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: Comparison of Earth and International Space Station Processed Samples 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
American Society for Gravitational and Space Research (ASGSR), New Orleans, LA 28 Nov 2012 – 2 Dec 2012 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) 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.
American Society for Gravitational and Space Research (ASGSR), New Orleans, LA 28 Nov 2012 – 2 Dec 2012 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 1 , λ λ λ λ 2 , λ λ λ λ 3 , d) as a function of the λ Steady-State Processing Conditions (V, G, C o ) Use the Above for Comparison to Limited # of DS μ g 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
American Society for Gravitational and Space Research (ASGSR), New Orleans, LA 28 Nov 2012 – 2 Dec 2012 Microstructural Considerations Why Directional Solidification? J.C. Williams: Phil. Trans. R. Soc. Lond. A (1995) 351, p. 435.
American Society for Gravitational and Space Research (ASGSR), New Orleans, LA 28 Nov 2012 – 2 Dec 2012 Microstructural Considerations: Evaluation λ λ λ λ 1 , Primary Dendrite Arm Spacing Statistically Compile and Relate to λ 3 , Tertiary Dendrite Arm Spacing λ λ λ Solidification Processing Conditions of: ● Growth Velocity (V) d, Primary Dendrite Trunk Diameter ● Temperature Gradient (G) Relative Dendrite Grain Orientation ● Alloy Composition (C o )
American Society for Gravitational and Space Research (ASGSR), New Orleans, LA 28 Nov 2012 – 2 Dec 2012 Expectations Solidification Processing in a Microgravity Environment Advantages: Minimize Thermo�Solutal Convection Minimize Buoyancy Effects 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
American Society for Gravitational and Space Research (ASGSR), New Orleans, LA 28 Nov 2012 – 2 Dec 2012 Microgravity Processing Al- 7 wt.% Si Sample Cartridge ESA Low Gradient Furnace (LGF) Insert 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 Microgravity Processed Sample MICAST 7 Eutectic Melt Back X-ray radiograph of MICAST7 X-ray radiograph of MICAST7 / Isotherm No terrestrial samples which are processed in LGF or SQF equivalent hardware under R and G L conditions which are identical to MICAST6, MICAST7
American Society for Gravitational and Space Research (ASGSR), New Orleans, LA 28 Nov 2012 – 2 Dec 2012 Microstructural Comparison: Earth and Microgravity Al – 7 wt. % Si Terrestrial: G = 15 K cm -1 V = 5 � � � � m s -1 V = 50 � � � � m s -1 MICAST6 Seed: MICAST6: V = 41 K cm -1 , G = 20 K cm -1 G = 22 � � � � m 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 1) Primary Dendrite Arm Spacing Terrestrial: G L = 41 Kcm -1 , 2) Primary Dendrite Trunk Diameter V = 85 mm s -1
American Society for Gravitational and Space Research (ASGSR), New Orleans, LA 28 Nov 2012 – 2 Dec 2012 Primary Dendrite Arm Spacing ( λ λ λ λ 1 ) Which primary dendrite arm spacing ( λ λ λ 1 ) to use? λ = 623 � � m � � 1) Geometrical Spacing: 2) Minimum Spanning Tree: Spacing= 412 ± 138 � � � � m 3) Nearest neighbor spacing = 368 ± 126 � � � � m → → → → Theoretical models predict nearest neighbor spacing
American Society for Gravitational and Space Research (ASGSR), New Orleans, LA 28 Nov 2012 – 2 Dec 2012 Theoretical Models for Primary Dendrite Arm Spacing t -G t )/(4Π 2 г T m /r t 2 )=1 for small R r t /2D l (m l G c � λ � � � = − � � � � � � − + � � � � � � � � � � � � � � Analytical Numerical Tip radius: Trivedi (1980) Hunt-Lu (1996) Primary spacing: Trivedi (1984) Hunt- Lu (1996) Trunk diameter: None Physical Properties for Al- 7 wt% Si Co 7 wt% Si m l -6.31 K/ wt% Si Metals Handbook, vol. 8 (1973) k 0.1 0.196 � m K Gunduz and Hunt (1985) г 4.3X10 -9 m 2 /s D l (Poirier compilation)
American Society for Gravitational and Space Research (ASGSR), New Orleans, LA 28 Nov 2012 – 2 Dec 2012 Primary Dendrite Trunk Diameter ( � � � � ) Dendrite Tip Radius Dynamic Growth Initial Trunk Diameter, φ φ 0 φ φ Reproducible and Predictable Microstructural Constituent Stagnant Growth Final Trunk Diameter, φ φ φ φ Trunk Diameter Rapidly Increases Until Diffusion Fields Overlap ( ▼)
American Society for Gravitational and Space Research (ASGSR), New Orleans, LA 28 Nov 2012 – 2 Dec 2012 Primary Dendrite Trunk Diameter ( ) “Initial” Trunk Diameter ( φ φ φ 0 ) Determination φ 12 0.5Ac 1.3Ac iameter/Tip Radius 3.6Ac 10 9.2Ac Primary Dendrite Tip Radius 8 Trunk Diamet 6 4 Highly Branched “Cellular” Fundamental of Solidification, Kurz and Fisher, Trans Tech, 1992 Dendrites Dendrites 2 1e�5 1e�4 1e�3 1e�2 1e�1 Dl Gl k/(ml R Co (k�1)) Esaka (1986 Ph.D. Thesis) Measured 0 from Succinonitrile-Acetone “alloys” grown at different V and G L . o = 6.59 ± 1.3 R tip
American Society for Gravitational and Space Research (ASGSR), New Orleans, LA 28 Nov 2012 – 2 Dec 2012 Primary dendrite trunk diameter ( � � �) � ) ) model ) After φ φ φ 0 the trunk diameter increases φ via dissolution of secondary arms and re-deposition on the trunk until the eutectic reaction. Assumptions: Assumptions: (1) Melting rate of an 1. Kirkwood model (1985) of arm of length, l ripening applies. 2. Secondary arm melts back (2) because of its curvature. 3. Mass of the melted arm (3) deposits on trunk surface where there is negative curvature. (4)
American Society for Gravitational and Space Research (ASGSR), New Orleans, LA 28 Nov 2012 – 2 Dec 2012 Primary dendrite trunk diameter ( ) model Mushy Zone Freezing Time ~ m l (C E -C o )/RG m
American Society for Gravitational and Space Research (ASGSR), New Orleans, LA 28 Nov 2012 – 2 Dec 2012 Primary Dendrite Arm Spacing ( λ λ λ λ 1 ) Primary Dendrite Trunk Diameter ( φ φ φ φ ) Comparison of Earth and ISS Processed Samples Comparison of Earth and ISS Processed Samples with Theoretical Models
American Society for Gravitational and Space Research (ASGSR), New Orleans, LA 28 Nov 2012 – 2 Dec 2012 �������������������������������� ��������������������������������� 1800 � m � � pacing (emparical), � Hunt�Lu calculations Terrestrial 1600 ISS Dendrite steepling 1400 Primary dendrite arm spacing 1200 1000 800 600 400 200 200 400 600 800 1000 1200 1400 1600 1800 Primary dendrite arm spacing (no convection), � � m � � � 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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