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The origin of dislocations with b = <110> in single crystals of β-nial compressed along <001> at elevated temperatures
Scripta METALLURGICA
Vol. 8, pp. 1049-1054,1974 Printed in the United States
Pergamon Press,
THE ORIGIN OF DISLOCATIONS W I T H b = I N SINGLE CRYSTALS COMPRESSED ALONG <001> AT ELEVATED TEMPERATURES
Inc.
OF ~-NiAI
Nestor J. Zaluzec and Hamish L. Fraser Department of M e t a l l u r g y and Mining Engineering and Materials Research Laboratory University of Illinois at Urbana-Champaign Urbana, Illinois 61801
(Received July 12, 1974)
Introduction It is well known that the preferred ~-NiAI
involves
(e.g.,
1-4).
glide of dislocations
Clearly,
none of the applied presumably
stress is resolved onto these preferred
some other type of slip system must be activated
77°K and 300°K,[ii0}
<001>
(4).
single crystals
by either glide or a combination
cations
Thus,
on temperature
plasticity
and strain rate in that study,
were the result of collision of two dislocations latter results,
dislocations
in C001> single crystals these
one would predict
of b = would become
are a number of reports
latter studies,
of[i12}
appears
(5).
and
to be produced of the type
Only very few dislo-
On the basis
above
predominant. 1000°K,
climb of
However,
there
plastic deformation
of{ii0}
(3,6-8).
In
that have been used to determine and transmission
the
electron micro-
(TEM). Recently,
Wasilewski,
must be exercised tors.
or another m e c h a n i s m
with b =.
is produced by operation
two of the techniques
and
and it was assumed that they
increasingly
that at temperatures
little or
slip systems,
that at higher temperatures
active slip system are surface slip analysis scopy
<001>,
of glide and climb of dislocations
of b = were observed
of these
[ii0} or {010}
it has been shown that between
deform by operation
Between ~ 3 0 0 ° K and 1050°K,
depending
in stoichiometric
when single crystals are deformed along
of plastic deformation must be invoked.
= ~I00>,
set of slip systems
of b = on either
Hutchings
and Loretto
(9) have shown that some care
in using surface offsets to deduce dislocation
They have demonstrated
Burgers
vec-
that the offset on the surface of a crystal is not 1049
1050
THE ORIGIN OF D I S L O C A T I O N S IN ~-NiAI
Vol.
8, No.
9
n e c e s s a r i l y caused by m o t i o n of d i s l o c a t i o n s of one single Burgers vector but may be the result of the motion of two or more dislocations h a v i n g different Burgers vectors.
In this case,
the offset w o u l d show a d i s p l a c e m e n t p a r a l l e l to
the vector sum of the component dislocations. ~-NiAI,
it is p o s s i b l e
A p p l y i n g this to the case of
for an offset p a r a l l e l to to be p r o d u c e d by motion
of two d i s l o c a t i o n s of b =.
In view of these uncertainties,
surface slip
trace analysis cannot be used to provide an unambiguous d e t e r m i n a t i o n of the m e c h a n i s m of p l a s t i c d e f o r m a t i o n in these crystals. The p u r p o s e of this b r i e f note is to p r e s e n t some recent TEM observations of d i s l o c a t i o n s in samples taken from <001> crystals c o m p r e s s e d at temperatures between
1000°K and 1300°K.
W h i l e the number of d i s l o c a t i o n s w i t h b = is
indeed greater in these crystals compared w i t h the number in similar crystals c o m p r e s s e d at lower t e m p e r a t u r e s =.
