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The Role of Convection and Growth Competition on Phase Selection in MicrogravityFor a wide range of compositions, Fe-Cr-Ni alloys can solidify by a two-step process: a metastable solid forms first, subsequently transforming into the stable solid phase. This two-step solidification produces a profoundly different microstructure, and therefore different properties, in the final solid. The delay time between the two steps of the solidification process varies from microseconds to seconds. This delay time is a strong function of composition and a weak function of the undercooling of the melt below the metastable liquidus. From the results obtained during the MSL-1 mission and in ground based electrostatic levitation testing at NASA MSFC, we know that convection also has a significant effect on the delay time. By examining the effect of convection on delay time over a wide range of convection, for several different alloys, we can gain a better understanding and better control of the microstructural evolution and final structure of stainless steel alloys. MSFC provides ESL for ground-based testing in a low-convection state, and the numerical modeling that enables estimation of the convection levels under the different process conditions.
Document ID
20040073516
Document Type
Other
Date Acquired
August 21, 2013
Publication Date
December 1, 2003
Publication Information
Publication: Biological and Physical Space Research Laboratory 2002 Science Review
Subject Category
Space Processing
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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IDRelationTitle20040073490Analytic PrimaryBiological and Physical Space Research Laboratory 2002 Science Review