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Gravitational Acceleration Effects on Macrosegregation: Experiment and Computational ModelingExperiments were performed under terrestrial gravity (1g) and during parabolic flights (10-2 g) to study the solidification and macrosegregation patterns of Al-Cu alloys. Alloys having 2% and 5% Cu were solidified against a chill at two different cooling rates. Microscopic and Electron Microprobe characterization was used to produce microstructural and macrosegregation maps. In all cases positive segregation occurred next to the chill because shrinkage flow, as expected. This positive segregation was higher in the low-g samples, apparently because of the higher heat transfer coefficient. A 2-D computational model was used to explain the experimental results. The continuum formulation was employed to describe the macroscopic transports of mass, energy, and momentum, associated with the solidification phenomena, for a two-phase system. The model considers that liquid flow is driven by thermal and solutal buoyancy, and by solidification shrinkage. The solidification event was divided into two stages. In the first one, the liquid containing freely moving equiaxed grains was described through the relative viscosity concept. In the second stage, when a fixed dendritic network was formed after dendritic coherency, the mushy zone was treated as a porous medium. The macrosegregation maps and the cooling curves obtained during experiments were used for validation of the solidification and segregation model. The model can explain the solidification and macrosegregation patterns and the differences between low- and high-gravity results.
Document ID
19990095039
Acquisition Source
Marshall Space Flight Center
Document Type
Conference Paper
Authors
Leon-Torres, J.
(Alabama Univ. Tuscaloosa, AL United States)
Curreri, P. A.
(NASA Marshall Space Flight Center Huntsville, AL United States)
Stefanescu, D. M.
(Alabama Univ. Tuscaloosa, AL United States)
Sen, S.
(Universities Space Research Association Huntsville, AL United States)
Date Acquired
August 19, 2013
Publication Date
January 1, 1999
Subject Category
Materials Processing
Meeting Information
Meeting: TMS Annual Meeting
Location: San Diego, CA
Country: United States
Start Date: February 28, 1999
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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