THE INFLUENCE OF PLASTIC DEFORMATION ON INTERNAL FRICTION IN TANTALUM-HYDROGEN ALLOYS

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THE INFLUENCE OF PLASTIC DEFORMATION ON INTERNAL FRICTION IN TANTALUM-HYDROGEN

ALLOYS

Li Guangyi, Pan Zhengliang, Wang Xiaowei, Xiao Jinguan

To cite this version:

Li Guangyi, Pan Zhengliang, Wang Xiaowei, Xiao Jinguan. THE INFLUENCE OF PLASTIC

DEFORMATION ON INTERNAL FRICTION IN TANTALUM-HYDROGEN ALLOYS. Journal

de Physique Colloques, 1985, 46 (C10), pp.C10-103-C10-106. �10.1051/jphyscol:19851023�. �jpa-

00225402�

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JOURNAL DE PHYSIQUE

Colloque C10, supplitment a u n012, Tome 46, ditcembre 1985 page C10-103

THE INFLUENCE OF PLASTIC DEFORMATION ON INTERNAL FRICTION IN TANTALUM-HYDROGEN ALLOYS

LI GUANGYI, PAN ZHENGLIANG, WANG XIAOWEI AND XIAO JINGUAN I n s t i t u t e of Metal Research, Academia S i n i c a , Shenyang, china

A b s t r a c t

-

Low f r e q u e n c y i n t e r n a l f r i c t i o n h a s been measured f o r p l a s t i c a l l y deformed t a n t a l u m charged w i t h hydrogen o v e r t h e t e m p e r a t u r e r a n g e from 90 t o 475K. A f t e r changing t h e a-peak (H-SK-Peak) i s d e p r e s s e d , b u t a pre- c i p i t a t i o n peak of h y d r i d e s a p p e a r s a t h i g h e r t e m p e r a t u r e . An a d d i t i o n a l t o r s i o n p l a s t i c d e f o r m a t i o n ( t w i s t ) shows a remarkable e f f e c t on t h e p r e c i - p i t a t i o n peak. Subsequent a g i n g t r e a t m e n t a t about 475K may e l i m i n a t e t h e e f f e c t c o m p l e t e l y . P o s s i b l e c a u s e s of t h e phenomena a r e d i s c u s s e d i n t h e l i g h t of t h e i n t e r a c t i o n between d i s l o c a t i o n s and s o l u t e s .

INTRODUCTION

The behaviour of hydrogen i n t a n t a l u m h a s been s t u d i e d by s e v e r a l i n v e s t i g a t o r s w i t h i n t e r n a l f r i c t i o n t e c h n i q u e . I n g e n e r a l t h e r e a r e two k i n d s of i n t e r n a l f r i c - t i o n peaks in Ta-H a l l o y s . One of them i s a s s o c i a t e d w i t h t h e i n t e r a c t i o n between d i s l o c a t i o n s and hydrogen atoms (atmosphere) (H-SK-Peak). The o t h e r i s d u e t o t h e p r e c i p i t a t i o n ( o r d i s s o l u t i o n ) p r o c e s s of h y d r i d e s from s o l i d s o l u t i o n ( p r e c i p i - t a t i o n peak). Following ( 4 1

,

t h e p r e c i p i t a t i o n peak i s c o n s i d e r e d t o b e a s s o c i a t e d w i t h t h e s t r e s s - a s s i s t e d p r e f e r e n t i a l p r e c i p i t a t i o n o r d i s s o l u t i o n of h y d r i d e s . At h i g h e r measurement f r e q u e n c i e s t h e p r e c i p i t a t i o n peak shows a s i g n i f i c a n t growth upon t h e r m a l c y c l i n g ( 1 , 2 , 3 ) . T h i s i s i n marked c o n t r a s t t o t h e r e s u l t s a t lower f r e q u e n c i e s [ 4 , 5 )

.

The c o n t r a r y r e s u l t s were e x p l a i n e d by ( 4 ) a s t h i s : The a- peak a s s o c i a t e d w i t h t h e d i s l o c a t i o n s puntched o u t i n p r e c i p i t a t i o n p r o c e s s of hy- d r i d e s s h i f t s towards h i g h e r t e m p e r a t u r e so a s t o become a main component of i n - t e r n a l f r i c t i o n n e a r t h e p r e c i p i t a t i o n t e m p e r a t u r e a t h i g h e r measurement f r e q u e n c i e s . The r e d u c t i o n of p r e c i p i t a t i o n peak measured a t lower f r e q u e n c i e s on t h e r m a l c y c l i n g i s due t o t h e lower peak t e m p e r a t u r e of a-peak and t h e change i n d i s t r i b u t i o n and morphology of h y d r i d e s a s s o c i a t e d w i t h t h e i n c r e a s i n g d i s l o c a t i o n d e n s i t i e s .

