View
2
Download
0
Category
Preview:
Citation preview
Diffusion in Fe-Ni PM alloys: microstructure and DICTRA simulations
Tomas Gomez-Acebo
Francisco Castro
CALPHAD XL, Rio de Janeiro, 22-29/95/2011
• Introduction – Ni in steels
• Microstructure of sintered Fe-Ni alloys
• Kinetic modelling
– Kirkendall porosity
• Diffusion at high pressures
Contents
CALPHAD XL, Rio de Janeiro, 22-29/95/2011 2
• Tendency to reduce (and avoid) the use of Ni
• … but it is essential in powder metallurgy
• Better understand the role of Ni diffusion during sintering
• Model the diffusion process and Ni homogenization
Objectives
CALPHAD XL, Rio de Janeiro, 22-29/95/2011 3
[W.C. Leslie, Met. Trans., vol.3, 1972, pp 5-26] • Does not form any carbides hence remains in solution
strengthening ferrite • Lowers critical cooling rate • Grain refiner • In combination with Cr, produces steels with greater hardenability,
higher impact strength and fatigue resistance than can be achieved in carbon steels.
• The notch toughness of ferritic steels can be improved by grain refinement and by additions of Ni.
• In the alloy steels, nickel is the most common of the alloying elements used to lower the transition temperature
• Nickel is the only element in the periodic table that increases toughness of Fe alloys
• Pt, Ni, Ru, Rh, Ir and Re [de Retana A.F et al., Metal Progress, Sept., 100, 105, 1971]
Ni in steels
CALPHAD XL, Rio de Janeiro, 22-29/95/2011 4
• Powder mixtures as multiple diffusion couples
– Fe-0.8 Mo, powder 60 m
– Ni: 2-6 wt-%, powder 0.5-7 m
– C (graphite): 0.2 wt-%
• Thermodynamic and kinetic modelling
– Mo not considered
– C: problems in calculations. Skipped
Experimental procedure
CALPHAD XL, Rio de Janeiro, 22-29/95/2011 5
SEM micrographs from the Nickel powder used
Commercial powder grade
Nickel carbonyl powder
6 CALPHAD XL, Rio de Janeiro, 22-29/95/2011
1000 °C – 0 min 1120 °C – 0 min 1120 °C – 15 min
Microstructures after quenching
• 10% Ni + 0.6% graphite + (Fe-0.8Mo) bal.
• Microstructural progress showing formation of “Nickel-rich”
areas – Notice constrained shrinkage due to dual particle size distributions
– First, grain boundary diffusion
7 CALPHAD XL, Rio de Janeiro, 22-29/95/2011
Kinetic data in Fe-Ni alloys
8 CALPHAD XL, Rio de Janeiro, 22-29/95/2011
0
1
2
3
4
5
6
7
8
9
10
11
10-15
DC
(FC
C,N
I,N
I,F
E)
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
MOLE_FRACTION NI
THERMO-CALC (2011.05.02:11.46) :
DATABASE:MOBFE1
T=1393.15, P=1E5, N=1.;
2011-05-02 11:46:57.99 output by user tgacebo from PCTGACEBO
