Download - Yong Du , W.W. Zhang, W. Xiong State Key Lab of Powder Metallurgy, Central South University, China
Yong Du, W.W. Zhang, W. Xiong State Key Lab of Powder Metallurgy, Central South University, China
R.X. Hu, P. NashThermal Processing Technology Center, Illinois Institute of Technology, USA
A Novel Approach for Acquiring Thermodynamic Database of Al Alloys and Investigation of
Microstructure during Solidification of Al Alloys
The 3rd International Symposium Light Metals and Composite Materials,
Belgrade, Serbia, September 12-14, 2008.
Celebration of the 200th Anniversary of University of Belgrade
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Contents1. Motivation
2. Experimental and computational approaches
3. Results and discussion
3.1 Thermodynamic data of Al alloys: case study for the Al-Ni-Si system
3.2 Solidification behaviors of Al356.1 alloy
Equilibrium solidification
Scheil model
Mircomodel
4. Summary
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Al-based alloys are widely used as aeronautic and civil materials
Among many commercial alloys (Al-, Fe-, Ni-, Mg-based etc. alloys), only Fe-based thermodynamic database is well established by Thermo-calc company, Sweden.
Currently: Lack of reliable thermodynamic and kinetic databases for Al alloys!
Our work: (I) to establish thermodynamic and kinetic databases for multi- component Al alloys via a hybrid approach of experiment, CALPHAD and first-principles methods
(II) to describe the microstructure and micro-segregation during solidifications of Al alloys using thermodynamic and kinetic databases.
Al-based alloys
1. Motivation1. Motivation
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Contents1. Motivation
2. Experimental and computational approaches
3. Results and discussion
3.1 Thermodynamic data of Al alloys: case study for the Al-Ni-Si system
3.2 Solidification behaviors of Al356.1 alloy
Equilibrium solidification
Scheil model
Mircomodel
4. Summary
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2.1 Experimental approach Phase diagram measurement:
Equilibrated alloys, diffusion couple, XRD, EPMA, DTA, DSC, SEM
Measurement of enthalpy of formation and heat capacity
Directional solidification:
Temperature gradient: 45K/cm; Growth rate: 0.04445cm/s XRD, EPMA
2.2 Computational approach CALPHAD method (thermodynamic modeling)
First-principles method (Enthalpy of formation computation)
Molecular dynamics (Diffusion coefficient caculation)
Point analysis for phase compositions
Area scan for solute redistribution in (Al)
SEM/EDX (Image) Fraction of phase
2. Experimental and computational approaches2. Experimental and computational approaches
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Fig. 1. Phase equilibria of the Al-Ni-Zn system at 1100 ℃determined by diffusion couple technique and equilibrated alloys
2. Experimental and computational approaches2. Experimental and computational approaches
Diffusion couple technique + equilibrated alloys
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Al SiNi
phase transition temperatures Composition range of the primary phases
Crystal structure isothermal section
Liquidus surface and reaction scheme for the ternary system
XRD, EPMA, DTA
annealed at 550oC for 1 month
Arc-melting
MetallographyEDX,EPMA
30 ternary alloys
3. Experimental procedure
2. Experimental and computational approaches2. Experimental and computational approaches
As-cast
Fig. 2. Experimental procedure to establish reaction scheme of the Al-Ni-Si system
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Calorimetry: Measurement of enthalpy of formationKleppa high temperature calorimeter
aAl (298K) + bNi (298K) + cX (298K)= AlaAl (298K) + bNi (298K) + cX (298K)= AlaaNiNibbXXcc (1473 K) (1473 K)
Hreaction (1)
AlAlaaNiNibbXXc c (298 K) = Al(298 K) = AlaaNiNibbXXc c (1473 K)(1473 K)
Hheat content (2)
(1) (1) -- (2) get: (2) get:
aAl (298K) + bNi (298K) + cX (298K) = AlaAl (298K) + bNi (298K) + cX (298K) = AlaaNiNibbXXcc (298 K) (298 K) (3)
298Kf reaction heat content
Samples preparation
Procedure (two steps)
Al
X
Ni Mixing Pressing
Elemental powder Sample pellets
Deoxidization
2. Experimental and computational approaches2. Experimental and computational approaches
Fig. 3. Procedure to measure the enthalpy of formation via calorimetry
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CALPHAD Method
0
1 1
lnn n
E magm i i i i m m
i i
G x G RT x x G G
Gibbs energy at reference states
Ideal entropy of mixing
Excess Gibbs energy
Magnetic contributions to the Gibbs energy
EmG
Em A BG x x
0 0[a b T
1 1( )( )A Bx x a b T
......]