(5), the great m a j o r i t y of d i s l o c a t i o n s have
It w i l l be shown that it is more s a t i s f a c t o r y to account for the
p r e s e n c e of d i s l o c a t i o n s of b = on the basis
of the e n e r g e t i c a l l y favor-
able i n t e r a c t i o n of two d i s l o c a t i o n s w i t h b = rather than assume the operation of the {ii0} glide system. E x p e r i m e n t a l Details Single crystals of n o m i n a l l y s t o i c h i o m e t r i c 8-NiAI have b e e n c o m p r e s s e d p a r a l l e l to <001> over a t e m p e r a t u r e range 1000°K - 1300°K at strain rates about 10-4/sec using an Instron testing machine.
The single crystals w e r e taken from
the same b a t c h as those used in previous experiments involved in p r o d u c i n g thinned sections have b e e n d i s c u s s e d e l s e w h e r e for this study,
(5).
(2,4,5) and the techniques
for t r a n s m i s s i o n electron m e t a l l o g r a p h y
A J E O L J S E M 200 electron m i c r o s c o p e was used
o p e r a t i n g at an a c c e l e r a t i n g voltage of 200 kV.
The Burgers
vectors of d i s l o c a t i o n s w e r e d e t e r m i n e d in the same manner as in p r e v i o u s w o r k (5), by noting i n v i s i b i l i t y in at least two d i f f r a c t i n g conditions
(i0).
Results and D i s c u s s i o n M a n y samples w e r e p r e p a r e d from crystals deformed in the t e m p e r a t u r e range 1000°K - 1300oK.
In each case the vast m a j o r i t y of dislocations o b s e r v e d in
these specimens had Burgers vectors of the type b =. taken from a crystal d e f o r m e d
5% at 1300°K;
ious Burgers vectors d e t e r m i n e d nearly all of the d i s l o c a t i o n s is c o n t a i n e d
in a network,
1 shows an area
the schematic d i a g r a m lists the var-
from c o n t r a s t experiments. in this area h a v e b =
has b =.
Fig.
It can be seen that and only one, w h i c h
Vol. 8, No. 9
THE ORIGIN OF DISLOCATIONS IN ~-NiAI
The Burgers consistent
with
Loretto
the type a[100]
of the e l a s t i c
=
most
;
anisotropy
deformed
Fig.
of d i s l o c a t i o n s dislocations
2 shows with
have
present
in NiAI,
a dislocation
a decrease
in e l a s t i c
a number
of
energy as a
and b =
w e r e
of a s u b - b o u n d a r y
which
short
segments
and again
the various
these
of b =.
dislocation
of b =
dissociates
a dislocation
Burgers
dislocations
dislocations
vectors
were
at one end into stable"
have in
of two sets
two sets
formed.
of
Fig.
are fully consis-
observation
three
component
3
w i t h b =
formed by i n t e r a c t i o n
An i n t e r e s t i n g
"elastically
these
of b = < l l 0 > h a v e
containing
formed.
also p r e s e n t
consists
intersected,
sub-boundaries,
were
the s u b - b o u n d a r i e s
of b = and w h e r e
into an
formed b y
reaction
of s u b - b o u n d a r i e s
in and b e t w e e n
appropriate
than
are
fully
of the crystal.
with b =
that
are
It should be noted
types
the s u g g e s t i o n
rather
that
involves
an example
and one w i t h b =,
~i00>
w i t h b =
different
an area b e t w e e n
tent w i t h
up the n e t w o r k
of the type b =.
11% at 1300°K,
of the d i s l o c a t i o n s
making
dislocations
shown
- a[ll0]
some d i s l o c a t i o n s
networks.
shows
(ii) h a v e
+ a[0103
In crystals Again,
that
of two d i s l o c a t i o n s
Lloyd and
result
of the d i s l o c a t i o n s
the s u g g e s t i o n
the i n t e r a c t i o n that
vectors
1051
is that
components
of b =
of the
of b = and one
of b :. It appears
from this
tion m i c r o s t r u c t u r e tween
850°K and
.
