Alternative Methodologies for Neural Networks that Predict Charpy Toughness Properties. STACEY RADEN (University of Tennessee Knoxville, TN 37966) JOHN M. VITEK PH.D. (Oak Ridge National Laboratory, Oak Ridge, TN, 37831)

Modeled after the human brain and its neural connections, artificial neural networks are nonlinear analytic tools that identify patterns between input and output data and can then be applied to predict behavior. A neural network is formed from multiple layers consisting of an input layer constructed from input nodes, a specified number of "hidden" layers constructed from "hidden" nodes, and an output layer constructed from output nodes. This advanced investigative tool was applied to the problem of predicting Charpy toughness in welds as a function of alloy composition, weld conditions, and heat treatment. The intent of this project was to compare these two methodologies to determine which approach is better suited for predicting the toughness of a weld. The first approach produced a neural network which predicts the Charpy value for given metal composition, welding conditions and heat treatment. This approach considered seventeen material inputs and one output (toughness). The second approach made use of the accepted fact that toughness versus temperature behaves in a sigmoidal fashion. The data were pre-processed to produce the parameters of a sigmoid function for each condition and a neural network was created to predict these curve parameters. This approach used sixteen material inputs and four outputs (four curve parameters). The first step in the analysis was to identify the optimum network architecture for each model (the optimum number of hidden nodes). Neural networks with a range of hidden nodes were trained and tested (up to twenty nodes for the first approach and up to six nodes for the second approach). Several pairs of training and testing data were considered to allow for the inherent noise in such an analysis. For the first approach (direct prediction of toughness), an architecture containing five hidden nodes was the optimal architecture. For the second approach (prediction of parameters for toughness versus temperature curve), the optimal architecture contained two hidden nodes. After calculating the root mean square error for both approaches, the first approach (direct calculation of Charpy toughness) seemed to be the most accurate. However, this method also seems to reproduce noise in the data and therefore may not be the best method to predict Charpy toughness.

An Artificial Nacre. DEANNA BRITTON (University of Tennessee Knoxville, TN 37996) APRIL MCMILLAN (Oak Ridge National Laboratory, Oak Ridge, TN, 37831)

Many structured organic-inorganic composites exist in nature. An example is mother-of-pearl, or nacre, which was investigated in this study. Nacre possesses an ordered brick-and-mortar arrangement composed of alternating layers of inorganic aragonite (CaCO3) approximately 500 nm in thickness and an organic protein matrix 50 nm thick. Nacre is well known for its excellent mechanical properties in particular its high toughness and strength, and these superior qualities can be attributed to the arrangement of the organic/inorganic elements which combines the elasticity and toughness of the protein layers and the strength and hardness of the aragonite. In order to develop an understanding of how organic and inorganic structures assemble, a synthetic approach was utilized to reproduce the structure of nacre. This study carried on the work of Dr. Nicholas Kotov, Oklahoma State University. Kotov fabricated the layered structure through demonstration of a technique called layer-by-layer assembly. Layer-by-layer assembly involves alternate immersions of glass slides in solutions of negatively-charged clay called montmorillonite, the bricks, and positively-charged polyelectrolyte called poly(diallydimethylammonium) chloride (PDDA) which serves as the mortar. Currently, a calibration curve for Layer Thickness versus Immersion time is being generated in order to understand the growth kinetics of the layers. The ability to manufacture artificial nacre may provide lightweight, rigid composites for biological tissues that possess a similar structure such as bone and teeth.

An Investigation of the Dependence of Fracture Toughness on Crystallographic Orientation in Single-Crystalline Cubic (ß) Silicon Carbide. GEORGE PHARR (Rice University Houston, TX 77005) YUTAI KATOH (Oak Ridge National Laboratory, Oak Ridge, TN, 37831)

