Student Abstracts: Materials Sciences at ORNL

Calibration and Testing of an Infrared Thermometer for Sub-Scale Brake Testing. DELIA DUMITRESCU (University of Michigan, Ann Arbor, MI 48152) PETER J. BLAU (Oak Ridge National Laboratory, Oak Ridge, TN 37831) .
This experiment investigated the optimal setup of an Infrared Thermometer for measurements at the interface of the brake pad and the disc in sub-scale brake testing. It determined the required input of the emissivities of two different materials, the angle placement of the sensor, and the reflection of the surrounding environment into the field of view. Measurements were taken using various setups and temperatures for the cast-iron disc and brake pad. The sensor readings were compared to thermocouple readings and the emissivity of materials was found to increase with increasing temperature for the cast-iron disc, and to decrease with increasing temperature for the brake pad. It is recommended that an emissivity value of 0.27 and 0.65 be used for the cast-iron and break-pad, respectively, as these correspond to the values for the predicted temperature ranges to be reached during the brake testing. The variations in temperature due to sensor angle should be minimized by aiming the camera at a zero angle to the material or, in cases when this is not possible, by using a first surface mirror at a 45 degree angle to reflect the heat radiation. That setup is optimal because it minimizes the reflectivity of the surroundings.

Evaluation of Nucleation Enhancement Methods for the Growth of Nanocrystalline Diamond Films. ADAM HOPKINS (Florida State University, Tallahassee, FL 32306) ROBERT SHAW (Oak Ridge National Laboratory, Oak Ridge, TN 37831) .
The growth of diamond films using a hot filament deposition reactor proceeds by means of nucleation, which occurs preferentially at damage sites on the substrate. It is anticipated that a greater number of nucleation sites will yield a smaller grain size in the film, with the target being the growth of a nanocrystalline diamond film (NCDF). Previous work used silicon substrates, which were abraded with diamond particles by hand to enhance the nucleation density. Here, other methods of enhancing the nucleation density were studied in addition to hand abrasion. Substrate abrasion in an ultrasonic bath, chemical etching of the substrate and chemically etching the substrate after abrasion in an ultrasonic bath have been examined. The substrates and films have been examined using scanning electron microscopy (SEM), atomic force microscopy (AFM), stylus profilometry and micro-Raman spectroscopy. The samples that have been examined showed large amounts of debris on the surfaces, most of which was invisible to the SEM; the elimination of debris will be critical to the growth of high quality films. The films grown in this work were not NCDF's as the nucleation densities were too low. It is hoped that future investigations will lead to high enough nucleation densities for the production of a NCDF.

Superconductivity: Long Length Critical Current Measuring System. FRANK PARTICA (Juniata College, Huntingdon, PA 16652) PATRICK M. MARTIN (Oak Ridge National Laboratory, Oak Ridge, TN 37831) .
The ability to measure the critical current, Ic, of superconducting tapes is important in the design of long length superconducting wires. To this end, a long length Ic system was created to characterize tapes over eight meters long. This system has the ability to pinpoint nonhomogeneous current sections in the wires within any 2-cm section along its length. Two unique probe attachments have been designed for this system of measurement. One is used to analyze the Ic every 32 cm along the length of a tape for a six-meter period. The other measures Ic every 16 cm over a 3-meter period. This system has been tested using a commercially available nonhomogeneous superconducting BiSCCO (Bi-Sr-Ca-Cu-O) wire 2.6 meters long. It successfully ran tests measuring the critical current every 32.06 cm and 16.03 cm over the whole length of the tape, and found the end-to-end Ic of the tape. The design of the system and attachments are easily expandable for characterization of both longer and wider superconducting wires.

Characterization of Self-Organized Criticality During Fracture of Carbon Fiber Reinforced Composite Materials. THOMAS ROGERS (University of Tennessee, Knoxville, Tn 37919) SRDAN SIMUNOVIC (Oak Ridge National Laboratory, Oak Ridge, TN 37831) .
Self-organized critical (SOC) behavior is exhibited by systems ranging from earthquakes to fluctuations in the stock market and is characterized by critical events occurring on all time and length scales after some critical state has been established. Classifying a phenomenon as SOC gives scientists a better foundation for describing and understanding many of the underlying principles of the process. The field of Self-Organized Criticality theory has led to insights in many areas of research. Based on the original theories of Bak, Tang, and Wiesenfeld, and expanded by numerous other studies, SOC models have given researchers valuable tools for exploring the behavior of complex systems. The work presented here explores the SOC behavior of the fracture properties of carbon fiber reinforced composite materials. Materials with randomly oriented fibers and materials with braided carbon fibers were subjected to laboratory tests (crushing) and the results were analyzed for possible SOC behavior patterns. In both types of materials evidence has been found to suggest that the progressive fracture follow SOC patterns. Establishing an SOC pattern of behavior in material fracture is an important step toward our goal of developing predictive stochastic finite element models.