The p u r p o s e of t h i s p a p e r i s t o i n v e s t i g a t e t h e i n f l u e n c e of d i s l o c a t i o n s on t h e p r e - c i p i t a t i o n peak. The d i s l o c a t i o n s were i n t r o d u c e d by p l a s t i c d e f o r m a t i o n i n s t e a d of t h e r m a l c y c l i n g .

HATERIAL AND EXPERINENT

The t a n t a l u m specimens of p u r i t y 99.95% w i t h l m m i n d i a m e t e r and 8 0 mm i n l e n g t h were used i n t h e i n v e s t i g a t i o n . The r e s u l t s of chemical a n a l y s i s of t h e t a n t a l u m w i r e a r e g i v e n i n T a b l e 1.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19851023

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JOURNAL DE PHYSIQUE

Table 1. Chemical a n a l y s i s of tantalum w i r e i n wt ppm

Oxygen and n i t r o g e n c o n t e n t s were e v a l u a t e d from t h e Snock peak h e i g h t s t o be about 84 a t ppm and 65 a t ppm r e s p e c t i v e l y

.

The o r i g i n a l specimen was cold-worked.

Hydrogen was introduced c u r r e n t d e n s i t y of 20 mA/cm i n o t h e specimen by a c a t h o d i c charging t e c h n i q u e w i t h

5 .

^As o l u t i o n of 10% H SO was used a s an e l e c t r o l y t e . 2 4

The low frequency i n t e r n a l f r i c t i o n and r e l a t i v e modulus ( f L ) were measured i n an automatic i n v e r t e d t o r s i o n perdulum

.

The maximum s t r a i n amplitude i n t h e s p e c i - men i s about 1 x 1 0 ~ . The experiment temperature was from 90 t o 475K. The measuring f r e q u e n c i e s were between 1 . 3 Hz and 5.3 H z . The h e a t i n g r a t e was c o n t r o l l e d over t h e whole temperature range. But t h e c o o l i n g r a t e , l a r g e r t h e n 2K/min, was o u t of c o n t r o l below about 150K.

RESULTS AND DISCUSSION

I n t e r n a l f r i c t i o n and r e l a t i v e qodulus a s a f u n c t i o n of t e m p e r a t u r e jn a cold-worked t a n t a l u m specimen show an a-peak (H-SK-Peak) a t about 100K(f=2.5'tIz).~he peak h e i g h t i s about 3 x 1 0 - ~ . This peak i s considered t o be due t o t h e i n t e r a c t i o n between d i s - l o c a t i o n and r e s i d u a l hydrogen i n t h e specimen. (Fig.1. c u r v e s A ) .

A f t e r charging t h e a- peak h e i g h t d e c r e a s e s , but a new peak appears a t - h i g h e r t e m p e r a t u r e (Fig.1, c u r v e s B)

.

The new peak was i d e n t i f i e d a s a p r e c i p i t a t i o n peak of h y d r i d e s . The f o l l o w i n g f e a t u r e s have been observed:

1. The peak h e i g h t i n c r e a s e s and s h i f t s Po t h e h i g h e r t e m p e r a t u r e a s i n c r e a s i n g hydrogen c o n c e n t r a t i o n .

2. The peak h e i g h t depends on t h e c o o l i n g ( o r h e a t i n g ) r a t e and measuring f r e - qu enc y

.

3. The peak c o n s i s t s of t r a n s i e n t and e q u i l i b r i u m components, a s shown i n Fig.2.

The c u r v e s i n Fig.2 were o b t a i n e d on c o o l i n g , but holding a t s e v e r a l g i v e n tem- p e r a t u r e s long enough f o r i n t e r n a l f r i c t i o n t o approach t o a s t a b l e v a l u e ( i n gene- r a l > 4 0 min.). The above c u r v e A might r e p r e s e n t i n t e r n a l f r i c t i o n on continuous c o n l i n g

.

The lower c u r v e B i s e q u i l i b r i u m component. It i s obvious t h a t t h e d i f - :erenee should b e t r a n s i e n t component.

