DISLOCATION RELAXATION PEAKS IN TANTALUM, INTRINSIC AND IMPURITY DEPENDENT EFFECTS

HAL Id: jpa-00220978

https://hal.archives-ouvertes.fr/jpa-00220978

Submitted on 1 Jan 1981

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

DISLOCATION RELAXATION PEAKS IN TANTALUM, INTRINSIC AND IMPURITY

DEPENDENT EFFECTS

U. Rodrian, H. Schultz

To cite this version:

U. Rodrian, H. Schultz. DISLOCATION RELAXATION PEAKS IN TANTALUM, INTRINSIC AND

IMPURITY DEPENDENT EFFECTS. Journal de Physique Colloques, 1981, 42 (C5), pp.C5-79-C5-

84. �10.1051/jphyscol:1981511�. �jpa-00220978�

CoZZoque C5, suppZ6ment au nO1O, Tome 42, octobre 1981 page CS-79

DISLOCATION RELAXATION PEAKS IN TANTALUM, INTRINSIC AND IMPURITY DEPENDENT EFFECTS

U. Rodrian and H. Schultz

Max-PZanck-Institut fiir MetaZZforschung, Institut fiir Physik, Heisenbergstr. 1, 0-7000 Stuttgart 80 and Institut fiir Theoretische und Angewandte Physik der Universitat Stuttgart, F. R. G.

A b s t r a c t . - I n v e s t i g a t i o n s o f t h e d i s l o c a t i o n r e l a x a t i o n p e a k s i n h i g h p u r i t y and oxygen doped t a n t a l u m s i n g l e c r y s t a l s w e r e car- r i e d o u t i n t h e t e m p e r a t u r e r a n g e between 20 K and 700 K . The o b s e r v e d e f f e c t s c a n b e d i v i d e d i n t o 3 g r o u p s : t h e hydrogen Snoek-Koster r e l a x a t i o n ( a H ) between 50 K

-

250 K , t h e y - r e l a x a - t i o n between 350 K

-

500 K , and a n oxygen Snoek-Kdster peak

(S.K.P.) above 500 K f o r a m e a s u r i n g f r e q u e n c y of a b o u t 1 H z . Only t h e e f f e c t s above 300 K v 7 i l l b e d i s c u s s e d h e r e . The y-re- l a x a t i o n c o n s i s t s of 2 s u b p e a k s y l and y2 which a r e r e l a t e d t o t h e i n t r i n s i c d i s l o c a t i o n m o t i o n a n d a n i n t e r a c t i o n o f d i s l o c a - t i o n s w i t h i n t e r s t i t i a l oxygen r e s p e c t i v e l y . The S.K.P. i s d i s - c u s s e d w i t h r e g a r d t o a new s u g g e s t i o n of A . S e e g e r .

1 . I n t r o d u c t i o n . - A f t e r p l a s t i c d e f o r c a t i o n o f b . c . c . r e f r a c t o r y m e t a l s s e v e r a l i n t e r n a l f r i c t i o n p e a k s a r e o b s e r v e d which a r e c a l l e d a , 8 , a n d y-peaks i n t h e n o m e n c l a t u r e of Chambers / 1 , 2 , 3 / . I n t h e d i s c u s s i o n o f t h e s e r e l a x a t i o n e f f e c t s i t h a s a l w a y s b e e n a problem t o i d e n t i f y t h e i n t r i n s i c d i s l o c a t i o n e f f e c t s . I n t r i n s i c p o i n t d e f e c t s a n d i m p u r i t i e s c a n i n t e r a c t w i t h t h e d i s l o c a t i o n s . I n p a r t i c u l a r m o b i l e i m p u r i t i e s c a n i n t e r f e r e w i t h t h e d i s l o c a t i o n n o t i o n . I n t h e c a s e o f t h e a - r e l a x a t i o n t h i s s i t u a t i o n i s m a n i f e s t e d by t h e l o n g s t a n d i n g u n c e r t a i n t y c o n c e r n i n g t h e r o l e of hydrogen i n t h e low t e n p e r a t u r e r e l a x a t i o n p r o c e s s e s ( s e e / 4 / f o r f u r t h e r r e f e r e n c e s ) . Looking f o r t h e k i n k p a i r f o r m a t i o n i n s c r e w d i s l o c a t i o n s , i . e . t h e y - r e l a x a t i o n , oxygen c o u l d p l a y a s i m i l a r r o l e s i n c e f o r t h e c a s e of t a n t a l u m e v e n t h e h i g h e s t p u r i t y s a m p l e s con- t a i n s m a l l amounts o f r e s i d u a l oxygen. F o r t h i s r e a s o n t h e r e e x i s t s o n l y l i t t l e i n f o r m a t i o n a b o u t t h e y - r e l a x a t i o n