Along with other desirable properties, the ability of silicon carbide (SiC) to retain high strength after elevated temperature exposures to neutron irradiation renders it potentially applicable in fusion and advanced fission reactors. However, properties of the material such as room temperature fracture toughness must be thoroughly characterized prior to such practical applications. The objective of this work is to investigate the dependence of fracture toughness on crystallographic orientation for single-crystalline ß-SiC. X-ray diffraction was first performed on the samples to determine the orientation of the crystal. Nanoindentation was used to determine a hardness of 39.1 and 35.2 GPa and elastic modulus of 474 and 446 GPa for the single-crystalline and polycrystalline samples, respectively. Additionally, crack lengths and indentation diagonals were measured via a Vickers micro-hardness indenter under a load of 100 gf for different crystallographic orientations with indentation diagonals aligned along fundamental cleavage planes. Upon examination of propagation direction of cracks, the cracks usually did not initiate and propagate from the corners of the indentation where the stresses are concentrated but instead from the indentation sides. Such cracks clearly moved along the {1 1 0} family of planes (previously determined to be preferred cleavage plane), demonstrating that the fracture toughness of SiC is comparatively so much lower along this set of planes that the lower energy required to cleave along this plane overpowers the stress-concentration at indentation corners. Additionally, fracture toughness in the <1 1 0> direction was 1.84 MPaom^1/2, lower than the 3.46 MPaom^1/2 measured for polycrystalline SiC (which can serve as an average of a spectrum of orientations), further demonstrating that single-crystalline ß-SiC has a strong fracture toughness anisotropy.

Analysis of holes in coated fuel particles, calculation of the ratio of resin to sand in a manufacturing mold, and observation of glass fiber properties in a polypropylene sample using x-ray tomography. PAUL FIKSE (Allegheny College meadville, PA 16335) G.E. ICE (Oak Ridge National Laboratory, Oak Ridge, TN, 37831)

X-ray tomography serves as a nondestructive means of creating 3-D images of samples with volumes from 5µm³ to 5mm³. It is often used to detect imperfections in manufacturing processes. Laser drilled holes in inert coated fuel particles were measured for depth and diameter of entry incision, the percentage of sand in a manufacturing mold was roughly estimated, and properties of glass fibers dispersed in a sample of polypropylene were observed. An individual sample is placed between a 5 micron diameter x-ray source and a detector (which consists of a microscope, a crystal, and a CCD). The sample is rotated about its axis and a number of images are taken. Each image depicts the amount of x-ray absorption for the particular orientation. Using a parallel-beam back projection algorithm, a 3-D reconstruction of the sample is obtained. Slices of tomograms were taken depicting the entry diameter of incision and a cross section of the incision depth for 6 C-SiC-C-Zr inert fuel particles. Two tomograms were also taken (inner and outer regions) of the sand mold used for lost foam cast molding - a process popular in automobile manufacturing. Slices of varying depth were taken from each and then analyzed with Photoshop® and ImageJ® for the percentage of sand present. The sample was found to be nearly consistent throughout with approximately 80.5% sand. Slices from a fiber-reinforced polypropylene tomogram were used to find the coordinates of the individual glass fibers' endpoints, with which an estimate of average fiber length was calculated. The isolated fibers were found to average 1073µm in length, far shorter than the length of bundled fibers, which were the majority of fibers present. The tomography machine proved only somewhat useful for examining the sand sample, yet highly effective in detecting contrast in the carbon layers of the fuel particles as well as the glass fibers in the polypropylene sample.

Comparisons of Austenitic Cast Stainless Steel Alloys Used for Steam Turbine Casings. CORY STINTON (University of Tennessee Knoxville, TN 37996) PHILIP J. MAZIASZ (Oak Ridge National Laboratory, Oak Ridge, TN, 37831)

