Diffusion in Fe-Ni PM alloys: microstructure and DICTRA ...Diffusion in Fe-Ni PM alloys:...

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


[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


• 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


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


Kinetic data in Fe-Ni alloys


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


1000 s = 16 min

• Guillet constitutional diagram for Ni steels (1910)

• Compositions in wt-%

• Still used

Guillet constitutional diagram


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


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


1000 °C

Sintered at 1120 °C for 30 min followed by furnace cooling to RT (10 h)


Sintered at 1120 °C for 30 min followed by slow cooling to 283 °C


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


950

1000

1050

1100

1150

1200

T (

ºC)

0 500 1000 1500

time [s]

DICTRA (2011-05-20:20.18.40) :


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) :


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) :


A (1120 °C, t=0)

B (1120 °C, 15 min)

Kirkendall plane


1120 °C – 15min

• Diffusion couple Ni-Fe, 1120 °C, 15 min

• Simulation: TCFE6 + MOBFE1

Isothermal diffusion


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


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) :


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


• 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


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


• 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


• 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


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


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


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


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


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


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


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


THANK YOU! (and see you at Calphad 2013

in San Sebastian, Spain)

Diffusion in Fe-Ni PM alloys: microstructure and DICTRA ...Diffusion in Fe-Ni PM alloys:...

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