i2

t a n t a l u m . We r e p o r t h e r e on some r e s u l t s f o r t h e r e l a x a t i o n e f f e c t s o b s e r v e d above 300 K .

2. E x p e r i m e n t a l p r o c e d u r e . - The e x p e r i m e n t s w e r e c a r r i e d o u t i n a n i n - v e r t e d t o r s i o n pendulum i n t h e t e m p e r a t u r e r a n g e from 20 K t o 700 K a t a v i b r a t i o n a m p l i t u d e o f ~ = 3 x 1 0 - ~ . The pendulum p r o v i d e d t h e p o s s i b i l i - t y f o r " i n s i t u " d e f o r m a t i o n o f t h e s a m p l e s a t a n y t e m p e r a t u r e .

The t a n t a l u m s i n g l e c r y s t a l s were p u r i f i e d by a n n e a l i n g i n u l t r a h i g h vacuum a t a p r e s s u r e of p<1x10-7 Pa. The i m p u r i t y c o n c e n t r a t i o n

(O+N+C) was d e t e r m i n e d by measurement o f t h e r e s i d u a l r e s i s t a n c e r a t i o Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1981511

C5-80 JOURNAL DE PHYSIQUE

RRR. A f t e r t h e above mentioned t r e a t m e n t t h e RRR was 25000. Some h i g h p u r i t y samples were doped w i t h 25 atppm oxygen a s d e t e r m i n e d by t h e RRR and t h e h e i g h t of t h e oxygen-Snoek peak. The hydrogen c o n t e n t of t h e samples was d e t e r m i n e d /5/ t o be between 4 5 and 60 atppm.

3. R e s u l t s f o r h i g h p u r i t y c r y s t a l s . - F i g u r e 1 shows a t y p i c a l spectrum a s o b t a i n e d a f t e r low t e m p e r a t u r e (T<375K) d e f o r m a t i o n . Below room tem- p e r a t u r e

-

from 50 K t o 250 K

-

we s e e a group o f e f f e c t s which were f o r m e r l y c a l l e d t h e a - r e l a x a t i o n . By comparison w i t h t h e r e s u l t s i n niobium / 4 / , we c o n s i d e r t h i s a s a hydrogen-S.K.P. and c a l l i t aH-relaxa- t i o n i n t h i s p a p e r . Using a s i m i l a r method a s Klam / 6 / , which was based on t h e assumption of s y m m e t r i c a l subpeaks on t h e 1 / T - s c a l e we can sepa- r a t e 4 subpeaks. These a r e c a l l e d a: t h r o u g h a 4 H b e g i n n i n g a t t h e h i g h t e m p e r a t u r e s i d e o f t h e a - r e l a x a t i o n . Out of t h e s e a: H and a: a r e en-

H H

hanced by h i g h t e m p e r a t u r e d e f o r m a t i o n , a 3 and a * a r e enhanced by low t e m p e r a t u r e d e f o r m a t i o n . Above 300 K one n o t i c e s f i r s t of a l l 2 s t a g e s of modulus d e f e c t r e c o v e r y , which c o i n c i d e w i t h t h e o n s e t of oxygen and n i t r o g e n m i g r a t i o n r e s p e c t i v e l y . A second measurement r u n v e r i f i e s t h a t d i s l o c a t i o n s have been pinned t o some e x t e n t by i n t e r s t i t i a l i m p u r i t i e s . T h i s , of c o u r s e , h i n d e r s t h e o b s e r v a t i o n of t h e y - r e l a x a t i o n which f a l l s i n t o t e m p e r a t u r e r a n g e of oxygen m i g r a t i o n .

