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Search Publications by: Geoffrey B. McFadden (Assoc)

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Displaying 76 - 97 of 97

Microsegregation in Peltier Interface Demarcation

July 1, 2000
Author(s)
Y Dabo, H N. Thi, Sam R. Coriell, Geoffrey B. McFadden, Q Li, B Billia
Experimental results on solute microsegregation induced by Peltier Interface Demarcation (PID) technique during directional solidification of Bi-1 wt % Sb alloys are presented. These data are compared with the results of numerical simulation and the theory

Convective and Morphological Instabilities During Crystal Growth

June 1, 2000
Author(s)
Sam R. Coriell, Geoffrey B. McFadden, B T. Murray
We have studied the effects of interface morphology on the dynamics of dendritic growth. The Ivantsov solution for an isothermal paraboloid of revolution growing into a pure, supercooled melt provides a relation between the bulk supercooling and a

On the Properties of Alpha/Alpha + Beta Diffusion Couples

January 1, 2000
Author(s)
William J. Boettinger, Sam R. Coriell, Carelyn E. Campbell, Geoffrey B. McFadden
The properties of diffusion couples in a ternary system are examined theoretically when one end member is composed of single-phase material (alpha) and the other end member is composed of two-phase material (α + Β). Using the model of Morral and co-workers

Effect of Surface Free Energy Anisotrophy on Dendrite Tip Shape

August 1, 1999
Author(s)
Richard J. Braun, J Zhang, John W. Cahn, Geoffrey B. McFadden, A A. Wheeler
We describe a mean field, free energy model that allows the computation of realistic phase diagrams for a particular set of ordering transitions in face-centered-cubic (FCC) binary alloys. The model is based on a sixth-order Landau expansion of the free

Shape Parameter for a Non-Axisymmetric Isothermal Dendrite

June 1, 1999
Author(s)
Geoffrey B. McFadden, Sam R. Coriell, R F. Sekerka
In previous work, we found approximate solutions for paraboloids having perturbations with four-fold axial symmetry in order to model dendritic growth in cubic materials. These solutions provide self-consistent corrections through second order in a shape

A Phase-Field Model of Solidification With Convection

March 1, 1999
Author(s)
D M. Anderson, Geoffrey B. McFadden, A A. Wheeler
We develop a phase-field model for the solidification of a pure material that includes convection in the liquid phase. The model permits the interface to have an anisotropic surface energy, and allows a quasi-incompressible thermodynamic description in

Analytic Solution for a Non-Axisymmetric Isothermal Dendrite

March 1, 1999
Author(s)
Geoffrey B. McFadden, Sam R. Coriell, R F. Sekerka
The Ivantsov solution for an isothermal paraboloidal dendrite growing into a pure, undercooled melt provides a relation between the bulk undercooling and a dimensionless product, the Peclet number, of the growth velocity and tip radius of the dendrite

Anisotropy of Interfaces in an Ordered HCP Binary Alloy

September 1, 1998
Author(s)
John W. Cahn, S C. Han, Geoffrey B. McFadden
A multiple-order parameter mean field theory of ordering on a binary hexagonal-close-packed (HCP) crystal structure is developed, and adapted to provide a continuum formulation that incorporates the underlying symmetries of the HCP crystal in both the bulk

Solute Trapping and Solute Drag in a Phase-Field Model of Rapid Solidification

September 1, 1998
Author(s)
N A. Ahmad, A A. Wheeler, William J. Boettinger, Geoffrey B. McFadden
During rapid solidification, solute may be incorporated into the solid phase at a concentration significantly different than that predicted by equilibrium thermodynamics. This process, known as solute trapping, leads to a progressive reduction in the

Interface Morphology During Crystal Growth: Effects of Anisotropy and Fluid Flow

August 12, 1998
Author(s)
Sam R. Coriell, B T. Murray, A A. Chernov, Geoffrey B. McFadden
We treat the effect of shear flows on the morphological stability of a crystal growing from solution by a step mechanism at a given constant velocity. We carry out some calculations for a shear flow that is sinusoidal in time.The interaction of fluid flow

Step Bunching: Influence of Impurities and Solution Flow

July 14, 1998
Author(s)
A A. Chernov, P G. Vekilov, Sam R. Coriell, B T. Murray, Geoffrey B. McFadden
Step bunching results in striations even at relatively early stages of its development and in inclusions of mother liquor at the later stages. Therefore, eliminating step bunching is crucial for high crystal perfection. The nature of step bunching

Multiple Similarity Solutions for Solidification and Melting

July 1, 1998
Author(s)
Sam R. Coriell, Geoffrey B. McFadden, R F. Sekerka, William J. Boettinger
We explore multiple one-dimensional similarity solutions during the solidification of a binary alloy and a pure material. The configuration is analogous that of a diffusion couple, for which multiple solutions in ternary alloys were discovered by Coates &

Internal waves in xenon near the critical point

June 1, 1996
Author(s)
Robert F. Berg, Margaret J. Lyell, Geoffrey B. McFadden, Ronald G. Rehm
Just above the liquid-vapor critical point, a fluid’s large compressibility causes a stable stratification in which the density varies by as much as 10% in 1 cm. This stratification supports internal gravity waves which we observed with an oscillator