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Presentation to the Committee on Microgravity Research

Presentation to the Committee on Microgravity Research. by Robert F. Sekerka University Professor Physics, Mathematics and Materials Science Carnegie Mellon University October 23, 2001. Questions to be Addressed.

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Presentation to the Committee on Microgravity Research

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  1. Presentation to the Committee on Microgravity Research by Robert F. Sekerka University Professor Physics, Mathematics and Materials Science Carnegie Mellon University October 23, 2001 Robert F. Sekerka for the Materials Science DWG

  2. Questions to be Addressed • Has microgravity research on this topic contributed any important knowledge to the larger field of which the research is a part? • What progress has been made on understanding the microgravity research questions posed on this topic? Robert F. Sekerka for the Materials Science DWG

  3. … important knowledge to the larger field …? YES • Understanding and control of solute segregation and microstructure • Understanding and control of industrially important materials processing • Accurate measurement of thermophysical properties • New ways of doing science and technology Robert F. Sekerka for the Materials Science DWG

  4. Progress: Understanding and control of microsegregation and microstructure • Plane-front solidification, defect and diffusion control in InSb:Te and Ge:Ga (Witt and Gatos) • Segregation control in Hg1-xCdxTe (Lehoczky) • Morphological stability (MEPHISTO): in SnBi (Favier) and BiSn facetted (Abbaschian) • Cellular morphologies: deep cells (Trivedi); mushy zones (Poirier) • Dendrites: IDGE (Glicksman); interactions, alloys, (Beckermann); transients (Koss) Robert F. Sekerka for the Materials Science DWG

  5. Interface morphologies during directional solidification Planar Cellular Dendritic Random Nucleation Planar Planar Planar Planar S L S L S L S L Electronic Materials Silicon, Gallium Arsenide Planar High Strength Metals and Alloys Cellular Dendritic Liquid Temperature Gradient Metal Casting Random Nucleation Growth Rate Robert F. Sekerka for the Materials Science DWG

  6. IDGE single dendrite(Glicksman et al.) Single dendrite grown from pure supercooled SCN. Simultaneous measurement of steady state growth speed and tip radius are necessary to test existing theories. Robert F. Sekerka for the Materials Science DWG

  7. Intertactions among dendrites Up to four dendrites grown toward one another from the vertices of a regular tetrahedron can be used to study interactions of the type that would occur during casting. Robert F. Sekerka for the Materials Science DWG

  8. PROGRESS: Understanding and control of industrially important processing • Benchmark data for coarsening in solid-liquid mixtures of Pb-Sn (Voorhees) • Role of gravity in liquid phase sintering in heavy W-Ni-Fe/Cu alloys (German) [tungsten carbide, silicon nitride, tool steels, cermets] • Microstructure control by deep undercooling (Flemings) [stainless steels] • Particle engulfment and pushing by solidifying interfaces, [metal matrix ceramic composites] e.g., Al-ZrO2, Al-SiC (Stefanescu) Robert F. Sekerka for the Materials Science DWG

  9. Benchmark data on coarsening in Pb-Sn(Voorhees et al.) • Measurements of size distribution and coarsening kinetics of Sn-rich solid particles in Pb-rich liquid. Microgravity enables uniform distributions. Benchmark data. Analysis involves no free parameters. Robert F. Sekerka for the Materials Science DWG

  10. Particle pushing of polystyrene spheres in SCN Robert F. Sekerka for the Materials Science DWG

  11. Progress: Accurate measurement of thermophysical properties • TEMPUS: International cooperation (equipment / samples / data) with Germans on containerless processing • Electrostatic levitation, JPL -> Loral -> Marshall & Caltech • Oscillation modes of levitated droplets used to measure surface tension and viscosity (Szekely/Trapaga) • Double recalescence (masked on Earth by transport) to reveal metastable phases (Flemings) • Use of AC calorimetry (decoupled heating from levitation) to get heat capacity of glass forming systems (Johnson) Robert F. Sekerka for the Materials Science DWG

  12. Mechanical properties of metallic glasses Robert F. Sekerka for the Materials Science DWG

  13. Measuring liquid diffusivities in space I In space Diffusive Flux Pure Diffusion On the Earth Diffusive Flux Convective Flux: Convective Diffusion Robert F. Sekerka for the Materials Science DWG

  14. Measuring liquid diffusivities in space II Robert F. Sekerka for the Materials Science DWG

  15. PROGRESS: New ways of doing science and technology • Use of H fields in Czochralski and Bridgman • Peltier pulsing interface demarcation technique • New paradigms for crystal defect and segregation control (interface shape and wall effects) • Seebeck detection of an interface • Interactive teleoperation of remote experiments • Sharing of raw data: • http://www.rpi.edu/locker/56/000756/ • http://liftoff.msfc.nasa.gov/Shuttle/msl/science/cslm.html • http://pmlab.esm.psu.edu/pmnasa.htm Robert F. Sekerka for the Materials Science DWG

  16. For progress to continue, NASA must: • Reaffirm the importance of a broad spectrum of materials research, experimental and modeling • Fund and build the facilities needed to conduct research aboard ISS • Honor our commitments for adequate and timely funding of approved PI’s • Eliminate intolerable delays in issuing and processing NRA’s and in flight schedules • Keep present materials researchers from defecting while adding new and exciting areas Robert F. Sekerka for the Materials Science DWG

  17. Thank you for your attention! Robert F. Sekerka for the Materials Science DWG

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