To s e e t h e a g i n g e f f e c t s more c l e a r l y we have conducted a s e r i e s of measurements shown i n f i g u r e 2 . I n t h i s s e r i e s t h e h i g h e s t tempera- t u r e r e a c h e d d u r i n g e a c h r u n was i n c r e a s e d by 25 K , s t a r t i n g a t 400 K . The s p e c t r u m above room t e m p e r a t u r e c o n t a i n s 3 r e l a x a t i o n p r o c e s s e s : t h e y - r e l a x a t i o n , which c o n s i s t s of 2 subpeaks y l and y 2 , and a n o t h e r p r o c e s s above 500 K , an oxygen S.K.P., a s e x p l a i n e d l a t e r . A l l maxima above 300 K have d i s a p p e a r e d a f t e r a n n e a l i n g a t 625 K e x c e p t y

2 ' The o v e r a l l c o n c e n t r a t i o n o f O+N+C i n o u r h i g h p u r i t y specimens was l e s s t h e n 5 atppm. We c o u l d n o t s p e c i f y , however, t h e oxygen con-

c e n t r a t i o n i t s e l f . To g e t a c l e a r e r p i c t u r e of t h e r o l e o f oxygen, we

r.7 r

-

0

b

8

-

7 - -

6

-

5 -

4 - -

3 -

2

-

-

1

-

0 ¹

270

f Z F i g . 1 : High p u r i t y Ta

s i n g l e c r y s t a l [ 11 1

I ,

260 f r e q u e n c y 16 Hz, deforma- t i o n :

3.1% t e n s i o n a t 375 K

+

0 . 5 % t e n s i o n a t 200 K 250

+

0 . 2 % t o r s i o n a t 295 K

240

0 100 200 300 400 500 600 T(K)

t r o l l e d amount of oxygen.

AG - G

(%)

- 5

-10

0 100 200 300 LOO 500 600 T ( K )

F i g . 2: Aging b e h a v i o u r of damping and modulus a f t e r low t e m p e r a t u r e d e f o r m a t i o n , d e f o r m a t i o n h i s t o r y s i m i l a r a s i n f i g u r e 1, h i g h p u r i t y Ta s i n g l e c r y s t a l [ 11 1

1,

f r e q u e n c y 1 Hz, c o n s e c u t i v e r u n s a r e shown

4 . R e s u l t s f o r oxygen doped c r y s t a l s . - F i g u r e 3 shows a spectrum of an oxygen doped sample i n t h e same s t a t e o f d e f o r m a t i o n a s f i g u r e 1 . The a H - r e l a x a t i o n i s s m a l l e r and s h i f t e d t o lower t e m p e r a t u r e s a s e x p e c t e d from t h e r e d u c t i o n of t h e f r e e d i s l o c a t i o n l e n g t h due t o t h e h i g h e r oxygen c o n c e n t r a t i o n . The more d r a s t i c changes, however, have o c c u r e d

F i g . 3 : T a s i n g l e c r y s t a l [ I l l ] , 25 atppm oxygen, f r e q u e n c y 16 Hz, deforma- t i o n :

3.6% t e n s i o n a t 372 K

+

0.5% t e n s i o n a t 198 K

+

0 . 2 % t o r s i o n a t 297 K

C5-82 JOURNAL DE PHYSIQUE

above room temperature. Starting at 300 K the modulus defect recovers which is manifested also by 2 "pseudopeaks" near 300 K and 400 K. At

475 K, about the same temnerature as in the high purity sample, there is a large y2-peak. In addition there is a very large peak near 650 K.

The aging behaviour of the spectrum in a doped sample is shown in figure 4. The annealing out of the as-relaxation shows the arrival of oxygen atoms at the dislocations. A totally different behaviour has the

Fiq. 4: Aging behaviour

-

of damping and modulus after low temperature de- formation, Ta single cry- stal [Ill], 25 atppm oxy- gen, frequency 1 Hz, all consecutive runs are s h w n

10

y2-peak, which has not dissappeared after anneals up to 650 K. The S.K.P. on the high temperature side of the y2-peak shows aging effects again. There exists no yl-peak in the doped specimen.

8 : i i o

- I:?., . .

. .

1 2 3 4 5 6 7 - . n :

1 1 1 1

1

1 1

.. _... j.:: '::'.:

^. _{. .}

.

-.

...

¹¹¹

...

.

