization curves for irradiated prototype n{sup +}/n/p{sup +} sensors, intended for use in the BTeV experiment. We tested pixel sensors from various vendors and with two pixel isolation techniques: p-stop and p-spray. Results are based on irradiation with 200 MeV protons up to 6 x 10{sup 14} protons/cm{sup 2}.
Date: November 13, 2002
Creator: al., Maria Rita Coluccia et
Partner: UNT Libraries Government Documents Department

Analysis of Depth-Sensing Indentation Tests with a Knoop Indenter

Description: The present work shows how data obtained in a depth-sensing indentation test using a Knoop indenter may be analyzed to provide elastic modulus and hardness of the specimen material. The method takes into account the elastic recovery along the direction of the short axis of the residual impression as the indenter is removed. If elastic recovery is not accounted for, the elastic modulus and hardness are overestimated by an amount that depends on the ratio of E/H of the specimen material. The new method of analysis expresses the elastic recovery of the short diagonal of the residual impression into an equivalent face angle for one side of the Knoop indenter. Conventional methods of analysis using this corrected angle provide results for modulus and hardness that are consistent with those obtained with other types of indenters.
Date: May 1, 2001
Creator: Riester, L
Partner: UNT Libraries Government Documents Department

Nanoindentation Results from Direct Molded vs. Machined UHMWPE Tibial Bearings

Description: Nanoindentation has been used to compare the micromechanical properties of direct molded vs. machined bearing surfaces on UHMWPE tibial components. Differences in micromechanical properties (hardness and elastic storage modulus) were observed between these two types of bearing surfaces, and are believed to result from (1) differences in surface roughness, and (2) differences in morphology of the UHMWPE. Clinical studies of in-vivo UHMWPE wear rates in acetabular cups have reported differences between direct molded and machined bearings.{sup 1,2} Other studies of retrieved components have reported differences as well.{sup 3} Variations in surface characteristics (rather than bulk properties) may cause these differences in wear behavior. This study's objective was to compare micro-mechanical interactions at the bearing surfaces of direct molded components with those of machined components. A nanoindenter was used to perform instrumented microindentations on these surfaces. Da ta was analyzed to study both the load vs. displacement behavior during the indentation cycle, and also to measure the elastic storage modulus and hardness as a function of depth.
Date: November 13, 1999
Creator: Higgins, J.E.; Joy, D.C.; Pharr, G.M.; Schmidt, M.A. & Swadener, J.G.
Partner: UNT Libraries Government Documents Department

Wear Resistant Amorphous and Nanocomposite Coatings

Description: Glass forming materials (critical cooling rate <10{sup 4}K.s{sup -1}) are promising for their high corrosion and wear resistance. During rapid cooling, the materials form an amorphous structure that transforms to nanocrystalline during a process of devitrification. High hardness (HV 1690) can be achieved through a controlled crystallization. Thermal spray process has been used to apply coatings, which preserves the amorphous/nanocomposite structure due to a high cooling rate of the feedstock particles during the impact on a substrate. Wear properties have been studied with respect to process conditions and feedstock material properties. Application specific properties such as sliding wear resistance have been correlated with laboratory tests based on instrumented indentation and scratch tests.
Date: March 26, 2008
Creator: Racek, O.
Partner: UNT Libraries Government Documents Department

Determining the toughness of ceramics from Vickers indentationsusing the crack-opening displacements: An experimental study

Description: Recently, a method for evaluating the fracture toughness of ceramics has been proposed based on the computed crack-opening displacements of cracks emanating from Vickers hardness indentations. In order to verify this method, experiments were carried out to determine the toughness of a commercial silicon carbide ceramic, Hexaloy SA, by measuring the crack-opening profiles of such Vickers indentation cracks. While the obtained toughness value of Ko = 2.3 MPavm was within 10% of that measured using conventional fracture toughness testing, the computed crack-opening profiles corresponding to this toughness displayed poor agreement with those measured experimentally, raising concerns about the suitability of this method for determining the toughness of ceramics. The effects of subsurface cracking and cracking during loading are considered as possible causes of such discrepancies, with the former based on evidence observed for secondary radial cracking which affected the crack opening profile and deduced toughness values.
Date: October 30, 2002
Creator: Kruzic, J.J. & Ritchie, R.O.
Partner: UNT Libraries Government Documents Department

The correlation of indentation size effect experiments with pyramidal and spherical indenters.

