TY - JOUR
T1 - Primary dendrite array morphology in Al-7 wt% Si alloy samples directionally solidified aboard the International Space Station
AU - Ghods, Masoud
AU - Upadhyay, Supriya R.
AU - Rajamure, Ravi S.
AU - Tewari, Surendra N.
AU - Grugel, Richard N.
AU - Poirier, David R.
AU - Lauer, Mark
N1 - Funding Information:
This research was supported by NASA-Grants (80NSSC20K0736, NNX08AN49G, NNX14AJ73G, and NNX15AC04G). Appreciation is expressed to all the scientists and engineers from NASA and ESA whose combined effort made this research possible, and to Dr. Men G. Chu (ALCOA) for providing the Al-7Si alloy feed-stock.
Funding Information:
This research was supported by NASA-Grants (80NSSC20K0736, NNX08AN49G, NNX14AJ73G, and NNX15AC04G). Appreciation is expressed to all the scientists and engineers from NASA and ESA whose combined effort made this research possible, and to Dr. Men G. Chu (ALCOA) for providing the Al-7Si alloy feed-stock. Fig. 12 is reprinted from Pergamon Press plc, Journal of Acta Metallurgica, Vol. 37, No. 4, Dupouy MD, Camel D and Favier JJ, Natural convection in directional dendritic solidification of metallic alloys?I. Macroscopic effects, 1143-1157, Copyright (1989), with permission from Elsevier.
Publisher Copyright:
© 2021 Elsevier B.V.
PY - 2021/5/15
Y1 - 2021/5/15
N2 - Under a NASA (National Aeronautics and Space Agency)-ESA (European Space Agency) collaborative research project, MICAST (Microstructure formation in casting of technical alloys under a diffusive and magnetically controlled convection conditions), three Al-7 wt% Si samples (MICAST-6, MICAST-7 and MICAST2-12) were directionally solidified aboard the International Space Station (ISS) to determine the effect of mitigating convection on the primary dendrite array morphology. MICAST-6 was processed with a step-increase in the growth speed from 5 to 50 µm s−1, MICAST-7 with a step-decrease from 20 to 10 µm s−1, and MICAST2-12 with constant speed of 40 µm s−1. Nearest-neighbor primary dendrite arm spacings and primary dendrite trunk diameters were measured on transverse sections taken at approximately 5 mm intervals along the length of the MICAST samples. In MICAST samples, especially in the steady-state growth regime, the observed primary dendrite nearest-neighbor spacings show a good agreement with predictions from the Hunt-Lu numerical model. The maximum to minimum (highest 10% to lowest 10%) nearest-neighbor spacing ratio in MICAST samples is 2.10 ± 0.27 in agreement with Hunt-Lu model, which assumes pure diffusive transport. Trunk diameters in MICAST samples also agree well with predictions from a coarsening based model. The terrestrial-grown equivalent samples, on the other hand, display smaller nearest-neighbor spacing, and larger primary dendrite trunk diameters than those predicted from the models. Thermosolutal convection appears to increase the dendrite tip radius, causing the trunk diameter to increase, while simultaneously reducing the primary dendrite spacing. This requires verification-experiments involving directional solidification followed by rapid quenching of the liquid-solid interface in metallic alloys in a low gravity environment. The International Space Station currently does not have on-board hardware to conduct such experiments.
AB - Under a NASA (National Aeronautics and Space Agency)-ESA (European Space Agency) collaborative research project, MICAST (Microstructure formation in casting of technical alloys under a diffusive and magnetically controlled convection conditions), three Al-7 wt% Si samples (MICAST-6, MICAST-7 and MICAST2-12) were directionally solidified aboard the International Space Station (ISS) to determine the effect of mitigating convection on the primary dendrite array morphology. MICAST-6 was processed with a step-increase in the growth speed from 5 to 50 µm s−1, MICAST-7 with a step-decrease from 20 to 10 µm s−1, and MICAST2-12 with constant speed of 40 µm s−1. Nearest-neighbor primary dendrite arm spacings and primary dendrite trunk diameters were measured on transverse sections taken at approximately 5 mm intervals along the length of the MICAST samples. In MICAST samples, especially in the steady-state growth regime, the observed primary dendrite nearest-neighbor spacings show a good agreement with predictions from the Hunt-Lu numerical model. The maximum to minimum (highest 10% to lowest 10%) nearest-neighbor spacing ratio in MICAST samples is 2.10 ± 0.27 in agreement with Hunt-Lu model, which assumes pure diffusive transport. Trunk diameters in MICAST samples also agree well with predictions from a coarsening based model. The terrestrial-grown equivalent samples, on the other hand, display smaller nearest-neighbor spacing, and larger primary dendrite trunk diameters than those predicted from the models. Thermosolutal convection appears to increase the dendrite tip radius, causing the trunk diameter to increase, while simultaneously reducing the primary dendrite spacing. This requires verification-experiments involving directional solidification followed by rapid quenching of the liquid-solid interface in metallic alloys in a low gravity environment. The International Space Station currently does not have on-board hardware to conduct such experiments.
KW - A1. Directional solidification
KW - A1. Fluid flows
KW - A1. Primary dendrite spacing
KW - A1. Primary dendrite trunk diameter
KW - A2. Microgravity conditions
KW - B1. Aluminum Alloys
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U2 - 10.1016/j.jcrysgro.2021.126077
DO - 10.1016/j.jcrysgro.2021.126077
M3 - Article
AN - SCOPUS:85101361480
VL - 562
JO - Journal of Crystal Growth
JF - Journal of Crystal Growth
SN - 0022-0248
M1 - 126077
ER -