2. Experimental and computational approaches2. Experimental and computational approaches
Fig. 5. Procedure of CALPHAD method
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VASP-Vienna VASP-Vienna Ab InitioAb Initio Simulation Package Simulation Package
Physical Fundamental: Density Function Theory
First principles calculation
theory : DFT Base set : Plane Waves Pseudopotential : UltraSoft Pseudopotential
Projector Augmented Wave method Exange and correlation : LDA, GGA, LDA + U
Total energy
T[n]: Kinetic Energy EH:Hartree Energy(e-e repulsion)Exc: Exchange and correlation energies V(r) :External potential
rdrnrV 3][nE ][nT ][nE H ][nE xc
Enthalpy of formation of AlNi2Si
2 2(AlNi Si) (AlNi Si) (Al) 2 (Ni) (Si)H E E E E
2. Experimental and computational approaches2. Experimental and computational approaches
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Contents1. Motivation
2. Experimental and computational approaches
3. Results and discussion
3.1 Thermodynamic data of Al alloys: case study for the Al-Ni-Si system
3.2 Solidification behaviors of Al356.1 alloy
Equilibrium solidification
Scheil model
Mircomodel
4. Summary
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Thermodynamic database for the Al-Fe-Mg-Mn-Si-Cu-Ni-Zn systemThermodynamic database for the Al-Fe-Mg-Mn-Si-Cu-Ni-Zn system
28 binary system 56 ternary systems
3.1 Thermodynamic data of Al alloys: case study for the Al-Ni-Si system3.1 Thermodynamic data of Al alloys: case study for the Al-Ni-Si system
Al-Fe, Al-Fe-Zn etc.: Literature Al-Mn, etc.: Present work (finished) Mn-Si-Cu, etc.: in progress
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The following phases are included in the modeling:Thermodynamic modeling
A symmetric model (Al,Ni,Si,Va)0.5(Al,Ni,Si,Va)0.5 for A2 and B2 and the one (Al,Ni,Si)0.75(Al,Ni,Si)0.25 for Fcc_A1 and Fcc_L12.
Fcc_A1Fcc_L12
Bcc_A2Bcc_B2
3.1 Thermodynamic data of Al alloys: case study for the Al-Ni-Si system3.1 Thermodynamic data of Al alloys: case study for the Al-Ni-Si system
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Thermodynamic modeling• Thermo-calc software accepts 1000 experimental data;
• Measured sections at 550, 800 and 1000 oC plus 13 vertical sections with 22 invariant equilibria [2003Ric, 2004Ric, 2006Cha, this work]: 3000 experimental data;
• Only key experimental data are used: three isothermal sections and 22 invariant reactions
Key References:
[2003Ric] K.W. Richter, H. Ipser: Intermetallics 11 (2003) 101 – 109.
[2004Ric] K.W. Richter, K. Chandrasekaran, H. Ipser: Intermetallics 12 (2004) 545 – 554.
[2006Cha] K. Chandrasekaran, K.W. Richter, H. Ipser: Intermetallics 14 (2006) 491 – 497.
80
70
60
50
40
30
20
10
0
Ni
Al Si
3.1 Thermodynamic data of Al alloys: case study for the Al-Ni-Si system3.1 Thermodynamic data of Al alloys: case study for the Al-Ni-Si system
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The Al-Ni-SiThe Al-Ni-Si ternary systemternary system
Wei Xiong, Yong Du et al., Int. J. Mater. Res. 99 (2008) 598-612.