The Effect of Cr Content and H2O Vapor on High Temperature Oxidation of Fe-Cr Model Alloys. JESSICA SCHENNING (University of South Florida, Tampa, Fl 33620) BRUCA PINT (Oak Ridge National Laboratory, Oak Ridge, TN 37831) .
The oxidation behavior of most stainless steels is a function of their chromium (Cr) content. In order to improve gas turbine engine efficiency these alloys are being used at higher operating temperatures and in more aggressive oxidizing environments. The oxidation performance of model Fe-Cr alloys was examined to determine the effect of water vapor (found in exhaust gas) on the minimum Cr content necessary to form a protective, Cr-rich external oxide scale. Samples of Fe with 10%-20% by wt. of Cr were exposed to temperatures from 700*C to 900*C and were oxidized in both dry air and air + 10% H2O. The experiments were conducted in 100h cycles, up to 500h, as well as in one hour cycles, up to 100h. It was found that H2O greatly accelerates oxidation attack. Higher Cr levels were required to form the protective surface in air + H2O than in dry air.

Growth of Epitaxial Gd2O3 Buffer Layers On Nickel Substrates Using a New Metal-Organic Solution Deposition Route for Superconducting YBCO Coated Conductors. MICHAEL SHANK (Indiana University of Pennsylvania, Indiana, PA 15701) M. PARANS PARANTHAMAN (Oak Ridge National Laboratory, Oak Ridge, TN 37831) .
Textured buffer layers are important to fabricate a high current Yttrium Barium Copper Oxide (YBCO) superconducting tape. The RABiTS (Rolling Assisted Biaxially Textured Substrates) process developed at Oak Ridge was used to make textured nickel substrates. The processing of YBCO superconductors is usually carried out under oxidizing atmospheres. The nickel substrate oxidizes in this process and forms nickel oxide with a different crystal structure. Therefore, the texture of the YBCO is destroyed and the superconductor carries very low currents. By adding a suitable buffer layer between the nickel substrate and the YBCO, this problem is solved. A metal-organic sol-gel deposition route was developed at Oak Ridge to fabricate thin films on nickel substrate. The problem with the sol-gel solution is that it becomes unstable when it is exposed to humid air. The method developed here is also a metal-organic route, but the solution is stable in air. The precursor solution is very easily made in seconds by mixing chemicals in a bottle and shaking. The precursors solutions are then spin-coated onto textured nickel substrates and heat-treated in a controlled atmosphere to produce Gd2O3 films with the right orientation. It has been called the "shake and bake" method. The results of the initial testing show hope that this process will work as well as the sol-gel route. The variables used were furnace temperature, residence time in furnace, and the concentration of the solution. The films grown are textured nicely and they show high degree of crystalline alignment with the nickel. The films made were Gd2O3, but this method will be used to process other buffer layers.

Friction Stir Welding of Aluminum Metal Matrix Composites. DANIEL STORJOHANN (South Dakota School of Mines, Rapid City, SD 57701) STAN DAVID (Oak Ridge National Laboratory, Oak Ridge, TN 37831) .
Friction Stir Welding is a new non-fusion welding technique that has gained a lot of attention recently. The focus of this research was to compare the microstructure evolution in metal-matrix composites (Al-MMC's) during the fusion welding processes with that of the friction stir welding process. The fusion welding processes include gas tungsten arc (GTA), electron beam (EB) and laser welding. Aluminum alloy 6061 reinforced with Al2O3 and aluminum alloy 2124 reinforced SiC were used in this investigation. The welds were characterized with optical microscopy and hardness measurements. Phase stability in these alloys were also calculated using thermodynamic software. Fusion welding lead to the decomposition of the reinforcing phases. However in the friction stir welds the reinforcing phases were retained. Thermodynamic calculations support the phase evolution in fusion welds.

