Directionally Solidified Aluminum –7 wt% Silicon Alloys ...
22
Directionally Solidified Aluminum – 7 wt% Silicon Alloys: Comparison of Earth and International Space Station Processed Samples American Society for Gravitational and Space Research (ASGSR), New Orleans, LA 28 Nov 2012 – 2 Dec 2012 Richard N. Grugel – Marshall Space Flight Center Surendra Tewari –Cleveland State University R.S. Rajamure – Cleveland State University Robert Erdman – University of Arizona David Poirier – University of Arizona
Transcript of Directionally Solidified Aluminum –7 wt% Silicon Alloys ...
Directionally Solidified Aluminum – 7 wt% Silicon
Alloys: Comparison of Earth and International Space
Station Processed Samples
American Society for Gravitational and
Space Research (ASGSR), New Orleans, LA
28 Nov 2012 – 2 Dec 2012
Richard N. Grugel – Marshall Space Flight Center
Surendra Tewari – Cleveland State University
R.S. Rajamure – Cleveland State University
Robert Erdman – University of Arizona
David Poirier – University of Arizona
This Investigation is a Collaborative Effort with the
European Space Agency (ESA) Program:
Microstructure Formation in Castings of Technical Alloys under
Diffusive and Magnetically Controlled Convective Conditions (MICAST)
American Society for Gravitational and
Space Research (ASGSR), New Orleans, LA
28 Nov 2012 – 2 Dec 2012
Diffusive and Magnetically Controlled Convective Conditions (MICAST)
The MICAST Microgravity Research Program Focuses on:•A systematic analysis of the effect of convection on the microstructural
evolution in cast Al-alloys.
•••• Experiments that are carried out under well defined processing conditions.
• Sample analysis using advanced diagnostics and theoretical modeling.
→The MICAST team investigates binary, ternary and commercial alloys
based on the Al-Si system.
Intent
Conduct a Thorough Ground-based Investigation
•••• Utilize Aluminum – 7wt. % Silicon Alloys♦ Directionally Solidify Samples having an Initial Aligned Dendritic Array
♦ Evaluate the Dendritic Microstructure (λλλλ1, λλλλ2, λλλλ3, d) as a function of the
Steady-State Processing Conditions (V, G, Co)
American Society for Gravitational and
Space Research (ASGSR), New Orleans, LA
28 Nov 2012 – 2 Dec 2012
Use the Above for Comparison to Limited # of DS μg Samples
•••• Partially melt and Directionally Re-Solidify terrestrially grown
dendritic mono-crystals of Al-7 wt% Si (9-mm dia, 25 cm long)
in microgravity.
American Society for Gravitational and
Space Research (ASGSR), New Orleans, LA
28 Nov 2012 – 2 Dec 2012
Outline• Microstructural Considerations
• Expectations• Expectations
• Ground-based Results
• Microgravity Results
• Comparative Comments
Microstructural ConsiderationsWhy Directional Solidification?
American Society for Gravitational and
Space Research (ASGSR), New Orleans, LA
28 Nov 2012 – 2 Dec 2012
J.C. Williams: Phil. Trans. R. Soc. Lond. A (1995) 351, p. 435.