(a) (b)
Fig. 6. Calculated isothermal sections with the experimental data at (a) 1000 and (b) 800 oC
Calculated isothermal sections
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The Al-Ni-SiThe Al-Ni-Si ternary systemternary system
(a)
Fig. 7. Calculated isothermal sections with the experimental data at (a) 750 and (b) 550 oC
(b)
Calculated isothermal sections
Wei Xiong, Yong Du et al., Int. J. Mater. Res. 99 (2008) 598-612.
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Fig. 8. Model-predicted vertical sections with the experimental data. (a) 80 at.% Ni; (b) 75 at.% Ni
The Al-Ni-SiThe Al-Ni-Si ternary systemternary system
(a) (b)
Model predicted vertical sections
Wei Xiong, Yong Du et al., Int. J. Mater. Res. 99 (2008) 598-612.
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The Al-Ni-SiThe Al-Ni-Si ternary systemternary system
Fig. 9. Model-predicted vertical sections with the experimental data. for 66.67 at.% Ni (a) CALPHAD predicted; (b) experimental constructed
(a) (b)
Model predicted vertical sections
Wei Xiong, Yong Du et al., Int. J. Mater. Res. 99 (2008) 598-612.
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The Al-Ni-SiThe Al-Ni-Si ternary systemternary system
Fig. 10. Model-predicted vertical sections with the experimental data. (a) 60 at.% Ni; (b) 55 at.% Ni
(a) (b)
Model predicted vertical sections
Wei Xiong, Yong Du et al., Int. J. Mater. Res. 99 (2008) 598-612.
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Fig. 11. Model-predicted vertical sections with the experimental data. (a) 50 at.% Ni; (b) 45 at.% Ni
The Al-Ni-SiThe Al-Ni-Si ternary systemternary system
(a) (b)
Model predicted vertical sections
Wei Xiong, Yong Du et al., Int. J. Mater. Res. 99 (2008) 598-612.
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(a)
The Al-Ni-SiThe Al-Ni-Si ternary systemternary system
Fig. 12. Model-predicted vertical sections with the experimental data. (a) 40 at.% Ni; (b) 30 at.% Ni
(b)
Model predicted vertical sections
Wei Xiong, Yong Du et al., Int. J. Mater. Res. 99 (2008) 598-612.
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The Al-Ni-SiThe Al-Ni-Si ternary systemternary system
Fig. 13. Model-predicted vertical sections with the experimental data. (a) 20 at.% Ni; (b) 10 at.% Ni
(a) (b)
Model predicted vertical sections
Wei Xiong, Yong Du et al., Int. J. Mater. Res. 99 (2008) 598-612.
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Table 1. Calculated enthalpy of formation for AlNi2Si (kJ/mole-atoms)
Composition CALPHAD Experiment VASP
AlNi2Si –55.00 –56.43 –56.36
Enthalpy of melting CALPHAD Experiment*
L = Al3Ni + (Al) + (Si) –14.13 –12.22
* DSC measurement (N.M. Martynova et al., Russ. J. Phys. Chem. 58 (1984) 616 – 617.
Table 2. Enthalpy of melting for the invariant eutectic L = Al3Ni + (Al) + (Si) (kJ/mole-atoms)
The Al-Ni-SiThe Al-Ni-Si ternary systemternary system Model predicted thermodynamic properties
Wei Xiong, Yong Du et al., Int. J. Mater. Res. 99 (2008) 598-612.