Current materials used for turbine casings under high temperatures and pressures are reaching their maximum temperatures and thus, their maximum reliable performance limits will soon also be attained. CF8C-Plus and CF8C-Plus+Cu/W, two variations of standard CF8C, are austenitic cast stainless steel alloys that have been developed by Oak Ridge National Laboratory (ORNL) and Caterpillar to replace these current materials, in order to increase the efficiencies and maximum operating temperatures of steam turbines. Specimens of each variation of the two new steels were aged at 700^oC, 750^oC, 800^oC, and 850^oC, for 3000 hours. Tensile and Charpy specimens were tested at room temperature (25^oC) to obtain statistical data for comparison. The specimens tested at room temperature, which were aged at 750^oC, were then selected to be further examined in the Scanning Electron Microscope (SEM) for fracture mode and microstructure analysis. When comparing the tensile data, CF8C-Plus and CF8C-Plus+Cu/W have Ultimate Tensile Strengths similar to CF8C, but their Yield Strengths are considerably higher than that of CF8C. The Charpy data showed that CF8C was the least ductile, that CF8C-Plus+Cu/W was the most ductile, and that the CF8C-Plus was in-between these two. Tensile ductility was much lower in the as-cast specimens of the CF8C-Plus+Cu/W than the aged specimens, but the opposite was true for CF8C-Plus. The SEM showed the presence of delta ferrite in the CF8C samples, but its presence was not detected in the other two new materials. The higher Yield Strength of CF8C-Plus and CF8C-Plus+Cu/W indicate that these materials are stronger after aging and more desirable than CF8C, which has similar Yield Strength and much lower ductility after aging due to the presence of weakening delta ferrite.

Data Acquisition Issues for Phosphor Thermometry. ROBERT MOORE (University of Louisiana at Lafayette Lafayette, LA 70504) STEVEN W. ALLISON (Oak Ridge National Laboratory, Oak Ridge, TN, 37831)

Phosphor thermometry is used for non-contact remote access temperature measurements. Certain characteristics of phosphor emission, like decay time, are temperature dependent and can be correlated with a reference to provide a method of temperature measurement. In order to achieve the correlation needed, every aspect of the calibration procedure must be fully understood. In early testing, several divergences from previous calibrations of La₂O₂S:Eu were discovered. The calibration curve produced in these experiments diverged from the previous values for temperatures that exceeded 70 ^oC. Certain aspects of the equipment setup and software appeared to cause these small differences. In addition, to investigate calibration effects from excitation source changes, a series of light emitting diodes (LEDs) were tested with a fluorescent ruby target. The ruby exhibited a similar response to two different LED wavelengths (405nm and 435nm). The procedures studied here are just examples of the characteristics of commonly used equipment for calibrations and excitation sources. The testing suggests that even the smallest changes can affect results in unexpected ways and must be understood in order to improve this thermometry approach.

Development of an ASTM Graphite Oxidation Test Method. ZACHARY VANE (Virginia Polytechnic Institute and State University Blacksburg, VA 24061) TIMOTHY BURCHELL (Oak Ridge National Laboratory, Oak Ridge, TN, 37831)

Graphite, one of the three allotropes of carbon, is a very useful material because of its unique chemical structure and properties such as mechanical strength, chemical inertness, and electrical conductivity. In order to advance our knowledge of various graphite brands, further research must be conducted to gain a greater insight into the process and effects of oxidation on graphite properties. Although the key processes and controlling elements of graphite oxidation have been identified, the behavior of this material during and after oxidation is not well established. Knowledge of this behavior is crucial in understanding what happens to the various graphite components in nuclear reactors. Thermogravimetric analysis (TGA) of small samples of AG 13-01, 20-20, and PGWX graphite at the Oak Ridge National Laboratory (ORNL) has been used to increase scientific understanding of the relationship between the rate of oxidation and the flow rates of gases, temperature, and the intrinsic reactivity of graphite. This helps to identify the more oxidation resistant forms of graphite. These TGA results then serve as a reference point for validating a potential procedure for characterization of larger samples using a vertical tube furnace (VTF). The information gathered from these experiments is geared towards the development of an American Society for Testing and Materials (ASTM) test method for the oxidation of graphite. Though only a few runs have been conducted, preliminary results have proved promising as data from both the TGA and VTF methods yielded almost identical activation energies. More research on all of the types of graphite is needed, but such results suggest that the current ORNL procedure using the vertical tube furnace may become a reliable ASTM test method.

