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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