Electrical properties of Al-In-Sn alloys directionally solidified in high and low gravitational fields
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I.
INTRODUCTION
T H E feasibility of producing high volume fraction immiscible alloys with finely dispersed microstructure by lowgravity solidification was demonstrated in 1974. t Ga-Bi samples solidified in free fall, with gravity level 10-4g (g = 980 cm/sec2), had much finer microstructure than the control samples solidified in normal gravity. It was also found that the electrical properties of the low-gravity solidified materials was significantly different from those of the control samples solidified under the same conditions except at one gravity. 2 The potential to synthesize in space a new class of electronic materials was suggested by these initial experiments. However, extensive studies along this line in space are limited due to the high cost and limited access to orbital experimentation facilities. In an attempt to gain more insight into the low-gravity processing on the material properties of immiscible alloys, we decided to carry out a systematic study of materials solidified directionally in a Bridgman furnace on NASA's KC- 135 aircraft. The advantages of using KC- 135 are that it is relatively inexpensive, has a short turnaround time, and provides the capability when combined with unidirectional solidification of having in one sample a series of identifiable sections grown in low-g or high-g. 3'4'5 The material chosen in this study is the ternary Al-ln-Sn alloy. ~ This alloy was chosen because the Al-ln binary has been well studied and the addition of Sn to the Al-ln binary would alter the interphase interfacial energy and the morphology of the solidliqmd interface and therefore the cast structure. This study would then help to identify the role of interphase interfacial energies during solidification with varying g-levels. In addition, the electrical properties of the binary Al-In, A1-Sn, and In-Sn alloys have been extensively studied. Therefore, an extension of the study to the ternary system is a logical choice. The specific alloy studied in this report is the Al18.9In-14.6Sn in weight percent.
M.K. WU, Professor, Department of Physics, J.R. ASHBURN, Research Assistant, Department of Physics, and W F. KAUKLER, Semor Research Assocmte, Department of Chemistry, are ~vKh The University of Alabama m Huntsville, AL. P. A CURRERI Js Materials Scientist, Space Scmnce Laboratory, NASA/Marshall Space Fhght Center, Marshall Space Fhght Center, AL 35812. Manuscript submitted July 14, 1986 METALLURGICAL TRANSACTIONS A
II.
EXPERIMENTAL
The Al-ln-Sn alloys were directionally solidified in a high temperature Bridgman-type furnace with a water-cooled quench block. The furnace system was used to process samples during maneuvers of NASA's KC-135 aircraft. The aircraft flies a series of parabolas during which the onboard experiment experiences up to 30 seconds of low gravity and up to 1.5 minutes of pullout and climb with up to 1.7 g acceleration. Therefore, a sample which is being solidified experiences a repetitive sequence of low-gravity (low-g) and high-gravity (high-g) forces parallel to the longitudinal
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