Directionally Solidified Aluminum 7 wt% Silicon Alloys: Comparison - - PowerPoint PPT Presentation

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Directionally Solidified Aluminum 7 wt% Silicon Alloys: Comparison - - PowerPoint PPT Presentation

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https://ntrs.nasa.gov/search.jsp?R=20130003181 2018-03-27T21:05:22+00:00Z American Society for Gravitational and Space Research (ASGSR), New Orleans, LA 28 Nov 2012 2 Dec 2012 Directionally Solidified Aluminum 7 wt% Silicon Alloys:

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SLIDE 1

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

https://ntrs.nasa.gov/search.jsp?R=20130003181 2018-03-27T21:05:22+00:00Z

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SLIDE 2

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.

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SLIDE 3

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 (λ λ λ λ1, λ λ λ λ2, λ λ λ λ3, 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.

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SLIDE 4

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
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SLIDE 5

Microstructural Considerations

Why 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.

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SLIDE 6

Microstructural Considerations: Evaluation

American Society for Gravitational and Space Research (ASGSR), New Orleans, LA 28 Nov 2012 – 2 Dec 2012

λ λ λ λ1, Primary Dendrite Arm Spacing Relative Dendrite Grain Orientation λ λ λ λ3, 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)
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SLIDE 7

Expectations

Solidification Processing in a Microgravity Environment

Advantages: Minimize ThermoSolutal 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

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SLIDE 8

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

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SLIDE 9

American Society for Gravitational and Space Research (ASGSR), New Orleans, LA 28 Nov 2012 – 2 Dec 2012

X-ray radiograph of MICAST7

Eutectic 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

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SLIDE 10

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

  • m s-1

V = 50

  • m s-1

MICAST6: G = 20 K cm-1 MICAST6 Seed: V = 41 K cm-1, G = 22

  • m s-1
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SLIDE 11

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 Diameter Terrestrial: GL = 41 Kcm-1, V = 85 mm s-1 1) Primary Dendrite Arm Spacing

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SLIDE 12

Primary Dendrite Arm Spacing (λ λ λ λ1)

Which primary dendrite arm spacing (λ λ λ λ1) to use?

American Society for Gravitational and Space Research (ASGSR), New Orleans, LA 28 Nov 2012 – 2 Dec 2012

= 623

  • m

3) Nearest neighbor spacing = 368 ± 126

  • m

→ → → →Theoretical models predict nearest neighbor spacing

2) Minimum Spanning Tree: Spacing= 412 ± 138

  • m

1) Geometrical Spacing:

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SLIDE 13

Theoretical Models for Primary Dendrite Arm Spacing

(ml Gc

t-Gt)/(4Π2 г Tm/rt 2)=1 for small R rt/2Dl

  • +

− − = λ

American Society for Gravitational and Space Research (ASGSR), New Orleans, LA 28 Nov 2012 – 2 Dec 2012

Analytical Numerical

Tip 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 m K Gunduz and Hunt (1985) Dl 4.3X10-9 m2/s (Poirier compilation)

Physical Properties for Al- 7 wt% Si

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SLIDE 14

Primary Dendrite Trunk Diameter (

  • )

American Society for Gravitational and Space Research (ASGSR), New Orleans, LA 28 Nov 2012 – 2 Dec 2012

Initial Trunk Diameter, φ φ φ φ0 Dendrite Tip Radius Reproducible and Predictable Microstructural Constituent Dynamic Growth

Trunk Diameter Rapidly Increases Until Diffusion Fields Overlap (▼)

Final Trunk Diameter, φ φ φ φ Stagnant Growth

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SLIDE 15

Primary Dendrite Trunk Diameter ( )

“Initial” Trunk Diameter (φ φ φ φ0) Determination

iameter/Tip Radius

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.

  • = 6.59 ± 1.3 Rtip

Dl Gl k/(ml R Co (k1))

1e5 1e4 1e3 1e2 1e1

Trunk Diamet

2 4 6

Highly Branched Dendrites “Cellular” Dendrites

Fundamental of Solidification, Kurz and Fisher, Trans Tech, 1992

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SLIDE 16

Primary dendrite trunk diameter (

  • )

) ) ) model

After φ φ φ φ0 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

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SLIDE 17

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

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SLIDE 18

Primary Dendrite Arm Spacing (λ λ λ λ1) Primary Dendrite Trunk Diameter (φ φ φ φ) 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

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SLIDE 19
  • pacing (emparical),
  • m

1200 1400 1600 1800 HuntLu calculations Terrestrial ISS

Dendrite steepling

American Society for Gravitational and Space Research (ASGSR), New Orleans, LA 28 Nov 2012 – 2 Dec 2012

Primary dendrite arm spacing (no convection),

  • m

200 400 600 800 1000 1200 1400 1600 1800

Primary dendrite arm spacing

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.

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SLIDE 20
  • iameter (emparical),
  • 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),

  • m

50 100 150 200 250 300

Primary dendrite trunk diame

50 100 150 Trunk dia model calculations using HuntLu tip radius Terrestrial ISS

Dendrite 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.

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SLIDE 21

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

  • m 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

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SLIDE 22

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.