Transcript AB INITIO CALCULATED LATTICE STABILITY OF SIGMA

Calculation of phase equilibria by
Thermocalc software
Prof. Jan Vřešťál,
Masaryk University in Brno, Czech Republic
Outline:
THERMOCALC program – various versions
(other programes: MTDATA, FACTSAGE, PANDAT..)
Database – pure metals, metalic solutions, intermetalics
Macros for calculation of binary phase diagrams
Prediction of phase equilibria in complex systems
Examples of using Thermocalc
Thermocalc as the software for calculation of phase diagrams by the Calphad method
can be used for calculation of phase diagrams using Compound Energy Formalism
(CEF) for the Gibbs energy models listed in the lecture.
The examples can be divided into 2 parts:
1. Examples using existing databases (solder, steel)
1. 1. Calculation of single equilibrium (TC does not discriminate upper case and
lower case in the name of commands)
Solder.tdb: AgPd.tcm,
Steel.tdb: FeNi.tcm
1.2. Calculation of phase diagrams
Solder.tdb: AgPd.tcm – continue, BiSn.tcm – continue,
BiCu.tcm (zoom), BiIn.tcm, CuSn.tcm
Steel.tdb: FeNi.tcm – continue
CrNi.tcm
1.3. Include magnetism and/or miscibility gap
Solder.tdb: AgPd.tcm – exclude misc-gap (delete starting point at 400 K)
Steel.tdb: FeNi.tcm – without „A_P_D Mag_ord BCC_A2“ no phase diagram
1.4. Calculate thermodynamic functions at chosen temperature
Solder.tdb: AgPd.tcm,(Gliquid:old,new), BiSn.tcm - continue
1.5. Phase diagram with metastable phases
Steel.tdb: Fe-C – phases all: equilibrium with graphite
Reject phase graphite: equilibrium with diamond
Reject phase graphite, diamond: equilibrium with cementite
1.6. Calculate consecutive equilibrium compositions – step command:
Solder.tdb: BiInstep.tcm, Steel.tdb: CrNistep.tcm, CuNistep.tcm
1.7. Calculate Scheil solidification scheme:
Solder.tdb: Scheil-BiIn.tcm, Steel.tdb: Scheil-CrNi.tcm, Scheil-CuNi.tcm
1.8. Calculate ternary phase diagram
Solder.tdb: Isothermal section: BiCuSn1000.tcm Isoplethal section: BiCuSn10Cu.tcm
Steel.tdb: FeCrNi1273.tcm
2. Examples to create own database for verification of
published parameters (special separate database)
2.1. Ta-V system: C.A. Danon, C. Servant: A thermodynamic evaluation of Ta-V
system. J. of Alloy and Comp. 366 (2004) 191-200
2. 2. Cr-Zr system: J. Pavlů, J.Vřešťál, M. Šob: Stability of Laves Phases in the Cr-Zr
system. Calphad 33 (2009) 382-387
2.3. Ru-Ge system: J.Zálešák: Final Report of Computational Thermodynamics. 2010.
Improve founded errors by the proper change of parameters, when necessary.
--------------------------------------------------------------------------------------------------------3. Examples to create experimental datafile (.POP-file) for the PARROT progam
(PANDAT Program) (special statements necessary to be used – see User Guide )
Structure of database - ThermoCalc
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Definition of reference states of elements
Definition of phases and their constituents models
Records: Values of thermodynamic functions
(pure components, compounds, solutions,
ordered phases)
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Advantage:
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Communication with other programes: diffusion,
solidification….
and with other databases
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Definition of reference state of elements - example
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ELEMENT /0.0000E+00
ELEMENT VA
0.0000E+00
ELEMENT IN
0.0000E+00
ELEMENT SN
0.0000E+00
ELEMENT ZN
0.0000E+00
ELEMENT BI
0.0000E+00
ELEMENT AG
0.0000E+00
ELECTRON_GAS
0.0000E+00
0.0000E+00
VACUUM
0.0000E+00
0.0000E+00
!
!