<001>
(ii).
w i t h b =
=
The
reason
of NiAI
are
formed by
stabilized
fully u n d e r s t o o d
and
compressed
(5) that the dislocaat t e m p e r a t u r e s
it is r e a s o n a b l e
interaction
increase
of testing
is i n c r e a s e d
further w o r k
on this
to assume
reduction
in numbers
aspect
that dis,
in elastic
of d i s l o c a t i o n s
and/or
be-
of the type b =
of two w i t h b =
by the a s s o c i a t e d
for the a p p a r e n t
as the t e m p e r a t u r e
et al.
up in the main b y d i s l o c a t i o n s
of our o b s e r v a t i o n s
p r o d u c t ~ = b e i n g gy
crystals
1300°K is made
On the b a s i s
locations
of
study and that by Fraser
strain
the enerwith
rate reduced
is in progress.
Acknowledqments The
support
of this
tract N u m b e r A T ( I I - I ) I I 9 8 ,
r e s e a r c h by the U. S. A t o m i c and the Center
sity of Illinois
is g r a t e f u l l y
Pugh
discussions.
for h e l p f u l
Energy
for Electron
acknowledged.
We w o u l d
Microscopy
A. Ball and R. E. Sma!iman,
A c t a Met.
14,
1517
Con-
of the Univer-
like to thank N e v i l l e
References i.
Commission,
(1966).
1052
THE
ORIGIN
OF D I S L O C A T I O N S
S. R. Butler,
IN ~-NiAI
and J. E. Hanlon,
Vol.
2.
R. R. Wasilewski, 234, 1357 (1967).
3.
R. T.
Pascoe
4.
M. H.
Loretto
5.
H.
6.
P. R. Strutt, R. A. Dodd and G. M. Rowe, Second Int. of Metals and Alloys, p. 1057 ASM, vol. III, (1970).
7.
P. R. Strutt, and S t r u c t u r e
8.
J. Bevk,
9.
R. J. Wasilewski,
and C. W. A. Newey,
L. Fraser,
Phys.
and R. J. Wasilewski, M. H.
Loretto
Star.
Phil.
Sol.
Mag.
Trans.
Met.
A.I.M.E.
Phil.
(1971).
Mag.
2_88, 667
Conf.
(1973).
on The S t r e n g t h
G. M. Rowe, J. C. I n g r a m and ¥. E. Choo, E l e c t r o n M i c r o s c o p y of Materials, p. 722, U n i v e r s i t y of C a l i f o r n i a Press (1972).
R. A. Dodd
and P. R. Strutt,
R. H u t c h i n g s
Met.
and M. H.
Trans.
Loretto,
4,
159
Phil.
(1973). Mag.
2_~9, 521
(1974).
i0.
P. B. Hirsch, A. Howie, R. S. Nicholson, D. W. Pashley and M. J. Whelan, E l e c t r o n M i c r o s c o p y of Thin Crystals, Butterworths, London, (1965).
ii.
C. H.
Lloyd
9
2__99357 (1968).
2__3, 1311
and R. E. Smallman,
Soc.
8, No.
and M. H. Loretto,
Phys.
Stat.
Sol.
r,
3__99, 163
(1970).
lit ,,,
/ i00 ~
~ 010 olo
100 ,i,,,,, .......
FIG.
:
i
in . . . . . . . . . . . . . . . . . . . .
1
A typical m i c r o g r a p h of d i s l o c a t i o n s in samples deformed 5% along <001> at 1300°K. Note that most of the d i s l o c a t i o n s have b =
Vol. 8, No. 9
THE ORIGIN OF DISLOCATIONS IN ~-NiAI
1053
0 %
1/
'
~ O 100
P ::
FIG.
j
':
2
D i s l o c a t i o n s in a sample d e f o r m e d 11% along (001> at 1300°K. Note that w h e r e the two types of d i s l o c a t i o n of b = i n t e r s e c t short segments of b = are formed. Bright field; d i f f r a c t i n g vector as shown; b e a m direction near (001).
i ii
S
I ,II,,iiii
- /
!oo
/
1
!t
0,,;'I
7~~:
tk ¢" \-
III II
FIG.
