Substitutional and Interstitial Diffusion in α2-Ti3Al(O)

E. Copland 1, D. J. Young 2, B. Gleeson 3, N. Jacobson 4

1 Case Western Reserve University, Cleveland, Ohio, USA 2 University of New South Wales, Sydney, NSW, Australia

3 Iowa Sate University, Ames, Iowa, USA 4 NASA Glenn Research Center, Cleveland, Ohio, USA

The reaction between Al2O3 and α2-Ti3Al was studied with a series of Al2O3/α2-Ti3Al multiphase diffusion couples annealed at 900, 1000 and 1100°C. The diffusion-paths were found to strongly depend on α2-Ti3Al(O) composition. For alloys with low oxygen concentrations the reaction involved the reduction of Al2O3, the formation of a γ-TiAl reaction-layer and diffusion of Al and O into the α2-Ti3Al substrate. Measured concentration profiles across the interaction-zone showed “up-hill” diffusion of O in α2-Ti3Al(O) indicating a significant thermodynamic interaction between O and Al, Ti or both. Diffusion coefficients for the interstitial O in α2-Ti3Al(O) were determined independently from the interdiffusion of Ti and Al on the substitutional lattice. Diffusion coefficients are reported for α2-Ti3Al(O) as well a γ-TiAl. Interpretation of the results were aided with the subsequent measurement of the activities of Al, Ti and O in α2-Ti3Al(O) by Knudsen effusion-cell mass spectrometry.

https://ntrs.nasa.gov/search.jsp?R=20070010751 2020-06-27T01:52:22+00:00Z

1

Subs

titut

iona

lSu

bstit

utio

nal a

nd In

ters

titia

lan

d In

ters

titia

l

Diff

usio

n in

D

iffus

ion

in αα

22--TiTi

33Al(O

)A

l(O)

E. C

opla

nd1,

4 , D

. J. Y

oung

2 , B

. Gle

eson

3 , N

. Jac

obso

n4

1 C

ase

Wes

tern

Res

erve

Uni

vers

ity, C

leve

land

Ohi

o2

Uni

vers

ity o

f New

Sou

th W

ales

, Syd

ney

Aus

tral

ia3

Iow

a St

ate

Uni

vers

ity, A

mes

Iow

a4

NA

SA G

lenn

Res

earc

h C

ente

r, C

leve

land

Ohi

o

TMS

Ann

ual M

eetin

g: 2

/25

-3/1

/200

7 –

Orla

ndo,

FL,

US

A

Nat

iona

l Aer

onau

tics

and

Spac

e Ad

min

istra

tion

ww

w.n

asa.

gov

2

Ti-A

l-O s

yste

m B. L

ee, N

. Sau

nder

s, Z

. Met

allk

d., 1

997,

88(

2), p

p. 1

52-1

61.

T=

1000

ºC

Al 2O

3on

ly o

xide

in e

quili

briu

m w

ith α

2-Ti

3Al +

γ-Ti

Al,

but…

both

pha

ses

mus

t be

satu

rate

d w

ith O

3

•ra

tiona

le…

poss

ible

MM

C a

nd o

xida

tion

of α

2-Ti 3A

l + γ-

TiA

l

•m

ulti-

phas

e co

uple

s: α

2/ A

l 2O3

resu

lts &

cal

cula

tions

•si

ngle

-pha

se c

oupl

es: α

2(O

) / α

2(O)

resu

lts &

cal

cula

tions

•pa

rtia

l the

rmod

ynam

ic p

rope

rtie

s in

α2-

Ti3A

l(O)

•su

mm

ary

outli

ne

4

•ar

c-m

elte

d: A

l, Ti

& T

iO2;

anne

aled

at T

= 90

0, 1

000,

110

0ºC

clos

ed s

yste

m:

Ta-fo

il (b

arrie

r for

SiO

)-in

SiO

2ca

psul

e

•H

IP b

ondi

ng (1

70 M

Pa, 1

100º

C fo

r 2 h

), po

ly-c

ryst

allin

e A

l 2O3

re-e

ncap

sula

ted,

reac

ted

900,

100

0, 1

100º

C fo

r t =

20

~ 50

0 h

•an

alys

is:

met

allo

grap

hy, o

ptic

al, E

PMA

and

mic

ro-h

ardn

ess

mul

ti-ph

ase

Ti-A

l / A

l 2O3

coup

les

allo

yco

mp.