Formation of Epitaxial MgO Thin Films on Textured Ni3at.%W Substrates by dc- and rf-reactive Magnetron Sputtering. BETHANY SPENCER (North Carolina Agricultural and Technical State University Greensboro, NC 27411) DHANANJAY KUMAR (Oak Ridge National Laboratory, Oak Ridge, TN, 37831)

Robust high temperature superconducting (HTS) wire is a layered composite comprised of a HTS compound, usually YBa₂Cu₃O₇ (YBCO), deposited on intermediate oxide layers grown on a metal/metal-alloy substrate. Buffer layers are generally required between the HTS film and the metal substrate in order to prevent oxidation of the substrate material and chemical poisoning of the superconducting thin film. Consequently, there is a great need to develop buffer architectures that could prevent inward oxygen diffusion to the metal substrate. In this context magnesium oxide (MgO) is very appealing because it has a much lower oxygen diffusion coefficient than other oxide buffer materials studied. If MgO can be grown epitaxially on the metal substrate, both the efficiency and the robustness of 2nd generation superconducting wires (coated conductors) could be significantly improved. Deposition parameters of a reactive magnetron sputtering process were varied in order to study whether an epitaxial film of MgO could grow on a biaxially textured Ni-3atomic%W (Ni-3%W) substrate. Film growth took place in a mixture of argon or argon 4% hydrogen and water vapor(H₂O) which was used as a controlled, low-level oxygen source. Two inch Mg and MgO targets were used for the metal source. The temperature, power, partial pressure of (H₂O), and deposition time were varied for each experimental run. X-ray diffraction techniques were used to determine the crystal structure and the quality of the deposited films. dc-sputtering with the Mg target failed to yield crystalline MgO films. This is mainly due to the high vapor pressure of Mg at the sputtering temperatures. However, rf-sputtering with the MgO target was successful. X-ray diffraction analysis indicated that the MgO and Ni-3%W layers had good in- and out-of-plane alignment and were cube-on-cube oriented. Atomic force microscopy measurements indicated an increase in surface roughness with the sputtering temperature. At temperatures below 400 ºC and H2O pressures above 1x10-6 Torr, (00l) oriented MgO films were successfully grown. More experiments should be performed to narrow down the parameters for the growth of MgO films with optimal orientation and intensity. Ultimately, the performance of MgO buffer layers should be tested with the electrical properties of HTS coatings.

Friction Stir Welding of Nickel-based Superalloy Inconel 738 and Friction Stir Weld Defects in Aluminum Alloy 5454. DEBORAH CARLSON (South Dakota School of Mines and Technology Rapid City, SD 57701) S.A. DAVID (Oak Ridge National Laboratory, Oak Ridge, TN, 37831)

Friction stir welding (FSW) is a relatively new solid-state joining technique in which a pin tool is inserted into a seam between two pieces of material and rotates at sufficient speed to plasticize the material. The pin tool travels along the length of the seam and welds the materials together. This research project involves two tasks involving FSW. The first task is to apply FSW techniques to the nickel-based superalloy Inconel 738 and to characterize the welds made. Traditionally, FSW has only been applied to low-temperature metals such as aluminum alloys and more recently to steels, but FSW of nickel-based superalloys has never been attempted before. A successful three inch weld was performed with a tungsten alloy pin tool at 12.7 mm/min and 800 rpm. The cross-section of the weld was characterized with optical and scanning electron microscopy. Results showed fine grains and also dissolution and re-precipitation of gamma prime particles inside the grains in the stir zone. Further research will be conducted on refining the welding conditions and analysis of the microstructure with transmission electron microscopy. The second task is to examine defects that occur during FSW of aluminum alloy Al 5454-H32 under certain welding conditions. Trials were performed at different translational and rotational speeds and the welds were characterized with optical microscopy. Torque, the forces in the X and Z directions, power, and energy were examined with the set welding parameters to find a correlation with the formation of weld defects. Temperature profiles across the length of the welds were calculated using heat flow analysis. In addition, hardness tests were conducted over the weld profile for several samples. Upon analysis of the data, it was determined that a correlation exists between defect formation and an increase in power, caused by an increase in torque and rotational velocity. This increase in power also leads to higher temperatures in the weld region. Monitoring the power consumed during FSW may provide an effective means of controlling defect formation.

