THE INTRINSIC DISLOCATION RELAXATION SPECTRUM OF NIOBIUM, TANTALUM AND TUNGSTEN

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THE INTRINSIC DISLOCATION RELAXATION SPECTRUM OF NIOBIUM, TANTALUM AND

TUNGSTEN

H. Schultz, G. Funk, U. Ziebart, R. Bauer

To cite this version:

H. Schultz, G. Funk, U. Ziebart, R. Bauer. THE INTRINSIC DISLOCATION RELAXATION SPEC-

TRUM OF NIOBIUM, TANTALUM AND TUNGSTEN. Journal de Physique Colloques, 1985, 46

(C10), pp.C10-289-C10-292. �10.1051/jphyscol:19851064�. �jpa-00225448�

JOURNAL DE PHYSIQUE

Colloque C10, suppl6ment au n012, Tome 46, d6cembre 1985 page ~ 1 0 - 2 8 9

THE INTRINSIC DISLOCATION RELAXATION SPECTRUM OF NIOBIUM, TANTALUM AND TUNGSTEN

H. SCHULTZ, G. FUNK, U. ZIEBART AND R. BAUER

Institut fur Physik im Max-Planck-Institut fiir Metallforschung and Institut fur Theoretische und Angewandte, Physik der Universitat Stuttgart, 0-7000 Stuttgart 80, F.R.G.

resum&.- Des monocristaux de haute puretP de Nb e t Ta o n t 6 t 6

-.

prepares aux c o n d i t i o n s q u i p e r m e t t r a i e n t 1 '$1 im i n a t i o n du hy- drogene, u t i l is a n t Pd evapork aux surfaces des k h a n t i l l ons.

Des expgriences de f r o t t e m e n t i n t k r i e u r avec un pendule de t o r s i o n montrent l e s p i c s i n t r i n s i q u e s a e t y. Les spectres de r e l a x a t i o n sont compar6s avec des r g s u l t a t s nouveaux aux c r i s t a u x de W. Les parametres d ' a c t i v a t i o n o n t 6 t 6 dgduites.

Abstract.- H i g h - p u r i t y s i n g l e c r y s t a l s o f Nb and Ta could be prepared f r e e o f hydrogen by a Pd-coating technique. Low-fre- quency t o r s i o n pendulum measurements a r e reported on such s i n g l e c r y s t a l s showing the i n t r i n s i c a and y r e l a x a t i o n . The d i s l o c a t i o n - i n t e r n a l f r i c t i o n spectra o f Nb and Ta are compared w i t h new r e s u l t s on W s i n g l e c r y s t a l s . The a c t i v a - t i o n parameters o f t h e a and y processes are reported.

Considerable e f f o r t s have been spent i n t h e past t o c l a r i f y the d i s l o c a t i o n - i n t e r n a l f r i c t i o n spectrum o f group V - t r a n s i t i o n metals (V,Nb,Ta), f o r references see e.g. (1)-(3). The low-temperature r e l a x a t i o n peaks (a,al ) a r e mostly masked by hydrogen contaminations. The o t h e r pronounced d i s l o c a t i o n r e l a x a t i o n peak ( y ) , t o be observed a t o r above room temperature, i s f r e q u e n t l y d i s t u r b e d by heavy i n - t e r s t i t i a l i m p u r i t i e s (O,N,C). We present here f o r h i g h - p u r i t y Nb and Ta s i n g l e c r y s t a l s t h e d i s l o c a t i o n - i n t e r n a l f r i c t i o n spectrum as observed between 15 K and 450 K i n t h e frequency range o f 1 Hz. The r e s u l t s show the i n t r i n s i c a and y peaks f o r the 1 Hz-frequency range (4). We compare t h e r e l a x a t i o n spectrum o f Nb and o f Ta w i t h t h e r e l a x a t i o n spectrum o f W, as obtained by new observations on high-pu- r i t y s i n g l e c r y s t a l s (5). I n W the s o l u b i l i t y o f i n t e r s t i t i a l i m p u r i t i e s i s ex- tremel y low and d i s l o c a t i o n motion i s scarely i n f l u e n c e d by i n t e r s t i t i a l impuri- t i e s . Only carbon i m p u r i t i e s may create some e f f e c t s i n the range o f t h e y maxi- mum (61, ( 7 ) . The p u r i f i c a t i o n treatments o f Nb and Ta c r y s t a l s , e s p e c i a l l y t h e removing o f hydrogen by palladium coatings, were described i n (8).

