DISLOCATION MOTION AT LOW TEMPERATURES IN HYDROGEN-FREE Nb

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DISLOCATION MOTION AT LOW TEMPERATURES IN HYDROGEN-FREE Nb

N. Kuramochi, S. Okuda

To cite this version:

N. Kuramochi, S. Okuda. DISLOCATION MOTION AT LOW TEMPERATURES IN HYDROGEN-FREE Nb. Journal de Physique Colloques, 1985, 46 (C10), pp.C10-285-C10-288.

�10.1051/jphyscol:19851063�. �jpa-00225447�

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JOURNAL DE PHYSIQUE

C o l l o q u e C 1 0 , s u p p l e m e n t au n 0 1 2 , Tome 46, d Q c e m b r e 1985 page C10-285

DISLOCATION MOTION AT LOW TEMPERATURES IN HYDROGEN-FREE Nb N. KURAMOCHI AND S. OKUDA

Institute of Materials Science, University of Tsukuba, Sakura-mura, Ibaraki 305, Japan

A b s t r a c t - I n t r i n s i c d i s l o c a t i o n motions i n Nb a t low t e m p e r a t u r e s a r e s t u d i e d u s i n g hydrogen-free specimens. I n t e r n a l f r i c t i o n measurements a f t e r d e f o r - mation i n l i q u i d n i t r o g e n &d a f t e r s l i g h t deformation i n d i c a t e t h a t t h e a- peak is composed of a t l e a s t two components, t h e a 1 and a 2 which a r e a t t r i b - u t e d t o k i n k d i f f u s i o n a l o n g screw d i s l o c a t i o n and k i n k p a i r f o r m a t i o n on non screw d i s l o c a t i o n r e s p e c t i v e l y .

I-INTRODUCTION

The i n t r i n s i c d i s l o c a t i o n motion i n Va b . c . c . m e t a l s i s of g r e a t i n t e r e s t because s e v e r a l d i s l o c a t i o n motions a r e e x p e c t e d t o t a k e p l a c e a t d i f f e r e n t t e m p e r a t u r e s due t o t h e l a r g e d i f f e r e n c e i n P e i e r l s p o t e n t i a l between screw and non-screw d i s l o c a - t i o n s / l , 2 / . On t h e o t h e r hand, t h e s e m e t a l s a r e a l s o known f o r t h e i r s t r o n g a f f i n i - t y w i t h hydrigen. So t h e i n t r i n s i c d i s l o c a t i o n motion i s h i n d e r e d by hydrogen, i . e . hydrogen atoms p i n down d i s l o c a t i o n s a t lower temperatures(<lOOK) and d i s l o c a t i o n motion i n t e r a c t i n g w i t h hydrogen t a k e s p l a c e a t above 100K. I n t e r n a l f r i c t i o n ( 1 F ) measurements(%600Hz) i n Nb w i t h a few at.ppm hydrogen shows t h a t t h e r e a r e a s m a l l r e l a x a t i o n peak due t o i n t r i n s i c d i s l o c a t i o n motion a t ".20K(a-peak) and a l a r g e r r e l a x a t i o n peak caused by i n t e r a c t i o n between d i s l o c a t i o n and hydrogen a t %170K(hydrogen c o l d work peak o r HCW p e a k ) / 3 / . I n o u r p r e v i o u s r e p o r t / 4 / , breakaway phenom- ena of d i s l o c a t i o n was u t i l i z e d t o c l a r i f y t h e n a t u r e of d i s l o c a t i o n motion below l O O K and t h e f o l l o w i n g s u g g e s t i o n was made f o r Nb: There a r e two k i n d s of d i s l o c a - t i o n motion between 6K and 100K. One i s t h e k i n k d i f f u s i o n a l o n g screw d i s l o c a t i o n s a t %20K and a n o t h e r a t h i g h e r t e m p e r a t u r e i s t h e k i n k p a i r f o r m a t i o n on non-screw d i s l o c a t i o n s . The r e l a x a t i o n peaks i n I F c o r r e s p o n d i n g t o t h e s e motions a r e named a s t h e a 1 and u2-peaks r e s p e c t i v e l y . These a r e c o n s i d e r e d a s component peaks of t h e a-peak. The a 1 and a2-peaks a r e c o n s i d e r e d t o correspond r e s p e c t i v e l y w i t h t h e a ' and a-peaks observed by o t h e r a u t h o r s / 2 / . These names a r e used h e r e because t h e s e two components seem t o be r e t a i n e d a l s o i n t h e HCW peak. A s t h e hydrogen-free specimen c o u l d n o t been o b t a i n e d u n t i l r e c e n t l y , t h e s e two p r o c e s s e s have n o t been v e r i f i e d c l e a r l y by o b s e r v a t i o n of r e l a x a t i o n peaks. Rodrigues and Kirchheim pro- posed an e f f e c t i v e method t o e l i m i n a t e t h e r e s i d u a l hydrogen i n a specimen/5/ and t h i s method was a p p l i e d t o t h e IF measurements/6-111. I n t h i s paper, t h e r e s u l t s of I F measurements on t h e Nb c o n t a i n i n g hydrogen a r e compared w i t h t h o s e on t h e hydro- g e n - f r e e Nb.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19851063

