Room: 315B
Session Chairperson: TBA
1:30 pm
OXIDE AND NITRIDE SUPERLATTICE COATINGS: William D. Sproul, BIRL, Northwestern University, 1801 Maple Avenue, Evanston, IL 60201
Over the past 10 years, three major advances in reactive sputtering technology have made it possible to deposit both conductive and non-conductive fully-dense films at high rates. These three advances are unbalanced magnetron (UBM) sputtering, partial pressure control of the reactive gas, and pulsed DC power. Multicathode UBM sputtering systems provide a dense secondary plasma that produces well-adhered, fully dense films. With both pulsed-dc power and partial pressure control, films such as aluminum oxide can now be deposited reactively at rates up to 78% of the pure metal rate. The reactive UBM sputtering process is used to deposit polycrystalline nitride superlattice films such as TiN/NbN or TiN/VN with hardnesses exceeding 50 GPa, more than double the hardness of either component in the film. The nitride superlattice work is being extended to oxide films. Clear, amorphous, nano-layered Al2O3/ZrO2 films have been deposited at high rates with a hardness of 10 GPa. Work is underway to deposit these films in a crystalline form, which should enhance their hardness.
2:05 pm
CONTROL OF INTERFACE STRENGTH IN NIOBIUM-ALUMINUM OXIDE MULTILAYERS BY ION BEAM ASSISTED DEPOSITION: G S. Was, H. Ji, J.W. Jones, Cooley Bldg., University of Michigan, Ann Arbor, MI 48109; N. Moody, Sandia National Laboratory, Div. 8712, MS 9403, Livermore, CA 94551
The toughness of a niobium-aluminum oxide multilayer depends on the interface strength, which can be controlled by both the orientation relationship of the constituents and the composition at the interface. As a first approximation to multilayers, niobium films were deposited onto {0001} sapphire substrates by ion beam assisted deposition (IBAD) under various conditions. In addition to the {110} fiber texture, strong in-plane texture was introduced by simultaneous ion bombardment. Stronger in-plane texture was developed with higher ion energy and ion to atom arrival rate ratio (R ratio). Different orientation relationships at the niobium-sapphire interface were achieved by varying the orientation of the sapphire substrates with respect to the ion beam incident direction. The hardness and modulus of the niobium layer were also modified by the ion bombardment. A dopant (Ag) was introduced at the interface at levels from a fraction of a monolayer to one monolayer during niobium layer deposition.
2:40 pm
CONTROLLING THE EVOLUTION OF TEXTURE IN SPUTTER DEPOSITED Mo FILMS: S.M. Yalisov, J.C. Bilello, University of Michigan, Department of Materials Science and Engineering, Ann Arbor MI 48119
Evolution of crystallographic ordering in sputter deposited polycrystalline refractory metal films has been observed in several laboratories. While the ordering in the growth direction, out-of-plane texture, is well known, the ordering in the plain of growth, in-plane texture, has only been reported by the ion enhanced growth community. The work presented here, will describe the conditions required for this behavior in the presence of energetic ions. Mo films were sputter deposited on amorphous substrates and grown to a large variety of thickness. The homologous temperature does not exceed 0.2 in any of the experiments performed. These films were characterized by a large battery of synchrotron x-ray, electron microscopy, and surface analysis. The data have led to an atomistic model to explain and predict the in-plane texturing based on shadowing and anisotropic growth rates which force a competitive grain growth mechanism during the growth. Detailed comparison to experiment will demonstrate the role that limited diffusion and mass transport play in the final microstructure of the film. Examples of how this model can be exploited to design a particular microstructure will be presented.
3:15 pm
CERAMIC-METALLIC COATINGS BY ELECTRON BEAM PHYSICAL VAPOR DEPOSITION PROCESS: Douglas Wolfe, M. Movchan, Jogender Singh, Applied Research Laboratory, Pennsylvania State University, University Park, PA 16804
Electron beam physical-vapor deposition (EB-PVD) process is considered to be a cost-effective and robust coating technology that has overcome some of the difficulties or problems associated with the metals spray, CVD and PVD processes. The EB-PVD process offers many desirable characteristics such as relatively high deposition rates (up to 100-500 mm/minute with an evaporation rate ~10-15 Kg/hour), dense coatings, precise composition control, columnar and poly-crystalline microstructure, low contamination, and high thermal efficiency. Various metallic and ceramic coatings (oxides, carbides, nitrides) have been deposited at relatively low temperatures. EB-PVD has the capability of producing multilayered nanolaminated metallic/ceramic coatings on large components by changing the processing conditions such as ingot composition, part manipulation, and electron beam energy. Attachment of an ion beam source to the EB-PVD process offers additional benefits such as dense coatings with improved adhesion.
3:50 pm BREAK
4:05 pm
COMMERCIAL APPLICATIONS OF PLASMA SOURCE ION IMPLANTATION: J.T. Scheuer, K.C. Walter, Los Alamos National Laboratory, Los Alamos, NM; W.G. Horne, Empire Hard Chrome, Chicago, IL; R.A. Adler, North Star Research Corporation, Albuquerque, NM 87109
Commercial plasma source ion implantation (PSII) equipment built by North Star Research Corporation has recently been installed at Empire Hard Chrome, Chicago, IL. Los Alamos National Laboratory has assisted in this commercialization effort via two Cooperative Research and Development Agreements to develop the plasma source for the equipment and to identify low-risk commercial PSII applications. The PSII system consists of a 1m x 1m cylindrical vacuum chamber with a pulsed, inductively coupled rf plasma source. The pulse modulator is capable of delivering pulses with peak currents of 100 kV and peak currents of 300 A at maximum repetition rate of 400Hz. The pulse modulator uses a thyratron to switch a pulse forming network which is tailored to match the dynamic PSII load. This presentation will focus on early commercial applications to production tooling and manufactured components and characterization of implanted coupons.
4:40 pm
SPUTTERED CHROME NITRIDE AS AN ALTERNATIVE TO ELECTROPLATED CHROME: Michael Graham, Keith Legg, Paul Rudnik, Peter Chang, BIRL, Northwestern University, Evanston IL 60201
BIRL has been involved in hardcoating development for engineering applications for several years. A major effort over the past four years has focused on the replacement of electroplated chrome in applications where the steel substrates have moderate hardnesses (Rc38-42) and therefore only modest support for hard PVD coatings. Much of the development work has been supported by the government through DARPA as part of an environmental thrust to eliminate pollution sources and health hazards from their OEM's as well as their repair facilities. BIRL has developed the use of duplex processing (plasma nitriding + sputter-coating) and thick PVD coating (15-20um) with CrN and demonstrated wear performance characteristics superior to commercial chrome plating. This paper reviews some of the process developments involved in these programs and the wear test results. Production cost estimates have also been conducted for certain components, and it has been demonstrated that PVD coating is competitive with electroplating when the total manufacturing process is taken into account.
5:00 pm
CHARACTERISTIC OF TiN FILM DEPOSITED ON STELLITE USING REACTIVE MAGNETRON SPUTTER ION PLATING: Whungwhoe Kim, Joungsoo Kim, Surface Treatment Group, KAERI, Taejon, Korea, Mingu Lee, Heesoo Kang, Wonjong Lee, Dept. of Materials Science, KAIST Taejon, Korea
TiN films were deposited onto stellite 6B alloy (Co base) by the reactive magnetron sputter ion plating. As the substrate bias increases, TiN film changes from columnar structure to dense structure due to densification and resputtering by ion bombardment. Oxygen, the major impurity, is decreased greatly when the substrate bias is applied. The preferred orientation of the TiN films changes from (200) to (111) with decreasing N2/Ar ratio. The change of the preferred orientation is discussed in terms of surface energy and strain energy which are related with the impurity contents and the ion bombardment damage. The hardness of the TiN film increases with increasing compressive stress generated in the film by virtue of ion bombardment.
Room: 340B
Session Chairperson: M.E. Fine, Northwestern University, Evanston, IL 60208
2:00 pm INVITED
TRANSITION METAL CARBIDES AND NITRIDES FOR ELECTRONIC DEVICES: Wendell S. Williams, Department of Physics, University of Illinois, Urbana, IL 61801
The need for thermally stable, diffusion-resistant but electronically conducting materials for interconnects in ultra large scale integrated circuits has led to the successful application of transition metal carbides and nitrides, particularly TiN. Another application is the use of superconducting NbN to make Josephson junctions NbN/Si/Nb and Nb/MgO/NbN. And high-temperature resistors with nearly zero temperature coefficients have been made from TaN. This family of materials, sometimes called "metallic ceramics," can be deposited as thin films by several processes, including reactive sputtering, metal-organic chemical vapor deposition and plasma-assisted chemical vapor deposition. An interesting but potentially troublesome characteristic of these NaCl-structured materials is their wide range of deviation from stoichiometry, involving many percent random atomic vacancies, scattering centers for conduction electrons. Hence film preparation requires that the non-metal/metal ratio be close to unity. It is not widely recognized that these defect-ridden crystal structures are non-equilibrium phases: when cooled slowly from high temperatures, some develop ordered phases with lower resistivities.
2:30 pm INVITED
ELECTROMIGRATION IN SUBMICRON Al-0.5%Cu INTERCONNECTS FOR SILICON ULSI: J.A. Prybyla, S.P. Riege, A.W. Hunt, Bell Laboratories, Lucent Technologies, Murray Hill, NJ 07974
Systematic studies of the influence of local microstructure on electromigration (EM) dynamics in submicron Al(0.5 wt % Cu) interconnects were performed using in-situ transmission electron microscopy (TEM) techniques. This approach has allowed us to observe in real-time voids forming, growing, migrating, pinning, failing a runner, and healing, all with respect to the detailed local microstructure of the runners. Here we will report and describe how grain boundaries dramatically influence almost all aspects of EM-induced void and failure dynamics in submicron runners. We also find a striking change in EM-mechanism as a function of temperature in the range 200-300°C. Studies as a function of linewidth and passivation state were also performed. Our findings have important implications for both electromigration modeling and conventional reliability testing.
3:00 pm INVITED
DOPANT ACTIVATION OF HEAVILY-DOPED Si BY HIGH CURRENT DENSITY: J.S. Huang K. N. Tu, Department of Materials Science & Engineering, UCLA, Los Angeles, CA 90095-1595
Novel dopant activation in the heavily boron-doped p+-Si was created by applying an electrical current of high current density. The heavily boron-doped p+-Si was obtained by ion implantation and annealed at 900°C for 30 min to achieve a partial boron activation. For additional activation, we gradually applied current until a current density of 2.5X10E7 A/cm2 was reached. The resistance of the p+-Si responded by a gradual increase, then it decreased with a precipitous drop. The resistance was reduced by a factor of 5 to 18. Mechanisms of the novel dopant activation will be proposed. Dopant activation in the heavily arsenic-doped n+-Si will also be discussed.
3:30 pm BREAK
3:50 pm INVITED
DEVELOPMENT OF LOW THERMAL-EXPANSION, HIGH-CONDUCTIVITY ALLOYS BASED ON THE Cu-Fe-Ni TERNARY SYSTEM: R.D. Cottle, R.K. Jain, C.C. Hays, Z. Eliezer, L. Rabenberg, Center for Materials Science and Engineering, The University of Texas at Austin, Austin, TX 78712; M.E. Fine, Northwestern University, Evanston, IL 60208
The FCC phase in Cu-Fe-Ni ternary system contains a miscibility gap within which tie-lines extend from nearly pure Cu toward the Invar composition, Fe - 36% Ni. This suggests that it should be possible to prepare alloys containing isotropic distributions of Invar within high conductivity, Cu-rich, matrices, and that the Invar fraction can be controlled by selecting starting compositions at various points along the tie line. The resulting combinations of low thermal expansion with high electrical and thermal conductivity will be of interest in the electronic circuit packaging industry. Technical difficulties in developing such alloys arise from incomplete solid solubility at high temperatures at the Cu-rich end of the series and from the slow approach to complete chemical phase separation at low temperatures. Quaternary element additions and mechanical deformation processes are being explored as approaches to creating more nearly homogeneous starting alloys. Microstructural developments and electrical and thermal properties will be reported and discussed.
4:20 pm
PROCESS OPTIMIZATION OF HIGH-STRENGTH, HIGH-CONDUCTIVITY Cu-Cr IN-SITU COMPOSITE: H. G. Suzuki, K. Adachi, S. Tsubokawa, T. Takeuchi, National Research Institute for Metals, 1-2-1 Sengen, Tsukuba 305, Japan
High-strength, high-conductivity Cu-Cr in-situ composites were developed through the optimization of various process variables. Ingots were obtained by vacuum induction melting. Dendritic Cr was in-situ precipitated during solidification. After hot forging and solution treatment at 1000C, repeated cold working was performed to get fine lamellar spacing of single crystalline Cr second phase. The analysis of microstructure by TEM showed dynamic recrystallization of Cu matrix and fine distribution of Cr precipitates. These structures give the strength level of 900 MPa and relative conductivity, IACS, of 78%. The mechanism of high strength and high conductivity will be discussed.