Grain Size Measurements using Image Analysis Software. EDUARDO ARAMAYO (Illinois Institute of Technology Chicago, IL 60616) MICHAEL PERSHING (Oak Ridge National Laboratory, Oak Ridge, TN, 37831)

Grain size measurements of metallographic specimens produced from software, such as Clemex Vision, can be generated much more rapidly than measurements taken by hand, greatly simplifying the analysis process. The standard for grain size measurement is set in ASTM E112, which defines a scale for grain size. The standard also explains how to take these measurements, offering a few different methods involving grain intercepts per test line. Clemex Vision software analyzes images based on routines that must be written and adjusted by the user for each field or image. A well written routine simply and easily gives accurate grain size measurements that include much more information than what is available from hand measurements, such as exact grain counts, grain area, length distribution, and anisotropy. Furthermore, the grain size can be verified through multiple methods at once rather than taking multiple counts for the same field. This work presents the results of routines that determine grain size by three different analysis methods in addition to a manual count method. The methods show good agreement giving confidence in the accuracy of the analysis. Comparing the results of image analysis on Nb-1Zr after a one-hour, 1530ºC anneal process with an image of the same material after a two-hour, 1530ºC anneal process illustrates important differences in average grain size and grain size distribution. These image analysis routines greatly simplify the grain analysis process while providing more detailed information.

Internal Nitridation of Fe-Al Alloys in Air. MATTHEW DWYER (Lehigh University Bethlehem, PA 18015) BRUCE PINT (Oak Ridge National Laboratory, Oak Ridge, TN, 37831)

Ferritic Fe-Al (10-20 at% Al) compositions are being evaluated for coatings in high temperature oxidizing environments including the next generation of ultra-supercritical steam plants. Ferritic compositions have been found to have a lower thermal expansion coefficient than intermetallic FeAl or Fe3Al and, therefore, have fewer coating-substrate thermal expansion mismatch problems than intermetallic coatings. However, the lower Al content in ferritic alloys reduces the oxidation resistance of these materials because less Al is available to maintain a protective Al2O3 layer. Consequently, additions of 1-5% Cr (all compositions in at.%) to Fe-Al alloys have been investigated as a way to increase their oxidation resistance. Recently, it was discovered that cast materials with 14% and 19% Al containing 0-5% Cr additions underwent extensive internal oxidation and nitridation in air at 900 C. The purpose of this study was to quantify the extent of internal attack as a function of Al and Cr content after 5,000h at 900 C and as a function of temperature at 700 -1000 C. Cast ingots are used to study oxidation behavior to assist in coating development. Both light-optical microscopy and scanning electron microscopy were used in conjunction with imaging software to quantify the extent of attack. The internal attack for this set of materials was unusual because the depth of penetration generally increased for the Fe-19Al alloys compared to the Fe-14Al materials. Also, the volume of internal precipitates increased with Cr content for the Fe-19Al alloys. Specimens of Fe-19Al-2Cr showed no internal attack at 700 or 800 C, but extensive internal attack at 900 and 1000 C. Alloys containing 1.1Ti showed no internal attack after the same exposures. This beneficial effect may be due to the effect of Ti on the oxide morphology. In plan view and in cross-section, the oxide on the Ti-containing alloys was relatively flat compared to the buckled oxide on the alloys without Ti. The buckling of the surface oxide may cause cracks that allow nitrogen and oxygen to penetrate deep into the material. Because Fe-Al coatings are limited to the 500 -700 C range, the severe internal attack that was observed at 900 and 1000 C is not likely to affect coating performance.

Magnetic Field Effects on the Tempering Behavior of SAE 1045 Steel. CARLOS CORREA-LOCKHART (Florida A&M University Tallahassee, FL 32304) GERARD M. LUDTKA (Oak Ridge National Laboratory, Oak Ridge, TN, 37831)

