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Isothermal Dendritic Growth - A Low Gravity Experiment

Published online by Cambridge University Press:  26 February 2011

M. E. Glicksman
Affiliation:
Materials Engineering Department, Rensselaer Polytechnic Institute, Troy, N.Y. 12180-3590
E. Winsa
Affiliation:
NASA Lewis Research Center, Cleveland, Ohio 44135
R. C. Hahn
Affiliation:
Materials Engineering Department, Rensselaer Polytechnic Institute, Troy, N.Y. 12180-3590
T. A. Lograsso
Affiliation:
Materials Engineering Department, Rensselaer Polytechnic Institute, Troy, N.Y. 12180-3590
E. R. Rubinstein
Affiliation:
Materials Engineering Department, Rensselaer Polytechnic Institute, Troy, N.Y. 12180-3590
M. E. Selleck
Affiliation:
Materials Engineering Department, Rensselaer Polytechnic Institute, Troy, N.Y. 12180-3590
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Abstract

The growth of dendrites in pure melts and alloys is controlled by diffusion-limited transport of heat and/or solute. The presence of temperature or concentration gradients within a molten phase subject to gravitational forces generally promotes convection, which in turn, modifies the diffusion processes. The vigor of melt convection is controlled by several parameters often expressed as a lumped dimensionless group, the Grashof number Gr = gβΔTℓ32, where g is the acceleration due to gravity; is the volumetric expansion coefficient; ΔT is the undercooling; ν is the kinematic viscosity; and ℓ is the relevant length scale, e.g., the characteristic diffusion distance. Dendritic growth, by its nature, does not permit independent manipulation of the controlling length scale, ℓ, which is determined by materials properties (e.g. diffusion coefficient or thermal diffusivity) and the undercooling or supersaturation. The reduction of g through orbital free fall is often the only practical way to lower Gr sufficiently to permit careful observation of the morphological and kinetic characteristics of isothermal dendritic growth. Previously conducted ground-based studies and the current approach to performing these studies in low earth orbit will be described.

Type
Research Article
Copyright
Copyright © Materials Research Society 1987

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References

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