4 . The peak t e m p e r a t u r e does n o t show s i g n i f i c a n t dependence on t h e measuring f r e - quency. By means of s h i f t i n g frequency from 1 . 3 t o 5.3 H z , an a c t i v a t i o n e n t h a l p y of 0.68 ev can be e s t i m a t e d .

5. Thermal c y c l i n g below room t e m p e r a t u r e does n o t show any o b s e r v a b l e e f f e c t on t h e h e i g h t of t h e p r e c , i p i t a t i o n peak.

6 . No amplitude dependence was observed n e a r t h e p r e c i p i t a t i o n peak t e m p e r a t u r e . Beside t h e abovementioned f e a t u r e s , t h e f o l l o w i n g phenomena were r e v e a l e d . A n a d d i t i o n a l i n - s i t u t o r s i o n p l a s t i c desormation by t w i s t i n g two t u r n s (about 7%

s h e a r s t r a i n i n s u r f a c e ) a t room t e m p e r a t u r e shows a marked i n f l u e n c e on t h e pre- c i p i t a t i o n peak ( F i g . 3 ) . A f t e r t h a t t h e specimen was h e a t e d . Fig.4 shows t h e i n t e r n a l p r e c t i o n and r e l a t i v e modulus on h e a t i n g p r o c e s s

.

^{I t}can be seen t h a t a pseudq peak i s accompainied w i t h r e c o v e r y of modulus over t h e t e m p e r a t u r e range, i n which oxygen atoms a r e c o n s i d e r e d t o b e a b l e t o move. The pseudo peak and modulus recovery show t h a t t h e s e g r e g a t i o n of oxygen t o t h e d i s l o c a t i o n s i s t a k i n g p l a c e i n t h e specimen. The i n c r e a s e of i n t e r n a l f r i c t i o n and t h e d e c r e a s e of mo-

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d u l u s d u r i n g holding a t 475K may b e a s s o c i a t e d w i t h t h e developing 0-SK-peak. On c o o l i n g i t i s evident t h a t a small 0-Sn6ek peak appears on a background n e a r l y e x p o n e n t i a l l y i n c r e a s i n g with temperature ( F i g . 4 ) .

A f t e r aging a t 475K, t h e i n f l u e n c e of t h e a d d i t i o n a l t w i s t on t h e p r e c i p i t a t i o n peak d i s a p p e a r s completely ( F i g . 5 ) .

The i n f l u e n c e s of a d d i t i o n a l t w i s t and subsequent aging on t h e p r e c i p i t a t i o n peak may appear r e p e a t e d l y

.

These r e s u l t s show t h a t d i s l o c a t i o n s may l a y an important r o l e i n t h e p r o c e s s of hydride p r e c i p i t a t i o n

.

As w e l l know#{ t h e s t r e s s f i e l d of d i s l o c a t i o n may in- t e r a c t w i t h t h e m i s f i t s t r a i n c r e a t e d by t h e formation of a h y d r i d e n u c l e u s , reducing t h e a c t i v a t i o n e n t h a l p y n e c e s s a r y f o r i t s appearance. The s t r e s s f i e l d of d i s l o c a t i o n can a l s o a c c e l e r a t e t h e d i f f u s i o n p r o c e s s , changing t h e k i n e t i c s of p r e c i p i t a t i o n . The c o r e of d i s l o c a t i o n i s u s u a l l y an easy p a t h f o r d i f f u s i o n . The i n v e s t i g a t i o n s w i t h TEM have r e v e a l e d t h a t i n low c o n c e n t r a t i o n Ta-H a l l o y s , t h e h y d r i d e s were found t o b e surround by dense d i s l o c a t i o n l o o p s . So i t i s r e a s o n a b l e t o suppose t h a t d i s l o c a t i o n s a r e p r e f e r e n t i a l s i t e s f o r h y d r i d e s n u c l e a t i o n and growth

.

P a r t i c u l a r l y when t h e deformation mode i n t h e measurment of i n t e r n a l p r i c - t i o n i s t h e same a s t h a t of p r e - p l a s t i c t w i s t , t h e r e s u l t a n t d i s t r i b u t i o n and morphology of t h e d i s l o c a t i o n s may be b e n e f i c i a l t o t h e s t r e s s - a s s i s t e d p r e f e r e n t i a l p r e c i p i t a t i o n o r d i s s o l u t i o n of h y d r i d e s

.