I
ii IIi
ii
3
A n e t w o r k of d i s l o c a t i o n s in a s p e c l m e n deformed 11% along (001> at 1300°K. The various Burgers vectors are consistent w i t h their b e i n g formed by i n t e r a c t i o n of a p p r o p r i a t e d i s l o c a t i o n s of b =. Bright field; d i f f r a c t i n g vector and a p p r o x i m a t e b e a m d i r e c t i o n as shown.
iiiiiii
i i
d
,]
Vol. 8, pp. 1049-1054,1974 Printed in the United States
Pergamon Press,
THE ORIGIN OF DISLOCATIONS W I T H b =
Inc.
OF ~-NiAI
Nestor J. Zaluzec and Hamish L. Fraser Department of M e t a l l u r g y and Mining Engineering and Materials Research Laboratory University of Illinois at Urbana-Champaign Urbana, Illinois 61801
(Received July 12, 1974)
Introduction It is well known that the preferred ~-NiAI
involves
(e.g.,
1-4).
glide of dislocations
Clearly,
none of the applied presumably
stress is resolved onto these preferred
some other type of slip system must be activated
77°K and 300°K,
<001>
(4).
single crystals
by either glide or a combination
cations
Thus,
on temperature
plasticity
and strain rate in that study,
were the result of collision of two dislocations latter results,
dislocations
in C001> single crystals these
one would predict
of b =
are a number of reports
latter studies,
of
appears
(5).
and
to be produced of the type
Only very few dislo-
On the basis
above
predominant. 1000°K,
climb of
However,
there
plastic deformation
of
(3,6-8).
In
that have been used to determine and transmission
the
electron micro-
(TEM). Recently,
Wasilewski,
must be exercised tors.
or another m e c h a n i s m
with b =
is produced by operation
two of the techniques
and
and it was assumed that they
increasingly
that at temperatures
little or
slip systems,
that at higher temperatures
active slip system are surface slip analysis scopy
<001>,
of glide and climb of dislocations
of b =
of these
[ii0} or {010}
it has been shown that between
deform by operation
Between ~ 3 0 0 ° K and 1050°K,
depending
in stoichiometric
when single crystals are deformed along
of plastic deformation must be invoked.
= ~I00>,
set of slip systems
of b =
Hutchings
and Loretto
(9) have shown that some care
in using surface offsets to deduce dislocation
They have demonstrated
Burgers
vec-
that the offset on the surface of a crystal is not 1049
1050
THE ORIGIN OF D I S L O C A T I O N S IN ~-NiAI
Vol.
8, No.
9
n e c e s s a r i l y caused by m o t i o n of d i s l o c a t i o n s of one single Burgers vector but may be the result of the motion of two or more dislocations h a v i n g different Burgers vectors.
In this case,
the offset w o u l d show a d i s p l a c e m e n t p a r a l l e l to
the vector sum of the component dislocations. ~-NiAI,
it is p o s s i b l e
A p p l y i n g this to the case of
for an offset p a r a l l e l to
of two d i s l o c a t i o n s of b =
In view of these uncertainties,
surface slip
trace analysis cannot be used to provide an unambiguous d e t e r m i n a t i o n of the m e c h a n i s m of p l a s t i c d e f o r m a t i o n in these crystals. The p u r p o s e of this b r i e f note is to p r e s e n t some recent TEM observations of d i s l o c a t i o n s in samples taken from <001> crystals c o m p r e s s e d at temperatures between
1000°K and 1300°K.
