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Use of Microgravity to Control the Microstructure of EutecticsThis grant began in June of 1996. Its long term goal is to be able to control the microstructure of directionally solidified eutectic alloys, through an improved understanding of the influence of convection. The primary objective of the present projects is to test hypotheses for the reported influence of microgravity on the microstructure of three fibrous eutectics (MnBi-Bi, InSb-NiSb, Al3Ni-Al). A secondary objective is to determine the influence of convection on the microstructure of other eutectic alloys. Two doctoral students and a masters student supported as a teaching assistant were recruited for this research. Techniques were developed for directional solidification of MnBi-Bi eutectics with periodic application of current pulses to produce an oscillatory freezing rate. Image analysis techniques were developed to obtain the variation in MnBi fiber spacing, which was found to be normally distributed. The mean and standard deviation of fiber spacing were obtained for several freezing conditions. Eighteen ampoules were prepared for use in the gradient freeze furnace QUELD developed at Queen's University for use in microgravity. Nine of these ampoules will be solidified soon at Queen's in a ground-based model. We hope to solidify the other nine in the QUELD that is mounted on the Canadian Microgravity Isolation Mount on MIR. Techniques are being developed for directional solidification of the Al-Si eutectic at different freezing rates, with and without application of accelerated crucible rotation to induce convection. For the first time, theoretical methods are being developed to analyze eutectic solidification with an oscillatory freezing rate. In a classical sharp-interface model, we found that an oscillatory freezing rate increases the deviation of the average interfacial composition from the eutectic, and increases the undercooling of the two phases by different amounts. This would be expected to change the volume fraction solidifying and the fiber spacing. Because of difficulties in tracking the freezing interfaces of the two solid phases, a phase-field model is also being developed. A paper demonstrating application of phase field methods to periodic structures has been submitted for publication.
Document ID
19980029708
Acquisition Source
Marshall Space Flight Center
Document Type
Contractor Report (CR)
Authors
Wilcox, William R.
(Clarkson Univ. Potsdam, NY United States)
Regel, Liya L.
(Clarkson Univ. Potsdam, NY United States)
Smith, Reginald W.
(Queens Univ. Kingston, Ontario Canada)
Date Acquired
September 6, 2013
Publication Date
March 1, 1998
Subject Category
Metallic Materials
Report/Patent Number
NASA/CR-1998-207561
NAS 1.26:207561
Funding Number(s)
CONTRACT_GRANT: NAG8-1266
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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