1997 TMS Annual Meeting: Tuesday Session

APPLICATIONS OF SENSORS AND MODELING TO MATERIALS PROCESSING: Session III

Session Chairs: S. Viswanathan, Oak Ridge National Lab., Oak Ridge, TN 37831-6083; J. Chun, Dept of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139

8:30 am

USE OF IMAGING PYROMETRY SENSOR IN METALLURGICAL PROCESSES: C. Lorenson, Quadtek, 14737 NE 87th St., Redmond, WA 98052

The Spyrometer imaging pyrometer brings a new dimension of imaging capabilities to temperature measurement technology by combining a high temperature video camera with scanning optical pyrometry. This gives operators the ability to observe process conditions while measuring the temperature of virtually any object or region in the field of view. Since the lens tube of the camera can be air or water cooled, it is possible to insert the optical lens tube inside furnaces giving very good view of many different types of metallurgical processes. Specific benefits in process knowledge and maintenance tasks for electric arc melting furnaces, anode furnace and casting wheels, flash smelters, reheat furnaces, and torpedo ladles in different types of metal industries will be discussed.

8:55 am

A COMPUTED TOMOGRAPHY SENSOR FOR SOLIDIFICATION IN METAL CASTING: J. Chun, N. Saka, M.H. Hytros, D. Kim, Dept. of Mechanical Engineering, R.C. Lanza, I.M. Jureidini, Dept of Nuclear Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139

We have developed a novel method, using X-ray photons and computed tomography (CT), for distinguishing the solidification front in metal casting processes directly and nondestructively. Depending on the metal, the density of the liquid and solid phases may differ anywhere from 4 to 12%. Computed tomography provides an excellent means of mapping this density difference into a two- or three-dimensional image. Using a Co60 radioisotope and a NaI scintillation detector, CT image reconstruction was performed on pure tin metal in a two-phase state. In addition, CT image reconstruction was done using a 6 MeV linear accelerator and CdWO4 scintillation detector array on pure and alloyed aluminum metals while they underwent solidification. As the speed of the data acquisition and image reconstruction improves, this sensor technology offers the possibility of real-time performance and eventual feedback control for the metal casting process.

9:20 am

LASER ULTRASONIC SENSING OF SOLID-LIQUID INTERFACES DURING BRIDGMAN SINGLE CRYSTAL GROWTH: H.N.G. Wadley, Y. Lu, D.T. Queheillalt, Intelligent Processing of Materials Laboratory, School of Engineering and Applied Science, University of Virginia, Charlottesville, VA 22903

Using a 3-D ray tracing methodology combined with laser ultrasonically measured elastic constant data near the melting point, ultrasonic propagation in cylindrical single crystal bodies containing either a convex or a concave solid-liquid interface have been simulated and used to design new sensing concepts. Ray paths, wavefronts, and time of flight (TOF) of rays that travel from a source to an arbitrarily positioned receiver have been calculated. Experimentally measured TOF data have been collected using laser generated/detected ultrasound on model systems with independently known interface shapes. Both numerically simulated data and experimental results have shown that the solidification (interfacial) region can be identified from ultrasonic transmission TOF data. Ultrasonic sensing in the diametral plane is the preferred sensing configuration. Since convex and concave solid-liquid interfaces result in distinctively different TOF data profiles, the interface shape (convex or concave) can be readily determined from the TOF data. When TOF data collected in the diametral plane are used in a nonlinear least squares algorithm, the interface curvature has been successfully reconstructed and ultrasonic velocities of both the solid and liquid obtained, the reconstruction errors were found to be less than 5%.