The heat treatment or tempering of steel is a required process to develop the appropriate combination of properties of strength, ductility, and toughness for the intended use. Tempering is a thermal process whereby the quenched-in metastable martensite phase decomposes into a combination of ferrite with an extremely fine dispersion of iron carbide (Fe3C). This process of heat treatment requires a large amount of energy to take the steel to the high austenitization temperature and subsequently quench and temper the metal. Prior research has shown that magnetic processing significantly accelerates the transformation kinetics for the decomposition of the parent paramagnetic austenite phase to any of the ferromagnetic transformation products when temperatures are below the ferrite phase Tc (Curie temperature). This research endeavor is investigating the hypothesis that since iron carbide also has a Tc of 210 C in the tempering temperature regime that accelerated tempering kinetics can be achieved in a SAE 1045 steel by conducting this process below the Fe3C Tc under the influence of magnetic field. In this study tempering experiments were preformed as a function of tempering temperature above and below the Tc and various magnetic field strengths. If this hypothesis is substantiated, the steel will temper at a lower temperature faster, which in turn, conserves the amount of energy used to process the steel. The application of the magnetic force to the heat treatment of steels will not only conserve energy, but will make heat treatment of steel more cost effective. To determine the direct effects of the magnetic fields on the steel specimens, Scanning Electron Microscopy (SEM), and Orientation Imaging Microscopy (OIM) analyses were used for quantitative microstructural evaluation along with microhardness measurements to compare tempered sample mechanical properties. The results and conclusions of this investigation will be presented in addition to providing recommendations for future research to optimize and implement this concept for specific industrial applications.

Optimization of the Growth of High Temperature YBCO Superconductor Films Using Metal Organic Deposition Technique and RABiTs Substrates. NAMITA BISARIA (Princeton University Princeton, NJ 08544) MARIAPPAN PARANS PARANTHAMAN (Oak Ridge National Laboratory, Oak Ridge, TN, 37831)

YBa₂Cu₃O_7-x (YBCO) coated conductor research using the solution deposition method has made progress in recent years towards the development of low cost superconductor wires. The potential uses of superconducting wires for electric power applications include underground transmission cables, oil-free transformers, superconducting magnetic-energy storage units, fault-current limiters, high-efficiency motors, and compact generators. A modified and low cost solution process has been developed to grow the high performance YBCO superconductor films. This solution process uses a variety of different organic precursors that decompose to form YBCO, and consequently there is flexibility in what compounds can be used as a precursor. This experiment uses the more stable copper propionate instead of copper trifluoroacetate as was found in previous and documented research. In the process of growing YBCO superconducting films, there are four general steps that have been followed and tailored to the new precursor and require optimization in this research. They are: the solution preparation from metal organic salts, the decomposition phase, the conversion process, and the final characterization through x-ray diffraction analysis and four probe current transport measurement of the superconductor films. The growth of these films was mediated by a stack of buffer layers (CeO₂, YSZ and Y₂O₃) on a textured Ni-W substrate. Preliminary results show that the YBCO films prepared by this process yielded a competitive critical current of 140 A at 77 K. The details of the synthesis and characterization of superconductor films are reported in detail.

Parameter Variations for Low Temperature Synthesis of Carbon Nanofibers. MATTHEW MUSGRAVE (James Madison University Harrisonburg, VA 22807) MICHAEL L. SIMPSON (Oak Ridge National Laboratory, Oak Ridge, TN, 37831)

Carbon nanofibers are cylindrical structures of stacked modified graphene sheets with a wide range of diameters and lengths. The synthesis of vertically aligned carbon nanofibers (VACNFs) by plasma enhanced chemical vapor deposition is conventionally done by heating a silicon substrate with nickel catalysts patterned on it and then creating an ammonia and acetylene plasma above it. By adding oxygen to the gas mixture the intent is to provide catalytic oxidation of the acetylene that should heat the catalyst particles allowing the substrate heater to operate at lower temperatures. By growing carbon nanofibers at a lower temperature a larger range of substrates can be used. Currently the VACNFs are grown at temperatures around 700 C. The synthesis of the vertically aligned carbon nanofibers is optimized at decreasing substrate temperatures by changing the ratio of ammonia, acetylene, and oxygen in the plasma and the power of the plasma. If there is too much ammonia, carbon nanofibers are damaged and lose the catalyst particles, and nanofibers will be covered in silicon oxide or completely etched away. If there is too much acetylene, the catalyst particles will be covered by a carbon film and VACNF synthesis will be impossible. A strategy was developed in that small changes to one parameter are made and the other parameters are adjusted after the quality of the material is assessed by scanning electron microscopy (SEM) and x-ray energy dispersive spectroscopy (EDS). SEM images of the carbon nanofibers are captured for determination of morphology, shape, height, and density measurements, and EDS is used to determine the concentration of carbon, silicon, and oxygen in the fibers. The images of nanofibers grown with oxygen are compared with images of a control group of nanofibers synthesized without oxygen. The results collected so far are preliminary, but it can be concluded that oxygen is not detrimental to the synthesis of VACNFs and can play a similar role as ammonia in etching amorphous carbon. Additionally small changes in the gas flow value of oxygen yield large differences in the appearance of the nanofibers compared to changes in the gas flow value of ammonia.