4:40 pm
THE CHARACTERISTICS OF ELECTRICAL CONDUCTIVITY AND PRECIPITATION OF Cr BY AGING IN Cu-Cr IN-SITU COMPOSITE: J. Yan, H.G. Suzuki, National Research Institute for Metals, 1-2-1 Sengen, Tsukuba 305, Japan
Aging treatment is one of the most important materials processing techniques for obtaining high electrical conductivity in Cu in-situ composite. In this work, we systematically investigated the effect of Cr precipitation on electrical conductivity of a Cu-15 wt % Cr in-situ composite, by means of aging treatment, electrical conductivity measurement, scanning electron microscopy, analytical electron microscopy, high resolution electron microscopy and X-ray lattice parameter measurement. The optimum aging condition for obtaining peak electrical conductivity has been determined. In addition, it is found that an appropriate amount of cold working can further enhance the electrical conductivity of the composite. The related mechanism has also been studied.
Room: 230A
Session Chairpersons: Alton T. Tabereaux, Reynolds Metals Company, Manufacturing Technology Laboratory, 3326 East 2nd Street, Muscle Shoals, AL; Peter Polyakov, Light Metals Department, Non-ferrous Metals Academy, Krasnoyarsk sabochiy St. 95, 660025, Krasnoyarsk, Russia
2:00 pm
IMPLEMENTATION OF POINT FEEDING IN THE SØDERBERG LINES AT HYDRO ALUMINUM KARMØY: Knut Arne Paulsen, Willy K. Rolland, Asbjørn Larsen, Hydro Aluminum a.s, Karmøy Plants, N-4265 Håvik, Norway; Marvin Bugge, Norsk Hydro a.s, Research Centre, N-3901 Porsgrunn, Norway
A concept for point feeding of alumina to Søderberg cells has been developed at Hydro Aluminum Karmøy. During 1996 and early 1997 the bar breaker equipment on all 340 cells will be replaced by point feeders. Alumina is fed by means of a fluidized feeder and mechanically forced into the bath. The lifetime of the equipment is comparable to that of the cathode life. The concept has proved to stabilize the operation of the cell. Furthermore, the stability improves the current efficiency and also allows the amperage to be increased. Implementation of point feeding includes revised operational procedures and new target values for the operational parameters and also affects the organization. The anode effect frequency has been reduced in several steps during the development period. Today, the anode effect frequency is about one tenth of the corresponding value for the previous bar breaker cells resulting in reduction of perfluorocarbon emissions.
2:25 pm
A UNIQUE, ECONOMIC SØDERBERG TO PREBAKE CONVERSION FOR THE RUSSIAN ALUMINIUM INDUSTRY: S. Tsymbolov, G. Necheav, Nadvoitsky Aluminium Smelter, Zavodskaya Street, 1, Nadvoitsy, 186430, Karelia, Russia; Lee E. Swartling, Kaiser Aluminum Technical Services, Inc. 6177 Sunol Boulevard, Pleasanton, CA 94566; G. Volfson, All-Russian Aluminium & Magnesium Institute, 86 Sredny Prospect, St. Petersburg, 199026, Russia
The majority of Russian aluminum smelting technology is Søderberg, historically associated with non-competitive performance and ecological problems. After conversion to conventional prebake cell technology was found economically unjustifiable, the Nadvoitsky Aluminium Smelter, Karelia, Russia commissioned the All-Russia Aluminium and Magnesium Institute and Kaiser Aluminum Technical Services Inc. to design a unique prebake technology cell with world class performance which could be economically retrofitted into the existing facility. This multi-national team utilizing state of the art modeling and process control technology, successfully designed and implemented a twelve pot test section at Nadvoitsy. Cell performance measured over twelve months has consistently exceeded minimum design indices and paces world class cell performance. Measurements of magnetic field, heat flow, and voltage distribution compare closely with predicted values. Design features, including a novel six anode superstructure, design methodology, test protocol, construction and operation practices, and cell performance data are presented in this paper.
2:50 pm
BATH TEMPERATURE MEASUREMENTS WITH THERMOCOUPLES: Paul Verstreken, Heraeus Electro-Nite Int. N.V., Grote Baan 27a, 3530-Houthalen, Belgium
After a brief introduction into the physical principles of thermoelectricity an overview of commonly used thermocouples is given. The construction of thermocouple sensors and assemblies is discussed. An overview of calibration procedures is given. Errors can arise from the materials (thermocouple wires and sheathing) used, and the way the actual measurement is performed. Reasons for drifting are discussed. There is a relation between the thermal properties (thermal mass and heat conductivity) of the sheathing material, the measuring procedure and the obtained accuracy of the temperature measurement. From this, recommendations on how to improve the quality of bath temperature readings, are made.
3:15 pm BREAK
3:35 pm
A NEW INSTRUMENT FOR FAST TEMPERATURE MEASUREMENT IN ALUMINIUM REDUCTION CELLS: Fucang Xu, Jie Li, Huazhang Wang, Yexiang Liu, Department of Metallurgy, Central South University of Technology, Changsha, Hunan 410083, China
A new instrument, with a single-chip microcomputer as its core and based on a new method named Dynamic Temperature Measurement, has been developed for fast temperature measurement in aluminium reduction cells. When a cold thermocouple is inserted into hot electrolyte, the instrument measures the thermocouple output curve and meantime identifies the parameters of a time series-analysis model which is used to describe the temperature-time curve. Until the convergence of the identification is verified, the instrument predicts the temperature of the electrolyte from the obtained information. In the way, the temperature can be indicated before the thermocouple output reaches its balance point, with the measurement process lasting only some 50 seconds and measurement accuracy reaching ±2°C, a range acceptable for industrial measurement.
4:00 pm
A DEVICE FOR CONTINUOUS ALUMINA FEED INTO AN ALUMINIUM ELECTRIC CELL: A.I. Begunov, E.V. Kudryavtseva, State Technical University, Lermontov Str. 83, Irkutsk, Russia
A new device is suggested here to cover the cell and feed alumina into it. The covering is designed having such thermal resistance that no crust develops on the electrolyte surface. Alumina is fed from the intermediate hopper, which is one piece with the covering plate, into the electrolyte through the narrow slot, the width of which ranges from 0.8 to 1.2 mm. The alumina feed rate is determined by its bulk properties ("sandy", "mealy", "moist"), the width and length of the slot and the intermediate hopper wall flare angle. The cold model of the device yielded the dependencies of alumina slot spead on the parameters mentioned above. The device has no crust-breaking appliances or volumetric dosers. Dosage is effected only to gravity feed of raw materials through a slot of predetermined cross-section. Because of that, low operation costs and high reliability of the suggested device are expected.
4:25 pm
VISUALISATION OF TAPPING OPERATIONS: Marcus Walker, Comalco Research Centre, P.O. Box 316, Thomastown, Australia 3074
The removal of molten aluminium from Hall- Heroult cells is known a "tapping". This operation causes process disturbances including entrainment of electrolyte and sludge in the tapped metal as well as producing localised wear of the cathode. This paper describes the use of a full scale physical model for determining the optimal tapping conditions to reduce both bath entrainment and cathode erosion for various cell operating strategies. Flow visualisation and numerical modelling has shown that the flow towards the tapping pipe is predominantly radial, however under and inside the pipe, the flow swirls intensely. Under certain conditions the swirling flow induces a vortex at the bath metal interface through which bath can be entrained in the flow. The swirling action was also seen to produce a region of locally high velocities on the cathode surface which enhances erosion of the cathode through a number of possible mechanisms.
4:50 pm
A NEW CONCEPT OF RESOLVING LADLE CLEANING AT SLOVALCO BY TECHMO: F. Zannini, F. Marchetti, R. Balasso, J. Ifju, Techmo Car SpA, Via R. Colpi 15/17, 35010 Limena (PD), Italy
Techmo has elaborated a new concept of resolving the problem of ladle cleaning based on standard features of the new aluminium smelter implemented by Hydro Aluminium's technology at SLOVALCO a.s. A thorough design work has resulted in a piece of equipment with new arrangement and orientation in good agreement with the tapping system and work organization of the plant. Some optimization was fulfilled in order to meet the requirements of the new plant in possible best manner.
Room: 232A
Session Chairs: B.G. Thomas, Dept of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign, 1206 West Green Street, Urbana, IL 61801; B.Q. Li, Dept of Mechanical Engineering, Louisiana State University, Baton Rouge, LA 70803
2:00 pm
NUMERICAL ANALYSIS OF FLOATING ZONE REFINING PROCESSES: S.P. Song, B.Q. Li, Department of Mechanical Engineering, Louisiana State University, Baton Rouge, LA 70803
A numerical model is developed to represent complex electromagnetic, thermal and free surface deformation phenomena in floating zone refining and single crystal growth processes. The model is developed using a coupled boundary element and finite element method, with finite element meshes used for the melting zone region and boundary elements for the exterior region or free space. The free surface deformation model is developed using the weighted residual method. With the model, the complex transport and free surface phenomena in a floating, zone system are studied as a function of various operating conditions including applied current, frequency, inductor position and shape, surface tension, floating zone diameter and height. Model development and numerical results are presented.
2:25 pm
MODELING OF SOLIDIFICATION AND VELOCITY OF ATOMIZED MOLTEN DROPLET DURING ATOMIZATION AND SPRAY FORMING: Y.H. Su, C.-Y. A. Tsao, Department of Materials Science and Engineering, National Cheng Kung University, Tainan, Taiwan, China
A mathematical model to describe the solidification behaviors of atomized droplets during flight, in terms of nucleation temperature, recalescence temperature, nucleation position, solid fraction at nucleation temperature, and droplet temperature and velocity, is formulated. The concept of transient nucleation is applied to model such short nucleation event. A maximum droplet velocity exists, beyond which droplet velocity shows an inflection phenomenon during the flight. For shorter flight distance, smaller droplet is faster to reach a given flight distance; however, for longer flight distance, the situation is reversed. Variations of the gas flow patterns have more effects on smaller droplet, and the effects are more significant at longer flight distance. A minimum surface heat transfer coefficient exists as the droplet flies. Prior to nucleation or recalescence, smaller droplet has lower temperature at a given flight distance, and has lower nucleation temperature. Medium size droplet flies over the shortest flight distance before the nucleation starts. Smaller droplet has larger solid fraction at the end of recalescence. Atomization gas has more effects on droplet momentum than on the heat content of the droplet.
2:50 pm
THE EFFECT OF FORCED COOLING A PERMANENT COMPOSITE MOLD ON AIR GAP FORMATION: D.R. Gunasegaram1, D. Celentano2, T.T. Nguyen1, 1CRC for Alloy and Solidification Technology (CAST) and CSIRO Division of Manufacturing Technology, Locked Bag 9, Preston 3072, Australia; 2International Center for Numerical Methods in Engineering, Edificio C-1 Campus Norte-UPC, Gran Capitan, s/n. 08034 Barcelona, Spain
It is well known that the air gap that forms between casting and mold during the solidification process of an aluminum alloy substantially alters the rate of heat transfer at this interface. This paper reports studies on the effect of force cooling a composite permanent mold on the initiation and growth of the air gap. Interesting comparisons are made with the case where no forced cooling is employed. The two experiments are simulated using a fully coupled thermo-mechanical model called VULCAN, a finite element code, and its temperature and displacement predictions are validated. The air gaps are measured using LVDTs. The alloy used is A356, and the mold comprises H13 steel and beryllium-copper. Air jets are used to force cool the mold component surrounding an isolated thick section of the casting. The inverse heat conduction problem is solved in order to obtain boundary conditions for VULCAN.
3:15 pm BREAK
3:25 pm
EFFECT OF TRANSVERSE DEPRESSIONS AND OSCILLATION MARKS ON HEAT TRANSFER IN THE CONTINUOUS CASTING MOLD: B.G. Thomas, D. Lui, B. Ho, G. Li, Y. Shang, Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign, 1206 West Green Street, Urbana, IL 61801
Results from mathematical models and plant experiments are combined to quantify the effect of transverse depressions and oscillation marks on heat transfer in the continuous casting mold. A heat transfer model has been developed to calculate transient heat conduction within the solidifying steel, coupled with the steady-state heat conduction with the continuous casting mold wall. The model features a detailed treatment of the interfacial gap between the shell and mold, including mass and momentum balances on the solid and liquid powder layers. The model predicts the solidified shell thickness down the mold, temperature in the mold and shell, thickness of the resolidified and liquid powder layers, heat flux distribution down the mold, mold water temperature rise, ideal taper of the mold walls, and other related phenomena. The important effect of non-uniform distribution of superheat is incorporated using the results from previous 3-D turbulent fluid flow calculations within the liquid cavity. Results from plant experiments confirm that transverse surface depressions and oscillation marks form at the meniscus and move down the mold. Measurements of mold thermocouple temperatures and breakout shell thickness were used to calibrate the models. The predicted local surface temperature fluctuations were consistent with transient mold temperature measurements. The results indicate that the surface depressions and oscillation marks are filled with mold flux, but still have a significant effect on decreasing heat transfer, especially locally. Insights are gained into the formation of associated surface cracks and breakouts.