9:45 am

EDDY CURRENT SENSORS FOR MONITORING THE NUCLEATION AND GROWTH OF Cd0.96Zn0.04Te BULK CRYSTALS: Haydn N.G. Wadley, K.P. Dharmasena, Bill W. Choi, Intelligent Processing of Materials Laboratory, School of Engineering and Applied Science, University of Virginia, Charlottesville, VA 22903

Non-contact eddy current sensing methods have been developed and applied to Cd0.96Zn0.04Te crystal growth to obtain a better understanding of the melt, solid nucleation, and the growth process. The application of this sensor approach relies on a large difference in liquid and solid electrical conductivities near the melting point and requires knowledge of the relationships between the electrical conductivity, melt composition, and temperature. Using a multi-frequency encircling eddy current sensor, the electrical conductivities of three different Cd1-yZnyTe (y = 0.00, 0.045, and 0.08) alloys were measured as a function of temperature in a laboratory-scale vertical Bridgman furnace. The measured solid and liquid electrical conductivities were then used in electro-magnetic finite element models to analyze the multifrequency responses of eddy current sensor designs during the simulated growth of a crystal. Three eddy current sensors were fabricated and installed in a vertical Bridgman furnace and used to monitor many Cd0.96Zn0.04Te growth runs One sensor was placed in the vicinity of the ampoule tip to detect undercooling/spontaneous nucleation and two other sensors ("absolute" and "differential" designs) placed to monitor the movement/curvature of the liquid-solid interface during crystal growth. The sensor data was used to characterize the initial melt state, detect the onset of nucleation, determine the growth velocity, and identify the shape of the interface.

10:10 am BREAK

10:20 am

ADVANCES IN SENSING COMPOUND SEMICONDUCTOR CRYSTAL GROWTH: J.P. Wallace, Casting Analysis Corp., RT 2 BOX 113, Weyers Cave, VA 24486

Monitoring compound semiconductor crystal growth using multifrequency eddy currents for sensing illustrates some of the extreme problems of measurement and interpretation of that are not often seen in metallic systems monitored through solidification. Using sensor arrays and scanning have produced a qualitative and quantitative basis for understanding some of the high temperature electrical conductivity mechanisms. The implications of these measurements of electrical conductivity variations are important in that they reflect the complex states of stress that will occur on cooling and heat treating following crystal growth. In particular, for the CdTe and the CdZnTe system, the measurements provide some proof of where the changes in majority defect types occur. The complex nature of the melt and the cooling solid coupled with the growth interface data provide a basis for analyzing the major events during growth and cool down.

10:45 am

GAUGING OF HOT TUBE, BAR, AND WELDS BY MULTIFREQUENCY EDDY CURRENT: J.P. Wallace, Casting Analysis Corp., C. Iheagwara, Magnetic Analysis Corp., RT 2 Box 113, Weyers Cave, VA 24486

Refinements in sensor design have produced low-cost rugged elements acting as loops coupled with stable detection hardware. This has allowed direct dimensional gauging of nonferrous and ferrous products above the curie point for absolute dimensions and electrical conductivities independently. The software was developed for the analysis of electrical conductivity profiles in CZ silicon crystal growth, then refined for the monitoring of bar properties, and then tube properties. Since in most metal working operations, speeds at the minimum of a few hundred feet per minute are encountered, the design of the gauge was optimized for a rapid measurement. Independently extracting electrical conductivity provides data in some metal system for determining the temperature of the monitored product. Applications in ferrous heat treatment will be discussed.

11:10 am

A REMOTELY OPERABLE SENSOR FOR PRECISION SURFACE MAPPING USING COHERENT FREQUENCY MODULATED (FM) LASER RADAR: M.M. Menon, R.E. Barry, P.T. Spampinato, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6305; A. Slotwinski, Coleman Research Corporation, Springfield, VA 22150; M.A. Dagher, Rockwell International Corporation, Canoga Park, CA 91303

A coherent FM laser radar based sensor is being developed for remote metrology of plasma facing material surfaces in the International Thermonuclear Experimental Reactor (ITER). The sensor is capable of three-dimensional mapping of the surface under examination, based on a series of precise range measurements. Sub-millimeter accuracy at large ranges (15 m) has been achieved. Other features that are being incorporated include the ability to operate under adverse environmental conditions involving a combination of very high gamma radiation (3x106 rad/h), ultra-high-vacuum (<10-7 torr), and high temperature (200°C). The paper will describe the basic principles of the sensor, together with experimental results obtained with the sensor. The paper will also outline the broad capabilities of the sensor, including its ability for remote rendering of "visual quality" images without the need for any external illumination. Research sponsored by the Office of Fusion Energy, U. S. Department of Energy, under contract DE-AC05-96OR22464 with Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corp.