I n a d d i t i o n , t h e i n t e r a c t i o n between d i s l o c a t i o n s and h y d r i d e s may a l s o be a cause of c r e a t i o n of t h e p r e c i p i t a t i o n peak . ( e q u i l i b r i u m component)

.

The d e p r e s s i o n of a-peak a f t e r charging provides f u r t h e r evidence f o r t h e p r e f e r e n - t i a l p r e c i p i t a t i o n of h y d r i d e s on t h e d i s l o c a t i o n s . According t o Seeger ' s model 171, t h e s t r e n g t h of a-peak:

A 4

^L2

Where L i s f r e e loop l e n g t h . A t lower temperature t h e h y d r i d e s a c t a s p i n i n g p o i n t s , which reduce t h e f r e e d i s l o c a t i o n loop l e n g t h .

Because t h e i n t e r a c t i o n enthalpy w i t h d i s l o c a t i o n f o r oxygen i s l a r g e r t h a n t h a t f o r hydrogen, oxygen can r e p l a c e hydrogen on d i s l o c a t i o n . A f t e r a g i n g hydrogen h a s n o t been a b l e t o f i n d o u t s u i t a b l e s i t e s on t h e d i s l o c a t i o n . A s a r e s u l t

,

t h e addi- t i o n a l twist-enhanced e f f e c t d i s a p p e a r s .

The r e p e a t e d deformation can draw d i s l o c a t i o n s from oxygen atmosphere, t h e r e b y t h e d i s l o c a t i o n s become f r e e . So t h a t t h e twist-enhanced e f f e c t appears a g a i n .

1. Hydrogen charging t h e deformed tantalum specimen d e c r e a s e s a-peak, b u t r e s u l t s i n a p r e c i p i t a t i o n peak.

2 . An a d d i t i o n a l i n s i t u t w i s t enhances t h e p r e c i p i t a t i o n peak. Subsequent aging e l i m i n a t e s t h e enhanced e f f e c t .

3 . I t i s suggested t h a t h y d r i d e s p r e c i p i t a t e p r e f e r e n t i a l l y on t h e d i s l o c a t i o n s and t h e p r e c i p i t a t i o n peak may be a s s o c i a t e d w i t h t h e i n t e r a c t i o n between d i s - l o c a t i o n and h y d r i d e .

REFERENCES

1. O.Buck, D.O.Thompson and C.A.Wert, J.Phys. Chem S o l i d s 3 2 , 2331(1971).

2. G.Cannelli and R . C a n t e l l i , Appl. Phys. 3 , 325(1975).

3 . G.Cannelli and F.M.Nazzolai, Nuovo C i m . 64B, 171(1969).

4 . 9.Yoshinari and M.Koiwa, Acta M e t a l l . Vol. 30, 1979(1982).

5. 0 . Y o s h i n a r i and M.Koiwa, Acta M e t a l l . Vol. 30, 1937(1932).

6. F.C.Larche. i n " D i s l o c a t i o n s i n S o l i d s . V4. Ed. F.R.N.Nabarro, . , (1979) North-

oila and

^{pub. CO}

.

^"

7 . A.Seeger, M.'nTeller, J . Diehl, Z.Pan, J.Zhang and T.Ke, Z.Yetallk. Sand 73, l ( 1 9 8 2 ) .

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C10-106 JOURNAL DE PHYSIQUE

F i g . 1. Q - l and f of cold-worked Ta F i g . 2 . Q ; ~ and f 2 of Ta-H a l l o y on b e f o r e and a f t e r c h a r g i n g . Curve B was c o o l i n g (T=3.2 K/min.) and h o l d i n g a t t a k e n on l S t c o o l i n g a f t e r c h a r g i n g . s e v e r a l t e m p e r a t u r e .

? = 3 . 3 K/min., f = 1 . 3 Hz.

P i o . 3 . I n f l u e n c e of a d d i t i o n a l t w i s t on F i g . 4 . Q-I and f 2 of Ta-H a l l o y a f t e r g-Y and f 2 Ta-H a l l o y . Cooling r a t e was a d d i t i o n a l t w i s t on h e a t i n g and a g i n g 2.1 K/min., h e a t i n g r a t e 1 . 7 K/min. a t 47513.

5 33

0

-

0 N

0 4 Ln \

X

-

_I _N^u

u u

3

2

I F i g . 5 . Q-' and f 2 of Ta-H specimen a f t e r a g i n g a t 475K. Cooling and h e a t i n g r a t e

was 3.2K/min. ₀ ₃₁

50 130 210 290 370