Interdiffusion coefficient at 1120 °C (MOBFE1)
0
1E-14
2E-14
3E-14
4E-14
5E-14
6E-14
7E-14
8E-14
0 20 40 60 80 100
D
D-Fe
D-Ni
Intrinsic diffusion coefficients at 1200 °C (Landolt-Börnstein)
Mo: 0.53
Fe: 53.10
Ni: 46.37
Mo: 0.7
Fe: 99.3
Ni: 0
Mo: 0.72
Fe: 96.14
Ni: 3.14
EDS analyses
10%Ni + 0.6%C + (Fe-0.8Mo) bal., 1120 °C – 15min
9
0
10
20
30
40
50
60
70
80
90
100
WE
IGH
T-P
ER
CE
NT
NI
0 5 10 15 20 25 30 35 40
10-6
DISTANCE
DICTRA (2011-03-16:16.24.13) :
TIME = 0,1,10,100,1000,10000,100000,1000000
CELL #1
2011-03-16 16:24:13.11 output by user tgacebo from PCTGACEBO
1000 s = 16 min
• Guillet constitutional diagram for Ni steels (1910)
• Compositions in wt-%
• Still used
Guillet constitutional diagram
10 CALPHAD XL, Rio de Janeiro, 22-29/95/2011
0
5
10
15
20
25
30
MA
SS
_P
ER
CE
NT
NI
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
MASS_PERCENT C
THERMO-CALC (2011.05.06:17.45) :
DATABASE:TCFE6
N=1, P=1E5, T=973;
FCC_A1CEMENTIT+FCC_A1
BCC_A2+CEMENTIT
2011-05-06 17:45:56.13 output by user tgacebo from PCTGACEBO
700 °C
0
5
10
15
20
25
30
MA
SS
_P
ER
CE
NT
NI
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
MASS_PERCENT C
THERMO-CALC (2011.05.06:17.48) :
DATABASE:TCFE6
N=1, P=1E5, T=1273;
FCC_A1
CEMENTIT+FCC_A1
2011-05-06 17:48:56.10 output by user tgacebo from PCTGACEBO
1000 °C
Sintered at 1120 °C for 30 min followed by furnace cooling to RT (10 h)
CALPHAD XL, Rio de Janeiro, 22-29/95/2011 11
Sintered at 1120 °C for 30 min followed by slow cooling to 283 °C
CALPHAD XL, Rio de Janeiro, 22-29/95/2011 12
Illustration of chemical gradients thus leading to different transformation products
10%Ni, 0.6%C,
(Fe-0.8Mo) bal
• Ni-Fe diffusion couple
• Heating 20 °C/s to 1120 °C
Calculated diffusion profile
13 CALPHAD XL, Rio de Janeiro, 22-29/95/2011
950
1000
1050
1100
1150
1200
T (
ºC)
0 500 1000 1500
time [s]
DICTRA (2011-05-20:20.18.40) :
2011-05-20 20:18:40.69 output by user tgacebo from PCTGACEBO
A B
0
10
20
30
40
50
60
70
80
90
100
WE
IGH
T-P
ER
CE
NT
FE
-12 -9 -6 -3 0 3 6
10-6
z [m]
DICTRA (2011-05-20:20.13.32) :
2011-05-20 20:13:32.14 output by user tgacebo from PCTGACEBO
A (1120 °C, t=0)
B (1120 °C, 15 min)
Kirkendall plane
0
10
20
30
40
50
60
70
80
90
100
WE
IGH
T-P
ER
CE
NT
FE
-12 -9 -6 -3 0 3 6
10-6
z [m]
DICTRA (2011-05-20:20.13.32) :
2011-05-20 20:13:32.14 output by user tgacebo from PCTGACEBO
A (1120 °C, t=0)
B (1120 °C, 15 min)
Kirkendall plane
14 CALPHAD XL, Rio de Janeiro, 22-29/95/2011
1120 °C – 15min
• Diffusion couple Ni-Fe, 1120 °C, 15 min
• Simulation: TCFE6 + MOBFE1
Isothermal diffusion