Production of Corrugated Micro- and Nanocrystalline Diamond Stripper Foils for the Spallation Neutron Source Using Chemical Vapor Deposition. DANIEL SHOEMAKER (University of Illinois at Urbana Champaign Urbana-Champaign, IL 61801) R. W. SHAW (Oak Ridge National Laboratory, Oak Ridge, TN, 37831)

Microwave plasma chemical vapor deposition (MPCVD) has been used to produce single-edge supported, micro- and nanocrystalline diamond films for use as stripper foils in the Spallation Neutron Source (SNS). Beam simulations have predicted that diamond foils will provide a longer lifetime in the SNS H^- beam (38 mA at 1 GeV) than conventional carbon foils, while the geometry of the SNS accumulator ring requires foils that are supported by only one edge. The freestanding diamond must have dimensions of at least 12 mm x 20 mm and an areal density of ~350 µg/cm², which corresponds to a thickness of ~1.0 µm. Films were deposited on silicon substrates, which were pretreated to enhance diamond nucleation in the MPCVD reactor by scratching in an ultrasonic bath using a slurry of diamond particles in methanol. The highest nucleation density was obtained by using a mixed slurry containing 0.3 g of 30-40 µm and 0.3 g of <0.25 µm diameter diamond particles in 20 mL of methanol. Microcrystalline diamond films were grown using MPCVD operating at 1300 W power in a 2% CH₄, 98% H₂ atmosphere at 50 torr. Films for use in the SNS typically were deposited in 110 min, while use of the mixed scratching slurry enabled growth of fully continuous films in less than 25 min. Nanocrystalline films were deposited at 900-1000 W in a 90% Ar atmosphere with 1-2% CH₄ and 8-9% H₂ at 130 torr. Due to cooling after deposition, the thermal expansion mismatch between diamond and silicon causes considerable stress in the film, which leads to scrolling once the substrate has been etched away. To prevent curling, photolithography was used to pattern 7 µm-deep U-shaped channels in the substrate, which ran along the unsupported edges of the foil and covered 20%-40% of its area. The corrugated foils remained flat after their backing was removed. While microcrystalline films with high nucleation density were sufficiently robust for transport and beam testing, nanocrystalline films have shown superior mechanical strength, fewer pinholes, and decreased surface roughness. These smoother films are expected to exhibit more reliable stripping efficiencies. Future work on this project will focus on making improvements to the processing techniques based on the results of nanocrystalline film beam testing in the Los Alamos Proton Storage Ring and the SNS.

Refurbishment of High Temperature Creep Frames for Generation IV Nuclear Reactor Material Testing. NATHAN OTTINGER (University of Tennessee Knoxville, TN 37996) TIMOTHY MCGREEVY (Oak Ridge National Laboratory, Oak Ridge, TN, 37831)

Generation IV nuclear fission reactors promise to be more efficient and produce less nuclear waste than reactors already in operation. Six reactor designs have been chosen as part of Gen IV, each with sustained operation temperatures ranging from 510 C to 950 C. One such reactor, the Very High Temperature Reactor (VHTR), will produce electricity as well as hydrogen for use in fuel cells. High temperature creep tests are necessary to obtain creep properties of materials appropriate for these reactors. The Applied Test Systems (ATS) creep frames are structurally in excellent condition. However, the Instron self-aligning hydraulic grips used to hold and equally distribute force throughout the specimen's cross section were either overheating to the point of meltdown or had lost hydraulic pressure. These grips were systematically taken apart and thoroughly inspected. In most cases, the overheating problem was found to be blocked coolant passages. Those without hydraulic pressure were completely rebuilt. Seals were replaced and the grips were refilled with hydraulic fluid. The creep frames also require some new load cells since the Gen IV tests will require significantly less load than the current load cells. CAD drawings were made for a hydraulic grip to load cell adapter plate that will accommodate the new load cells. Capacitance extensometers are currently needed for seven of the machines. Portions of previously used extensometers exist, and CAD drawings will be made of the parts needed to turn the portions into usable extensometers. Financial limitations will make the completion of this refurbishment highly unlikely. However, by the projects conclusion, the hydraulic grips will be ready for long term high temperature tests, the load cells will be ready to mount, and several more machines may have operable extensometers.