Microstructural Considerations: Evaluation
American Society for Gravitational and
Space Research (ASGSR), New Orleans, LA
28 Nov 2012 – 2 Dec 2012
λλλλ1, Primary Dendrite Arm Spacing
Relative Dendrite Grain Orientation
λλλλ3, Tertiary Dendrite Arm Spacing
d, Primary Dendrite Trunk Diameter
Statistically Compile and Relate to
Solidification Processing Conditions of:
● Growth Velocity (V)
● Temperature Gradient (G)
● Alloy Composition (Co)
ExpectationsSolidification Processing in a Microgravity Environment
Advantages: Minimize Thermo-Solutal Convection
Minimize Buoyancy Effects
American Society for Gravitational and
Space Research (ASGSR), New Orleans, LA
28 Nov 2012 – 2 Dec 2012
Minimize Buoyancy Effects
Intent: Produce Segregation Free Samples Grown Strictly
by Heat Transfer and Solute Diffusion
Purpose: Better Understand the Relationship between
Processing – Microstructural Development
Application: Maximize Material Properties
Microgravity Processing
American Society for Gravitational and
Space Research (ASGSR), New Orleans, LA
28 Nov 2012 – 2 Dec 2012
Al- 7 wt.% Si
ESA Low Gradient
Furnace (LGF) Insert
Sample Cartridge
Microgravity Science Research
Facility (MSRF) Aboard the ISS
American Society for Gravitational and
Space Research (ASGSR), New Orleans, LA
28 Nov 2012 – 2 Dec 2012
X-ray radiograph of MICAST7Eutectic Melt Back
Microgravity Processed Sample MICAST 7
X-ray radiograph of MICAST7/ Isotherm
No terrestrial samples which are processed in LGF or SQF equivalent hardware
under R and GL conditions which are identical to MICAST6, MICAST7
American Society for Gravitational and
Space Research (ASGSR), New Orleans, LA
28 Nov 2012 – 2 Dec 2012
Terrestrial:
G = 15 K cm-1
Microstructural Comparison: Earth and Microgravity
Al – 7 wt. % Si
V = 5 µµµµm s-1 V = 50 µµµµm s-1
MICAST6:
G = 20 K cm-1
MICAST6 Seed:
V = 41 K cm-1,
G = 22 µµµµm s-1
American Society for Gravitational and
Space Research (ASGSR), New Orleans, LA
28 Nov 2012 – 2 Dec 2012
Microstructural Analysis of Directionally Solidified Al -7 wt. % Si Alloy Samples
2) Primary Dendrite Trunk DiameterTerrestrial: GL = 41 Kcm-1,
V = 85 mm s-1
1) Primary Dendrite Arm Spacing
Primary Dendrite Arm Spacing (λλλλ1)Which primary dendrite arm spacing (λλλλ1) to use?
American Society for Gravitational and
Space Research (ASGSR), New Orleans, LA
28 Nov 2012 – 2 Dec 2012
= 623 µµµµm
3) Nearest neighbor spacing = 368 ± 126 µµµµm
→→→→Theoretical models predict nearest neighbor spacing
2) Minimum Spanning Tree:
Spacing= 412 ± 138 µµµµm
1) Geometrical Spacing:
Theoretical Models for Primary Dendrite Arm Spacing
(ml Gct-Gt)/(4Π2 г Tm/rt
2)=1 for small R rt/2Dl
])1([24
21
tr
R
LGLD
ktCLm
LG
+−
−=λ
American Society for Gravitational and
Space Research (ASGSR), New Orleans, LA
28 Nov 2012 – 2 Dec 2012
Analytical NumericalTip radius: Trivedi (1980) Hunt-Lu (1996)
Primary spacing: Trivedi (1984) Hunt- Lu (1996)
Trunk diameter: None
Co 7 wt% Si
ml -6.31 K/ wt% Si Metals Handbook, vol. 8 (1973)
k 0.1
г 0.196 µm K Gunduz and Hunt (1985)
Dl 4.3X10-9 m2/s (Poirier compilation)
Physical Properties for Al- 7 wt% Si
R
Primary Dendrite Trunk Diameter (����)
American Society for Gravitational and
Space Research (ASGSR), New Orleans, LA
28 Nov 2012 – 2 Dec 2012
Initial Trunk
Diameter, φφφφ0
Dendrite Tip Radius
Reproducible and Predictable
Microstructural Constituent
Dynamic Growth
Trunk Diameter Rapidly Increases Until Diffusion Fields Overlap (▼)
Final Trunk
Diameter, φφφφ
Stagnant Growth
Primary Dendrite Trunk Diameter ( )“Initial” Trunk Diameter (φφφφ0) Determination
Tru
nk
Dia
me
ter/
Tip
Ra
diu
s
8
10
12
0.5Ac
1.3Ac
3.6Ac
9.2Ac
American Society for Gravitational and
Space Research (ASGSR), New Orleans, LA
28 Nov 2012 – 2 Dec 2012
Primary Dendrite Tip Radius
Esaka (1986 Ph.D. Thesis) Measured 0 from
Succinonitrile-Acetone “alloys” grown at
different V and GL.
o= 6.59 ± 1.3 Rtip
Dl Gl k/(ml R Co (k-1))
1e-5 1e-4 1e-3 1e-2 1e-1T
run
k D
iam
ete
r/T
ip R
ad
ius
2
4
6
Highly
Branched
Dendrites“Cellular”
DendritesFundamental of Solidification, Kurz and Fisher, Trans Tech, 1992
Primary dendrite trunk diameter (����) ) ) ) model
After φφφφ0 the trunk diameter increases
via dissolution of secondary arms and
re-deposition on the trunk until the
eutectic reaction.