Description: Experiments were conducted in annealed iridium using pyramidal and spherical indenters over a wide range of load. For a Berkovich pyramidal indenter, the hardness increased with decreasing depth of penetration. However, for spherical indenters, hardness increased with decreasing sphere radius. Based on the number of geometrically necessary dislocations generated during indentation, a theory that takes into account the work hardening differences between pyramidal and spherical indenters is developed to correlate the indentation size effects measured with the two indenters. The experimental results verify the theoretical correlation.
Date: January 1, 2001
Creator: Swadener, J. G. (John G.); George, Easo P. & Pharr, G.M.
Partner: UNT Libraries Government Documents Department

Properties of boron/boron-nitride multilayers

Description: Boron-Nitride films are of interest for their high hardness and wear resistance. Large intrinsic stresses and poor adhesion which often accompany high hardness materials can be moderated through the use of a layered structure. Alternate layers of boron (B) and boron-nitride (BN) are formed by modulating the composition of the sputter gas during deposition from a pure B target. The thin films are characterized with TEM to evaluate the microstructure and with nanoindentation to determine hardness. Layer pair spacing and continuity effects on hardness are evaluated for the B/BN films.
Date: June 1, 1996
Creator: Jankowski, Alan Frederic; Wall, Mark A.; Hayes, Jeffrey P. & Alexander, Kathleen B.
Partner: UNT Libraries Government Documents Department

Metal Coordination‐Mediated Functional Grading and Self‐Healing in Mussel Byssus Cuticle

Description: Article demonstrates direct evidence of Fe3+ and Fe2+ gradient distribution across mussel byssal cuticle threads thickness, which shows more Fe2+ inside the inner cuticle, to support the hypothesis that the cuticle is a functionally graded material with high stiffness, extensibility, and self‐healing capacity.
Date: October 24, 2019
Creator: Xu, Quan; Xu, Meng; Lin, Chun-Yu; Zhao, Qiang; Zhang, Rui; Dong, Xiaoxiao et al.
Partner: UNT Libraries

Trends in the design of front-end systems for room temperature solid state detectors

Description: The paper discusses the present trends in the design of low-noise front-end systems for room temperature semiconductor detectors. The technological advancement provided by submicron CMOS and BiCMOS processes is examined from several points of view. The noise performances are a fundamental issue in most detector applications and suitable attention is devoted to them for the purpose of judging whether or not the present processes supersede the solutions featuring a field-effect transistor as a front-end element. However, other considerations are also important in judging how well a monolithic technology suits the front-end design. Among them, the way a technology lends itself to the realization of additional functions, for instance, the charge reset in a charge-sensitive loop or the time-variant filters featuring the special weighting functions that may be requested in some applications of CdTe or CZT detectors.
Date: October 7, 2003
Creator: Manfredi, Pier F. & Re, Valerio
Partner: UNT Libraries Government Documents Department

AlGaN UV LED and Photodiodes Radiation Hardness and Space Qualifications and Their Applications in Space Science and High Energy Density Physics

Description: This presentation provides an overview of robust, radiation hard AlGaN optoelectronic devices and their applications in space exploration & high energy density physics. Particularly, deep UV LED and deep UV photodiodes are discussed with regard to their applications, radiation hardness and space qualification. AC charge management of UV LED satellite payload instruments, which were to be launched in late 2012, is covered.
Date: May 31, 2011
Creator: Sun, K. X.
Partner: UNT Libraries Government Documents Department

Investigation of depth-area relationships associated with nanoindentations

Description: Determination of hardness from indentation testing requires the measurement of the contact area. For indents generated at very low loads (<20 mN) or shallow depths (<250 nm), optical methods do not have sufficient resolution. One approach utilized in current state-of-the-art mechanical properties microprobes (MPM) involves the measurement of indenter depth. Calculation of the plastic area then requires a relation between depth and contact area. This relation is generally derived either by assuming the indenter is perfectly sharp (``Ideal Indenter`` assumption) or by calibrating the shape using materials having known hardness and elastic modulus values. The validity of both approaches was examined by using a Scanning Force Microprobe (SFM) to measure the actual dimensions of the residual impressions made by the MPM. The SFM data revealed that the ``Ideal Indenter`` assumption underestimates the actual plastic area. This result accounts for the fact that hardness values measured with the MPM are typically higher than those obtained with conventional hardness testers.
Date: October 1, 1994
Creator: Riester, L. & Ferber, M. K.
Partner: UNT Libraries Government Documents Department