3:50 pm
CHANGE OF PATTERN OF SOLIDIFICATION IN INGOTS CAST FROM THE BOTTOM, REPRESENTED BY A MATHEMATICAL MODEL AND ITS EFFECT ON THE APPARITION OF DEFECTS IN THE SEAMLESS TUBES OF C.V.G SIDOR: J. Rodriguez, A. Valles, C.V.G SIDOR, Puerto Ordaz, Venezuela, M. Rao, Universidad Nacional Experimental de Guayana, Puerto Ordaz, Venezuela
This paper shows a mathematical model based on finite elements, applied to bottom cast ingots of C.V.G Sidor Plant. The model was used as a strategy to determine the thermal effects that are produced when the solidification conditions are modified, without interfering with the production process. The modification consisted of placing a thermal insulant on top of mould. The results obtained by the model indicated that the solidification time increases with insulant on top of the mould. With these results a significant number of casts were run with and without insulant. Later by means of a metallurgical analysis it was determined that the ingots cast with insulant reduce the level of nonmetallic inclusions and the presence of internal blistering in seamless pipes.
4:15 pm
MATHEMATICAL MODELING AND EXPERIMENTAL MEASUREMENTS OF EXOTHERMIC PHENOMENA IN NON FERROUS SYSTEMS: S.A. Ferenczy, S.A. Argyropoulos, Dept of Metallurgy and Materials Science, University of Toronto, 184 College Street, Toronto, Ontario, Canada M5S 3E4
Microexothermic and macroexothermic phenomena have been indentified various non-ferrous systems, which from recent experimental and mathematical studies have been shown to enhance heat and mass transfer. This paper will present experimental results and computer simulations describing the transient exothermic dissolution of nickel cylinders into liquid aluminum. Axisymmetric heat, mass and momentum equations the SIMPLER algorithm was modified to incorporate phase change and the microexothermic macroexothermic events. Dissolution experiments were performed and the results compared to the mathematical simulation. The development of coupled temperature, concentration and momentum boundary layers are examined.
Room: 231A
Session Chairperson: Dr. E. Ozberk, Sherritt International, Bag 1000, Fort Saskatchewan, AB, T8L 2P2
2:00 pm
DEVELOPMENT OF AUTOMATIC MATERIAL HANDLING AND MONITORING SYSTEMS IN AN EXISTING ELECTROLYTIC ZINC PLAN: T. Yamada, R. Togashi, T. Aichi, Akita Zinc Co., Ltd., Iijima Refinery, Akita, Japan
Mainly due to the strong yen and the relatively low metal price, the zinc refineries in Japan are being forced to reduce man power. At IIjima, a new automatic material - handling system for cathode transportation was developed and the first system went to service in August 1994. The work was started in 1993 and all installation will be finished in the summer 1997. The critical part of this work was to achieve the designed cycle time because of the fairly complex cell-layout. As the cathodes are placed opposite direction in every other unit, cranks must be able to move toward two directions (X and Y) at the same time and to stop precisely at the tolerance level of a few millimeter. The central monitoring system for machine operation run by an original application software with MICROSOFT EXCEL© on WINDOWS 95©, was started in June 1996. There had been one person only for operating a manual crane before. Now an operator of a stripping machine can control the automatic crane for the same row at the same time. As a result, only one person can operate both a crank and a stripping machine for one row. And more labour saving is expected in the future.
2:25 pm
INDUSTRIAL SIZE "PLACID ELECTROWINNING CELL": C.Frías, M.A. García, G. Díaz, Tecnicas Reunidas, S.A., R & D Centre, Madrid, Spain
Under the auspicious of the Commission of the European Union, a consortium composed of six European organizations has developed the PLACID process, into the Brite Euram II Programme. The project began on January 1993 and was finished on April 1996. The PLACID process is based on a novel technology able to deal with different lead bearing materials, mainly lead oxide secondaries: Lead-acid batter pastes, lead fumes, furnace slags, oxide residues, etc., producing "four nines" pure lead in an efficient manner with a benign influence on the environment. In the PLACID process, lead is leached in warm, slightly acidic, brine to form soluble lead chloride. This solution is purified by cementation with lead powder. Pure lead is then won from the lead chloride electrolyte on the cathode of the electrowinning cell and is collected. This electrolytic cell is the heart of the process and it was especially developed to give optimum performance. Hydrochloric acid is reformed in the cell and returned to the leaching bath; reagent net consumption in the process is irrelevant. This paper is concerning the development of the PLACID electrowinning cell up to industrial size electrodes. The performed work has covered three levels of development: laboratory study, bench scale experimentation and pilot plant prototype testing (16 Kg/h electrolytic lead production). After 1,000 hours operating time, the achieved results of the pilot plant electrowinning cell have been very satisfactory, demonstrating the ability of the Placid electrowinning cell to produce top quality electrolytic lead (above 99.99% Pb) with high current efficiency and low energy consumption.
2:50 pm
CHARACTERIZATION OF ANTIMONY-GELATIN ADDITIVES IN ZINC SULPHATE ELECTROLYTES USING IMPEDANCE ANALYSIS: X. Tang, Southwire Copper Division, 372 Central High Rd., Carrollton, GA 30117; P. Yu, T.J. O'Keefe, University of Missouri-Rolla, Department of Metallurgical Engineering and Graduate Center for Materials Research, Rolla, MO 65409-1170; G. Houlachi, Noranda Technology Centre, Pointe-Claire, Quebec, H9R 1G5, Canada
Impedance measurements were used to investigate the electrochemical characteristics of acidic zinc sulphate electrolytes containing Sb3+, gelatin and their mixtures. The data were correlated with cyclic voltammetry curves made using synthetic as well as industrial electrolytes. The cyclic voltammetry results were similar to those obtained in previous studies in that antimony caused a depolarizing effect while gelatin gave an increase in the potential for zinc nucleation on an aluminum substrate. The electrochemical impedance spectroscope (EIS) evaluations were conducted on electrodeposited zinc at three overpotential values. The potentials were chosen to represent various current density regions in the zinc polarization curves. The antimony and gelatin gave characteristic impedance plots which correlated with expected behaviour, particularly current efficiency. Both antimony and glue appear to modify the intermediate zinc reaction sequence, but in different ways. The data strongly suggest that film formation and stability are major factor in the zinc ion reduction mechanism.
3:15 pm
EFFECTS OF ANTIMONY AND CONTINUOUS GELATIN ADDITION ON CURRENT EFFICIENCY IN THE HUDSON BAY ZINC ELECTROWINNING TANKHOUSE: P. Merrin, Hudson Bay Mining & Smelting Co., Limited, Flin Flon, Manitoba, R8A 1N9, Canada
This study was conducted at Hudson Bay Mining and Smelting's zinc electrowinning tankhouse to determine the effects of varying levels of antimony and continuous gelatin addition on current efficiency. The levels of antimony and gelatin were varied between 0.010-0.030 mg/l and 0-10 mg/l respectively, using the fresh electrolyte as reference. The test was designed to determine the optimum operating point for current efficiency, and to investigate any interaction that occurs between the two components. An non-linear mathematical model relating these three variables was produced, giving an optimum operating point of 6.5 mg/l of gelatin and increasing current efficiency with decreasing antimony levels. Individually, the antimony concentration was approximately linear with current efficiency, while gelatin concentration was parabolic. An interaction term is present but is not significant enough to improve the ability of the tankhouse to handle purification upsets in antimony.
3:40 pm
THE EFFECTS OF SOME FOAMING REAGENTS ON ACID MIST CONTROL AND ZINC ELECTROWINNING FROM KIDD CREEK ZINC ELECTROLYTE: A.M. Alfantazi, D.B. Dreisinger, University of British Columbia, Department of Metals and Materials Engineering, Vancouver, B.C., V6T 1Z4, Canada; J. Synnott, M. Boissoneault, Falconbridge Ltd., Kidd Creek Division, P.O. Bag 2002, Timmins, Ontario, P4N 7K1, Canada
The effects of five commercially available foaming reagents (range of 0 to 25 ppm) namely Dowfroth 250 Saponin, Yucca, Licorice and Meta-Para Cresol on acid mist control, current efficiency, polarization behaviour, and deposit morphology and orientation were investigated using a bench scale electrolysis apparatus (cell volume 3L). The deposition was carried out at 500 Am-2 and 38°C for 3 hours from Kidd Creek zinc electrolyte. The acid mist control capability of the various reagents was studied and compared by characterizing the foam layer generated during actual electrowinning conditions and by direct quantitative measurements of acid mist levels on top of the electrowinning cells. Within the range considered, the addition of these reagents reduced the current efficiency, refined the grain size of the deposit, and changed to preferred orientation of most of the deposits. Among the reagents tested, acid mist measurements indicated that Licorice and Dowfroth 250 were the best acid mist suppressant at emissions of 0.30 mg/m3 and 0.31 mg/m3 respectively while Yucca and MPC produced the most mist at 3.0 mg/m3 and 3.3 mg/m3 emission rates respectively.
4:00 pm
ELECTROPURIFICATION OF ZINC LEACHING SOLUTION: S. Yamashita, K. Hata, S. Goto, Department of Metallurgy, Chiba Institute of Technology, Chiba, Japan
The average consumption of zinc dust for purification of zinc leaching solution is more than 25 kg per ton of electrolytic zinc. Authors proposed to remove impurities in zinc leaching solution by electrolysis instead of cementation by zinc dust. The effects of copper and arsenic on electrodeposition of cobalt in zinc sulfate solution were examined fundamentally by using potentiostat. The mesh cathodes of stainless steel and lead anodes are used in the electrolytic cell for removal of cobalt and an electrolyte is circulating rate of electrolyte, concentration of copper and arsenious ions on removal of cobalt are studied. Removal of Ni, and Cd are also examined.
4:25 pm
Cl ANION ELIMINATION FROM Zn SULPHATE SOLUTION BY PERIODICAL REVERSE ELECTROLYTIC SYSTEM: T. Yoshida, M. Kahata, M. Dobashi, M. Suzuki, Mitsui Mining and Smelting Co. Ltd., Sairama, Japan
In Japan, almost 30% of steel is produced by electric arc furnace (EAF) melting of iron scrap. And the dust from EAF includes approximately 20-30 wt % of Zn and 3.5 wt % of C1. They are treated as industrial waste to recover Zn as Zn oxide mainly by pyro metallurgical process. On the other hand, high purity zinc recovery by direct hydro-metallurgical processing is one of the most effective method. In this case, Cl in the EAF dust is dissolved in liquid phase by leaching, but the Cl anion in electrolyte attacks anode which is made of a lead base alloy. Several processes have been proposed to remove Cl anion from acidic sulfate solution. In this study, an electrolytic process is established to eliminate Cl anion from Zn sulfate electrolyte. It is known that Cl anion can be removed by anode oxidation. From our study it can be said that the elimination rate of Cl anion depend on the anode material, i.e. the elimination rate is Pb - Ag alloy > Pb DSE. Furthermore in industrial electro-winning process, electrolyte includes Mn dioxide. Therefore, the effect of Mn in electrolyte should also be considered for Cl elimination. It seems that Mn dioxide deposition on anode decreases the efficiency of Cl anion removal. The periodical reverse system was induced to prevent from efficiency decrease. By using periodical reverse system, deposited Mn dioxide is removed very rapidly when the current was reversed for short time. More than 95% of Cl anion can be removed in extremely short period than conventional method. At the symposium the detailed data will be presented about Cl anion elimination by periodical reverse system.
4:50 pm
THE ROLE OF COPPER AND ANTIMONY ADDITIVES IN THE REMOVAL OF COBALT FROM ZINC SULPHATE SOLUTIONS: V. Van der Pas, D. Dreisinger, University of British Columbia, Department of Metals and Materials Engineering, Vancouver, British Columbia, V6T 1Z4 Canada
Zinc sulphate electrolyte used for zinc electrowinning must be purified for cobalt ions. The cobalt is removed in a cementation stage by the addition of zinc dust. Copper and antimony are frequently used additives which enhance the cementation of cobalt. This paper aims at a better understanding of how copper and antimony promote the removal of cobalt. Initial experiments were done in a batch cementation reactor. Copper and antimony precipitated in the early stages of cementation indicating that a preferential substrate was formed. The individual role of copper and antimony was further investigated in an electrochemical cell. On a microscale, the growth process, morphology and the composition of the precipitates under various conditions were examined with SEM and XRD. It was found that cobalt could not be deposited in its pure form but as a cobalt-zinc alloy with zinc as the prime constituent. The effect of copper addition is of increasing the cathodic surface area of zinc dust by precipitating as numerous dendrites. Antimony acts as a cathodic surface onto which a cobalt-zinc alloy with an increased cobalt content is deposited.
Room: 230B
Session Chairperson: Kurt Ehrke, Aluminium Essen GmbH, Sulterkamp 71, D-45356 Essen, Germany
2:00 pm
REFRACTORY SOLUTIONS DESIGNED TO OVERCOME CORUNDUM GROWTH IN ALUMINIUM FURNACES: Duncan Jones, Morganite Thermal Ceramics Ltd., Liverpool Road, Neston, South Wirral, L64 3RE, England
Corundum is an extremely hard, high temperature form of aluminium oxide. Its formation in aluminium melting furnaces and metal treatment units can lead to a reduction in operating efficiency and premature failure of the furnace lining. The formation of corundum is known to be dependent on several factors, including furnace atmosphere, operating temperature, alloy composition and refractory type. The paper describes solutions to this phenomenon identifying its cause and effect whilst highlighting refractory design criteria. Results from an extensive testing programme, classifying resistance to corundum growth against various qualities of refractory product are discussed.