(at.%

)ph

ase

1 ~

3Ti

-(49,

52,

55)

Al

γ-Ti

Al

8Ti

-27A

l-10O

α2-

Ti3A

l(O)

α2-

Ti3A

lα

2-Ti

3Al

α2-

Ti3A

lα

2-Ti

3Al(O

)

9 ~

10Ti

-(40,

48)

Al

α2

+ γ

4Ti

-25A

l5

Ti-3

2Al

6TI

-35A

l7

Ti-3

3.35

Al-5

O

no re

actio

n, ig

nore

reac

tion,

but

igno

re

5

α2-

Ti3A

l / A

l 2O3

coup

les

mar

ker

Al 2O

3

γ-Ti

Al

α2-

Ti3A

l

Ti-3

2Al /

Al 2O

3,t=

500

h

sqrt

. tim

e (1

0-2s1/

2 )0

510

1520

thickness (μm)

020406080100

k p = 4

.0+0

.2

k p = 0

.72+

0.04

k p = 0

.12+

0.02

1100

o C

1000

o C

900o C

k p (10

11cm

2 s-1)

1100

ºC

1000

ºC

900º

C

6

α2-

Ti3A

l / A

l 2O3

coup

les

Al 2O

3=

2Al γ,

α2+

3Oγ,α

2…

“gas

/ so

lid”

Al,

O s

uppl

ied

at a

ctiv

ity o

f γ/ A

l 2O3

J O>>

JA

l(fr

om d

iffus

ion

path

)

J O→

thro

ugh γ-

laye

r int

o α

2(O

)

J Al→

γ-la

yer g

row

th a

nd e

nric

hes α

2(O

)

“up-

hill”

diffu

sion

of O

in α

2(O

)

T=

1100

ºC

J Ofr

om lo

w to

hig

h X O

:

D OA

lmus

t be

+ve

and

sign

ifica

nt…

+ve

ther

mod

ynam

ic in

tera

ctio

n be

twee

n O

and

Ti +

Al

xCD

xCD

J∂∂

−∂∂

−=

Al

Ti OA

lO

Ti OO

O~

~~

EPM

A e

rror

, Ti

O2-l

ayer

7

•Ti

and

Al s

ubst

itutio

nal;

O in

ters

titia

l, bu

t [O

Ti6]

onl

y st

able

site

s

•lim

ited

kine

tic in

tera

ctio

n be

twee

n la

ttice

s pl

us J

O>>

JA

l, tr

eat:

Ti-A

l “ps

eudo

bin

ary”

and

O “

tran

sien

t equ

ilibr

ium

”

•co

rrec

t pro

files

: r(T

i, A

l) =

1.45

, 1.4

3Å;

V m(α

2, γ)

≈10

.0 c

m3 m

ol-1

Ti, A

l:

O:tr

eatin

g di

ffusi

on in

Ti-A

l-O

γ-Ti

Al(

L10)

α2-

Ti3A

l (D

O19

) ()

()

mVN

NN

CA

lTi

ii

+=

mVN

CO

O=

C. J

ones

, B. L

ukle

y, E

. Cop

land

, Int

erm

etal

lics,

14,

(200

6), p

. 54.

8

conc

entr

atio

n pr

ofile

s

Dis

tanc

e (μ

m)

020

040

060

080

0

Concentration (at.%)

020406080Ti Al O

α2-

Ti3A

l(O)

γ-Ti

Alra

w E

PMA

dat

a

Ti a

nd A

l are

n’t d

iffus

ing!