TETRAGONAL_A6
114.82
0.0000E+00
BCT_A5
118.69
0.0000E+00
HCP_A3
65.39
0.0000E+00
RHOMBO_A7
208.98
0.0000E+00
FCC_A1
107.87
0.0000E+00
!
!
!
!
!
Definition of phases and their constituents - example
(see models)
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PHASE LIQUID:L Z 1 1 !
CONSTITUENT LIQUID:L :AG,BI,IN,SN,ZN : !
$
PHASE BCT_A5 Z 1 1 !
CONSTITUENT BCT_A5 :AG,BI,IN,SN,ZN : !
$
PHASE TETRAGONAL_A6 Z 2 1 1 !
CONSTITUENT TETRAGONAL_A6 :AG,BI,IN,SN,ZN:VA : !
$
PHASE FCC_A1
Z 2 1 1 !
CONSTITUENT FCC_A1 :AG,BI,IN,SN,ZN:VA : !
$
PHASE FCT Z 1 1 !
CONSTITUENT FCT :AG,BI,IN,SN,ZN : !
Structure of records – Go - example
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G(PHASE,ELEMENT1;0)
G(PHASE,ELEMENT2;0)
TM
BM
T(lower) Polynomial for G(T,p) T(upper)
N/Y Literature !
PARA G(BCC,Cr;0) 298.15 GHSERCR 6000 N SGTE !
FUN GHSERCR 298.15 -8856.94+157.48*T26.908*T*LN(T)+.00189435*T**2-1.47721
E-06*T**3+139250*T**(-1); 6000 N SGTE !
Structure of records - GE - example
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L(PHASE,ELEM.1,ELEM.2;ORDER OF INTERACTION)
TM
BM
T(lower) L- Redlich - Kister polynomial T(upper) Literature !
GE = x1x2 i Li (x1 – x2 )i
-
R-K polynomial
PARAM L(FCC_A1,CR,FE:VA;0) 298. 10833.-7.477*T; 6000. HQ91 !
Calculation of phase diagram - example
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Macro (AgSn.log):
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GO DATA
sw avr
define-element
Sn Ag
Reject phase /all
Restore phase bct_a5 fcc liq hcp
epsilon
get
$-------------------------GO GES
list-phase-data fcc
@?continue
$-------------------------GO POLY
set-condition t=973 x(Ag)=0.95 p=1E5
n=1
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Calculate-equilibria
set-axis-variable 1 x(Ag) 0 1 .025
s-a-v
2
t 300 1200 10
map
$-------------------------POST
set-diagram-axis x m-f Sn
s-d-a y t-C
make-experimental-datafile
SnAg.dat
set-title Sn-Ag Phase diagram
plot
SCREEN
set-interactive
Basic types of phase diagrams
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Systems with complete miscibility of components in solid phase
Systems with incomplete miscibility of components in solid phase
–
primary solid solutions
- eutectics
- peritectics
Systems of components with no solubility in solid phase (eutectics, peritectics)
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Systems with intermedial phases
- compounds (Hume-Rothery– „electrons“: Cu7Zn3)
- intermetallic phases (Zintl – „ions“: K4Sn9)
- intermetallic phases (covalent: GaAs)
- ordered phases (CuAu),
- Frank-Kasper phases (, , Laves - topologically ordered)
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Secondary solid solutions (components soluble in intermedial phases)
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Models for solid solutions and liquid (example)
FCC:
BCC:
HCP:
Liquid:
2\
2\
2\
1\
1 1
1 3
1 0.5
1
Models for intermetallics (example)
Laves_C14:
Laves_C15:
Laves_C36:
2 \ 2
2 \ 2
2 \ 2
1
1
1
or
3\ 4
6
2
or
3\ 8
12 4
Assignment of lattice sites in models
Sublattice
Laves_C14
Laves_C15
Laves_C36
1
4f
8a
4e, 4f
2
6h
16d
6g, 6h
3
2a (Cr)
(two sublattice model)
4f (Cr)
Creating database
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Problems:
Condition of database consistency
- models used
- names used
- numerical data used