The damping spectra o f Nb, Ta, W, f o l l o w i n g some standard treatments (1% ten- s i o n + 0.2% low-temperature t o r s i o n ) show common properties, see Figs. ( 1 ) - ( 3 ) : A pronounced a r e l a x a t i o n a t low temperatures w i t h more o r l e s s pronounced subpeaks, depending on t h e m a t e r i a l and t h e annealing treatments, and a pronounced

peak near o r above room temperature. No pronounced peaks appear i n our

single

c r y s t a l s . See our s i m i l a r r e s u l t s on

I%,

( 9 ) , (10). Only i n Nb a small "200 K ma- ximum" appeared p a r t l y i n our i n v e s t i g a t i o n s ( i n (11) c a l l e d "W-Stage"), which may

be

t o d i s l o c a t i o n - o i n t defect i n t e r a c t i o n s (deformation incuced p o i n t de- f e c t s o r d e f e c t clusters!.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19851064

~ 1 0 - 2 9 0 JOURNAL DE PHYSIQUE

1.20

100 ,200 300 400

T CKI

-

Fig.1

-

Damping spectrum of a high-puri- t y niobium s i n g l e crystal in the hydrogen - f r e e s t a t e following small p l a s t i c deformations (1% tension a t 293K + 0.2% t o r - sion a t 160K), frequency fs1.2H.z.

A t low temperatures the

a maxi-

mum (Tmax

=

39.510, near 200K a small "200K maximum", and a t 279K the

y

maximum.

Fig.2

-

As Fig.1, but f o r a high-purity tantalum sing1 e c r y s t a l . The

a

relaxation with subpeaks, Tmax(q)

⁼

31.5K3 Tmax(az)

⁼

21.9K.

A t 358K the

y

maximdm.

Frequency change t o f

=

12 Hz s h i f t s the

y

maximum t o 402K and creates an asymmetrical broader

y

maximum. The determination of re1 iabl e activation parameters requires special considerations, see /4/.

Fig.3

::

I f ^{G n g} spectrum of a high-puri-

.; 'kl

! ! F

t y tungsten s i n g l e crystal f o l l o - wing small p l a s t i c deformations

.

^(1%

tension +0.2% torsion a t 475K).

A t low temperatures the

a

rela- xation with pronounced substruc-

1.65

t u r e , a t 620K ( f

=

1.3 Hz) the

y

maximum.

Run ( 2 ) , following r u n ( 1 ) , shows the recovery of the

y

maximum,

o-l

600 1.45

accompanied by a change of the

0 200 400

substructure of the

a relaxation.

T CKI-

The s u b s t r u c t u r e o f t h e a maximum i s most pronounced i n W, l e s s pronoynced i n Ta, and n m n Nb. However, t h e a peak i n Nb as p l o t t e d a g a i n s t T- i s ve- r y broad and cannot be r e l a t e d t o one s i n g l e r e l a x a t i o n process. See a l s o r e c e n t r e s u l t s o f S. Okuda e t a l . (12) on t h i s t o p i c . Annealing i n t h e temperature range

o f t h e y peak leads t o t h e disappearance o f t h e y and i n t h e case o f W (as w e l l as i n Mo (8), ( 9 ) ) t o a c h a r a c t e r i s t i c change o f t h e s u b s t r u c t u r e o f t h e a r e l a x a t i o n . See F i g . 3, curve (1) and curve ( 2 ) : t h e subpeak a t 100 K grows, t h e o t h e r subpeaks a t 50 K and 180 K s h r i n k . T h i s i n d i c a t e s t h a t t h e l o w e r i n g o f t h e y maximum by an- n e a l i n g i s n o t simply a p i n n i n g e f f e c t , b u t i s r e l a t e d t o a rearrangement o f d i s - l o c a t i o n s , (13), (9). Such a change o f t h e s u b s t r u c t u r e o f t h e a process c o u l d n o t be s t u d i e d f o r Nb and Ta, because annealing treatments above room temperature i n Nb and Ta introduced again t r a c e s o f hydrogen, l e a d i n g t o a p i n n i n g o f d i s l o c a t i o n s a t l o w temperatures.

The a c t i v a t i o n parameters o f the a, a ' and y processes a r e given below, f o r Nb no s e p a r a t i o n i n subpeaks o f t h e ci process a r e c a r r i e d o u t and t h e value H(a) i s r e p r e s e n t a t i v e f o r t h e whole a range. I t should be f u r t h e r noted t h a t f o r H(a) i n Nb no r e l i a b l e background separation was p o s s i b l e , due t o t h e l i m i t a t i o n o f our measurements t o T

5

15 K.

t a n t a l um:

H ( a 1 ' ) = 0.034

+

0.005 eV, -c0(al1) = ( 4

+

^{3) x}

lo-'

s H(a) ⁼ 0.057

+

0.004 eV, r,(a) = ( 8

+

^{4) x 10-lls}

H(y) = 0.85

...

