Transcript Presentation to the Committee on Microgravity Research

Carnegie Mellon
Presentation to the Committee on
Microgravity Research
by
Robert F. Sekerka
University Professor
Physics, Mathematics and Materials Science
Carnegie Mellon University
October 23, 2001
October 23, 2001
Robert F. Sekerka for the
Materials Science DWG
1
Carnegie Mellon
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?
October 23, 2001
Robert F. Sekerka for the
Materials Science DWG
2
Carnegie Mellon
… 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
October 23, 2001
Robert F. Sekerka for the
Materials Science DWG
3
Carnegie Mellon
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)
October 23, 2001
Robert F. Sekerka for the
Materials Science DWG
4
Carnegie Mellon
Interface morphologies during directional solidification
cells
Planar
Planar
S
Cellular
Planar
L
S
Dendritic
Planar
L
S
Random Nucleation
Planar
L
S
L
(a)
deep
cells
Electronic Materials
Silicon, Gallium Arsenide
Planar
Liquid Temperature
Gradient
(b)
Cellular
High Strength
Metals and Alloys
Dendritic
“mushy zone ”
Random
Nucleation
Metal Casting
Growth Rate
(c)
October 23, 2001
Robert F. Sekerka for the
Materials Science DWG
5
Carnegie Mellon
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.
October 23, 2001
Dendrite
Robert F. Sekerka for the
Materials Science DWG
6
Carnegie Mellon
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.
October 23, 2001
Robert F. Sekerka for the
Materials Science DWG
7
Carnegie Mellon
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)
October 23, 2001
Robert F. Sekerka for the
Materials Science DWG
8
Carnegie Mellon
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.
October 23, 2001
Robert F. Sekerka for the
Materials Science DWG
Ground-based
coarsening of
Pb-Sn alloy
Microgravity
coarsening of
Pb-Sn alloy
9
Carnegie Mellon
Particle pushing of polystyrene spheres in SCN
October 23, 2001
Robert F. Sekerka for the
Materials Science DWG
10
Carnegie Mellon
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)
October 23, 2001
Robert F. Sekerka for the
Materials Science DWG
11
Carnegie Mellon
Mechanical properties of metallic glasses
October 23, 2001
Robert F. Sekerka for the
Materials Science DWG
12
Carnegie Mellon
Measuring liquid diffusivities in space I
In space
Diffusive Flux
Pure Diffusion
On the Earth
Diffusive Flux
Convective Flux:
Convective Diffusion
October 23, 2001
Robert F. Sekerka for the
Materials Science DWG
13
Carnegie Mellon
Measuring liquid diffusivities in space II
Self-diffusivity of Indium vs. Temperature
12
+
10
Diffusivity [10 -5 cm2/s]
+
2
+


8
6
2
4
2
0
October 23, 2001









 


 

 

+

200

+
+
+
++
+
+
+

+
400
Banish et al. (190 keV, 24 keV)
+ Foster and Reynik
 Lodding
Mathiak et al.
 Carreri, Paoletti & Vincentini, 1.6/0.8 mm dia.
Ogloblya, Lozovoi & Chumakov, 0.5 mm dia.
600
800
Temperature [°C]
Robert F. Sekerka for the
Materials Science DWG
1000
14
Carnegie Mellon
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
October 23, 2001
Robert F. Sekerka for the
Materials Science DWG
15
Carnegie Mellon
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
October 23, 2001
Robert F. Sekerka for the
Materials Science DWG
16
Carnegie Mellon
Thank you for your attention!
October 23, 2001
Robert F. Sekerka for the
Materials Science DWG
17