15 CALPHAD XL, Rio de Janeiro, 22-29/95/2011
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Ato
mic
fra
cti
on
Ni
-12 -10 -8 -6 -4 -2 0 2 4 6
10-6
z [m]
THERMO-CALC (2011.05.19:13.46) : TIME = 900
CELL # 1
Ni Fe
• Velocity of the atomic planes in the lattice-fixed frame of reference
• Two velocity peaks
Velocity of the atomic planes
16 CALPHAD XL, Rio de Janeiro, 22-29/95/2011
z
x
VDD
JJJV
v
m
Ni
m
FeNi
VaFeNi
1''
''
0
2
4
6
8
10
12
14
10-11
v [
m/s
]
-12 -10 -8 -6 -4 -2 0 2 4 6
10-6
z [m]
Ni Fe
0
5
10
15
20
25
10-3
Maxim
um
po
re f
racti
on
-12 -10 -8 -6 -4 -2 0 2 4 6
10-6
z [m]
Maximum pore fraction (model of Höglund & Agren, 2005)
17
-12
-9
-6
-3
0
3
6
9
12
15
d(-
JV
a)/
dz
-12 -10 -8 -6 -4 -2 0 2 4 6
10-6
z [m]
THERMO-CALC (2011.05.19:19.57) :
2011-05-19 19:57:21.88 output by user tgacebo from PCTGACEBO
Ni Fe
Derivative of the vacancy flux
z
v
Vz
J
m
1)( Va
Ni Fe
t
dtz
JVy
0
VamVa
)(
Va
Va
1 y
yf p
(Only for positive values of the integrand)
CALPHAD XL, Rio de Janeiro, 22-29/95/2011
PRESSURE EFFECT ON FE-NI DIFFUSION
CALPHAD XL, Rio de Janeiro, 22-29/95/2011 18
• Diffusion coefficient decreases with increasing pressure
– Traditional model: relate to the melting point diffusivity
– Melting point increases with pressure
– Same diffusivity at same homologous temperature, T/TM
• Activation volume
Pressure dependence on diffusion
CALPHAD XL, Rio de Janeiro, 22-29/95/2011 19
Activation volume
VPSTUSTHG
TV
GV
Activation volume
For interstitials: MVV Migration volume
VPQQ
QMRTRTMRT
RTRT
QMM
ii
iii
mgmgiii
0
0
0
MQln)ln(
magnetic-nonfor 1;1
exp
Qi0: for 1 bar
20 CALPHAD XL, Rio de Janeiro, 22-29/95/2011
• Diffusion couples Fe-Ni
– P up to 23 GPa
– T=1280 – 1700 °C
• [Goldstein, Trans. Metall. Soc. AIME, 233 (1965) 812]
• [Yunker, Earth and Planetary Sci. Lett., 254 (2007) 203]
• Thermodynamic and mobility data:
– TCFE6 and MOBFE1 (modified introducing the pressure term in mobility)
Experimental data
21 CALPHAD XL, Rio de Janeiro, 22-29/95/2011
• Preliminary assessment results:
– V(fcc&Fe,Fe)=13.2E-06 m3/mol
– V(fcc&Ni,Ni)=0.91E-06 m3/mol
– V(fcc&Fe,Ni)=5.9E-06 m3/mol
– V(fcc&Ni,Fe)=4.1E-06 m3/mol
Diffusion profiles at 1, 12 and 23 GPa
CALPHAD XL, Rio de Janeiro, 22-29/95/2011 22
0
10
20
30
40
50
60
70
80
90
100
AT
OM
IC-P
ER
CE
NT
FE
-300 -200 -100 0 100 200 300 400 500
DISTANCE (um)
THERMO-CALC (2011.05.20:17.50) :
12GPa, 1600C, 2h
12GPa, 1500C, 2h
12GPa, 1600C, 10h
12GPa, 1600C, 0.5h
2011-05-20 17:50:25.82 output by user tgacebo from PCTGACEBO
0
10
20
30
40
50
60
70
80
90
100
AT
OM
IC-P
