Carnegie Mellon October 23, 2001Robert F. Sekerka for the Materials Science DWG 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

Carnegie Mellon October 23, 2001Robert 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?

Carnegie Mellon October 23, 2001Robert 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

Carnegie Mellon October 23, 2001Robert 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 Hg 1-x Cd x Te (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)

Carnegie Mellon October 23, 2001Robert F. Sekerka for the Materials Science DWG 5 Interface morphologies during directional solidification Planar SL SL Cellular Planar SL Dendritic Planar SL Random Nucleation Liquid Temperature Gradient Growth Rate Random Nucleation Dendritic Cellular Planar Electronic Materials Silicon, Gallium Arsenide High Strength Metals and Alloys Metal Casting

Carnegie Mellon October 23, 2001Robert 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.

Carnegie Mellon October 23, 2001Robert 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.

Carnegie Mellon October 23, 2001Robert 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-ZrO 2, Al-SiC (Stefanescu)

Carnegie Mellon October 23, 2001Robert 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.

Carnegie Mellon October 23, 2001Robert F. Sekerka for the Materials Science DWG 10 Particle pushing of polystyrene spheres in SCN

Carnegie Mellon October 23, 2001Robert 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)

Carnegie Mellon October 23, 2001Robert F. Sekerka for the Materials Science DWG 12 Mechanical properties of metallic glasses

Carnegie Mellon October 23, 2001Robert F. Sekerka for the Materials Science DWG 13 Measuring liquid diffusivities in space I Pure Diffusion On the Earth Diffusive Flux Convective Flux: In space Convective Diffusion

Carnegie Mellon October 23, 2001Robert F. Sekerka for the Materials Science DWG 14 Measuring liquid diffusivities in space II

Carnegie Mellon October 23, 2001Robert 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:

Carnegie Mellon October 23, 2001Robert 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

Carnegie Mellon October 23, 2001Robert F. Sekerka for the Materials Science DWG 17 Thank you for your attention!