Effect of Magnetic Impurities on Superconductive Properties of Bulk MgB2. THOMAS THERSLEFF (University of Wisconsin - Madison, Madison, WI 53706) M. PARANS PARANTHAMAN (Oak Ridge National Laboratory, Oak Ridge, TN 37831) .
The discovery of MgB2 as a superconducting material by Ahimitsu et al. in January 2001 has stimulated the interest of the research community in hopes of finding a cheap superconductor with strong superconductive properties. MgB2 becomes superconducting at a transition temperature (referred to as Tc) of 39K, which is relatively high for a non-oxide superconductor. The critical current density (Jc) and the critical field (Hc) for MgB2, however, are relatively low when compared to other high temperature superconductors. In this paper, the effect of magnetic impurities on these superconductive properties is analyzed in bulk MgB2 samples. The magnetic impurities used are Gadolinium, Iron, Nickel, and Manganese. Samples were prepared by mixing MgB2 powder with the dopant of choice, placed in a tantalum tube, and reacted for 15 minutes in a flowing Ar4%H2 furnace at 880oC. X-Ray diffraction (XRD) data indicated that the Nickel and Manganese are soluble in MgB2 up to 5%. As the Mn content increases, the lattice parameters a decreased and c increased up to 5%. Detailed measurements were done on Manganese doped samples. Data collected on a DC SQUID magnetometer indicate that the Tc of Mn-doped MgB2 remains constant around 38.3 K. Detailed magnetic hysteresis data are reported. These results will help the scientific community to better understand the mechanics behind MgB2 and how to use it in the future.

X-Ray Diffraction on Paper mill tubes. KARINA ULLOA (University of Texas at Brownsville, Brownsville, TX 78520) JAMES KEISER (Oak Ridge National Laboratory, Oak Ridge, TN 37831) .
The work presented in this paper is a subset of a much larger project. It is a collaboration between ORNL, IPST, PAPRICAN, and Pulp and Paper industry. Industry investigates cracking in composite tubes used in Kraft recovery boilers. The focus of the larger project is to understand why cracking occurs in stainless steel clad carbon steel tubes. The focus of this paper is to investigate the residual stresses in the stainless steel clad layer and how commonly used tube cleaning processes affect residual stresses. Specifically x-ray diffraction will be used to measure residual stresses in stainless steel cladding for each of the following conditions: as removed from the boiler; after being cleaned with a wire wheel; and after being cleaned using a flapper wheel. This data will be analyzed to help determine why cracking occurs and how to prevent cracking in future tubes.

Precision Electrolytic Nanofabrication. KENT WILCHER (University of Tennessee, Knoxville, TN 37919) JAMES W. LEE (Oak Ridge National Laboratory, Oak Ridge, TN 37831) .
The ability to manipulate individual molecules is of fundamental importance in the development of the next generation of nanoscale devices. One of the major difficulties encountered in the fabrication of such devices is the creation of the interface between macroscopic structures and individual molecules. This project involved the fabrication of nanoelectrodes by precise electrolytic deposition of metal onto a substrate. The substrate consisted of two gold electrodes separated by a distance of approximately one micron, fabricated using electron beam lithography. Metal was then deposited on the tip of one of the electrodes by applying a potential across the gap using a programmable pulse current source while under an electrolytic solution containing metal compounds. The focused electric field generated across the gap between the two electrodes theoretically allows for deposition of metal only at the tip of the negative electrode. The amount and location of the deposition was monitored in situ using an Atomic Force Microscope (AFM). The goal of this project was to demonstrate the ability to create a nanometer-scale gap suitable for molecular applications.

Development of Ductile Cr Alloys for Use in Molten Salt Environments . JESUS ZAMORANO (University of Texas at Brownsville, Brownsville, TX 78520) JAMES KEISER (Oak Ridge National Laboratory, Oak Ridge, TN 37831) .
Chromium offers a highly desirable combination of high melting point, good high-temperature mechanical properties, and excellent high-temperature corrosion resistance in many environments. However, inadequate ductility at room-temperature has severely limited its use as a structural alloy. Work by Scruggs in the 1960's [1] indicated that the room-temperature ductility of Cr could be significantly improved by the addition of MgO. We have succeeded in replicating this work and are developing this class of alloys for possible use as structural alloys or overlay coatings in the aggressive molten salt environments encountered in the paper and pulp industry. This poster will present room-temperature tensile characterization data for the developmental alloy Cr-6MgO-0.5Ti-0.3La2O3 (weight percent) consolidated from blended or blended and ball milled Cr, MgO, Ti, and La2O3 powders. Preliminary results of the corrosion behavior of this alloy in molten smelt (alkali salt byproduct of the Kraft pulping process; mat erial collected at a commercial papermill) at 975C will be presented. [1] D.M. Scruggs, American Rocket Society Journal, 31, 11, pp. 1527-1533 (1961).