ER
CE
NT
FE
-150 -100 -50 0 50 100 150 200 250
DISTANCE (um)
THERMO-CALC (2011.05.20:17.51) :
23GPa, 1600C, 6h
23GPa, 1700C, 6h
2011-05-20 17:51:28.62 output by user tgacebo from PCTGACEBO
0
10
20
30
40
50
60
70
80
90
100
AT
OM
IC-P
ER
CE
NT
FE
-150 -100 -50 0 50 100 150 200 250
DISTANCE (um)
THERMO-CALC (2011.05.20:17.48) :
1GPa, 1280C, 6h
1GPa, 1150C, 18h
1GPa, 1420C, 2h
2011-05-20 17:48:45.21 output by user tgacebo from PCTGACEBO
0
10
20
30
40
50
60
70
80
90
100
AT
OM
IC-P
ER
CE
NT
FE
-150 -100 -50 0 50 100 150 200 250
DISTANCE (um)
THERMO-CALC (2011.05.20:17.48) :
1GPa, 1280C, 6h
1GPa, 1150C, 18h
1GPa, 1420C, 2h
2011-05-20 17:48:45.21 output by user tgacebo from PCTGACEBO
0
10
20
30
40
50
60
70
80
90
100
AT
OM
IC-P
ER
CE
NT
FE
-300 -200 -100 0 100 200 300 400 500
DISTANCE (um)
THERMO-CALC (2011.05.20:17.50) :
12GPa, 1600C, 2h
12GPa, 1500C, 2h
12GPa, 1600C, 10h
12GPa, 1600C, 0.5h
2011-05-20 17:50:25.82 output by user tgacebo from PCTGACEBO
0
10
20
30
40
50
60
70
80
90
100
AT
OM
IC-P
ER
CE
NT
FE
-150 -100 -50 0 50 100 150 200 250
DISTANCE (um)
THERMO-CALC (2011.05.20:17.51) :
23GPa, 1600C, 6h
23GPa, 1700C, 6h
2011-05-20 17:51:28.62 output by user tgacebo from PCTGACEBO
Interdiffusion coeff. at 1, 12 and 23 GPa
-15.0
-14.5
-14.0
-13.5
-13.0
-12.5
-12.0
LO
GD
C(F
CC
,NI,
NI,
FE
)
0 10 20 30 40 50 60 70 80 90 100
MOLE_PERCENT FE
1GPa, 1280C, 6h
1GPa, 1150C, 18h
1GPa, 1420C, 2h
-15.0
-14.5
-14.0
-13.5
-13.0
-12.5
-12.0
LO
GD
C(F
CC
,NI,
NI,
FE
)
0 10 20 30 40 50 60 70 80 90 100
MOLE_PERCENT FE
23GPa, 1600C, 6h
23GPa, 1700C, 6h
-15.0
-14.5
-14.0
-13.5
-13.0
-12.5
-12.0
LO
GD
C(F
CC
,NI,
NI,
FE
)
0 10 20 30 40 50 60 70 80 90 100
MOLE_PERCENT FE
12GPa, 1600C, 2h
12GPa, 1500C, 2h
12GPa, 1600C, 10h
12GPa, 1600C, 0.5h
23 CALPHAD XL, Rio de Janeiro, 22-29/95/2011 -15.0
-14.5
-14.0
-13.5
-13.0
-12.5
-12.0
LO
GD
C(F
CC
,NI,
NI,
FE
)
0 10 20 30 40 50 60 70 80 90 100
MOLE_PERCENT FE
23GPa, 1600C, 6h
23GPa, 1700C, 6h
-15.0
-14.5
-14.0
-13.5
-13.0
-12.5
-12.0
LO
GD
C(F
CC
,NI,
NI,
FE
)
0 10 20 30 40 50 60 70 80 90 100
MOLE_PERCENT FE
1GPa, 1280C, 6h
1GPa, 1150C, 18h
1GPa, 1420C, 2h
-15.0
-14.5
-14.0
-13.5
-13.0
-12.5
-12.0
LO
GD
C(F
CC
,NI,
NI,
FE
)
0 10 20 30 40 50 60 70 80 90 100
MOLE_PERCENT FE
12GPa, 1600C, 2h
12GPa, 1500C, 2h
12GPa, 1600C, 10h
12GPa, 1600C, 0.5h
• (On-going work)
• Study of Ni diffusion in Fe powders
• Modelling the pressure effect on diffusion
Summary and conclusions
24 CALPHAD XL, Rio de Janeiro, 22-29/95/2011
THANK YOU! (and see you at Calphad 2013
in San Sebastian, Spain)
Recommended