5 ^-

(I 12

1

100 200 300 400 500 600 T(K)

Table 1 : Activation parameters

I ^I

I

I

I

^{Y1 , Y2}

'

high purity ^, H (eV) 1.243 1.124 tantalum 1

I

t0.05 f0.04

I

f0(s-l)

I

1 x 1 0 ~ ~ 2 x 1 0 ~ ~ i oxygen doped ^I _{H (ev)} ^I

' --

I

^1.170

1 tantalum k0.04

f0(s-' )

I --

6x10'~

S.K.P.

2.204 k0.35

1 x 1 0 ~ ~ 2.242 f0.17

5x10'~

L- 1 I

and the S.K.P.. In the high purity samples the values were obtained after a separation of y l and y2 by the same method as in the case of the aH-relaxation.

5. Discussion.- The intrinsic dislocation relaxation is usually dis- cussed in terms of 2 mechanisms: thermally activated kink diffusion and kink pair formation /2/. Because of the particular properties of screw dislocations in the b.c.c. structure / 7 , / the kink pair formation in screw dislocations is expected at temperatures T>room temperature for low frequency measurements; all other intrinsic dislocation effects take place below 300 K. Above 300 K one should therefor encounter bas- icly 1 intrinsic dislocation effect and dislocation

-

impurity inter- actions.

The height of the y-relaxation increases after low temperature de- formation. Because the relative density of screw dislocations increases after low temperature deformation / 8 / , screw dislocation segments seem to be involved in both subpeaks of the y-relaxation. As to the depend- ence on deformation temperature there is also a correlation between the y-relaxation and the low temperature components of the as-relaxation

-

H H

a3 and a4 - which also seem to involve screw dislocation segments.

The 2 subpeaks y l and y2 react much differently to the presence of oxygen atoms. When discussing this point one has to keep in mind that even in our high purity samples we might have an oxygen concentration up to 1 atppm. The arrival of oxygen atoms at the dislocations suppresses y1 (fig. 2) and higher oxygen concentrations can prevent the appearance of y1 from the start (fig. 4). In contrast to that is the increase of y2 with increasing oxygen concentration (cp. fig. 2 and fig. 4) and its stability with oxygen present at the dislocation line (fig. 4): the peakheight is stable or increases slightly as a function of annealing temperature in the doped as well as in the high purity samples. The activation parameters of y2 are very similar to those of the oxygen- Snoek peak ( H = 1.1 eV, fo= 2x10 s-I / 9 / )

.

The y2-peak of figure 4 is 20 times higher than the oxygen-Snoek peak in the undeformed sample, i.e. plastic deformation enhances y2. It is impossible that this in- crease is due to the pick up of oxygen, because an increase in oxygen concentration by an order of magnitude should have shown up in the high purity samples very clearly.

The above observations lead us to the following interpretation:

y 1 is caused by kink pair formation in screw dislocations. y2 is caused by the motion of screw dislocation serpents interactinq with oxygen atoms. We therefor suggest the motion of oxygen decorated kinks in screw

C5-84 JOURNAL DE PHYSIQUE

d i s l o c a t i o n s a s t h e u n d e r l y i n g mechanism.

I t i s a l s o i n t e r e s t i n g t o s e e t h a t i n t h e doped sample t h e p i n n i n g s t a g e d u e t o oxygen atoms shows 2 s u b s t a q e s : S n o e k - o r d e r i n g by l o n g r a n g e i n t e r a c t i o n and d i f f u s i o n o f oxygen t o t h e d i s l o c a t i o n ( C o t t r e l l - p i n n i n g ) / l o / . T h i s h a s a l s o b e e n o b s e r v e d by o t h e r a u t h o r s / 1 1 / and c a n b e u s e d a s a method t o compare t h e p u r i t y of d e q a s s e d s a m p l e s . The a b s e n c e o f t h e f i r s t s u b s t a g e i n o u r h i g h p u r i t y s a m p l e s and t h e f a c t t h a t p i n n i n g by oxygen atoms comes t o a n e n d b e f o r e t h e c o m p l e t e sup- p r e s s i o n o f t h e a H - r e l a x a t i o n d e m o n s t r a t e s t h e h i g h p u r i t y o f o u r samples.