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C10-286 JOURNAL DE PHYSIQUE

The s t a r t i n g m a t e r i a l was Nb p o l y c r y s t a l l i n e w i r e of 0.5mm i n d i a m e t e r purchased from M a t e r i a l s Research Corporation. The w i r e was d e c a r b u r i z e d a t c2000K i n an oxygen atmosphere and followed by an a n n e a l i n g i n U H V ( % ~ X ~ O - ~ P ~ ) a t 2200-2500K f o r s e v e r a l h o u r s . A f t e r c o o l i n g down, Pd l a y e r was formed on a s u r f a c e by e v a p o l a t i o n w i t h i n t h e UHV f u r n a c e b e f o r e t a k i n g o u t i n t h e a i r . Specimens were made by c u t t i n g o f f t h i s w i r e i n t o about 17mm i n l e n g t h . RRR of t h e specimens was %2500 and hydrogen c o n c e n t r a t i o n i n t h i s s t a t e was e s t i m a t e d t o b e a few at.ppm from t h e r e s i s t - i v i t y measurements. T h i s r e s i d u a l hydrogen was removed by a n n e a l i n g t h e specimens a t 420K i n t h e a i r f o r 3-7days/5/. Hydrogen c o n c e n t r a t i o n a f t e r t h i s 420K a n n e a l i n g was n o t measured by RRR b u t t h e absence of hydrogen was confirmed by d i s a p p e a r a n c e of t h e HCW peak i n I F measurements. D i s l o c a t i o n motion was d e t e c t e d by measuring I F and r e s o n a n t p e r i o d ( P ) of t h e specimen, where f l e x u r a l vibration(%600Hz) was e x c i t e d e l e c t r o s t a t i c a l l y and t h e t y p i c a l maximum s t r a i n amplitude(emax) was 1-2x10-6.

Measurements were made d u r i n g warmup r u n between l i q u i d helium t e m p e r a t u r e and room temperature(RT).

111-RESULTS AND DISCUSSION

As a l r e a d y mentioned, t h e experiment of d i s l o c a t i o n breakaway i n Nb c o n t a i n i n g r e s i d u a l hydrogen s u g g e s t e d t h e e x i s t e n c e of d i s l o c a t i o n motions below l O O K a s f o l l o w s : k i n k d i f f u s i o n a l o n g non-screw d i s l o c a t i o n below 6K, k i n k d i f f u s i o n a l o n g screw d i s l o c a t i o n ( t h e al-peak) and k i n k p a i r f o r m a t i o n on non-screw d i s l o c a t i o n ( a 2 - peak).

I n a hydrogen c o n t a i n i n g specimen t h e a2-peak seems t o be b a r e l y observed a f t e r de- f o r m a t i o n a s shown i n Fig.1. When t h e specimen i s v i b r a t e d a t h i g h a m p l i t u d e , t h e hydrogen p i n n i n g can b e broken t o some e x t e n t ( d i s 1 o c a t i o n breakaway) and t h e l a r g e a2-peak can b e expected t o appear. But t h e complete shape of t h e peak cannot b e ob- s e r v e d because r e p i n n i n g by hydrogen t a k e s p l a c e a t t e m p e r a t u r e lower t h a n t h a t of t h e a 2 / 4 , 7 / . F i g u r e 2 shows an example of t h e r e s u l t o b t a i n e d i n a Pd c o a t e d s p e c i - men. The Pd c o a t e d specimen was deformed 7% by bending a t RT i n t h e a i r , s o hydrogen contamination t o o k p l a c e simultaneously(hereafter t h i s specimen w i l l b e c a l l e d as RT deformed specimen). C u r v e s ( 1 , l ' ) were o b t a i n e d immediately a f t e r deformation.