2:20 pm
USE OF SMALL DIAMETER IMMERSION HEATERS IN MOLTEN ALUMINUM: Mark Palmer, Pyrotek Inc., E. 9503 Montgomery Avenue, Spokane, WA; Andre Teytu, Atherm, Rue de Moirind 13, 38420 Domene, France
Small diameter electric immersion heaters offer unique benefits when used in molten aluminum heating applications. The 1" diameter heaters allow greater flexibility in vessel design than traditional immersion heating systems. The electric heating elements are inside a Sialon sheath, which is non-wedded by molten aluminum and offers long life. Since the development of these heaters, they are being used in many different types of molten aluminium holding vessels. Pechiney Aluminium Engineering utilizes these small heaters in Alpur degassing vessels and the Pechiney Deep Bed Filter Heaters are also used in die casting holding furnaces for both primary and supplemental heating applications. The net result of using the small immersion heaters is high metal heat-up rates, compact vessel designs, energy savings, uniform metal temperatures, and user friendly equipment designs. The paper describes the capabilities of the heaters, the design flexibility they allow, and performance results obtained from initial installations.
2:40 pm
IMPACT OF GOOD METAL CIRCULATION AND FURNACE OPERATION FOR INCREASED PERFORMANCES FOR SIDEWELL FURNACES: G. Riverin, W. Stevens, Arvida Research and Development Centre, Alcan International Limited, 1955 Mellon Blvd., Jonquière, Québec, Canada G7S 4K8; D. Bristol, Alcan Rolled Products Company, P.O.Box 837, Greensboro, 30642; Y. Kocaefe, Université du Québec à Chicoutimi 555, Boul. de l´Université E, Chicoutimi, Quebec, Canada G7H 2B1
Sidewell furnaces have long been operated for scrap melting, including UBC. The paper discusses important criteria for the optimum energy and melt rate performances for these types of furnaces. Intensive work has been done in several Alcan recycling installations in order to increase these furnace performances. Several operating parameters are outlined combined with the importance of melt stirring in the main hearth and in the sidewell. Mathematical and physical modeling provided key elements responsible for better furnace operation. The impact and advantages of the improved melt stirring and furnace operation are explained and discussed in detail.
3:00 pm
CAST HOUSE WATER TREATMENT WITH AEC TECHNOLOGY: Ed Grodecki, Betz Water Management Group, 4150 Washington Road, Bldg.2, Suite 206, McMurray, PA 15317
REPLACEMENT PAPER
Presented by: George Binczewski
3:20 pm
MOLTEN ALUMINUM PLUS WATER--A DIFFERENT POINT OF VIEW: George J. Binczewski, S C Systems, PO Box 6154, Moraga, CA 94570
For forty years, the Aluminum Industry has conducted and sponsored investigations directed at establishing a better understanding of the safety aspects associated with the sometimes explosive occurrence which may happen when there is a physical contact between molten aluminim and water. Industry concern has resulted in a poling of resources among companies, associations, and technical organizations. There has been a substantial funding of investigative projects conducted by capable research organizations employing sophisticated techniques. While useful information has been gained and translated into operational procedures, the basic cause remains elusive. A completely different, and additional, investigative approach is suggested based on cumulative experience and observation of daily occurrences. This can provide the informational basis to alleviate the safety and liability concerns associated with direct contact between molten aluminum and water.
3:40 pm BREAK
3:50 pm
THIN GAUGE TWIN-ROLL CASTING, PROCESS CAPABILITIES AND PRODUCT QUALITY: O. Daaland, M.L.Nedreberg, A.B.Espedaal, Enge Alwestad, Hydro Aluminium a.s, R&D Materials Technology, N-4265 Håvik, Norway
Traditionally industrial twin roll casters have been operated at gauges 6-7 mm, depending on the type of caster and the final product requirements. Over the past few years it has become apparent that a significant increase in productivity can be achieved when the casting gauge is reduced. Hydro Aluminium embarked on an extensive R & D thin gauge casting program in the beginning of the 1990's, and this paper presents results of a five year lasting project (joint program between Hydro Aluminium and Lauener Engineering). Based on over 400 casting trials the major benefits and limitations of casting at reduced gauge and increased speed are outlined. Important aspects for product quality are discussed including: cooling rates and dendrite structure, microstructural characteristics (as-cast grain structure and texture), segregation behaviour, surface quality and mechanical properties after thermomechanical processing. Results for casting of several alloys (including the 5xxx and 8xxx-system) are given. Additionally, numerical modelling results of the strip casting process are included.
4:10 pm
PECHINEY JUMBO 3CMTM--START-UP OF THE NEUF-BRISACH THIN STRIP CASTER: Pierre-Yves Menet, Pechiney Rhenalu Neuf-Brisach, Z.I.Biesheim, BP 49, F-68600 Neuf-Brisach, France; Robert Cayol, Pechiney Aluminium Engineering, Centr'Alp-725 rue Aristide Bergès, F-38340 Voreppe, France; Jacques Moriceau, Pechiney Rhenalu Melting and Casting Direction of Technology, Centr'Alp-725 rue Aristide Bergès, F-38340 Voreppe, France
Following extensive research and development work at the Pechiney Research Center in Voreppe, a new Jumbo 3CMTM thin strip caster has been installed at the Pechiney Rhenalu Neuf-Brisach plant. First of its generation, it is capable of casting a 2m wide strip under a maximum load of 2900 tons. This paper reviews the various features of the equipment which make possible the casting of thin strip of aluminum alloys covering a wide range of applications, from foil stock to can stock. Initially scheduled for start-up in June '96, the equipment was started on time. Performances concerning the installation itself and the casting of several alloys are given. A video of the installation and an actual casting will be shown during the Cast-Shop session.
4:30 pm
AN UPDATE ON DOWN-GAUGING THE FATA-HUNTER SPEEDCASTERTM AT NORANDAL, HUNTINGTON (TN): R. Beals, B. Taraglio, C. Romanowski, FATA Hunter Inc., 6147 River Crest Drive, Riverside, CA 92507
The first of a new generation of Thin-Gauge/High-Speed FATA Hunter machines is now in operation at Norandal's Huntington (TN) facility. Following the late February 1996 start-up of the machine, a down-gauging program was commenced which combined normal 5 mm gauge production with a series of pilot production trials at progressively lighter gauges. This paper overviews this start-up program and compares the production rates and metallurgical characteristics of the thin-gauge cast material with conventional-gauge, twin-roll cast strip. In addition, a brief video tape of the FATA Hunter 86" wide SpeedCasterTM in operation will be presented.
4:50 pm
MAGNETIC EDGE DAMS IN A TWIN ROLL ALUMINIUM CASTER: Craig Anderson, Peter Davidson, Engineering Department, Cambridge University, Cambridge CB2 1P2, United Kingdom
In the twin roll casting process, molten aluminium is fed between two cooled rotating rollers where it cools, solidifies and is carried by roller rotation to the nip, where it is compressed to a single sheet and expelled. To prevent aluminium escaping laterally, from the roller edges, dams are required. Physical edge dams are subject to erosion from the rollers and molten metal and require maintenance and replacement. Hence there is a strong economic case for using magnetic edge dams, where the interaction of a magnetic field and a current provide sufficient repulsive force to contain the molten aluminium, which do not physically touch either the rollers or molten metal and require little or no maintenance. This paper discusses the theory behind high frequency magnetic edge dams and describes the design and construction of a practical system. Laboratory testing of the magnetic edge dam system is shown to give good agreement with theory and the installation and operation of the system on an experimental twin roll caster is described.
5:10 pm
DECOATING TECHNOLOGY FOR THE ALUMINIUM INDUSTRY: O.H. Perry, Stein Atkinson Stordy Ltd., Midland House, Ounsdale Road, Wombourne, Wolverhampton WV5 8BY, England
The technology for recycling aluminium scrap has evolved over a number of years through five major changes as follows: direct charging, side bay melter with puddlers, rotary furnaces, shredding and flat belt delacquering machines, shredding and rotary kilns, today it is now possible to fully decoat any aluminium material which can be shredded. With the invention of IDEX® rotary kiln systems all materials from UBC, extrusions, coated foils, through to 6 micron aseptic foils can be successfully reclaimed and either remelted or processed with minimal metal loss. During 1996 three systems have been commissioned in the Americas for decoating materials which contain 3 to 80% VOC by weight and ranging from 4 to 7 tonnes per hour. This paper discusses the changing technology and the current "state of the art" in rotary kiln technology.
Room: 330C
Session Chairperson: John Morral, Univ. of Connecticut, Dept. of Metallurgy, Storrs, CT 06269
2:00 pm INVITED
ALUMINIUM-BASED NANOPHASE COMPOSITES BY DEVITRIFICATION: A.L. Greer, University of Cambridge, Department of Materials Science & Metallurgy, Pembroke Street, Cambridge CB2 3QZ, UK
Al-TM-Ln alloys (TM... transition metal; Ln...lanthanide) can be rapidly quenched into a fully amorphous state and then partially devitrified to give a nm-scale microstructure of aluminium crystallites uniformly dispersed in an amorphous matrix. This is a highly unusual microstructure for an aluminium alloy, indicating a high density of independent nucleation events in the glass. This study focuses on the development and stability of microstructure in a series of Al-Ni-Y alloys. The effects of various single- and two-stage heat treatments are explored. The emphasis is on the particular features associated with the unusual nm-scale among these is the overlap between coarsening and further transformation arising from capillarity effects on the crystallites.
2:30 pm INVITED
KINETICS OF NANOPHASE CRYSTALLIZATION IN Al-Fe-Gd ALLOYS: A.A. Csontos, G.J. Shiflet, Materials Science and Engineering, University of Virginia, Charlottesville, VA 22903
This presentation will provide results an the formation and subsequent growth of nanocrystalline aluminum phases in an amorphous matrix. A prototype for this family of metallic glass alloys that can be transformed into nanocrystalline material is the Al90Fe5Gd5 system. Detailed measurements of nanocrystalline isothermal growth from an amorphous Al90Fe5Gd5 matrix were made from 150 to 500°C. Coupled with growth of the nanocrystals, measurements of Gd and Fe segregation between the nanocrystal and the matrix were secured in a TEM with a field emission gun. Both Fe and Gd are preferentially rejected into the remaining matrix as the aluminum-rich nanocrystal grows. After reaching a specific size, which varies with temperature, growth slows down and funkier changes are slight until subsequent nucleation and growth of compound phases. such as Al4Gd occur. The relative stability of the formation of nanocrystals from an amorphous matrix will be addressed. Research supported by the University of Virginia Academic Enhancement Program.
3:00 pm INVITED
DIFFUSION FIELD IMPINGEMENT DURING PRIMARY CRYSTALLIZATION OF ALUMINUM NANOCRYSTALS: D.R. Allen, J.C. Foley, J.H. Perepezko, Materials Science and Engineering, University of Wisconsin - Madison, 1509 University Avenue, Madison, WI 53706
Aluminum-rich glasses containing about 85 at% Al and a combination of transition and rare earth element additions have yielded microstructures of Al nanocrystals in an amorphous matrix with nanocrystal volume fractions approaching 20% and excellent mechanical properties. A high density of nanocrystals (>1020 m-3) develops during the primary crystallization reaction but growth is limited. A new kinetics analysis shows that diffusion field the nanocrystals. The kinetics model has been applied to DSC exotherms that correspond to primary fcc nanocrystal formation. A thermodynamic model of the fcc-liquid phase support heat evolution rate calculations used in the model. The results indicate that modification of the nucleant density should be the primary focus in limiting nanocrystal growth due to reduced length scales.
3:20 pm
MICROSTRUCTURAL AND THERMAL ANALYSES OF CRYSTALLIZATION IN ULTRAFINE AMORPHOUS TITANIA PARTICLES: J.-S. Yin, L. He, G.L. Griffin*, E. Ma, Mechanical Engineering, *Chemical Engineering, Louisiana State University, Baton Rouge, LA 70803
Ultrafine amorphous titania particle aggregates, with a mean particle size of 145 nm, were prepared using a hydrolysis technique in an aerosol reactor. Their crystallization bahavior has been studied using transmission electron microscopy, differential scanning calorimetry, X-ray diffraction, and scanning electron microscopy. The amorphous powder crystallized into anatase with a crystallization enthalpy of 27 kJ/mol and an apparent activation energy of 2.0 eV. The anatase phase nucleated preferentially in contact regions between neighbouring particles. This crystallization mode is interpreted as a consequence of the presence of appreciable local pressure (stress) which was predicted by model calculations and observed under TEM. An analysis suggests that the pressure effect reduces the relative stability of the amorphous phase by enhancing the thermodynamic driving force for nucleation and possibly also the crystallization kinetics. The nucleation and growth behavior observed has important implications when these amorphous particles are used as precusors to form nanocrystalline titania. The results are also discussed in comparison with the crystallization behavior reported previously for other ultrafine-structured oxides.
3:40 pm BREAK
3:55 pm INVITED
PRESSURE INDUCED CRYSTAL-TO-AMORPHOUS TRANSFORMATIONS: R.B. Schwarz, P.J. Yvon*, Center for Materials Science, Los Alamos National Laboratory, Los Alamos, NM 87545, *Present address: SRMA, Centre d'Etudes Saclay 91191 Gif/Yvette, France
Pressure-induced crystal-to-glass transformations have been observed in tetrahedrally coordinated elements (e.g. Ge, Si), ionic and molecular crystals (alpha-SiO2, FeSiO4, AlPO4, Fe PO4, SnBr4), and hydroxides (ice, Ca(OH)2, Co(OH)2). In these materials, the crystal transforms polymorphically to a higher density glassy phase. Crystal-to-glass transformation have also been observed to occur through pressure-induced reactions between mixtures of elements such as germanium and aluminum. This paper reviews the formation of amorphous phases in alloys and elemental mixtures and discusses the possibility of obtaining bulk amounts of amorphous phases.
