Simulating the initiation of a channel during directional solidification of a superalloy
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work was supported by Creative Research Initiatives of the Korean Ministry of Science and Technology.
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Simulating the Initiation of a Channel during Directional Solidification of a Superalloy P.K. SUNG, D.R. POIRIER, and S.D. FELICELLI A severe form of macrosegregation, known as “freckles,” is cause to scrap directionally solidified (DS) and dendritic single-crystal (SC) castings of Ni-base superalloys, which are used as critical components in gas-turbine engines.
P.K. SUNG, Research Assistant Professor, and D.R. POIRIER, Professor, are with the Department of Materials Science and Engineering, The University of Arizona, Tucson, AZ 85721. S.D. FELICELLI, Research Scientist, is with Centro Ato´mico Bariloche, 8400 S.C. de Bariloche, Argentina. Manuscript submitted April 24, 2000.
202—VOLUME 32A, JANUARY 2001
Freckles are observed as long and narrow trails, aligned roughly parallel to the direction of gravity in both DS and SC castings and are enriched in the normally segregating elements and depleted in the inversely segregating elements.[1] The ability to predict the formation of freckles in the castings is a critical issue at the present time. In this article, the initiation of an internal channel is investigated with two-dimensional simulations of the solidification of a Ni-base superalloy. The model for solidification of multicomponent alloys given by Felicelli et al.[2,3] is used. In the governing equations, the simplifying assumptions are made as follows: (1) only solid and liquid phases are present, i.e., no pores form; (2) the liquid is Newtonian and incompressible; (3) the flow is laminar; (4) the solid and liquid phases have equal and constant physical properties except in the body force term of the momentum equation; (5) the Boussinesq approximation is made in the buoyancy term of the momentum equation; (6) there is no diffusion of solute in the solid phase; and (7) the solid phase is stationary. With these assumptions, the continuity and momentum equatio
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