The s m a l l a-peak and t h e l a r g e HCW peak(%3.8~10-3) a r e s e e n i n c u r v e 1. Curves(2,2') and ( 3 , 3 ' ) were o b t a i n e d a f t e r hydrogen d e g a s s i n g t r e a t m e n t f o r 48h and 168h respec- t i v e l y . As can be s e e n , hydrogen d e g a s s i n g brought about an i n c r e a s e of t h e a-peak and d e c r e a s e of t h e HCW peak which was completely d i s a p p e a r e d a f t e r 148h d e g a s s i n g ( c u r v e 3 ) . The e f f e c t of 420K a n n e a l i n g on P which correspond t o t h e e l a s t i c modulus of t h e specimen a l s o can b e seen: P a f t e r 420K a n n e a l i n g ( c u r v e s 2 ' and 3 ' ) becomes l a r g e r a t t h e lowest t e m p e r a t u r e b u t becomes s m a l l e r a t h i g h e r temperatures(above 150K). T h i s i n d i -

c a t e s t h a t d i s l o c a - ₁₇₃₀

,-. : ¹⁷⁷⁰

-

^a

a 1810

T ' 0 0

a 7

-

5

0 60 120 180 240 300

T E M P E R A T U R E l K 1

~ i g . -internal friction(^-1) and- r e s o n a n t p e r i o d ( P ) of a Pd c o a t e d specimen(7% b e n t a t RT).

t i o n s a r e f r e e d from 25

hydrogen p i n n i n g b u t pinned down by some e x t e n t w i t h o t h e r 20-

i m p u r i t i e s ( o x y g e n o r

n i t r o g e n ) d u r i n g 420 ^{I S -} K a n n e a l i n g . F i g u r e

3 shows t h e a-peak g

o b t a i n e d a f t e r 148h

-

^lo

a n n e a l i n g i n an ex- panded s c a l e ( c u r v e 1 ) . T h i s peak ap- p e a r s a t h i g h e r tem- p e r a t u r e t h a n t h e a 1

peak observed i n F i g . o 20 P O 60 80 loo ( l . l ' ) : i m m e d i a t e l y a f t e r d e f o r - 1 b u t i s r e a s o n a b l y TEMPERRJURE I K I mation, ( 2 , 2 ' ) : a f t e r 48h anneal- c o n s i d e r e d a s t h e a 1 Fig.1 I n t e r n a l f r i c t i o n i n g a t 420K, ( 3 , 3 ' ) : a f t e r 168h

peak. S i n c e t h e observed i n Nb c o n t a i n i n g a n n e a l i n g a t 420K. ~ ~ ~ ~ = 1 . 1 x 1 0 - ~ a c t i v a t i o n volume of r e s i d u a l hydrogen. 1:as- f o r a l l measurements.

k i n k d i f f u s i o n pro- a n n e a l e d , 2:10.2% b e n t a t c e s s is s m a l l e r t h a n RT.

1 1 1 1

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S i n c e t h e a2-peak i s caused by movement of non- F i g . 4 I n t e r n a l friction(^-1) s c r e w d i s l o c a t i o n , t h e a2-peak cannot b e observed and r e s o n a n t p e r i o d ( P ) of a H- a f t e r 420K a n n e a l i n g . A c c o r d i n g l y , i t i s neces- f r e e specimen deformed 5.7% i n s a r y f o r t h e o b s e r v a t i o n of t h e a2-peak t o deform l i q u i d n i t r o g e n . ( l . l 1 ) : a s de- t h e specimen a f t e r hydrogen d e g a s s i n g w i t h o u t formed, ( 2 , 2 ' ) : a f t e r 170K an- p i c k i n g up of hydrogen. S i n c e hydrogen atoms a r e n e a l i n g , ( 3 , 3 ' ) : a f t e r 280K an- c o n s i d e r e d t o i n t r u d e i n t o t h e b u l k t h r o u g h a n e a l i n g . Measurements were broken Pd s u r f a c e l a y e r d u r i n g d e f o r m a t i o n i n t h e made w i t h ~ ~ ~ ~ = 4 X 1 0 - 7 + a i r , t h e r e a r e two p o s s i b l e methods t o p r e v e n t