Analysis of Failed and Nickel-coated 3093 Beam Clamp Components at the East Tennessee Technology Park (ettp)

Description: The U.S. Department of Energy and its contractor, Bechtel Jacobs Company (BJC), are undertaking a major effort to clean up the former gaseous diffusion facility (K-25) located in Oak Ridge, TN. The decontamination and decommissioning activities require systematic removal of contaminated equipment and machinery followed by demolition of the buildings. As part of the cleanup activities, a beam clamp, used for horizontal life lines (HLLs) for fall protection, was discovered to be fractured during routine inspection. The beam clamp (yoke and D-ring) was a component in the HLL system purchased from Reliance Industries LLC. Specifically, the U-shaped stainless steel yoke of the beam clamp failed in a brittle mode at under less than 10% of the rated design capacity of 14,500 lb. The beam clamp had been in service for approximately 16 months. Bechtel Jacobs approached Argonne National Laboratory to assist in identifying the root cause of the failure of the beam clamp. The objectives of this study were to (1) review the prior reports and documents on the subject, (2) understand the possible failure mechanism(s) that resulted in the failed beam clamp components, (3) recommend approaches to mitigate the failure mechanism(s), and (4) evaluate the modified beam clamp assemblies. Energy dispersive x-ray analysis and chemical analysis of the corrosion products on the failed yoke and white residue on an in-service yoke indicated the presence of zinc, sulfur, and calcium. Analysis of rainwater in the complex, as conducted by BJC, indicated the presence of sulfur and calcium. It was concluded that, as a result of galvanic corrosion, zinc from the galvanized components of the beam clamp assembly (D-ring) migrated to the corroded region in the presence of the rainwater. Under mechanical stress, the corrosion process would have accelerated, resulting in the catastrophic failure of the yoke. As suggested by Bechtel ...
Date: October 11, 2010
Creator: Singh, D.; Pappacena, K.; Gaviria, J.; Burtsteva, T. & Division, Nuclear Engineering
Partner: UNT Libraries Government Documents Department

Indenter geometry effects on the measurements of mechanical properties by nanoindentation with sharp indenters

Description: The measurement of mechanical properties by nanoindentation methods is most often conducted using indenters with the Berkovich geometry (a triangular pyramid) or with a sphere. These indenters provide a wealth of information, but there are certain circumstances in which it would be useful to make measurements with indenters of other geometries. We have recently explored how the measurement of hardness and elastic modulus can be achieved using sharp indenters other than the Berkovich. Systematic studies in several materials were conducted with a Vickers indenter, a conical indenter with a half-included tip angle of 70.3{degrees}, and the standard Berkovich indenter. All three indenters are geometrically similar and have nominally the same area-to-depth relationship, but there are distinct differences in the behavior of each. Here, we report on the application of these indenters in the measurement of hardness and elastic modulus by nanoindentation methods and some of the difficulties that occur.
Date: May 1, 1996
Creator: Tsui, T. Y.; Pharr, G. M. & Oliver, W. C.
Partner: UNT Libraries Government Documents Department

Influence of large-strain deformation on the microstructure, texture, and mechanical response of tantalum bar

Description: Numerous studies have established the influence of impurities, crystallographic texture, temperature, and strain rate separately or collectively on the constitutive response of annealed tantalum, in particular plate Ta-stock. However, fewer detailed studies have examined the evolution of crystallographic texture and the mechanical response of tantalum bar or rod material following prestraining to large strains {epsilon} > I. In this paper the influence of large plastic prestraining on the microstructure evolution, texture evolution, and mechanical response of high-purity tantalum bar material is presented. Tantalum cylinders annealed at 1200 {degrees}C were quasi-statically upset forged, with intermediate lubrication, to true strains of 0.4, 0.95, and 1.85. Microstructural and textural banding within the starting Ta-bar was characterized in detail. It was found that different oriented bands evolved differently during large-strain forging leading to significant scatter in the mechanical response. Aspects of defect storage, work-hardening response, and texture evolution in Ta-bar as a function of forging strain are discussed.
Date: March 1, 1996
Creator: Gray, G.T. III; Bingert, S.R.; Chen, S.R.; Bingert, J.F. & Wright, S.I.
Partner: UNT Libraries Government Documents Department