Assumptions:
American Society for Gravitational and
Space Research (ASGSR), New Orleans, LA
28 Nov 2012 – 2 Dec 2012
Assumptions:
1. Kirkwood model (1985) of
ripening applies.
2. Secondary arm melts back
because of its curvature.
3. Mass of the melted arm
deposits on trunk surface
where there is negative
curvature.
(1)
(2)
(3)
(4)
Melting rate of an
arm of length, l
Mushy Zone Freezing Time ~ ml(CE-Co)/RGm
Primary dendrite trunk diameter ( ) model
American Society for Gravitational and
Space Research (ASGSR), New Orleans, LA
28 Nov 2012 – 2 Dec 2012
Primary Dendrite Arm Spacing (λλλλ1)
Primary Dendrite Trunk Diameter (φφφφ)
Comparison of Earth and ISS Processed Samples
American Society for Gravitational and
Space Research (ASGSR), New Orleans, LA
28 Nov 2012 – 2 Dec 2012
Comparison of Earth and ISS Processed Samples
with Theoretical Models
Primary dendrite arm spacings as
compared to Hunt-Lu calculationsP
rim
ary
den
dri
te a
rm s
pacin
g (
em
pa
ric
al)
, µµ µµ
m
1200
1400
1600
1800
Hunt-Lu calculations
Terrestrial
ISSDendrite steepling
American Society for Gravitational and
Space Research (ASGSR), New Orleans, LA
28 Nov 2012 – 2 Dec 2012
Primary dendrite arm spacing (no convection), µµµµm
200 400 600 800 1000 1200 1400 1600 1800
Pri
mary
den
dri
te a
rm s
pacin
g (
em
pa
ric
al)
,
200
400
600
800
1000
�ISS-DS: Good agreement with predictions from Hunt-Lu model.
� Terrestrial DS (“Not Steepled”) : Good agreement with predictions from Hunt-Lu model.
�Terrestrial DS (“Steepled”): Convection decreases primary dendrite arm spacing.
Primary dendrite trunk diameter as compared to trunk
diameter model calculations, using rt (Hunt-Lu)P
rim
ary
den
dri
te t
run
k d
iam
ete
r (e
mp
ari
ca
l), µµ µµ
m
200
250
300
American Society for Gravitational and
Space Research (ASGSR), New Orleans, LA
28 Nov 2012 – 2 Dec 2012
Primary dendrite trunk diameter (no convection), µµµµm
0 50 100 150 200 250 300
Pri
mary
den
dri
te t
run
k d
iam
ete
r (e
mp
ari
ca
l),
0
50
100
150
Trunk dia model calculations usingHunt-Lu tip radius
Terrestrial
ISSDendrite steepling
�ISS-DS: Good agreement with predictions from the trunk-diameter model.
�Terrestrial DS (“Not Steepled”) : Good agreement with predictions from model.
�Terrestrial DS (“Steepled”): Convection increases trunk diameter.
Conclusions• Primary dendrite arm spacings of Al-7 wt% Si alloy
directionally solidified in low gravity environment of space
(MICAST-6 and MICAST-7: Thermal gradient ~ 19 to 26 K cm-1,
Growth speeds varying from 5 to 50 µµµµm s-1) show good
agreement with the Hunt-Lu model.
American Society for Gravitational and
Space Research (ASGSR), New Orleans, LA
28 Nov 2012 – 2 Dec 2012
• Primary dendrite trunk diameters of the ISS processed
samples show a good fit with a simple analytical model
based on Kirkwood’s approach, proposed here.
• Natural convection,
– decreases primary dendrite arm spacing.
– appears to increase primary dendrite trunk diameter.
• Need more samples processed in Microgravity
Acknowledgments
This investigation is supported by NASA Grant NAS8-
02060. Appreciation is expressed to Dr. Men G. Chu,
Technical Fellow-Solidification Technology, ALCOA
American Society for Gravitational and
Space Research (ASGSR), New Orleans, LA
28 Nov 2012 – 2 Dec 2012
Technical Fellow-Solidification Technology, ALCOA
Technical Center, Pittsburgh, PA . Support from the
Materials and Processing Laboratory of the Marshall
Space Flight Center is also greatly acknowledged.