^0.92 eV, ~ , ( y ) = 10-l3

....

^10-14s

niobium:

H(ci) = 0.10 ? 0.005 eV, =,(a) = ( 5

+

^{3 ) x 10-14s}

H(y) = 0.67

+

^0.02 eV, -c,(y) = (1.5

+

^{0.5) x 10-13s}

The a c t i v a t i o n parameter H(y) f o r Ta was d i f f i c u l t t o o b t a i n , due t o changes o f t h e peak shape a t t h e h i g h e r frequency o f measurements. A l l parameters a r e ob- t a i n e d by frequency changes between

-

1 Hz and

-

16 Hz. The a c t i v a t i o n parameter values f o r tungsten a r e n o t y e t f i n a l l y derived.

The r e s u l t s presented here a r e compatible w i t h i n t e r p r e t a t i o n s suggested ear- l i e r (1): The y process can be r e l a t e d t o k i n k - p a i r f o r m a t i o n i n screw d i s l y a t i o n s , t h e a process t o k i n k - p a i r f o r m a t i o n i n non-screw d i s l o c a t i o n s . F o r a l l , a2

. . . .

we suggested e a r l i e r t h e motion o f geometrical k i n k s i n screw d i s l o c a t i o n s , based on values o f t h e a c t i v a t i o n volumes o f a ' and a i n Mo (9). However, t h e p a r t l y ve- r y complex behaviour o f the a, a ' r e l a x a t i o n l e t s us agree w i t h (14) i n t h e sense t h a t the p o s s i b i l i t y o f d i s l o c a t i o n motion on d i f f e r e n t g l i d e planes should be con- sidered, too.

The obtained values o f t h e a c t i v a t i o n enthalpy H(a) i n Nb and Ta can be com- pared w i t h t h e known a c t i v a t i o n enthal py values o f H-Snoek-Koster re1 axations.

These values can be f i t t e d w e l l t o Seeger's theory o f the Snoek-Koster process

( I S ) , (16), f o r t h e case o f a d i l u t e atmosphere u s i n g

~ j

⁼ 0.16 eV, t h e bind-

~ ~ ~ - ~

i n g enthalpy H - d i s l o c a t i o n , as determined by Maul (17) o r niobium. For d e t a i l s and references see (4).

References:

( 1 ) G. Fantozzi and I.G. R i t c h i e , J. de Physique 42, C 5

-

3 (1981) ( 2 ) G. Funk, M. Maul and H. Schultz,

J.

de physique

3,

C 9

-

711 (1983)

( 3 ) N. Kuramochi, H. Mizubayashi and S. Okuda, phys. s t a t . sol. ( a )

77,

633 (1983) (4) G. Funk. D i s s e r t a t i o n U n i v e r s i t a t S t u t t q a r t (1985)

(5) U. ~ i e b a r t , to be published

-

( 6 ) R.-H. S c h n i t z e l , Trans. Met. Soc. AIME, 233, 186 (1965)

( 7 )

R.-J.

Gray and Z.C. Szkopiak,

J.

de PhysfqTie 32, C 2

-

163 (1971) ( 8 ) G. Funk and H. Schultz, Z. Metallkde. 76, 31171985)

( 9 ) R. Grau and H. Schultz, J. de Physique72, C-5

-

49 (1981) see a l s o R. Grau, D i s s e r t a t i o n U n i v e r s i F i t S t u t t g a r t (1981) (10)

R.

Grau and H. Schultz, J. de Physique

3,

C 9

-

705 (1983)

C10-292 JOURNAL DE PHYSIQUE

(11) F. De Lima and W. Benoit, phys. s t a t . s o l . ( a )

67,

565 (1981) see also: J. de Physique 42, C 5

-

85 (1981)

(12) S. Okuda, N. Kuramochi, TTMotoyama, T. A r a i , and N. Matsumoto, Yamada Conf.

on D i s l o c a t i o n s i n S o l i d s (1984), t o be published

(13) P. A s t i g , J.P. Peyrade and

P.

Groh, S c r i p t a Met.

15,

477 (1981)

(14) J. San Juan, G. Fantozzi, C. Esnouf, F. Vanoni, and A. Bernalte, J. de Phy- sique 44, C 9

-

685, (1983)

see a l s o : J. San Juan,

ThPse

Lyon (1984) (15) A. Seeger, phys. s t a t . s o l . ( a ) 55, 457 (1979)

(16) T. Ogurtani and A. Seeger, J. Apfl. Phys.

57,

193 (1985) ( 1 7) M. Maul, D i s s e r t a t i o n U n i v e r s i t a t S t u t t g a r t (1981 )