A comparison study on the densification behavior and mechanical properties of gelcast vs conventionally formed B{sub 4}C sintered conventionally and by microwaves

Description: The utilization of microwave energy for reaching high temperatures necessary to densify B{sub 4}C powder is compared with conventional means of sintering by evaluating the mechanical properties after densification. Microwave energy has been shown to be an effective means for achieving high sintered densities, even though temperatures of {approximately} 2,250 C are required. In this study, green preforms of B{sub 4}C specimens were sintered by both conventional and microwave heating. This study also utilized an advanced forming method called ``Gelcasting`` developed at ORNL. Gelcasting is a fluid forming process whereby high solids suspensions of powders containing dissolved monomers are cast into a mold, then polymerized or ``gelled`` in situ. This investigation compares microstructures and mechanical properties of both Gelcast B{sub 4}C and ``conventionally`` die-pressed B{sub 4}C. The microstructures and final mechanical properties of B{sub 4}C specimens are discussed.
Date: June 1, 1996
Creator: Menchhofer, P.A.; Kiggans, J.O.; Morrow, M.S. & Schechter, D.E.
Partner: UNT Libraries Government Documents Department

Effects of adhesion on the measurement of thin film mechanical properties by nanoindentation

Description: Experiments have been performed on soft aluminum films deposited on hard ceramic substrates to explore the influences of interfacial adhesion on mechanical property measurement by nanoindentation. The substrate materials included soda-lime silicate glass, aluminum oxynitride (ALON), and (100) sapphire. Thin films of high purity aluminum were sputtered onto each substrate to a thickness of 500 nm. Because the films were deposited simultaneously, the only major difference in the specimens was the nature of the substrate, which exerts an important influence on film adhesion through interfacial chemistry. Of the substrates examined, aluminum adheres strongly to glass and sapphire, but poorly to ALON. In addition, two different types of aluminum films on sapphire were examined - one with and the other without a 10 nm interlayer of amorphous carbon which significantly reduces film adhesion. Testing revealed important differences in the hardness of the specimens when measured by standard nanoindentation methods. Characterization of the residual hardness impressions by high resolution scanning electron microscopy showed that the hardness differences arise from an influence of interfacial debonding and film delamination on pile-up in the film. Furthermore, when the pile-up is accounted for in contact area determinations, the film hardness is actually independent of the substrate, thus indicating that the hardness differences observed in nanoindentation testing are an artifact of the testing analysis procedure. Results of the experiments are documented and discussed. 8 refs., 6 figs., 1 tab.
Date: June 1, 1997
Creator: Tsui, T.Y.; Ross, C.A. & Pharr, G.M.
Partner: UNT Libraries Government Documents Department

Inaccuracies in Sneddon`s solution for elastic indentation by a rigid cone and their implications for nanoindentation data analysis

Description: Methods currently used for analyzing nanoindentation load-displacement data to determine a material`s hardness and elastic modulus are based on Sneddon`s solution for the indentation of an elastic half-space by a rigid axisymmetric indenter. Although this solution is widely used, no attempts have been made to determine how well it works for conditions of finite deformation, as is the case in most nanoindentation experiments with sharp indenters. Analytical and finite element results are presented which show that corrections to Sneddon`s solution are needed if it is to be accurately applied to the case of deformation by a rigid cone. Failure to make the corrections results in an underestimation of the load and contact stiffness and an overestimation of the elastic modulus, with the magnitude of the errors depending on the angle of the indenter and Poisson`s ratio of the half-space. For a rigid conical indenter with a half-included tip angle of 70.3{degrees}, i.e., the angle giving the same area-to-depth ratio as the Berkovich indenter used commonly in nanoindentation experiments, the underestimation of the load and contact stiffness and overestimation of the elastic modulus may be as large as 13%. It is shown that a simple first order correction can be achieved by redefining the effective angle of the indenter in terms of the elastic constants. Implications for the interpretation of nanoindentation data are discussed.
Date: May 1, 1996
Creator: Bolshakov, A. & Pharr, G.M.
Partner: UNT Libraries Government Documents Department