4:25 pm
STABLE VS. METASTABLE PHASE EQUILIBRIA IN FACETED/NON-FACETED METALLIC GLASS SYSTEMS: T.M. Adams, M.J. Kaufman, Materials Science and Engineering, University of Florida, Gainesville, FL 32611
Since metallic glasses can be used as precursors for nanocrystalline structures, it is important to understand the relationship between the transformation characteristics of the stable faceting phases and the metastable ordered phases (MOP's) in faceted/non-faceted systems. Such an understanding of the competitive nucleation and growth kinetics should allow better control of the transformation structures. Following some past work on Al-Ge alloys, it has been proposed that, in general, for faceted/non-faceted systems, no equilibria exist between the MOP's and the stable faceted phases. In order to support this assertion of generality, the Hf-Be and Al-Ge systems are being investigated. Crystallization of amorphous melt spun ribbons and co-evaporated thin films is effected by standard furnace anneals and in-situ electron beam heating. Once annealed, the resulting microstructures are characterized using XRD and TEM. In addition, in-situ hot-stage TEM is used to examine the relationship between the MOP and the stable faceting phase while the transformations are occurring. All of this work is being done in the vicinity of the stoichiometric composition of the most stable MOP (Hf-50Be and Al-50Ge). Basic modelling efforts of the metastable phase equilibria are also under way using THERMOCALC with estimated heats of formation for the MOP's determined through DSC/DTA and empirical formulations.
4:45 pm
STRUCTURAL TRANSITIONS IN TI/AL NANOLAYERED THIN FILMS: R. Banerjee, X.D. Zhang and H. L. Fraser, Materials Science and Engineering, Ohio State University, Columbus, OH 43210; M. Asta, A.A. Quong, Computational Materials Science, Sandia National Laboratories, Livermore, CA, R. Ahuja, Multi Arc Scientific Coatings, Troy, MI
Nanolayered materials often exhibit unusual structural features which are significantly different from those of their bulk counterparts. Such structural transitions could lead to novel properties of the material motivating research directed towards engineering the structure at the nanoscale. Laminated thin films based on Ti, Al and Ti-aluminides have potential application as coatings for components used in high temperature aerospace applications. A series of structural transitions were observed in Ti/Al multilayered thin films on reducing the layer thickness of the Ti and Al layers1. An hcp-fcc transition was found to occur in the Ti layers on reduction of the layer thickness to 5 nm. Al too exhibited an fcc-hcp transition on reducing the layer thickness to 2.5 nm. Interestingly, a 2.5 nm Ti layer had an hcp structure. An atempt was made to explain these transformations in the stacking sequence of the Ti and Al layers using a model initially proposed by Redfield and Zangwill. Subsequently, first principles electronic structure calculations are in progress to determine the effect of bulk, interfacial and thin film strain energies on the structural stability of the multilayers. Initial results suggest that strain energy may be playing a pivotal role in determining the structure.
5:05 pm
NANOSTRUCTURES AND PROPERTIES IN RAPIDLY SOLIDIFIED Ti(50)Ni(50-X)Cu(X) ALLOYS: V.G. Pushin, S.B. Volkova, N.M. Matveeva*, A.S. Chistjakov, Institute of Metal Physics, Ural Division of Russian Academy of Sciences, S. Kovalevskoi 18, 620219 Ekaterinburg, Russia; *Baikov Institute of Metallurgy, Russian Academy of Sciences,Leninskij prospect 49, 117911 Moscow, Russia
Rapidly solidified Ti-Ni-Cu alloys prepared by melt spinning were studied. It is found that under super rapid cooling rates alloys with 25-40 at% Cu are formed in initial amorphous state, with 15-25 at% Cu in amorphous-crystalline state, with 15 at% Cu don't become amorphous under spinning. Crystallization heat treatment of amorphous alloys leads to the formation of nano-scale TiNi-based solid solution, which undergo martensitic B2->B19 martensitic transition in cooling. Temperatures of martensitic transformations for RS-alloys have been established to be lower, than for same alloys prepared under traditional cooling rates, because of nano-scale grain size of B2-phase crystalizing from amorphous structure. The martensite in a nano- and micro grains may have different morphology and orientations. Nanophase (B2-TiNiCu) and nanocomposite (B2+B11(TiCu)) structures formed under crystallization by means of laser treatment, heating effect of electrical current and high temperature treatment were investigated. The ribbons with such structures in optimum state have good elastic and shape memory properties.
Room: 332
Session Chairpersons: Sungho Jin, Lucent Technologies, Bell Laboratories, Room 7G-326, 700 Mountain Avenue, NJ 07974; Iver E. Anderson, Ames Laboratory, Iowa State University, 122 Metals Development Bldg., Ames, IA 50011
2:00 pm INVITED
THE INFLUENCE OF MICROSTRUCTURE ON THE FAILURE OF EUTECTIC SOLDERS: John W. Morris, Jr., H. Reynolds, Department of Materials Science and Mineral Engineering, University of California, Berkeley, and Center for Advanced Materials, Lawrence Berkeley Laboratory, CA 94720
There are three key mechanisms of failure during the life of microelectronic solder joints: overload failure during handling, thermal fatigue failure during service, and, particularly in the case of joints for optoelectronic devices, dimensional changes during service. Each of these failure modes is strongly influenced by microstructure of the solder, which is, in turn, affected by the composition of the solder, the chemical nature of the substrate, and the manufacturing process that is used to create the joint. The present talk will discuss the varieties of microstructure that are found in common solder joints, their influence on lifetime and failure mode, and the metallurgical techniques that can be used to control microstructure and modify the nature and kinetics of joint failure.
2:25 pm INVITED
DIFFUSION PROCESSES IN LEAD BASED SOLDERS USED IN MICROELECTRONIC APPLICATIONS--AN OVERVIEW: Devendra Gupta1, J. M. Oberschmidt2, K. Vieregge3, 1IBM T. J. Watson Research Center, P.O. Box 218, Yorktown Heights, NY 10598; 2IBM Semiconductor Research and Development Center, Rt. 52-AP1, Hopewell Junction, NY 12533; 3Hoogovens Aluminium GmbH, 5400 Koblenz, Germany
Lead based solders are main stay of the microelectronic industry. Besides their use in printed boards, they are employed in interconnections of Si chip-to-substrates such as the multi-chip-modules, the thermal-conduction-module, the tape-automated bonding etc. During their service, the solder interconnections, commonly known as C-4 joints, are subjected to temperatures of the order of 100°C which translate to homologous temperatures of T/Tm 0.5 where Tm is the melting temperature in Kelvin. At these temperatures, a host of diffusion and related phenomena become operative notably the diffusion in the lattice and grain boundaries, creep and fatigue which eventually determine reliability of the device packaging. We have carried out extensive diffusion studies on the Pb-In and Pb-Sn solders over a range of composition using radioactive tracer techniques. We will discuss therein the various diffusion process, their modifications through ternary solute additions such Au and Cu and the role of unstable microstructure particularly in the eutectic solders.
2:50 pm INVITED
DEFORMATION, FATIGUE CRACKING AND COARSENING IN A LEAD-TIN EUTECTIC: T. Plookphol1, Donald S. Stone1 and S.-M. Lee2, 1Materials Science and Engineering Dept., University of Wisconsin, Madison, WI; 2Samsung Electronics Co., Suwon, Korea
Over the last several years, we have experimented with lead-tin eutectic carefully controlled microstructure in order to learn about creep, microstructural evolution, and fatigue cracking in this alloy. The purpose of those experiments has been to formulate a mechanistic basis for modeling the creep-fatigue interaction. In this paper we review the work. Creep tests, tensile tests, and load relaxation tests combined with microstructural characterization and theoretical modeling have helped to provide insight into the roles of dislocations and colony boundary sliding during creep. Colony boundary sliding impacts upon cracking and coarsening during fatigue. Work hardening and dynamic recovery during creep affect subsequent coarsening. Fatigue experiments examining the effects of frequency and strain range on fatigue crack growth have revealed transitions in mode of crack growth accompanying the onset of colony boundary sliding at low strain rates. Experimental studies of the effect of prior deformation on subsequent coarsening reveal that the factor by which coarsening accelerates depends on the rate of deformation. *Supported by the Wisconsin Alumni Research Foundation.
3:15 pm BREAK
3:25 pm
A NEW METHODOLOGY TO MEASURE DAMAGING STRAINS IN LEAD/TIN SOLDERS: Abbas I. Attarwala1 and Juan M. Sanchez2, 1Hewlett-Packard Company, IC Business Development Division, Palo Alto, CA 94304; 2Center for Materials Science, The University of Texas at Austin, TX 78712
A new methodology was developed to isolate and measure the damaging strains in lead/tin solders. The new methodology is based on load controlling cycling as opposed to strain controlled cycling. Under load controlled cycling conditions it is easy to separate out the effects of the different strain components. It was determined that the damaging strains were primarily creep strains, even at a cyclic rate of 0.5 Hz at a temperature of -40°C. Fractographic analysis of the fractured specimens confirmed that failure even at -40°C occurs by creep processes. The envelope strain curve generated from load controlled cycling data is a direct measure of the damaging strains stored in the material. A new parameter, 
D was identified. D is the damaging strain stored per cycle. The damaging strains per cycle measured for various solder compositions tested at varying frequencies, temperatures and microstructures could all be correlated by simple linear relationships. It was observed that the damaging strain stored during the secondary creep region of the envelope strain curve ranges from 2% strain to 18% strain depending on the test conditions.
3:45 pm
CREEP CRACK PROPAGATION OF 63Sn/37Pb WITH EMPHASIS ON COLONY BOUNDARY DEFORMATION AND RUPTURE: Scott A. Schroeder1 and M. R. Mitchell1 and A. G. Evans2, 1Rockwell Science Center, 1049 Camino Dos Rios, Thousand Oaks, CA 91360; 2Division of Applied Sciences, Harvard University, Pierce Hall, 29 Oxford Street, MA 02138
Experiments on deformation and rupture of eutectic Sn/Pb solder will be discussed. These involve in-situ field emission SEM observations made during tensile and thin-walled torsional shear testing at room and elevated temperatures. Deformation concentrates on colony boundaries, leading to cavitation, cracking, and tertiary creep. Cavity formation also induces a large anelastic (time-dependent recoverable strain) effect. Progressive colony boundary damage has been mapped from sequential in-situ images. Subsequent strain field mapping and animations, highlight and quantify the relative deformations. High magnification image sequences characterize cavity growth and coalescence mechanisms. Upon combining with calculations of stress distribution, creep induced cavitation and crack propagation have been quantified.
4:05 pm
MECHANICAL PROPERTIES OF Pb/Sn SOLDERS AT THE TEMPERATURE RANGE OF -200°C TO 150°C: W. Kinzy Jones, Yanqing Liu, Marc A. Zamino, Gerardo L. Gonzales, Department of Mechanical Engineering, Florida International University, Miami, FL 33199
The mechanical properties (E, 
0.2, UTS and 
%) of five Pb-Sn solder alloys (63Sn/37Pb, 62Sn/36Pb/2Ag, 96Sn/4Ag, 95Pb/5Sn, 90Pb/10Sn) commonly used in electronic packaging have been determined over the temperature range of -200°C to 150°C using uniaxial tensile test, dynamic mechanical analysis, and acoustic pulse method. The following results have been found: (1) the elastic moduli decreases linearly with increasing temperature until 70°C, then rapidly drop for the temperature 100°C and above; the strength (0.2, UTS) decreases with increasing temperature with the exception that for the solid solution solder (95Pb/5Sn, 90Sn/10Sn) which remain approximately constant; (3) the ductility change is complex: for lead matrix solid solution solders; the total elongation (r) increasing slowly with increasing temperature, the uniform elongation (u) is relatively high (>20%), and decreases slowly with increasing temperature, and the neck elongation (n) increases sharply with increasing temperature; whereas, for the eutectic solders (63Sn/37Pb, 62Pb/36Ag/2Ag, 96Sn/4Ag), the super-plasticity occurs at high temperature (>100°C), while at low temperature (-150°C) the brittle fracture occurs, the higher uniform elongation occurs at about -100°C.
4:25 pm
A MODEL OF REACTIVE WETTING FOR THIN DROPS: James A. Warren1, W. J. Boettinger1, A. R. Roosen2, 1Metallurgy Division, 2Ceramic Division, Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899
When a liquid alloy spreads on a substrate, interdiffusion may result in melting of the substrate of the substrate and/or formation of intermetallic phases. We investigate the former case and describe the evolution of the non-planar interface on the lower surface of the drop. An approximate diffusion analysis is performed for a drop whose height is much smaller than its width. The coupling between the melting process and the rate of advance of the triple junction is explored for a variety of contact angle conditions. Numerical solution of the governing equation are performed and compared to experimental results for Bi-Sn alloys spreading of a droplet on a grain boundary.