W h i l e the number of d i s l o c a t i o n s w i t h b =
indeed greater in these crystals compared w i t h the number in similar crystals c o m p r e s s e d at lower t e m p e r a t u r e s =
(5), the great m a j o r i t y of d i s l o c a t i o n s have
It w i l l be shown that it is more s a t i s f a c t o r y to account for the
p r e s e n c e of d i s l o c a t i o n s of b =
of the e n e r g e t i c a l l y favor-
able i n t e r a c t i o n of two d i s l o c a t i o n s w i t h b =
The single crystals w e r e taken from
the same b a t c h as those used in previous experiments involved in p r o d u c i n g thinned sections have b e e n d i s c u s s e d e l s e w h e r e for this study,
(5).
(2,4,5) and the techniques
for t r a n s m i s s i o n electron m e t a l l o g r a p h y
A J E O L J S E M 200 electron m i c r o s c o p e was used
o p e r a t i n g at an a c c e l e r a t i n g voltage of 200 kV.
The Burgers
vectors of d i s l o c a t i o n s w e r e d e t e r m i n e d in the same manner as in p r e v i o u s w o r k (5), by noting i n v i s i b i l i t y in at least two d i f f r a c t i n g conditions
(i0).
Results and D i s c u s s i o n M a n y samples w e r e p r e p a r e d from crystals deformed in the t e m p e r a t u r e range 1000°K - 1300oK.
In each case the vast m a j o r i t y of dislocations o b s e r v e d in
these specimens had Burgers vectors of the type b =
5% at 1300°K;
ious Burgers vectors d e t e r m i n e d nearly all of the d i s l o c a t i o n s is c o n t a i n e d
in a network,
1 shows an area
the schematic d i a g r a m lists the var-
from c o n t r a s t experiments. in this area h a v e b =
has b =
Fig.
It can be seen that and only one, w h i c h
Vol. 8, No. 9
THE ORIGIN OF DISLOCATIONS IN ~-NiAI
The Burgers consistent
with
Loretto
the type a[100]
of the e l a s t i c
=
most
anisotropy
deformed
Fig.
of d i s l o c a t i o n s dislocations
2 shows with
have
present
in NiAI,
a dislocation
a decrease
in e l a s t i c
a number
of
energy as a
and b =
of a s u b - b o u n d a r y
which
short
segments
and again
the various
these
of b =
dislocation
of b =
dissociates
a dislocation
Burgers
dislocations
dislocations
vectors
were
at one end into stable"
have in
of two sets
two sets
formed.
of
Fig.
are fully consis-
observation
three
component
3
w i t h b =
formed by i n t e r a c t i o n
An i n t e r e s t i n g
"elastically
these
of b = < l l 0 > h a v e
containing
formed.
also p r e s e n t
consists
intersected,
sub-boundaries,
were
the s u b - b o u n d a r i e s
of b =
into an
formed b y
reaction
of s u b - b o u n d a r i e s
in and b e t w e e n
appropriate
than
are
fully
of the crystal.
with b =
that
are
It should be noted
types
the s u g g e s t i o n
rather
that
involves
an example
and one w i t h b =
~i00>
w i t h b =
different
an area b e t w e e n
tent w i t h
up the n e t w o r k
of the type b =
11% at 1300°K,
of the d i s l o c a t i o n s
making
dislocations
shown
- a[ll0]
some d i s l o c a t i o n s
networks.
shows
(ii) h a v e
+ a[0103
In crystals Again,
that
of two d i s l o c a t i o n s
Lloyd and
result
of the d i s l o c a t i o n s
the s u g g e s t i o n
the i n t e r a c t i o n that
vectors
1051
is that
components
of b =
of the
of b = and one
of b :
from this
tion m i c r o s t r u c t u r e tween
850°K and
<001>
(ii).
w i t h b =
=
The
reason
of NiAI
are
formed by
stabilized
fully u n d e r s t o o d
and
compressed
(5) that the dislocaat t e m p e r a t u r e s
it is r e a s o n a b l e
interaction
increase
of testing
is i n c r e a s e d
further w o r k
on this
to assume
reduction
in numbers
aspect
that dis
in elastic
of d i s l o c a t i o n s
and/or
be-
of the type b =
of two w i t h b =
by the a s s o c i a t e d
for the a p p a r e n t
as the t e m p e r a t u r e
et al.
up in the main b y d i s l o c a t i o n s
of our o b s e r v a t i o n s
p r o d u c t ~ =
crystals
1300°K is made
On the b a s i s
locations
of
study and that by Fraser
strain
the enerwith
rate reduced
is in progress.