F o r t h e maximum on t h e h i g h t e m p e r a t u r e s i d e o f t h e y - r e l a x a t i o n t h e p r e d o m i n a n t f e a t u r e i s i t s d r a s t i c s h i f t t o h i g h e r t e m p e r a t u r e s w i t h i n c r e a s i n g oxygen c o n c e n t r a t i o n ; a b e h a v i o u r a s e x p e c t e d f o r a S n o e k - K o s t e r mechanism. T h i s s h i f t i n peak t e m p e r a t u r e s h o u l d come from t h e dependence of t h e p r e e x p o n e n t i a l f a c t o r on t h e i m p u r i t y c o n c e n t r a - t i o n a t t h e d i s l o c a t i o n l i n e / 1 2 , 1 3 / . A c c o r d i n g t o t h e t h e o r y of A . S e e g e r / 1 3 / t h e a c t i v a t i o n e n e r q y s h o u l d b e i n d e p e n d e n t o f t h e i m p u r i t y c o n c e n t r a t i o n and g i v e n by t h e f o l l o w i n a e x p r e s s i o n

H ~ . ~ . ~ .

'

^{2Hk + H~}

^-

Here 2Hk d e n o t e s t h e k i n k p a i r f o r m a t i o n e n e r g y o f t h e i n v o l v e d d i s l o -

~ -

c a t i o n and HM t h e m i g r a t i o n e n e r g y o f t h e i n v o l v e d i n t e r s t i t i a l . Com- p a r i n g t h e a c t i v a t i o n e n e r g i e s o f y l , t h e oxygen-Snoek p e a k , a n d t h e p e a k on t h e h i g h t e m p e r a t u r e s i d e of t h e y - r e l a x a t i o n t h i s p r e d i c t i o n i s w e l l f u l f i l l e d . Work on s a m p l e s w i t h d o p i n q s of d i f f e r e n t t y p e s of i n t e r s t i t i a l s o l u t e s ( O , N , C ) would b e r e q u i r e d t o c o n s o l i d a t e t h e v a l i - d i t y of t h i s p r e d i c t i o n .

Acknowledgement.- The a u t h o r s t h a n k P r o f . D r . A. S e e g e r f o r s u p p o r t a n d d i s c u s s i o n s .

6 . L i t e r a t u r e . -

/ I / R . H . Chambers i n : P h y s i c a l A c c o u s t i c s , V o l . 3A, Ed. W . P. Mason, Academic P r e s s , New York, (1 9661, p. 1 2 3

/ 2 / A . S e e g e r and C . W i i t h r i c h , I1 Nuovo Cim.

22

B , 38 ( 1 9 7 6 )

/ 3 / G . F a n t o z z i , W . B e n o i t , C . E s n o u f , and J . P e r e z , Ann. Phys. F r . 4 , 7 ( 1 9 7 9 )

/ 4 / M. Maul and H . S c h u l t z , t h i s c o n f e r e n c e

/ 5 / Y. Maul, T h e s i s , U n i v e r s i t a t S t u t t q a r t , ( 1 9 8 1 )

/ 6 / R . Klam, H . S c h u l t z , and H.-E. S c h a e f e r , A c t a Met.

27,

2 0 5 ( 1 9 7 9 ) / 7 / J. W. C h r i s t i a n , P r o c . 2nd I n t . Conf. o n S t r e n g t h o f Y e t a l s a n d

A l l o y s , A s i l o m a r , ASY ( 1 9 7 0 ) , p. 31

/ S / B . Z e s t 5 k and A . S e e g e r , Z . M e t a l l k u n d e

69,

( 1 9 7 8 1 , p. 1 9 5 , p . 355 and p . 491

/ 9 / R . W . Powers and Y . V. D o y l e , J . A p p l . P h y s . 30, 514 ( 1 9 5 9 ) / l o / G . Schoeck and A . S e e g e r , A c t a Met.

2,

469 (1-9)

/ 1 1 / G . F e r r o n , M . Q u i n t a r d , and J . d e F o u q u e t , P r o c . 6 t h ICIFUAS, Tokyo, U n i v e r s i t y o f Tokyo P r e s s , Tokyo, (19771, p . 671 / 1 2 / G . S c h o e c k , A c t a v e t .

11,

617 ( 1 9 6 3 )

/13/ A. S e e g e r , p h y s . s t a t . s o l . ( a )

55,

457 ( 1 9 7 9 )