4:45 pm
EFFECT OF COMPOSITE STRENGTHENING STRATEGIES ON THE MICROSTRUCTURAL EVOLUTION IN A TIN-SILVER SOLDER: A.W. Gibson, S.L. Choi, J.L. McDougall, T.R. Bieler, K.N. Subramanian, Department of Materials Science and Mechanics, Michigan State University, East Lansing, MI 48824
Pending Federal regulations provide the impetus for using Pb-free solders. Automotive electronics and solders are exposed to thermal cycles in the range of -40°C to 150°C under cyclic and quasi-static conditions, and they experience low and high frequency mechanical fatigue vibrations. Since coarsening of microstructural features is known to affect fatigue resistance, the effects of aging behavior is investigated using eutectic Sn-Ag solder as a model system, with and without intentionally added intermetallic strengthening phases. Small single shear lap specimens with a size similar to joints in microelectronic applications are used to obtain microstructures that are obtained in real solder joints. Eutectic Sn-Ag solder joint microstructures coarsen when aged between 40 and 150°C for as little as a week. The microstructural evolution and its effect on mechanical properties is monitored with ageing temperature and time, and the kinetics of ageing is determined. The effects of adding composite intermetallic phases on the solder interface and ageing behavior are compared to the model Sn-Ag system.
5:05 pm
FORCED DIFFUSION THERMOGRAPHY FOR NONDESTRUCTIVE EVALUATION OF MICROSTRUCTURES: David A. Jahnke, Bela I. Sandor, Nuclear Engineering and Engineering Physics Dept., University of Wisconsin, 153 Engineering Research Building, Madison, WI 53704
Forced Diffusion Thermography (FDT), differential temperature detection across a material flaw while providing a controlled AC heat flux input, has been developed recently for structural integrity assessment in large structures. This paper presents FDT to identify microscopic flaws by both finite element analysis and experimentation. The technical difficulties are the production of a microscopic width heat flux line pattern and the spatial and temperature resolution of the infrared camera. A finite element model one millimeter square and one-third millimeter deep of tin solder material with various surface crack sizes specimens with known microscopic flaws were performed using an infrared camera with a temperature resolution of one mK. A seven mW helium-neon laser provided an AC heat input area of 250 micron wide by five millimeters long to the specimen's surface. The results show that this method can be applied to detect flaws in small specimens of solder and similar materials.
5:25 pm
TiN-BASED, ACTIVE METAL CONTAINING SOLDERS FOR JOINING OF ALUMINA: Tim Schwilm, O.T. Inal and Frederick G. Yost, Materials and Metallurgical Engineering Department, New Mexico Tech, Soccoro, NM 87801; Sandia National Laboratories, Albuquerque, NM 87815
Room: 340C
Session Chairs: E.H. Chason, Sandia National Laboratories, Albuquerque, NM 87185-1415; R.C. Cammarata, Surface and Interface Science Branch, Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375
SURFACE AND INTERFACE STRESS EFFECTS ON THIN FILM GROWTH: R.C. Cammarata, Surface and Interface Science Branch, Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375
Associated with any solid surface is a surface stress. It is an intrinsic thermodynamic quantity that represents the reversible work per unit area needed to elastically stretch the surface. In materials where there is a large surface area to volume ratio, such as thin films, surface stresses can have a major influence on the growth and structure. In the case of a solid-solid interface, there are two interface stresses that represent the work needed to stretch the two phases on either side of the interface. Simple models for surface and interface stresses will be presented. These will then be used to analyze thin film epitaxial growth as well as intrinsic stress generation in nonepitaxial films. It will be shown that surface and interface stresses play a central role in determining the critical thickness for epitaxy, and can lead to significant intrinsic stresses in nonepitaxial films, especially during the early stages of growth.
2:40 pm INVITED
STRESS MONITORING DURING THIN FILM GROWTH: Jerrold A. Floro, Eric Chason, Sandia National Labs, P.O. Box 5800, Albuquerque, NM 87185-1415
Thin films are typically deposited under severe kinetic constraints, resulting in highly non-equilibrium microstructures. These films often exhibit stress levels far in excess of the bulk yield strength. The origin and evolution of the film stress during deposition is, in most cases, poorly understood. We have developed a technique for real-time measurement of film stress during deposition--the Multi-beam Optical Stress Sensor (MOSS). MOSS is a technique for determination of stress through measurement of the substrate curvature. It has the virtues of low sensitivity to ambient vibration, simplicity of setup, and ease of use. We will describe the technique, and demonstrate its use for the particular case of SiGe heteroepitaxial growth on Si. We first discuss the elastic/plastic behavior of SiGe, and then focus on the surface segregation of Ge during SiGe growth. The latter topic, while somewhat specialized, is well-suited to demonstrate the interpretation of MOSS data, and to highlight both the strengths and limitations of the technique.
3:20 pm
ELASTIC MODULUS MEASUREMENT OF THIN FILM USING A DYNAMIC METHOD: Y. Kim, Department of Metallurgical Engineering, Chonnam National University, Kwangju, 500-757, Korea
The effect of external medium (air in this study) and specimen damping was estimated for the elastic modulus measurement using the sonic resonance method. A two-layer composite model was developed and applied for measuring the elastic modulus of thin film that is generally difficult to measure. The Ti coated Si wafer composites were produced using magnetron sputtering and used to test the developed model.
3:40 pm BREAK
4:00 pm INVITED
EPITAXY AND STRESS IN METAL THIN FILM COMPOUNDS AND MULTILAYERS: B.M. Clemens, T.C. Hufnagel, V. Ramaswamy, M.C. Kautzky, C.T. Wang, Department of Materials Science and Engineering, Stanford University, Stanford, CA 93405-2205
Epitaxial growth can be used to control and help understand thin film properties. We use sputter deposition to grow a variety of epitaxial thin film structures, including compounds and multilayers. The large stresses observed in these materials can have a large effect on properties. Using in-situ stress measurements and x-ray diffraction we study the stress evolution during growth and relate this behavior to thin film structure and properties. For Fe on Cu (001), we find that Fe is fcc up to a thickness of 10-12 monolayers, whereupon bcc Fe is observed in first the Pitsch and then the Bain orientations. The fcc Fe shows some relaxation of the misfit from the Cu, as do the Pitsch orientation bcc, which is in tension, and the Bain orientation bcc, which is in compression. In the giant magnetostrictive compound TbFe2, we have used epitaxy and differential thermal contraction to control the stress and hence the orientation of magnetization. This understanding and and control can lead to improved device performance.
4:40 pm
THE MECHANICAL BEHAVIOR OF PZT THIN FILMS DEPOSITED BY A SOL-GEL TECHNIQUE: D.F. Bahr, J.S. Wright, L.F. Francis, N.R. Moody*, W.W. Gerberich; Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455, *Sandia National Laboratories, Livermore, CA 94550
Lead-zirconate-titanate (PZT) thin films are used in microelectromechanical systems (MEMS) as piezoelectric components. Both the mechanical and electrical properties of the PZT layer must be known in order to understand the piezoelectic response of the PZT for use as either a sensor or actuator. These properties are controlled by the composition and structure of the PZT film and its interface. Variations in PZT film structure and morphology are caused by changing solution processing conditions. PZT films have been deposited to thicknesses between 400 and 600 nm onto a multilayered electrode structure of platinum, titanium, titanium dioxide and silicon oxide. Nanoindentation has been used to characterize the effects of grain size and structure on the mechanical properties of the PZT films. The effects of the substrate and the multilayered electrode are accounted for to determine the modulus and hardness of the PZT films.
5:00 pm
ADHESION OF CVD TiN ON 316L SURGICAL STAINLESS STEEL OBTAINED IN A MASS TRANSFER REGIME: M.H. Staia, School of Metallurgy and Materials Science, Universidad Central de Venezuela, Apartado 49141, Caracas 1042-A, Venezuela; C. Julia Schmutz, Swiss Centre for Electronics and Microtechnology Incorporated, P.O. Box 41, Neuchatel, Switzerland
An investigation has been undertaken to study the adhesion of TiN coatings deposited by using CVD process at 900°C on surgical stainless steel. The microscratch test method (CSEM) was employed to evaluate the coating adhesion. Three scratches were performed at progressive load under the test conditions. Observation of the surface damages by means of an optical microscope permitted to determine the critical load. No acoustic emission detections or frictional force fluctuations could be correlated with the optical observations. In this investigation, the critical load corresponds to the regular occurrence of delamination. Scanning electron microscopy provided the essential and detailed information about the mode of failure of the coatings along the scratch channel. It was found that the coatings presented high plastic deformation and cohesive fracture at values lower than the critical load, Lc.
Room: 330E
Session Chairpersons: Hamish L. Fraser, Dept. of Materials Science and Engineering, Ohio State University, Columbus, OH 43210; Hubert I. Aaronson, Dept. of Materials Science & Engineering, Carnegie Mellon University, Pittsburgh, PA 15213
2:00 pm INVITED
PHASE TRANSFORMATION BEHAVIOR OF GAMMA TITANIUM ALUMINIDE ALLOYS DURING SUPERTRANSUS HEAT TREATMENT: S.L. Semiatin*, V. Seetharamann, D.M. Dimiduk*, Y-W. Kim, K.H.G. Ashbee* *Wright Laboratory Materials Directorate, WL/MLLM, Wright-Patterson AFB OH 45433; UES, Inc., 4401 Dayton-Xenia Rd., Dayton OH 45432
Recent work has suggested that near-fully lamellar or fully-lamellar microstructures may provide attractive combinations of room and elevated temperature properties in near-gamma titanium aluminide alloys. The development of such microstructures via thermal processing high in the two-phase (alpha+gamma) field or in the single-phase (alpha) field is described. In particular, the interaction of the dissolution of gamma grains and the growth of alpha grains during isothermal and transient heat treatment processes will be summarized. Models for the kinetics of gamma grain dissolution and alpha grain growth will be presented. The broad application of such models for the design of heat treatments to obtain fully lamellar microstructures will be illustrated for several forged gamma components.
2:30 pm
THE ROLE OF THE 
2 PHASE IN ULTRAFINE LAMELLAR MICROSTRUCTURES DEVELOPED IN TWO-PHASE 
-TiAl ALLOYS: P.J. Maziasz, C.T. Liu, Metals & Ceramics Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831- 6115
-TiAl alloys (i.e., Ti-47Al-2Cr-2Nb(at.%)) have ultrafine fully-lamellar structures after processing or heat-treatment above the 
-transus temperature; such structures produce outstanding high-temperature strength. The lamellar colonies consist of fine laths of 2 and phases, with 100-200 nm average lamellar spacings and 200-500 nm 2-2 spacings. Generally these structures are dominated by /2 interfaces rather than / interfaces, and they are relatively free of various structural defects often found in fully-lamellar structures. Aging studies of different alloys at 800-1000°C indicates that dissolution of the fine 2 lamellae is one of the critical first steps that triggers instability and continuous coarsening of the overall lamellar structure during aging or creep. This paper focuses on detailed TEM/AEM characterization of the 2 component of the microstructure and how that information feeds into designing better TiAl alloys. Research supported by the U. S. Department of Energy, Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Industrial Technologies, Advanced Industrial Materials (AIM) Program, and Assistant Secretary for Defense Programs, Technology Management Group, Technology Transfer Initiative, under contract DE-AC05-96OR22464 with Lockheed-Martin Energy Research Corp.
2:50 pm
MICROSTRUCTURE EVOLUTION THROUGH THE 
PHASE TRANSFORMATION IN A TI-48 AT.% AL ALLOY: T. Kumagai, E. Abe, M. Nakamura, National Research Institute for Metals, Tsukuba-shi, Ibaraki 305, Japan
The (disordered h.c.p.) 
(TiAl; ordered L10 structure) massive transformation is partially suppressed even in a Ti-48 at.%Al alloy, when the alloy is quenched rapidly from the high temperature a phase filed. The untransformed (meaning 'not massively transformed') regions show an extremely fine 2 (Ti3Al; ordered DO19 structure) / lamellar structure rather than an 2 single phase structure, which is commonly observed in the quenched alloys with Al concentration of less than 47 at.%Al. By the subsequent aging treatment this fine 2/ lamellar structure changes easily to the fine grain structure, which is quite similar to the massively transformed grain structure. The microstructural development of the extremely fine 2/ lamellae during the isothermal aging treatments is presented and the phase transformation through the 2/ lamellar structure will be discussed.
3:10 pm
THE GAMMA TO ALPHA TRANSFORMATION IN A TI-48AL ALLOY: K. Muraleedharan, T.M. Pollock, Dept. of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA 15213; P. Wang, V.K. Vasudevan, Dept. of Materials Science and Engineering, University of Cincinnati, Cincinnati, OH 45221
The transformation from to in a Ti-48Al alloy during aging in the + phase field between 1275-1350°C is reported using microhardness, optical, scanning and transmission electron microscopy. The results indicate that on heating a primary structure to temperatures in the two-phase + phase field, packets of a nucleate within the grains in four orientations parallel to the four {111}g planes. The a platelets generally nucleate at grain boundaries and stacking faults on {111} planes bounded by 1/6<112] Shockley partial dislocations appear to serve as nuclei for them. The a precipitation kinetics, volume fraction and packet thickness depend strongly on the aging temperature, generally increasing with increase in temperature. These changes are also accompanied by significant hardening with time at temperature, from the initial value to a maximum, followed by a decrease at longer times. The morphology of the resulting microstructures, nucleation mechanisms, orientation relationship between the phases, sub-structure development and kinetics of precipitation during the transition will be discussed.