Acknowledqments The
support
of this
tract N u m b e r A T ( I I - I ) I I 9 8 ,
r e s e a r c h by the U. S. A t o m i c and the Center
sity of Illinois
is g r a t e f u l l y
Pugh
discussions.
for h e l p f u l
Energy
for Electron
acknowledged.
We w o u l d
Microscopy
A. Ball and R. E. Sma!iman,
A c t a Met.
14,
1517
Con-
of the Univer-
like to thank N e v i l l e
References i.
Commission,
(1966).
1052
THE
ORIGIN
OF D I S L O C A T I O N S
S. R. Butler,
IN ~-NiAI
and J. E. Hanlon,
Vol.
2.
R. R. Wasilewski, 234, 1357 (1967).
3.
R. T.
Pascoe
4.
M. H.
Loretto
5.
H.
6.
P. R. Strutt, R. A. Dodd and G. M. Rowe, Second Int. of Metals and Alloys, p. 1057 ASM, vol. III, (1970).
7.
P. R. Strutt, and S t r u c t u r e
8.
J. Bevk,
9.
R. J. Wasilewski,
and C. W. A. Newey,
L. Fraser,
Phys.
and R. J. Wasilewski, M. H.
Loretto
Star.
Phil.
Sol.
Mag.
Trans.
Met.
A.I.M.E.
Phil.
(1971).
Mag.
2_88, 667
Conf.
(1973).
on The S t r e n g t h
G. M. Rowe, J. C. I n g r a m and ¥. E. Choo, E l e c t r o n M i c r o s c o p y of Materials, p. 722, U n i v e r s i t y of C a l i f o r n i a Press (1972).
R. A. Dodd
and P. R. Strutt,
R. H u t c h i n g s
Met.
and M. H.
Trans.
Loretto,
4,
159
Phil.
(1973). Mag.
2_~9, 521
(1974).
i0.
P. B. Hirsch, A. Howie, R. S. Nicholson, D. W. Pashley and M. J. Whelan, E l e c t r o n M i c r o s c o p y of Thin Crystals, Butterworths, London, (1965).
ii.
C. H.
Lloyd
9
2__99357 (1968).
2__3, 1311
and R. E. Smallman,
Soc.
8, No.
and M. H. Loretto,
Phys.
Stat.
Sol.
r,
3__99, 163
(1970).
lit ,,,
/ i00 ~
~ 010 olo
100 ,i,,,,, .......
FIG.
:
i
in . . . . . . . . . . . . . . . . . . . .
1
A typical m i c r o g r a p h of d i s l o c a t i o n s in samples deformed 5% along <001> at 1300°K. Note that most of the d i s l o c a t i o n s have b =
Vol. 8, No. 9
THE ORIGIN OF DISLOCATIONS IN ~-NiAI
1053
0 %
1/
'
~ O 100
P ::
FIG.
j
':
2
D i s l o c a t i o n s in a sample d e f o r m e d 11% along (001> at 1300°K. Note that w h e r e the two types of d i s l o c a t i o n of b =
i ii
S
I ,II,,iiii
- /
!oo
/
1
!t
0,,;'I
7~~:
tk ¢" \-
III II
FIG.
I
ii IIi
ii
3
A n e t w o r k of d i s l o c a t i o n s in a s p e c l m e n deformed 11% along (001> at 1300°K. The various Burgers vectors are consistent w i t h their b e i n g formed by i n t e r a c t i o n of a p p r o p r i a t e d i s l o c a t i o n s of b =
iiiiiii
i i
d
,]