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Contents1. Motivation
2. Experimental and computational approaches
3. Results and discussion
3.1 Thermodynamic data of Al alloys: case study for the Al-Ni-Si system
3.2 Solidification behaviors of Al356.1 alloy
Equilibrium solidification
Scheil model
Mircomodel
4. Summary
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Thermodynamic database
Kinetic databaseReal solidification condition
Kinetic database input Impurity diffusivity of Ni, Mg, Mn, Si in liquid Al and solid (Al)
Energy of solid/liquid interface
Specific latent heat of solidification
Geometric factor for coarsening
t3 32 2,0 f0
λ (t) λ G Mdt
Liquid
Solid
3.2 Solidification behaviors of Al356.1 alloy 3.2 Solidification behaviors of Al356.1 alloy
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L L (Al) : (Al) :
Calculated- 615Calculated- 615ooC, Measured-616 C, Measured-616 ooCC
L L (Al)+(Si)+ (Al)+(Si)+αα-AlMnSi :-AlMnSi :
CalculatedCalculated- 573- 573ooC, C, MeasuredMeasured-575 -575 ooCC
Fig. 14. The DSC curve of equilibrium solidification of multi-component Al 356.1 alloy (∆T=3 oC)
EquilibriumEquilibrium Solidification: Solidification: Complete diffusion in both liquid and solid phases
Al356.1 is annealed at 550oC for 45 days
3.2 Solidification behaviors of Al356.1 alloy 3.2 Solidification behaviors of Al356.1 alloy
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Table 3. The comparison between the non-equilibrium calculation and the experimental solidification of multi-component Al 356.1 alloy (∆T=6oC)
Scheil model calculationScheil model calculation Measured [1990Bae]Measured [1990Bae]
L L (Al) at (Al) at 615 615 ooCC L L (Al) at (Al) at 614 614 ooCC
L L (Al) + (Al) + -AlMnSi at -AlMnSi at 588 588 ooCC L L (Al) + (Al) + -AlMnSi at -AlMnSi at 594 594 ooCC
L L (Al) + (Si) + (Al) + (Si) + -AlNiSi -AlNiSi+ + -AlMnSi at -AlMnSi at 572 572 ooCC
L L (Al) + (Si) + (Al) + (Si) + -AlNiSi -AlNiSiat at 575 575 ooCC
L L (Al) + (Si) + Mg (Al) + (Si) + Mg22SiSi
+Al+Al88NiMgNiMg33SiSi66++-AlMnSi at -AlMnSi at 556 556 ooCC
L L (Al) + (Si) + Mg (Al) + (Si) + Mg22SiSi
+ Al+ Al88NiMgNiMg33SiSi6 6 at at 554 554 ooCC
Scheil model: Scheil model: No diffusion in solid phase, complete diffusion in liquid
1990Bac: L. Bäckerud et al., Solidification Characteristics of Aluminum Alloys, Vol. 2, Foundry Alloys, AFS/Skanaluminium, Sweden (1990).
3.2 Solidification behaviors of Al356.1 alloy 3.2 Solidification behaviors of Al356.1 alloy
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Fig. 15. Microstructure (directional solidification with a cooling rate of
2K/S)
Micromodel:Micromodel:
3.2 Solidification behaviors of Al356.1 alloy 3.2 Solidification behaviors of Al356.1 alloy • complete diffusion in liquid• back diffusion in solid phases• undercooling
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Cylindrical model
Scheil model
ExperimentSphere model
Secondary dendrite: sphere, cylinder
(I) Diffusion in solid phase;
(II) The growth of dendirte;
(III) Solute super-cooling, temperature gradient
super-coolingYong Du et al., Z. Metallkd., 96, 1351-1362 (2005)
Fig. 16. Si distribution in the primary (Al) during the directional solidification of
multi-component Al 356.1 alloy (Cooling rate: 2K/S)
3.2 Solidification behaviors of Al356.1 alloy 3.2 Solidification behaviors of Al356.1 alloy Micromodel:Micromodel:
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Contents1. Motivation
2. Experimental and computational approaches
3. Results and discussion
3.1 Thermodynamic data of Al alloys: case study for the Al-Ni-Si system
3.2 Solidification behaviors of Al356.1 alloy
Equilibrium solidification
Scheil model
Mircomodel
4. Summary
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A thermodynamic database of Al-Fe-Mg-Mn-Si-Cu-Ni-Zn-
(+more elements) system is being constructed;
A kinetic database of Al-Fe-Mg-Mn-Si-Cu-Ni-Zn system is
being constructed;
Hybrid approach: Key experiment + CALPHAD + First-
principles method;
The thermodynamic and kinetic database are used to
describe the solidification behaviors of Al alloys.
4. Summary4. Summary
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Prof. Dr. Yong DuState Key Lab of Powder Metallurgy
Central South UniversityChangsha, Hunan, 410083, P.R. China
E-mail: [email protected]: +86-731-8710855http://www.imdpm.net
Thank you for your attention!Welcome to China!
Thank you for your attention!Welcome to China!