3:30 pm BREAK
3:50 pm
THE ORDERING TIE LINES AND TIE TRIANGLES IN TITANIUM ALUMINIDES: D.-H. Hou, H.L. Fraser, Department of Materials Science and Engineering, Ohio State University, Columbus, OH 43210
The site occupancies of alloying elements in TiAl and the ordering states in orthorhombic titanium aluminides are investigated using the newly developed Ordering Tie Line (OTL) analysis. The OTL, which can represent the atom configuration in an ordered alloy in a graphical and intuitive way, is a parameter that is unique to ordered alloys. There are two properties of an OTL, one being its slope, indicating the trend for sublattice occupancy, and the other the compositional endpoints, corresponding to the compositions of the individual sublattices. The slope can be determined conveniently by Atom Location by Channeling Enhanced Microanalysis (Alchemi) experiments, whereas the compositional endpoints may be determined either from additional information concerning the ordering scheme or determined by other experiments/simulations. In the present study, compositional endpoints are determined by simulation using the dynamical theory of electron diffraction. The OTL analysis which was originally developed for ternary compounds has been further extended to quaternary systems such as TiAl with two alloying elements and ternary system with three sublattice sites such as the orthorhombic alloys based on Ti2AlNb. For the TiAl alloys, the effect of alloying elements of Nb, Cr, Mo and Mn on the OTL are determined and discussed. For the orthorhombic alloy, it will be shown how the ordering state can be described by the Ordering Tie Triangle (OTT), and how to measure the OTT by the Alchemi experiments. Since the OTL can provide a direct measure of the ordering state, it will be an important parameter for alloy design. This work has been supported by the US ONR, Dr. George Yoder as Program Manager.
4:10 pm
DECOMPOSITION OF -TiAl/2-Ti3Al LAMELLAR STRUCTURE: J. Zhang, Z.H. Zhang, D.X. Zou, Z. Y. Zhong, Central Iron and Steel Research Institute, Beijing 100081, China
It's found in the cast Ti-46.5Al-2.5V-1.0Cr (at%) ingot, that the discontinuous coarsening (DC) dominates the decomposition of the lamellar structure when annealing at temperatures lower than 1273K while the continuous coarsening (CC) does at the temperature between 1373K and 1473K. In the case of CC, the lamellae coarsened segmentally and then the FL microstructure decomposed to a finer equiaxed near gamma (NG) microstructure as annealing time went on. The TEM observation showed that the prior lamellae are quite neat and perfect and the annealed lamellae have inner terminations. Thus, the Rayleigh's perturbation and breakdown of lamellae was believed to have occurred along with the CC. Furthermore, a cycle heat treatment of 1173K-1423K has been designed to increase the density of the inner terminations of lamellae. After that, the FL microstructure has been decomposed to a more homogeneous and even finer equiaxed NG microstructure.
4:30 pm
MICROSTRUCTURE EVOLUTION DURING POSTWELD HEAT TREATMENT OF GAS TUNGSTEN-ARC AND ELECTRON BEAM WELDS IN CAST Ti-48Al-2Cr-2Nb ALLOY: W.A. Baeslack III, C.M. Jensen, H. Zheng, Department of Industrial, Welding and Systems Engineering, Ohio State University , Columbus, OH 43210; T.J. Kelly, GE Aircraft Engines, 1 Neumann Way, Evendale, OH 45215
The microstructures of multi-pass gas tungsten-arc (GTA) welds produced in cast Ti-48Al-2Cr-2Nb (at.%) have been evaluated in the as-welded condition and following postweld heat treatment over a range of temperatures from 1000 to 1300°C. Although postweld heat treatment did not significantly affect the cast, HIP'ed and heat-treated base metal microstructure, it did promote transformation of a predominantly lamellar 2+ microstructure in the as-welded fusion zone, to microstructures comprised principally of equiaxed grains. An increase in the heat treatment temperature resulted in an increased proportion of 2 located principally at grain boundaries and grain boundary triple points. These microstructural changes were associated with softening and toughening of the fusion zone, both of which increased with an increase in postweld heat treatment temperature. Featureless, hard bands (>400 DPH as-welded) observed to parallel the fusion boundaries, which exhibited an extremely fine lamellar microstructure, were also softened by postweld heat treatment, although they remained harder than the surrounding weld metal microstructure. This work was supported by a grant to the Carnegie Mellon University from the Air Force Office of Scientific Research.
4:50 pm
INTERACTION BETWEEN TIAL AND ALN AT HIGH TEMPERATURES: Y. Paransky, E.Y. Gutmanas, Department of Materials Engineering, Technion, Haifa 32000, Israel
In this work, interfacial reactions between TiAl intermetallic and aluminum nitride have been studied in the 800-1200°C temperature range. Titanium aluminides are developing as a new group of materials for high temperature applications. Their load bearing capacity can be considerably improved by introducing high strength ceramic fibers, such as SiC or boron. Due to the high reactivity of Ti-containing materials, chemical interaction between fibers and TiAl matrix takes place at the processing and/or service temperatures resulting in deterioration of mechanical properties. Fibers can be protected by a thin coating layer which dissolves slowly enough to prevent the matrix from attacking the fiber during the composite lifetime. AlN is a possible choice for such a coating in Ti-containing matrices. Interfacial reactions between AlN and TiAl matrix have been studied using the diffusion couple approach. Phases growing at the interface between TiAl and AlN have been identified by XRD, SEM/EDS, AES and TEM; the kinetics of reaction layer growth has also been investigated. It has been found that AlN is more stable in TiAl than in pure Ti. In the latter case, the dissolution of AlN is faster due to the higher activity of Ti and high diffusivity or nitrogen in Ti.
Room: 230C
Session Chairpersons: James C. Daley, Daley & Associates, 1020 W. Cactus Wren Drive, Phoenix, AZ 85021; John M. Rapkoch, Davy International, 2440 Camino Ramon, San Ramon, CA 94583
RECYCLING OF MAGNESIUM ALLOY SCRAP, A NECESSITY: Christine Brassard, Lisabeth Riopelle, Oddmund Wallevik, Hydro Magnesium Market Development Center, 21644 Melrose Avenue, Southfield, MT 48075-9705
The use of magnesium alloys is growing rapidly, particularly in die cast parts for the automotive industry. Supporting this growth in the future means that Mg has to be an economically and ecologically attractive material, and recycling of alloy scrap becomes a necessity. What kinds of magnesium scrap will be on the market? What are the opportunities and challenges for this emerging recycling industry? Different recycling processes have been developed, and operation facilities are today recycling large volumes of class 1 diecast returns based on a flux refining technology. Characterization of the recovered metal demonstrates that the performance of appropriately recycled magnesium alloy is comparable to an alloy made from primary electrolytic metal. The sludge generated from this process can also be recycled through the existing primary Mg operations in order to close the environmental loop.
1:55 pm
INMETCO CADMIUM RECOVERY FACILITY: George Cingle III, INMETCO, 245 Portersville Road, Ellwood City, PA 16117; Gerald LaRosa, Davy International, One Oliver Plaza, Pittsburgh, PA 15222
The INMETCO Cadmium Recovery Facility currently processes commercial and industrial nickel/cadmium batteries at their Ellwood City, PA plant. The facility receives recycled nickel/cadmium batteries to recover cadmium shot product and nickel/iron scrap. The technology employed for the dismantling of industrial cells and the distillation of cadmium is under license from SAFT-NIFE in Sweden. In addition, INMETCO has installed a thermal pretreatment pilot unit for processing commercial and consumer cells which has recently demonstrated encouraging results. The INMETCO facility began detailed design in February 1995. The first cadmium distillation furnace was brought on-line December 1995, and the complete facility was operational April 1996. The facility can process 2450 short tons per year of industrial cells and 630 short tons per year of consumer cells. The facility design incorporated provisions for future expansion to allow INMETCO the ability to keep up with the forecasted growth of recycling nickel/cadmium batteries through the year 2000.
2:20 pm
COPPER RECYCLING FROM INDUSTRIAL WASTE BY MATTE SMELTING: Kazuhiro Asai, Yasuhito Kawasaki and Junzo Hino, Nippon Mining & Metals Co. Ltd., Toranomon 2-10-1, Minato-ku, Tokyo 105, Japan
Hitachi Refinery of Nippon Mining & Metals Co., Ltd. installed a reverberatory type recycling furnace in 1978 in order to treat the industrial wastes which contain metal elements such as copper, gold and silver. Waste materials and pyrite such as galvanizing sludge, hydroxide slime and dust, are smelted together, and sulfidized copper, iron and precious metals are transformed into matte and other metallic elements are oxidized into slag. This copper matte is transported to Saganoseki smelter, and copper and precious metals are recovered. Recently it became difficult to get pyrite economically because of the decrease of pyrite production. Therefore, new treating process of the liquid waste has been investigated at Hitachi. In this process, the sulfide or sulfate from the liquid waste are smelted as the sulfur source instead of pyrite.
2:45 pm BREAK
3:00 pm
THE SUBMERGED ARC FURNACE AND ITS APPLICATION IN THE NON-FERROUS RECYCLING INDUSTRY: Gero Rath, Mannesmann Demag, Huttentechnik MDH
Residues from the non-ferrous industry contain highly valuable metallic substances which make their recovery by thermal treatment desirable from the economic and environmental point of view. The electric slag resistance furnace, a variant of the submerged arc furnace is one which is used more frequently for these recycling purposes. In the last decade Mannesmann Demag has built and commissioned most of these furnaces. The paper will give an overview of the operational applications and characteristics based on the experience gained so far in lead and copper recycling.
3:25 pm
AUTOMATIC SORTING OF ALUMINUM PACKAGINGS FROM DOMESTIC REFUSE: G.J. Nijhof ea., Hoogovens R&D, P.O. Box 10.000, 19709 CA IJmuiden, The Netherlands
This work is part of a major European research project on the re-use of packaging materials in their post consumer state. The first stage of the recovering of aluminum from a waste stream is to free the non-ferrous metals with an Eddy Current machine. Previous research has given excellent results on the separation of aluminum from pre-separated packaging material. At this moment there were two reasons for a new test series: In the Netherlands all cities are obliged to collect the organic waste separately from the other waste, thus leading to a rest fraction with a high potential on aluminum. The newest generation Eddy Currents work with a higher separation efficiency. This report will discuss the results of these test series. The recovered aluminum is used for remelting trials in another sub-project of this research programme.
3:50 pm
PILOT SCALE INVESTIGATION OF FLEXIBLE ALUMINUM PACKAGING BY THERMAL PRETREATMENT: H. Rossel, R. Pietruck, VAW aluminum AG, Research & Development, Georg-von-Bosselager-Strabe 25, 53117 Bonn, Germany; Y. Bertaud, Y. Caratini, Pechiney CRV, Vorreppe, France
Laminates with aluminum are typically combined with other materials like plastics, paper, etc. The aluminum content is considerably below 50%. Therefore the separation of the laminate partner by a thermal procedure before the melting process is a successful solution. The paper reports the practical experiences with a pilot equipment in the 100kg-scale. Additionally the numerical approach to simulate the thermal process is presented. This work is part of a major European research project (PACK-EE) on the re-use of packaging materials in their post consumer state. Preliminary information on this project can be found in Light Metals, 1996.
4:15 pm
REMELTING AND PURIFICATION OF ALUMINUM PACKAGING WASTE: G.H. Nijhof ea., Hoogovens R&D, P.O. Box 10.000, 1970 CA IJmuiden, The Netherlands
This work is part of a major European research project on the re-use of packaging materials in their post consumer state. Recovering aluminum from household refuse leads to a mix-up with other metals, e.g. copper and steel. The aluminum industry aims to make packaging materials from waste packagings. Therefore, a purification step is required during the remelting operation. This research is focused on the removal of excess iron from the melt. The technique used is the formation of intermetallic compounds of FeMn by adding Mn, followed by separating these intermetallics from the molten metal. Theoretical studies of the ternairy and quarternairy phase diagrams, using computer modeling, have predicted the possible limits of purification. After laboratory trials some large scale remelting experiments have been performed to study the applicability of this technique.
Room: 231C
Session Chairpersons: Richard D. Hagni, Chairman, Geol./Geophysics Dept., Univ. Missouri, Rolla, MO; Kenneth A. Brunk, Mineral Consultant, Former Vice President, Newmont Gold Co. Denver, CO
THE ROLE OF PROCESS TECHNOLOGY AS A KEY BUSINESS UNIT: Kenneth A. Brunk, Minerals Consultant, and Former Vice President, Newmont Gold Company, Aurora, CO 80016
This address discusses how "Mineral Processing Technology" can play a major role in the life and profitability of a mining company. Examples of past and present technological breakthroughs and their impacts will be examined. Also, the future of processing technology will be emphasized.