hydrogen c o n t a m i n a t i o n d u r i n g d e f o r m a t i o n . One i s d e f o r m a t i o n i n l i q u i d h e l i u m o r l i q u i d n i t r o g e n and a n o t h e r i s s l i g h t d e f o r m a t i o n i n t h e a i r s o a s n o t t o b r e a k a Pd f i l m on a specimen s u r f a c e . F i g u r e 4 shows a r e s u l t a f t e r d e f o r m a t i o n i n l i q u i d n i - t r o g e n ( t h i s specimen w i l l b e c a l l e d a s LNT deformed specimen). The specimen was deformed 5.7% by bending i n l i q u i d n i t r o g e n f i l l e d i n a measuring chamber and a f t e r removal of l i q u i d n i t r o g e n w i t h o u t h e a t i n g up, i t was c o o l e d down t o l i q u i d helium t e m p e r a t u r e . Then c u r v e 1 was o b t a i n e d d u r i n g warmup from 6K t o 170K. Curves 2 and 3 were o b t a i n e d a f t e r a n n e a l i n g a t 170K and 280K r e s p e c t i v e l y . The growth of t h e a-peak a f t e r 170K a n n e a l i n g i s t h o u g h t t o b e a t t r i b u t a b l e t o a n n i h i l a t i o n of p o i n t d e f e c t s c r e a t e d d u r i n g d e f o r m a t i o n / l 2 / . 280K a n n e a l i n g brought about hydrogen con- t a m i n a t i o n and t h e HCW peak emerged i n c u r v e 3. Comparing t h e a-peak i n t h e LNT deformed specimen w i t h t h e a l - p e a k o b t a i n e d i n t h e RT deformed specimen, it i s a p p a r e n t t h a t t h e peak t e m p e r a t u r e of t h e f o r m e r i s h i g h e r t h a n t h e l a t t e r and t h e peak w i d t h of t h e former is b r o a d e r , These r e s u l t s s u g g e s t t h a t t h e a-peak i n t h e LNT deformed specimen h a s subcomponent a p a r t from t h e a1-peak, i . e . t h e a2-peak. The a2-peak can b e s e p a r a t e d from t h e a-peak a s f o l l o w s : t h e a-peak o f t h e LNT deformed specimen was p l o t t e d a s a f u n c t i o n o f r e c i p r o c a l t e m p e r a t u r e i n F i g . 5 ( c u r v e 1 ) . The a1-peak i n t h e RT deformed specimen i s a l s o p l o t t e d a f t e r s u b t r a c t i o n of background and peak h e i g h t a d j u s t m e n t s o a s t o c o i n c i d e i n t h e lower t e m p e r a t u r e s i d e . Then t h e d i f f e r - e n c e between two peaks i s shown a s c u r v e 3 which i s c o n s i d e r e d a s t h e a2-peak. The peak t e m p e r a t u r e o f t h e a 2 i s about 55K. Peak t e m p e r a t u r e i s r e a s o n a b l y c o n s i s t e n t w i t h t h e p r e v i o u s e s t i m a t i o n / 4 / . On t h e o t h e r hand, F i g . 6 shows a n example of t h e t h a t of k i n k p a i r f o r m a t i o n pro- ₁₇₄₀

! , ^! , F i g . 3 I n f l u e n c e o f Emax c e s s , t h e measurement of t h e

a c t i v a t i o n volume of t h i s peak woud b e of i n t e r e s t . C u r v e s ( 1 , 1 ' ) and ( 2 , 2 ' ) i n F i g . 3 were ob- t a i n e d w i t h ~ ~ ~ ~ = 1 . 1 ~ 1 0 - 6 and

-

5

1 . 7 ~ 1 0 - ~ r e s p e c e i v e l y . Curves ( 3 , ¹⁷⁶⁰ 3 ' ) were measured w i t h ~ ~ ~ ~ = l . 1 x

m"

10-6 a g a i n a f t e r t h e measurement of c u r v e s ( 2 , 2 ' ) t o c o n f i r m t h e

-

r e p r o d u c i b i l i t y . It i s s e e n

t h a t t h e peak t e m p e r a t u r e i s

-

⁰

h a r d l y a f f e c t e d by t h i s change & ^30-

i n Emax. ~ f p r e - e x p o n e n t i a l

f a c t o r of t h i s p r o c e s s i s a s - o

sumed a s 1 0 1 4 s - l / l l / , t h e peak o TEMPERATURE 20 40 60 80 I K ) 100 s h i f t of l e s s t h a n 0.5K r e s u l t s

i n t h e a c t i v a t i o n volume of l e s s

t h a n 6b3. T h i s i s a n a c c e p t a b l e v a l u e a s an a c t i - v a t i o n volume f o r k i n k d i f f u s i o n . T h e r e f o r e t h e 1980 peak i n F i g . 3 i s r e a s o n a b l e a s t h e a l - p e a k . The ^A a b s e n c e of t h e a2-peak i s e x p l a i n e d a s f o l l o w s : ; ²⁰²⁰

