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Simulation of cellular-dendritic solidification structures of binary alloys in three-dimensional growth using a multiparticle diffusion-limited aggregation model

  • T. A. M. Haemers , D. G. Rickerby and E. J. Mittemeijer EMAIL logo
Published/Copyright: February 10, 2022
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Abstract

Solidification in binary alloy melts was simulated with two different three-dimensional models, that differ in the way the role of the solid/liquid interface energy on the solidification is expressed: either surface rearrangement or a surface curvature-dependent attachment probability was applied. In the melt, the simultaneous diffusion of all diffusing particles (atoms) was taken into account. Cellular –dendritic growth modes, as observed in practice, could be well simulated. The surface rearrangement model is essential for exhibiting details (as facetting) and the effect of the next-nearest neighbour interaction.


Prof. E. J. Mittemeijer Max-Planck-Institut für Metallforschung Heisenbergstr. 3, D-70569 Stuttgart, Germany Tel.: +49 711 689 3311 Fax: +49 711 689 3312

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Appendix: Discretization of the Laplacian in an f. c. c. lattice

In one dimension, the discretization of the second derivative of ρi,t is (in the following, the subscripts i and t have been omitted.

x2ρx=(ρx1+ρx+12ρx)/Δx2

where Δx is the distance between two lattice points.

In two dimensions this becomes

2ρx,y=x2ρx,y+y2ρx,y =( ρx1,y+ρx+1,y2ρx,y+ρx,y+1 +ρx,y12ρx,y )/Δx2

and for three dimensions, it follows

(A-1) 2ρx,y,z=x2ρx,y,z+y2ρx,y,z+z2ρx,y,z =( ρx1,y,z+ρx+1,y,z+ρx,y+1,z+ρx,y1,z +ρx,y,z1+ρx,y,z+16ρx,y,z )/Δx2

In order to arrive at an expression for Δ2ρx,y,z for the f. c. c. lattice where the individual ρ values in the discretized expression (as Eq. (A-1)) pertain to ρ values at nearest neighbour lattice sites, we proceed as follows.

First, recognizing that p nearest neighbours in the f. c. c. lattice are on a distance 122 times the lattice constant times Δx, an Equation analogous to Eq. (A-1) can be given

(A-2) 2ρx,y,z=( ρx122,y,z+ρx+122,y,z+ρx,y+122,z+ρx,y122,z +ρx,y,z122 +ρx,y,z+122 6ρx,y,z )/(122Δx)2 =2( ρx122,y,z+ρx+122,y,z+ρx,y+122,z +ρx,y122,z+ρx,y,z122 +ρx,y,z+122 6ρx,y,z )/Δx2

where positions with coordinates (x, y, z) do not correspond with sites of the f. c. c. lattice. To get (partial) coincidence with sites of the f. c. c. lattice sites, Eq. (A-2) can be rotated over each of the three axes. Rotation of 45° over the x axis results in

(A-3) 2ρx,y,z=2( ρx122,y,z+ρx+122,y,z+ρx,y+12,z+12+ρx,y12,z+12 +ρx,y+12,z12+ρx,y12,z126ρx,y,z )/Δx2

with only the terms (ρ values) on the x axis not on a site of the f. c. c. lattice.

Rotation of 45° over the z axis results in

(A-4) 2ρx,y,z=2( ρx+12,y+12,z+ρx+12,y12,z+ρx12,y+12,z+ρx12,y+12,z +ρx,y,z122 +ρx,y,z+122 6ρx,y,z )/Δx2

with only the terms (ρ values) on the z axis not on a site of the f. c. c. lattice.

Rotation of 45° over the y axis results in

(A-5) 2ρx,y,z=2( ρx+12,y,z+12 +ρx+12,y,z12 +ρx,y+122,z+ρx,y122,z +ρx12,y,z+12 +ρx12,y,z12 6ρx,y,z )/Δ2x

with only the terms (ρ values) on the y axis not on a site of the f. c. c. lattice.

Now, to finally get an Equation with all terms (ρ values) pertaining to nearest neighbour sites of the f. c. c. lattice, first, Eqs. (A-3), (A-4) and (A-5) are added, secondly, Eq. (A-2) is subtracted from this sum. Then, after dividing the left- and right-hand sides of the Equation by 2, the final result is

2ρx,y,z=( ρx+12,y+12,z+ρx12,y+12,z+ρx+12,y12,z+ρx12,y12,z +ρx+12,y,z12 +ρx+12,y,z+12 +ρx12,y,z+12 +ρx12,y,z12 +ρx,y+12,z+12 +ρx,y12,z+12 +ρx,y+12,z12 +ρx,y12,z12 12ρx,y,z )/Δx2

which for an f. c. c. lattice represents the discretized Laplacian of ρi,tin terms of nearest neighbour values of ρi,t

Received: 2004-02-16
Accepted: 2004-09-17
Published Online: 2022-02-10

© 2004 Carl Hanser Verlag, München

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