EPM

A e

rror

, TiO

2-lay

er

“up-

hill”

diffu

sion

of O

Dis

tanc

e (μ

m)

020

040

060

080

0

Concentration (molcm-3

)

0.00

0.02

0.04

0.06

0.08

Ti Al O

α2-

Ti3A

l(O)

γ-Ti

Alco

rrec

ted

prof

ile

()

()

mVN

NN

CA

lTi

ii

+=

mVN

CO

O=

Al 2O

3/ T

i-25A

lT

= 11

00°C

, 250

h

9

D(N

i) in

α2-

Ti3A

l and

γ-Ti

Al

com

posi

tion

(NA

l)0.

200.

250.

300.

350.

400.

450.

500.

55

interdiffusivity (cm2s

-1) 10

-13

10-1

2

10-1

1

10-1

0

10-9

Ti-2

5Al

Ti-3

2Al

Ti-3

5Al

Ti-3

3Al-5

O

α2-

Ti3A

l(O)

γ-Ti

Al

T=

1100

ºC

aver

age

valu

es

1100

°C

3.9±

1.0x

10-1

41.

4±0.

5x10

-11

Ti-3

2Al

3.4±

0.9x

10-1

45.

1±2.

0x10

-12

Ti-2

5Al

900°

C

3.3±

0.7x

10-1

35.

9±0.

9x10

-11

Ti-3

2Al

2.6±

0.5x

10-1

32.

8±0.

4x10

-11

Ti-2

5Al

1000

°C

1.2±

0.2x

10-1

26.

1±0.

7x10

-11

Ti-3

3.3A

l-5O

5.2±

1.3x

10-1

25.

4±0.

3x10

-11

Ti-3

5Al

3.0±

1.5x

10-1

26.

3±0.

6x10

-11

Ti-3

2Al

2.7±

0.3x

10-1

29.

9±0.

5x10

-11

Ti-2

5Al

(cm

2 sec

-1)

(cm

2 sec

-1)

Allo

yγ

D~2

~ αD

10

Arr

heni

us b

ehav

ior /

com

paris

on

α2

γ

DO

(cm

2 s-1

)E a

(kJm

ol-1

)D

O(c

m2 s

-1)

E a(k

Jmol

-1)

1169

-136

6-

-3.

0x10

-321

0co

ncen

trat

ion

Kai

num

a, In

den

(199

7)

845-

1310

1031

2±6

2.8

295±

10co

ncen

trat

ion

Spre

ngel

(199

6)

881-

1400

--

1.5

291±

10tr

acer

Kro

ll, (1

992)

897-

995

0.3

290±

15-

-tr

acer

Rüs

ing,

Her

zig

(199

5)

897-

995

n/a

≈350

--

conc

entr

atio

nR

üsin

g, H

erzi

g(1

995)

750-

1250

1.5x

10-6

117±

52x

10-5

152±

2co

ncen

trat

ion

Hira

no, I

ijim

a(1

984)

900-

1100

0.3

290±

251.

1x10

-514

0±40

conc

entr

atio

nPr

esen

t res

ults

Met

hod

Ref

eren

ceT

(°C

)

104 /T

(K-1

)6

78

910

11

ln(Dα2)

-34

-32

-30

-28

-26

-24

-22

Spre

ngel

Hira

no

Ti-3

2Al R

usin

gTi

-25A

l

104 /T

(K-1

)6

78

910

11

ln(Dγ)

-32

-30

-28

-26

-24

-22

Spre

ngel

Hira

noK

roll

Kai

num

a

γ-Ti

Al

α2-

Ti3A

l

11

•J O

>> J

(Al,T

i)…“t

rans

ient

equ

ilibr

ium

”(K

irkal

dyet

al.

1958

-64)

O, l

ocal

equ

ilibr

ium

; red

istr

ibut

es w

ith T

i-Al s

ubst

itutio

nall

attic

e

•pr

edic

t int

erdi

ffusi

onco

effic

ient

ratio

:

inte

rstit

ial d

iffus

ion

of O

in α

2-Ti

3Al

0~

~~

Al

Ti OA

lO

Ti OO

O≅

∂∂−

∂∂−

=xC

DxC

DJ

i

AlOTi O

O

Ti OAl

CCDD

ΔΔ−

=~~

T=

1100

ºC

CAl

0.01

80.

