Molecular Dynamics Study of Solidification in the Aluminum-Silicon System Supervisor: Dr. Jeffrey J...
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Transcript of Molecular Dynamics Study of Solidification in the Aluminum-Silicon System Supervisor: Dr. Jeffrey J...
Molecular Dynamics Study of
Solidification in the Aluminum-
Silicon System
Supervisor: Dr. Jeffrey J Hoyt
Peyman Saidi
Winter 2013
Aluminum – Mineral Commodity Summary 2011
0.10
1.60
2.00
3.30
8.65
13.76
13.80
22.00
32.50
33.00
23.0 17.9 2.0
43.45
54.50
98.50
0 20 40 60 80 100
Wheels
Heads
Suspension Arms and Links
Transmissin Cases
Brake Calipers
Steering Knuckles
Blocks
Bumper Beams
Closures
Subframes
Transfer Cases
IP Beams
Front Structures
Complete BIW
2
Motivation (Importance of Aluminum Alloys)
T. Hosch, et al. Material science and engineering A 528 (2010) 226–232.
Al-Si Eutectic 250μm/s
Al-Si Eutectic 20μm/s Al-Si Eutectic 950μm/s
3
Motivation (Quench Modified Aluminum Silicon Alloy)
4
Melting Point
Temperature
Step
Advacancy
Kink
Growth of Silicon crystals
5
Twin Planes Twin Planes
Twin PlanesTwin Planes
Propagation mechanism in Silicon dendrites is based on interaction of twinning.
Quench modified fibrous silicon is twin free.What is the growth mechanism of quench modified silicon in Aluminum-Silicon alloy?
What is the critical condition for the transition from anisotropic to isotropic growth for Silicon dendrites?
What is the magnitude and anisotropy of step kinetic coefficient, free energy and the stiffness of the interface?
What is the effect of twins on kinetic parameters at different undercooling and compositions?
D. R. Hamilton and R. G. Seidensticker J. Appl. Phys. 31, 1165 (1960)
Twin Plane Reentrant Edge Mechanism (TPRE)
6
Molecular Dynamics Method:
A model describing all interactions in the system
Cutoff distanc
e
Newton’s equations of motion:
Stability of System
G=H-TS
H: Heat Content
S: Randomness
H=U+PV
U: Internal Energy
U=K+E
K: Kinetic Energy
Vibration
Rotation
Translation
E: Potential Energy
Interaction of atoms
Where are we?
Implementing model in MD code
Potential energies for all interactions
Aluminum Silicon Al-Si
What do we need to run a MD simulation?
7
Molecular Dynamics models: Aluminum (Embedding Atom Method)
M. S. Daw and M. I. Baskes PHYSICAL REVIEW B 29, 6443 (1984)
Aluminum
FCC Crystal structure, metallic bond
8
Molecular Dynamics models: Silicon (Stillinger-Weber)
F. H. Stillinger and T. A. Weber PHYSICAL REVIEW B 31, 5262 (1985)
Silicon
Diamond crystal structure, covalent bonds
9
Molecular Dynamics models: Aluminum Silicon Interactions (AEAM)
A. M. Dongare et al. PHYSICAL REVIEW B 80, 184106, 2009.
Idea:
Reformulation of Embedding Atom Method by extracting a three body term from the Embedding functional in order to make these two methods (EAM and SW) compatible with each other.
Implementing A-EAM
Aluminum Potential Silicon Potential Al-Si Potential
10
Silicon Potential (Stillinger Weber)
11
Silicon Potential (Modified Stillinger-Weber)
The difference between cohesive energy of diamond and wurtzite structures should be the same as the value calculated with DFT.
Modification should not affect the characteristics of the Stillinger-Weber potential which accurately predicts silicon properties.
Diamond structure was stabilized by taking into account interaction with the third neighbor.
12
Silicon Potential (Modified Stillinger-Weber)
13
Pure Components: Gibbs-Helmholtz relation
Alloy: The alloy’s free energy as a function of composition
Semi Grand Canonical Monte Carlo (SGCMC) simulation:
Aluminum-Silicon Potential
Target: Aluminum-Silicon Potential should predict phase diagram accurately.
U1 U2-U1
Atom Switches back
T, C, P=0 random Si atom is switched to Al
P. Sindzingre, D. Frenkel. Chem. Phys. Lett. (1987) 35–41.
14
So far
Angular Embedding atom method was implemented on Molecular Dynamics code
A modified potential for Silicon was proposed
Current work
Making an accurate potential for Al-Si interactions
Studying and modeling nucleation and solidification growth
Studying the crystalline anisotropies of the interfacial free energy.
Characterizing the magnitude and anisotropy of the step kinetic coefficient.
Examining a faceted to non-faceted transition of the interface by changing undercooling.
Developing a model for the nucleation and growth phenomena.
Studying the effect of twinning on crystal growth
Studying growth rate as a function of undercooling on twinned Si crystals in contact with liquid.
Studying growth rate as a function of composition on twinned Si crystals in contact with liquid.
Results and Future Work
Thank You