Retained Austenite Decomposition in SAE 52100 Steel Using Magnetic Fields. BRIE WITHERSPOON (Florida A&M University Tallahassee, FL 32304) GERARD M. LUDTKA (Oak Ridge National Laboratory, Oak Ridge, TN, 37831)

When hypereutectoid steel is raised to a high temperature such as 800 - 900 C and then rapidly cooled, the material undergoes phase transformations such as austenite to martensite, carbide, bainite, or pearlite. In some instances for high quench rates the austenite may not completely transform to martensite and undesirable, residual austenite is retained in the final microstructure. Thermodynamic arguments predict that ambient temperature magnetic field treatment will reduce the amount of retained austenite in hypereutectoid as-quenched steel samples. The goal of this research is to determine the influence of various magnetic field processing parameters on the final amount of retained austenite in a SAE 52100 steel. Demonstration and implementation of this novel concept would ultimately reduce the amount of energy used in the processing of hypereutectoid steels for industrial use. Since in commercial practice retained austenite becomes stabilized against conversion to martensite after ~2 hours following a quench, one series of tests were done varying the amount of time the samples were held after being quenched from 850 C to see if magnetic fields can overcome this detrimental issue. Other variables investigated were the amount of time a magnetic field was applied to the samples, and its field strength. X-Ray diffraction, optical microscopy, Scanning Electron Microscopy (SEM), and Orientation Imaging Microscopy (OIM) analyses were run on eleven samples for microstructural evaluation, and to determine the remnant amount of retained austenite (for conversion efficiency). X-ray data provide quantitative information regarding the amount of phase constituents in the microstructure, specifically martensite and austenite. The optical microscopy and SEM show qualitative information about the microstructure such as grain size and morphology. The OIM analysis shows textured or preferred grain orientation, phase identification and quantitative metallography, such as grain size. This presentation will summarize the results of this investigation and discuss their ramifications for potential industrial applications.

Unforeseen heating during the ultrasonic welding of Aluminum alloys. LING XU (Georgia Institute of Technology Atlanta, GA 30332) ZILI FENG (Oak Ridge National Laboratory, Oak Ridge, TN, 37831)

Ultrasonic welding is a relatively new process to join two metal plates in a lap weld. For the ultrasonic welding process, the plates rest on an anvil while the sonotrode pushes down on them, applying heavy pressure. The sonotrode conveys the ultrasonic frequencies which cause heat, friction, and structural breakdown in the welded material. It has been discovered that stress patterns occur in areas far away from the weld area that are induced by unforeseen heating of such area. This creates obvious concerns for the feasibility of ultrasonic welding in the manufacturing environment. It is the purpose of this experiment to test that when a second weld is made on two plates that have already been joined, if the extraneous heating created by the second weld will have an effect on the initial joint. To test the effect of extraneous stress, two welds were made on each set of plates to test the impact of welds on each other. The time set of the weld was the initial variable in order to find the time which allows for maximum heating in the expected areas. Single welds were made under different time sets to see at what time the two plates would be fully bonded. The distance between the two welds was the primary variable to find if there is an optimal distance where the heating occurs. Spacing between the two welds ranged from 1 inch to 3 inches, in quarter inch increments. Further testing determined the effect a second weld had on two plates that are already joined by the first weld. The amount of heating was determined by the intensity values of the increased stress areas as recorded by an infrared video camera. The experiment determined that the second weld indeed caused heating on the first weld and sometimes even broke the original bond. The ultrasonic vibrations created by the second weld, affected the first weld in a high degree, creating enough stress within the weld to create heating and possibly failure.