2:35 pm
OPERATION OF NEWMONT'S BIOOXIDATION DEMONSTRATION PLANT AND PRODUCTION OF GOLD FROM LOWER GRADE REFRACTORY ORES: R.M. Perry, F.-P. Sawyer, A.J. Schindler, M.I. Shutey, Newmont Gold Company, Carlin, NV 89822; H.B. White, Newmont Metallurgical Services, Salt Lake City, UT 841O8
Test work on biooxidation pretreatment of low grade refractory gold has been ongoing at Newmont Gold Company since 1988, including laboratory testing and pilot biooxidation heaps (400 to 25,000 st). Metallurgical results of an oxidation process utilizing Thiobacillus ferroxidans have culminated in the design, construction and operation of a 780,000 ton bioxidation demonstration facility. The facility has processed 780,000 tons of refractory ore, using a batched process with separate pads for bioxidation and ammonium thiosulfate gold extraction. Siliceous sulfide refractory (SSR) and carbonaceous (CSR) ores are treated separately during biooxidation pretreatment unit operation. Procedures and results of grinding, agglomeration and pad biooxidation cycle (180 days) are followed by lime neutralization, and dumped on oxide leach pads, or stacked on the ammonium thiosulfate leach pad. Gold is leached with either cyanide for SSR ores or ammonium thiosulfate for preg-robbing CSR ores.
3:00 pm
BIOLEACHING AND PROCESSING OF A REFRACTORY GOLD ORE: N.S. Lynn, Lyntek, Inc., 775 Mariposa Street, Denver, CO 80204
A new process has been developed to bioleach refractory gold ores to expose the precious metal values using Thiobacillus ferrooxidans bacteria. The ore is hosted in a limestone rock with secondary replacement of carbonaceous and pyritic minerals. Crushing, stacking, bioleaching, rinsing and neutralization have been completed in a 45-day total time cycle. The use of sulfuric acid operation, and concentrated Thiobacillus ferroxidans population allows the short bioleaching cycle. The ore is then processed using conventional carbon-in-leach cyanide recovery techniques.
3:25 pm BREAK
3:35 pm
OXYGEN DIFFUSION INTO WET ORE HEAPS IMPEDED BY WATER VAPOR UPFLOW: R.W. Bartlett, K.A. Prisbrey, Univ. of Idaho, College of Mines and Earth Resources, Moscow, ID 83844-3025
Natural bioxidation of shallow, refractory ore heaps, relying on gaseous oxygen diffusion from the heap surface is attractive because of its simplicity and potential low cost, especially without using a lined pad, which is possible if percolation of leachate through the heap is avoided. In this case, the excess oxidation enthalpy must be removed by water evaporation from within the wet ore heap, and the rising water vapor flux within it will impede the downward oxygen flux. An analysis of this process shows that for typical values of pyrite grades and limited temperature increases. In the ore heap, the oxidation rate and penetration into the heap is reduced to values between about 30 percent and 50 percent of those obtained when leachate percolation occurs and water evaporation is not significant mechanism of heat removal.
4:00 pm
ECONOMIC CRITERIA FOR CHOOSING BIOHEAP PRETREATMENT OF MIXED OXIDE/REFRACTORY GOLD ORE: Robert W. Bartlett, Univ. of Idaho, College of Mines & Earth Resources, Moscow, ID 83844-3O25
Bioheap pretreatment of sulfidic refractory gold ore prior to cyanide leaching is a promising new technology, especially for low-grade ores that cannot be oxidized by pressure leaching or roasting. Ores containing both refractory and amenable gold require economic decisions whether, or not, to pretreat before cyanide leaching. This choice is more complex than familiar ore/waste cut-off grade decisions. Pretreatment may increase recovery but delays receiving revenue. An equation has been developed that computes a "critical cyanide leachable gold grade" for determining whether pretreatment will be profitable. If the ore's actual cyanide leachable grade, without pretreatment, is above critical grade, pretreatment will not pay. The parameters in this equation are: waste/ore cut-off grade, pretreatment yield, total gold grade, pretreatment operating cost and project's financial discount rate. Calculations are provided for use in mine development planning when bioheap pretreatment is an available option.
Room: 315A
Session Chairpersons: V. Selvamanickam, Intermagnetics General Corporation, Latham, NY; M.J. Kramer, Ames Laboratory, Ames, IA
CRITICAL CURRENT IN SMALL ANGLE GRAIN BOUNDARIES: C. S. Pande, R.A. Masumura, Naval Research Laboratory, Washington, DC 20375-5343
It is now well known that even small angle grain boundaries (misorientation angle 
¾ 10) show drastic reduction in inter-grain critical current. Drawing upon on our previous work, we show that this reduction must be ascribed to the stress field in proximity of the dislocations forming the small angle boundary. The alternate view that the reduction is due to the presence of dislocation cores is investigated by calculating their size as a function of misorientation. We show that the concept though probably valid for large misorientation ( 
10) leads to serious disagreement with experiments for small values ( ¾ 10).
2:20 pm INVITED
DIRECT OBSERVATION OF CURRENT DISTRIBUTIONS IN THIN SUPERCONDUCTORS USING MAGNETO-OPTIC IMAGING: T.H. Johansen, M. Baziljevich, H. Bratsberg, Department of Physics, University of Oslo, Box 1048 Blindern, 0316 Oslo, Norway; Y. Shen, P. Vase, NKT Research Center, Sognvej 11, 2605 Brøndby, Denmark
A thin film of YBa2Cu3O7- prepared by laser ablation and shaped by etching as a long strip was studied by magneto-optic imaging. The penetration of a perpendicular magnetic field was investigated in detail, and a model-independent method of determining the space-resolved current distribution was developed. The inverse magnetic problem, i.e., that of using a field map to derive the underlying current distribution, is formulated and solved analytically for the strip geometry. The observed current profile across the strip gives direct evidence for the assumptions made in the Bean model. Also other geometries were investigated, demonstrating the new application of magneto-optics as a tool to determine current flow patterns.
2:40 pm INVITED
FABRICATION OF BIAXIALLY-TEXTURED THICK FILM Y-Ba-Cu-O SUPERCONDUCTOR: V. Selvamanickam, M.S. Walker, P. Haldar, R.S. Sokolowski, Intermagnetics General Corporation, Latham, NY 12110; A. Ivanova, A.E. Kaloyeros, State University of New York at Albany, Albany, NY 12222; D.E. Fenner, Fenner Engineering Associates, Simsbury, CT 06070
High current densities have been recently demonstrated at 77 K in thick film YBCO superconductor deposited on biaxially-textured metallic substrates. The effort at Intermagnetics has been directed towards the development of an industrially scaleable process based on biaxially-textured substrate technology. Biaxially-textured metallic substrates have been fabricated in long lengths with an average in-plane orientation better than 10° and an average out-of-plane orientation better than 7°. Buffer layers that are structurally and chemically compatible with YBCO have been deposited on the metallic substrates with a biaxial texture similar to that of the substrate. Metal-Organic Chemical Vapor Deposition (MOCVD) has been used for deposition of YBCO since this technique enables a high rate of deposition that is not limited by line-of-sight. Stoichiometric, dense, and biaxially-textured films of YBCO superconductor have been successfully deposited by MOCVD on the biaxially textured substrates. This research was partially supported by the Department of Energy.
3:00 pm INVITED
HIGH CRITICAL CURRENT DENSITY TAPES BY EPITAXIAL DEPOSITION OF SUPERCONDUCTING THICK FILMS ON BIAXIALLY TEXTURED METAL SUBSTRATES: A. Goyal, D.P. Norton, M. Paranthaman, E.D. Specht, J.D. Budaj, D.M. Kroeger, D.K. Christen, Q. He, B. Saffian, F.A. List, D.F. Lee, S. Shoup, P.M. Martin, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6116
A method to obtain long lengths of flexible, biaxially oriented substrates with smooth, chemically compatible surfaces for epitaxial growth of high temperature superconductors is reported. The technique uses well established, industrially scaleable, thermomechanical processes to impart a strong biaxial texture to a base metal like Ni. This is followed by vapor deposition of epitaxial buffer layers (metal and/or ceramic) to yield chemically compatible surfaces for HTS film deposition. Substrates prepared using this method are referred to as Rolling Assisted Biaxially Textured Substrates (RABITS). Epitaxial YBCO films grown using laser ablation on RABITS have critical current densities exceeding 7 x 105 A/cm2 at 77 K in zero-field and have field dependences similar to epitaxial films on single crystal ceramic substrates. The texture of the base metal has been achieved in lengths over 1 m and scaleable techniques are being pursued to deposit epitaxial multilayers. Deposited conductors made using this technique offer a potential route for the fabrication of long lengths of high Jc wire capable of carrying high currents in high magnetic fields and at elevated temperatures. Research sponsored by U.S. DOE under contract DE-AC05 960R22464.
3:20 pm INVITED
TRANSPORT BEHAVIOR OF GRAIN BOUNDARIES IN YBa2Cu3O7
: A COMPARISON BETWEEN THIN FILM AND BULK Bi-CRYSTALS: D.J. Miller, V.R. Todt, M. St. Louis-Weber,* D.G. Steel, X.F. Zhang, K.E. Gray, U. Balachandran*, Materials Science Division and *Energy Technology Division, Argonne National Laboratory, Argonne, IL 60439
The structure and transport properties of grain boundaries in thin film and bulk bi-crystals of YBa2Cu3O7
have been studied in detail. The thin film bi-crystals were prepared by sputter deposition onto SrTiO3 bi-crystal substrates while the bulk bi-crystals were prepared by a dual-seeded melt textured growth process. The structures of these two types of grain boundaries can be very different: thin film boundaries typically exhibit meandering and impurity phases that extend through the thickness of the film while the bulk boundaries tend to be very straight and relatively free of impurity phases. A comparison of the transport behavior between these two types of boundaries will be presented and the implications of the similarities and differences will be discussed. This work was partially supported by the U.S. Department of Energy, Basic Energy Sciences-Materials Sciences, under Contract No. W-31-109-ENG-38 and by the National Science Foundation through the Science and Technology Center for Superconductivity under Contract No. DMR 91-20000.
3:40 pm BREAK
3:50 pm INVITED
PROCESS OPTIMIZATION FOR YBCO THICK FILMS: J.S. Abell, T.C. Shields, J. Langhorn, S.C. Watcham, School of Metallurgy and Materials, University of Birmingham, Birmingham B15 2TT, UK
Superconducting thick films are finding technological exploitation in various applications; for example as inductive components in power engineering designs such as fault current limiters, and as microwave devices like filters in cellular communications applications. For efficient performance in these different fields superconducting properties require optimisation with respect to different parameters such as critical current density (Jc) and surface resistance (Rs). The microstructural control to deliver these properties demands careful processing. Flux pinning additions, composition control, doping, and novel processings techniques have been employed to improve the characteristics of the films. Barrier layer technology to enable the exploitation of low dielectric loss and economically attractive alumina substrates has been studied. The relationship between processing, microstructure and superconducting behavior will be discussed.
4:10 pm
MULTI-WAFER MANUFACTURING OF LARGE-AREA YBCO THIN FILMS FOR R.F. DEVICE APPLICATIONS: C.N. Soble, V.C. Matijasevic, Z. Lu, T. Kaplan, K. von Dessonneck, Conductus, Inc., Sunnyvale, CA 95123
Scaling up PVD and CVD techniques to reasonable manufacturing levels has been a scientific and engineering challenge for companies developing HTS materials for commercial applications. In this paper, we discuss the process development and optimization work associated with ramping up a multi-wafer reactive co-evaporation deposition system capable of depositing high quality YBCO on 2" to 8" wafers (R-pl sapphire or LaAlO3). YBCO thin films deposited using this technique exhibit good electrical properties with transition temperatures 85-87 K and Jc >2 x 106 A/cm2 at 77K. Microwave surface resistance, R, is <1 m
at 10 GHz and 77 K. HTS films on R-pl and LaAlO3 have been fabricated into r.f. devices for applications in NMR spectroscopy, Magnetic Resonance Imaging, and wireless communications.
4:30 pm INVITED
PHASE DIAGRAM AND CATION DISORDER STUDIES IN RE1+xBa2xCu3O7+
, RE= Pr, Nd, Sm, Eu, and Gd: M. J. Kramer, H. Wu, K.W. Dennis, R.W. McCallum, Ames Laboratory, Iowa State University, Ames, IA 50011
For the light rare earth elements, the orthorhombic REBa2Cu3O7- structure forms not as a line compound but with varying degrees of RE+3 substitution on the Ba+2 sites and additional oxygen incorporated in the basal plane to balance charge. It has been demonstrated that for RE = Nd, Pr, (Nd + Pr), and (Nd + Gd), the occupation of RE on Ba sites is a function of the oxygen partial pressure (pO2) and temperature. Not only is the minimum value of x effected but for a fixed value of x, large changes in the superconducting transition are observed. By manipulating the pO2 and T profile, phase assemblage can be modified. Under proper processing conditions, these second phases can form pinning sites in these materials, resulting in enhanced high field critical currents. Supported by U.S. Department of Energy, under Contract No. W-7405-Eng-82.
4:50 pm INVITED
THE EFFECT OF PROCESSING PARAMETERS ON Hg-1223 TAPE FABRICATION: R. Meng, Y.Wang, B. Hickey, K. Ross, Y. Xue, C.W. Chu, Texas Center for Superconductivity, University of Houston, Houston, TX 77204-5932
We have developed a process to fabricate Hg-1223 tape on a metal substrate with a transition temperature of 130 K and a self-field critical current density of 2 x 104 A/cm2 at 77 K. However, the reproducibility of the tape is poor and weak links exist in the