020

0.02

20.

024

0.02

60.

028

0.03

00.

032

0.03

40.

036

CO

0.00

8

0.01

0

0.01

2

0.01

4

0.01

6

Ti-2

5Al

Ti-3

2Al T

i-27A

l-10O

D OA

l/ D OO

= 0.

44±0

.08

12

calc

ulat

ed D OO

•, n

o in

ters

ectin

g di

ffusi

on p

aths

…

•re

gion

of p

ure

O e

nric

hmen

t,

•EP

MA

and

mic

ro-h

ardn

ess;

ass

ume

D OO

cons

t.

D OO

/D Al

=10

0 ~

1000

xCD

xCD

Ji

∂∂−

∂∂−

=A

lTi O

Al

OTi O

OO

~~

~

xCD

JxC

i

∂∂−

=→

=∂∂

OTi O

OO

Al

~~

0

)2(

),

(D

tx

erf

CC

Ct

xC

sO

s=

−−

Ti OO

D~(1

0-10 c

m2 s

-1)

Arr

ehen

ius

Beh

avio

ur

1100

°C10

00°C

900°

CD

O(c

m2 s

-1)

E a(k

Jmol

e-1)

I(Ti-2

5Al)

4.0±

1.0

0.75

±0.1

50.

2±0.

10.

014

200±

23

II(Ti

-32A

l)5.

5±1.

50.

6±0.

150.

15±0

.10.

6024

0±37

III(T

i-35A

l)6.

5±1.

51.

0±1.

50.

15±0

.12.

3725

2±10

Allo

y

13

Al

1015

2025

3035

4045

500

5

10

15

Ti

75

80

85

901

23

45

6

78

9

•ar

c-m

elte

d pu

re-A

l, Ti

& T

iO2,

anne

aled

in c

lose

d sy

stem

:

Ta-fo

il in

SiO

2ca

psul

e

•un

i-axi

al h

ot p

ress

(110

0ºC

for 2

~ 4

h);

T=

1100

ºC fo

r 100

h

•an

alys

is:

met

allo

grap

hy, o

ptic

al &

EPM

A

used

mul

ti-al

loy

EPM

A s

tand

ard…

TiO

2su

rfac

e-la

yer

sing

le-p

hase

α2(

O) /

α2(

O) c

oupl

es allo

yco

mp.

(at.%

)

1Ti

-25.

8Al-0

.1O

4Ti

-24.

7Al-3

.9O

5Ti

-28.

5Al-4

.0O

6Ti

-32.

0Al-3

.9O

2Ti

-29.

6Al-0

.3O

3Ti

-33.

6Al-0

.1O

9Ti

-31.

1Al-7

.8O

7Ti

-23.

5Al-7

.7O

8Ti

-28.

0Al-7

.7O

14

Al

1015

2025

3035

4045

500

5

10

15

Ti

75

80

85

90

cons

tant

Ti /

Al r

atio

Ti /

Al ≈

2.9,

2

.3,

2.0

x (μ

m)

-100

0-5

000

500

1000

CO(mole/cm3)

0.00

0

0.00

2

0.00

4

0.00

6

0.00

8

0.01

0x O

x m

x (μ

m)

-100

0-5

000

500

1000

x Ox m

x (μ

m)

-100

0-5

000

500

1000

Ti / Al ratio

123456x O

x m

7 / 1

8 / 2

9 / 3

x m–

x o=

186μ

mx m

–x o

= 10

9μm

x m–

x o=

173μ

m

xCD

xCD

Ji

∂∂−

∂∂−

=A

lTi O

Al

OTi O

OO

~~

~

xCD

Ji

∂∂−

=→

OTi O

OO

~~

T=

1100

ºC, 1

00 h

15

calc

ulat

ed J

Oan

d D OO

x (μ

m)

-150

0-1

000

-500

050

010

0015

00

JO (10-10

mole/cm2s)

0.0

0.2

0.4

0.6

0.8

1.0

CO (m

ole/

cm3 )

0.00

00.

002

0.00

40.