During 420K a n n e a l i n g of hydrogen d e g a s s i n g ,

-

²

i m p u r i t y atoms(oxygen o r n i t r o g e n ) becomes mo- a 2100 b i l e and a r e dominantly c o l l e c t e d by non-screw

d i s l o c a t i o n s due t o e l a s t i c i n t e r a c t i o n . Thus, l o

non-screw d i s l o c a t i o n s a r e l o c k e d p r e f e r e n t i a l l y by i m p u r i t y atoms d u r i n g t h e a n n e a l i n g . T h i s i s &

a l s o r e s p o n s i b l e f o r t h e h a r d e n i n g a t h i g h e r tem-

,

p e r a t u r e s a f t e r 420K a n n e a l i n g shown i n Fig.2. 0 50 170 180 240 300 TEMPERATURE I K I

. ,";-"

2

\

-

1

'

^-3

I I I I

on i n t e r n a l f r i c t i o n ( 9 - 1 ) and r e s o n a n t p e r i o d @ ) of a Pd c o a t e d Nb(7%

b e n t a t RT) measured a f t e r H d e g a s s i n g . Emax=

1 . 1 ~ 1 0 - 6 f o r c u r v e s ( 1 , l ' ) and ( 3 , 3 ' ) , 1 . 7 ~ 1 0 - 5 f o r c u r v e (2,2 ' ⁾

.

^Numbers

i n d i c a t e a n o r d e r of t h e measurements

.

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C10-288 J O U R N A L DE PHYSIQUE

r e s u l t s f o r t h e s l i g h t deformation. The s p e c i - men was f i r s t deformed 0.7% a t 420K, t h e n g i v e n t h e d e g a s s i n g t r e a t m e n t and f i n a l l y t h e s p e c i - men was g i v e n a d d i t i o n a l d e f o r m a t i o n of 0.6%

bending a t 420K. Curve 1 i n Fig.6 was o b t a i n e d a f t e r t h i s deformation. I n t h i s c a s e , t h e s m a l l HCW p e a k ( % 6 ~ 1 0 - 4 ) a p p e a r e d , showing a s m a l l hydrogen c o n t a m i n a t i o n d u r i n g t h e d e f o r - mation. However t h e a-peak appeared l a r g e r which i s shown i n c i r v e I. Then, t h e specimen was annealed a t 420K t o d e g a s s hydrogen and s u p p r e s s t h e a2-peak and c u r v e 2 was o b t a i n e d a f t e r t h e a n n e a l i n g . T h i s remaining peak i n c u r v e 2 i s c o n s i d e r e d t o b e t h e al-peak.

T h e r e f o r e t h e d i f f e r e n c e i n c u r v e s 1 and 2 i s thought a s t h e a2-peak which i s shown by c u r v e 3. The t e m p e r a t u r e of t h i s a2-peak i s almost t h e same as t h a t o b t a i n e d i n t h e LNT deformed specimen. Thus t h e e x i s t e n c e of t h e a2-peak was confirmed i n b o t h c a s e s . As f o r t h e a c t i v a t i o n yolume f o r t h i s a2-peak, s i n c e t h e a2-peak i s n o t observed w i t h o u t accompanying t h e al-peak, it i s d i f f i c u l t t o d e t e c t t h e peak s h i f t by v a r y i n g t h e E~~~ and a c l e a r r e s u l t w i t h r e s p e c t t o t h e peak s h i f t h a s n o t been o b t a i n e d y e t . The experiment i s now i n p r o g r e s s and w i l l b e g i v e n elsewhere.

The a u t h o r s wish t o e x p r e s s t h e i r g r a t i t u d e t o P r o f . H. Mizubayashi f o r d i s c u s s i o n .

Fig.5 I n t e r n a l f r i c t i o n v s r e c i p r o c a l t e m p e r a t u r e , f o r t h e LNT deformed specimen(1) , t h e RT deformed specimen (2) and t h e d i f f e r e n c e between c u r v e s 1 and 2 ( 3 ) . To o b t a i n c u r v e 3 , t h e a- peak h e i g h t i n c u r v e 2 was ad- j u s t e d t o c o i n c i d e w i t h t h a t of c u r v e 1 a t low t e m p e r a t u r e s i d e .

Fig.6 I n t e r n a l f r i c t i o n of a Pd c o a t e d specimen deformed 0.7% a t 42bK. 1: immediately a f t e r a d d i - t i o n a l d e f o r m a t i o n of 0.6%(1.3%

i n a l l ) a f t e r 420K a n n e a l i n g , 2 : a f t e r f u r t h e r a n n e a l i n g a t 420 K, 3 : t h e d i f f e r e n c e between

c u r v e s 1 and 2. ~ ~ ~ ~ ' l . 0 x 1 0 - ~ . REFERENCES

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/2/ G. F a n t o z z i and I . G . R i t c h i e , J. d e Phys. g (1981) 3.

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