Conference Review: Feature

The Symposium Imaging of Dynamic Processes: Multimedia Hightlights

Iver E. Anderson

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SYMPOSIUM PRESENTATIONS Of the ten presentations delivered to meeting attendees, five are spotlighted via multimedia enhancement on the JOM web site as a supplement to the June 2002 issue. The featured clips provide excellent examples of some of the information that can be gathered and applied in understanding a variety of processes. Featured Presentations “Thermal Imaging of Solidification,” William Hofmeister (Vanderbilt University) “Visualization of Primary Austenite and Primary Ferrite Solidification Modes in Fe-Ni-Cr Gas Tungsten Arc Welds,” Aaron C. Hall, Charles V. Robino, John Brooks, Mark Reece, and Danny O. MacCallum (Sandia National Laboratories) “Schlieren Imaging in Materials Processing,” Steven P. Mates (National Institute of Standards and Technology) “Increased Understanding of Gas Atomization from Gas Flow Imaging and High Speed Cinematography,” I.E. Anderson and R.L. Terpstra (Iowa State University, Ames Laboratory) and S. Rau (University of Bremem) and R. Figliola (Clemson University) “Studying Changes in Surface Topography by White Light Interferometry,” Borge Holme (SINTEF) Other Presentations “Three Dimensional Microstructural Evolution in Succinonitrile,” Mark A. Palmer (Kettering University) and Martin E. Glicksman and Krishna Rajan (Rensselaer Polytechnic Institute) “Investigation of Bubble Nucleation Site Density during Quenching Heat Treatment Process Using Video Imaging,” M. Maniruzzaman, S.H. Ma, R.D. Sisson (Worcester Polytechnic Institute) “Imaging Spatial Heat Flow and Dynamic Instabilities in Melt Spinning,” Matthew J. Kramer, Ralph E. Napolitano, Halim Meco, Matthew Sawka, Kevin W. Dennis, and R. William McCallum (Iowa State University, Ames Laboratory) “The Use of High Speed Imaging for Thermomechanical Characterization of Melt Pool Dynamics during Rapid Solidification,” H. Meco, M.J. Kramer, R.E. Napolitano, M. Sawka, K.W. Dennis, and R.W. McCallum (Iowa State University, Ames Laboratory) “Imaging and Particle Image Velocimetry of Granular Flows,” Daniel Steingart and James W. Evans (University of California at Berkeley)

High-resolution imaging is critical to enhancing our understanding of the many processing techniques that enable the manufacture of materials both advanced and mundane. If it is true that “one picture is worth a thousand words,” then it is reasonable to extrapolate that this value can be increased by orders of magnitude if a correlated series of images is collected into a movie or video recording. The effect can be more pronounced if the images can slow down or speed up (by use of time-lapse photography) the action of a dynamic process.

Exploration of this concept was the subject of the two-session symposium Imaging of Dynamic Processes, which was held during the 2002 TMS Annual Meeting, February 17–21, in Seattle, Washington. The symposium’s participating authors and the titles of their presentations are listed in the sidebar. The program was conducted under the auspices of the joint Processing Modeling and Control Committee of the TMS Extraction & Processing Division and the TMS Materials Processing & Manufacturing Division. Owing to the multimedia aspects of the symposium, the presentations were not collected for presentation in a traditional conference proceedings volume. Instead, highlights from the symposium are underscored in this conference review, and multimedia highlights have been selected and embedded into the JOM web version of this article for your further study and analysis.

As the on-line presentations illustrate, visualization can provide in-situ process information on either a global or local scale, enabling pieces of sensor data to mesh as a coherent process description. Certainly, materials scientists oftentimes require an enhanced understanding of a phase or physical transformation that cannot be thoroughly characterized via indirect or direct sensing and/or post-process analysis. The high level of process information presented by imaging is invaluable for both developing new techniques and gaining fundamental insights into the operation of existing processes. Eventually, such information can be used to develop process control techniques featuring fully closed-loop logic—something that can be enhanced by artificial intelligence and enable high-level materials manufacturing concepts.

Within this context, the symposium was organized to attract researchers having wide-ranging interests yet common problems in collecting visual information on materials-processing techniques, grouped according to processing approach.

One category concerns solidification processing, and the initial lecture focused on using thermal imaging at Vanderbilt University to study the solidification of a levitated droplet and a surface deposition layer. Thermal imaging allowed the researchers to investigate the relationship between bulk undercooling and solidification velocity in levitated droplets of pure metallic materials and alloys. Researchers from Sandia National Laboratories presented an intriguing collection of high-speed, high-magnification videos of solidification during the gas-tungsten-arc welding of Fe-Ni-Cr alloys. Detailed analysis of the digitized images enabled the researchers to measure solid-liquid interface velocity in the solidifying welds. In work performed at Rensselaer Polytechnic Institute, video imaging was used to study solid-state grain coarsening in thin films of optically transparent succinonitrile. The visualization results permitted the development of an alternative explanation of the phenomena.

An alternative visualization tool, white-light interferometry, was applied to a series of studies conducted at SINTEF Materials Technology. Surface topology changes extending to the nanometer range were studied in processes as diverse as paint drying, surface etching, corrosion, and mechanical strain (Video 3b). At Worcester Polytechnic Institute, bubble nucleation during the transparent-fluid quenching of high-temperature metal samples was studied by high-speed videography. The researchers employed a fully instrumented sample to gain a detailed understanding of the heat-transfer process during quenching.

Researchers at Ames Laboratory, Iowa State University, reported on using stop-action digital photography to analyze the time-temperature evolution of the melt jet and melt pool in a single-roller free-jet melt spinner. Computer-aided combinations of spatial and thermal images were used to provide the boundary conditions necessary for heat-transfer and solidification modeling. In a complementary presentation, results from the melt-spinning study were reported as pertain to the rapid solidification of several rare-earth-containing permanent-magnet alloys. The process parameters that influence melt-pool stability and shape were discussed in detail, particularly with regard to the ribbon-solidification process.

Work from the National Institute of Standards and Technology was outlined using schlieren optical techniques to study supersonic gas flows in both gas atomization and thermal-spray processes (Video 5b). Results were presented on schlieren optical arrangements for optimizing image quality in the study of gas-only flows and in-situ process observations. High-speed cinematography and schlieren imaging were applied to a fundamental study of gasatomization processing by researchers at Ames Lab. The high-speed movies allowed in-situ observation of atomization process dynamics and evidence of progress toward ideal primary atomization dominance.

In the symposium’s final presentation, researchers from the University of California at Berkeley reported the use of high-speed videography to study the flow of dense, large particles from two-dimensional hoppers. Detailed changes in the velocity and spatial distribution of uniform spheres undergoing various discharge flow processes were studied.