006

0.00

8

DO (10-10

cm2/s)

05101520

7/1

8/2

9/3

D OO

~ in

depe

nden

t of X

Obu

t sm

all T

i / A

l dep

ende

nce

(?)

Ti-A

l / A

l 2O3

coup

les

α2(

O) /

α2(

O) c

oupl

es

allo

yD

OO

(10-1

0 cm

2 /s) T

= 11

00°C

Ti /

Al (

coup

le)

DO

O(1

0-10 c

m2 /s

) T=

1100

°C

Ti-2

5Al

4.0±

1.0

2.9

(7 /

1)4.

8 ±1

.0

Ti-3

2Al

5.5±

1.5

2.3

(8 /

2)6.

2 ±1

.5

Ti-3

5Al

6.5±

1.5

2.0

(9 /

3)6.

1 ±2

.0

16

Al

2025

3035

Ti

65

70

75

80

O5

0

10

15T

= 11

00ºC

,10

0 h

•pr

ofile

s fli

pped

rela

tive

to d

iffus

ion

path

•cl

assi

c “u

p-hi

ll”pr

ofile

for O

…

ther

mod

ynam

ic in

tera

ctio

n: T

i-Al →

O

•Ti

-Al i

nter

actio

n zo

ne d

ecre

ases

with

XO

O →

Ti-A

l: k

inet

ic /

ther

mod

ynam

ic ?

expe

ct s

imila

r Δμ (

Ti,A

l)fo

r eac

h X O

x (μ

m)

-400

-200

020

040

0

Ti / Al ratio

2.0

2.2

2.4

2.6

2.8

3.0

CO(mole/cm3)

0.00

0

0.00

2

0.00

4

0.00

6

0.00

8

0.01

0x O

x m

Ti / Al ratio

2.0

2.2

2.4

2.6

2.8

3.0

CO(mole/cm3)

0.00

0

0.00

2

0.00

4

0.00

6

0.00

8

0.01

0

Ti / Al ratio

2.0

2.2

2.4

2.6

2.8

3.0

CO(mole/cm3)

0.00

4

0.00

6

0.00

8

0.01

0

0.01

2

0.01

4

9 / 7

6 / 4

3 / 1

J Ti

J AlJ O

97

6

4

31

cons

tant

CO

17X O

(at%

)0

24

68

10

DAl (cm2/s)

10-1

3

10-1

2

10-1

1

10-1

0

sing

le-p

hase

m

ulti-

phas

e Sp

reng

el (1

996)

Hira

no (1

984)

Rus

ing

(199

5)

Ti-3

3Al-4

O

Ti-2

5Al

Ti-3

2Al

Ti-3

5Al

x (μ

m)

-200

-100

010

020

0

JAl (10-11

mole/cm2s)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

3/1

6/4

9/7

CA

l (m

ole/

cm3 )

0.02

40.

026

0.02

80.

030

0.03

20.

034

0.03

6

DAl (cm2/s)

10-1

3

10-1

2

10-1

1

10-1

0

calc

ulat

ed J Al

and

D Al

increasing O

•Ti

-Al a

nd O

diff

usio

n is

n’t i

ndep

ende

nt

•X O

not c

ontr

olle

d in

pre

viou

s st

udie

s:

Spre

ngel

: Si

O2

caps

ules

, no

Ta-fo

il

Rus

ing:

flo

win

g A

r-at

mos

pher

e

18

Al

2025

3035

15

Ti

65

70

75

801

3

46

79

Al

2025

3035

15

Ti

65

70

75

80

“int

erse

ctin

g”pa

ths:

9-1

, 7-3

, 6-4

“up-

hill”

Al d

iffus

ion

xCD

xCD

Ji

∂∂−

∂∂−

=A

lTi O

Al

OTi O

OO

~~

~

xCD

xCD

Ji

∂∂−

∂∂−

=A

lTi A

lAl

OTi A

lOA

l~

~~

•9-

1 an

d 7-

3 do

n’t i

nter

sect

; 7-3

and

6-4

are

par

alle

l…

new

cou

ples

nee

ded

to d

eter

min

e ki

netic

inte

ract

ion

O →

Ti-A

l

•9-

1 di

ffusi

on p

ath

show

s “u

p-hi

ll”A

l diff

usio

n:

O d

isso

lutio

n m

ust:

incr

ease

a(A

l), d

ecre

ase

a(Ti

) (or

bot

h)

19

ther

mod

ynam

ic m

easu

rem

ents

mul

ti-ce

ll K

EMS

pres

sure

mea

sure

men

t

ikik

ST

Ip

+=)i(

activ

ity m

easu

rem

ent

⎥⎥ ⎦⎤

⎢⎢ ⎣⎡ ⋅⋅

⋅=

⎥⎥ ⎦⎤

⎢⎢ ⎣⎡ ⋅=

)i()

Au

()

()

(SS

)i()

Au

()

Au

()i(

)i(iAu

Aui

o

o

oo

o

opp

Ag

Rg

IIpp

pp

a

( i =

Ti,

Al,

Al 2O

)

o iio

)i()i()i(

IIpp

a=

=

20

a(A

l) vs

. XO

104 /T

(K-1

)

5.5

6.0

6.5

7.0

7.5

8.0

a(Al) 0.00

1

0.010.

11

Ti-3

0Al

Ti-2

8Al-4

OTi

-28A

l-7.9

O

Ti-3

5Al-2

0O

1400

1300

1200

1100

1000

T(o C

)

α2(

O) +

γ +

Al 2O

3

α2(

O)

α-T

i(Al,O

)

1500

increasing O

refe

renc

e st

ate:

{A

l(l) +

Al 2O

3(s)}

21

a(Ti

) vs.

XO

104 /T

(K-1

)

5.5

6.0

6.5

7.0

7.5

8.0

a(Ti) 0.11

Ti-3

0Al

Ti-2

8Al-4

OTi

-28A

l-7.9

O

Ti-3

5Al-2

0O

1400

1300

1200

1100

1000

T(o C

)

α-T

i(Al,O

)

1500

increasing O

refe

renc

e st

ate:

{Ti

(s) +

Y2O

3(s)}

22

•α

2/ A

l 2O3

and α

2(O

) / α

2(O) c

oupl

es…

Ti-A

l-O re

actio

n be

havi

or

•un

satu

rate

d α

2(O) r

educ

es A

l 2O3:

γ-la

yer,

“up-

hill”

J Oin

α2(

O)

•J O

>> J

Al;

trea

t sub

st. a

nd in

ters

titia

l lat

tices

inde

pend

ently

Ti-A

l “ps

eudo

bin

ary”

D=

D(C

i), s

catte

r in

data

(effe

ct o

f XO)

“tra

nsie

nt e

qu.”

: D OA

l/ D

OOan

d D OO

, sl

ight

Ti /

Al d

epen

denc

e

•α

2(O

) / α

2(O

) cou

ples

: co

nfirm

D OA

l/ D

OOan

d D OO

beha

vior

,bu

t Ti-A

l int

erdi

ffusi

onre

duce

d >

10x

with

XO

0.00

5 →

0.08

ther

mod

ynam

ic in

tera

ctio

n +

chan

ge in

mob

ility

(?)

diffi

cult

to o

bser

ve k

inet

ic a

spec

t; th

erm

odyn

amic

s is

cle

ar

•m

ore

wor

k is

nee

d…

sign

ifica

nt in

sigh

t to

oxid

atio

n of

Ti-A

l allo

ys

sum

mar

y

23

ackn

owle

dgem

ents

:

Judy

Aup

ing

(NA

SA G

lenn

), Ja

mes

Sm

ith (N

ASA

Gle

nn)

Chr

istia

n C

hatil

lon

(Sai

nt M

artin

d’H

ères

, Fra

nce)

,N

ASA

Gle

nn R

esea

rch

Cen

ter –

Dire

ctor

s D

iscr

etio

nary

Fun

dU

nive

rsity

of N

ew S

outh

Wal

es, S

ydne

y, A

ustr

alia

–A

RC

Gra

nt