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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 l.jpg

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


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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


Important knowledge to the larger field yes l.jpg
… 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


Progress understanding and control of microsegregation and microstructure l.jpg
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


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Interface morphologies during directional solidification microstructure

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


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IDGE single dendrite microstructure(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


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Intertactions among dendrites microstructure

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


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PROGRESS: Understanding and control of microstructureindustrially 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


Benchmark data on coarsening in pb sn voorhees et al l.jpg
Benchmark data on coarsening in Pb-Sn microstructure(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


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Particle pushing of polystyrene spheres in SCN microstructure

Robert F. Sekerka for the Materials Science DWG


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Progress: Accurate measurement of thermophysical properties microstructure

  • 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


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Mechanical properties of metallic glasses microstructure

Robert F. Sekerka for the Materials Science DWG


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Measuring liquid diffusivities in space I microstructure

In space

Diffusive Flux

Pure Diffusion

On the Earth

Diffusive Flux

Convective Flux:

Convective Diffusion

Robert F. Sekerka for the Materials Science DWG


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Measuring liquid diffusivities in space II microstructure

Robert F. Sekerka for the Materials Science DWG


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PROGRESS: New ways of doing science microstructure 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


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For progress to continue, NASA must: microstructure

  • 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


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Thank you for your attention! microstructure

Robert F. Sekerka for the Materials Science DWG