PROPERTIES OF NbTi50 SUPERCONDUCTING COMPOSITE WIRE

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PROPERTIES OF NbTi50 SUPERCONDUCTING COMPOSITE WIRE

Zhou Lian, Li Chengren, Wu Xiaozu, Zhou Nong, Zhang Tingjie, Wang Keguang

To cite this version:

Zhou Lian, Li Chengren, Wu Xiaozu, Zhou Nong, Zhang Tingjie, et al.. PROPERTIES OF NbTi50

SUPERCONDUCTING COMPOSITE WIRE. Journal de Physique Colloques, 1984, 45 (C1), pp.C1-

437-C1-440. �10.1051/jphyscol:1984190�. �jpa-00223746�

JOURNAL DE PHYSIQUE

Colloque Cl, supplément au n° 1, Tome h5, janvier 1984 page Cl-437

PROPERTIES OF NbTi50 SUPERCONDUCTING COMPOSITE WIRE

Zhou Lian, Li Chengren, Wu Xiaozu, Zhou Nong, Zhang Tingjie and Wang Keguang

Baoji Institute for Non-Ferrous Metal Research, P.O. Box 71, Baoji, Shaanxi, China

Résumé - Dans cet article sont présentées les mesures du courant critique à 4,2K sur des fils multifilamentaires de Nb Ti (50 % en poids) à des champs jusqu'à HC2. Les me- sures indiquent que les meilleurs échantillons ont d'excel- lentes propriétés de courant critique en particulier à champ moyen. Le courant critique à 4,2K est par exemple de 3460 A/

mm2 à 5T, et de 1020 A/mm2 à 8T. Le rOle crucial joué par des traitements thermiques multiples dans l'obtention de hautes valeurs du courant critique pour des alliages de Nb Ti

(50 %) est discuté. La force de pinning et les acpects de microstructure sont discutés.

Abstract - The results of critical current measurements of HbTi50 multifilamentary wire at 4.2 K in the fields up to Hc2 are reported in this paper. The measurements show that the best optimized samples have excellent critical current properties, especially in mid-field. Its Jc(4.2K), for in- stance, is 3460 A/mm

2

at 5 T, and 1020 A/mm

2

at 8 T. The crucial role played by multiple heat treatments in develop- ing high Jc values in NbTi50 alloy are described. The flux pinning force and microstructural features are discussed.

INTRODUCTION

Our institute chose Nb-50w/

o

Ti as a standard alloy in 60's and has developed single-core, multifilamentary wire,cable and strands etc.

for applications in China. Recent years a program to optimize Jc of NbTi has been carried out and significant enhancement of Jc obtained through multiple heat treatment and processing cycles, which has been reported by Li Chengren/1/.

The results of critical current measurement at 4.2 K and the fields up to Bc2 as well as TEH examination for optimized samples are pre- sented in this paper. The optimization process to obtain high Jc is discussed in some details with respect to Jc-B properties, bulk flux pinning force and microstructural features.

EXPERIMENTAL PROCEDURE

Three samples with different heat treatment conditions are used in this study. The samples have outside dia. of 0.2, 0.33 and 0.5 mm with 61 filaments of 18, 27.5 and 45>»-m dia., respectively. Theyare made through multiple arc-melt, extrusion and cold work etc/1/.

The details of the samples studied are given in Table 1 .

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984190

Cl-438 JOURNAL DE PHYSIQUE

T a b l e 1

.

D e t a i l s o f NbTi50 Samples I n v e s t i g a t e d sample d i a m e t e r f i l a m e n t Cu/NbTi d i a . of t i m e s of

mm number f i l a m e n t h e a t t r e a t

The c r i t i c a l c u r r e n t measurements were c a r r i e d o u t a t t h e 'High Mag- n e t i c F i e l d Lab' i n Grenoble. A

5 MW

B i t t e r magnet w i t h f r e e b o r e of 50 mm a n d f i e l d up t o 15T w a s used. The s h o r t samples a b o u t 80 t o ⁹⁰ cm l o n g e a c h were wound on a p o l y e s t e r sample h o l d e r w i t h a d i a . of 2 8 mm. The d i s t a n c e between t h e v o l t a g e t a p s on t h e samples was 40 cm. The c r i t i c a l c u r r e n t w a s measured by a s t a n d a r d t e c h n i q u e / 2 / . The J c v a l u e s q u o t e d i n t h i s p a p e r were d e f i n e d w i t h 0.1p-v/cm v o l t - a g e c r i t e r i o n u n l e s s d e s c r i b e d o t h e r w i s e .

T r a n s m i s s i o n e l e c t r o n microscopy s t u d i e s were performed. The f o i l s f o r TELU were p r e p a r e d from l o n g i t u d i n a l s e c t i o n s of t h e w i r e s u s i n g a m e c h a n i c a l t h i n n i n g , f o l l o w e d by e l e c t r o p o l i s h i n g t e c h n i q u e . A e l e c - t r o l y t e o f 5% H2SO4 and

95%

methanol, c o o l e d t o -70°C, w a s u s e d w i t h a n o p e r a t i n g v o l t a g e o f -12 V. S e l e c t e d a r e a d i f f r a c t i o n p a t t e r n s were a l s o t a k e n from e a c h sample t o d e t e r m i n e i f d - T i p r e c i p i t a t e s were p r e s e n t . The sub-band s i z e were d e r i v e d from a c o u n t of t h e num- b e r of sub-band i n t e r c e p t i n g a u n i t l e n g t h of a l i n e p e r p e n d i c u l a r t o t h e drawing a x i s of t h e w i r e .

RESULTS AND DISCUSSION

C r i t i c a l C u r r e n t Fig.1 shows t h e c r i t i c a l c u r r e n t d e n s i t y v s . magne- t i c f i e l d a t 4.2K f o r t h e t h r e e samples s t u d i e d . The r e s u l t s r e f l e c t a s i g n i f i c a n t e f f e c t o f h e a t t r e a t m e n t o n c r i t i c a l c u r r e n t . A l l t h e t h r e e samples i n v e s t i g a t e d were c o l d worked w i t h same a r e a r e d u c t i o n a n d h e a t t r e a t e d a t same t e m p e r a t u r e , b u t t h e y have d i f f e r e n t J c v a l - u e s due t o d i f f , e r e n t t i m e s o f h e a t t r e a t m e n t p u t i n t o them. The sam- p l e CH661 which w a s h e a t t r e a t e d 6 t i m e s , h a s t h e b e s t J c v a l u e of 3460

~ / m 3

a t 51,4.2K; w h i l e w i t h d e c r e a s i n g t h e t i m e s o f h e a t t r e a t - ment t h e o t h e r two samples have l e s s J c v a l u e s o f 2450 A/mm2 a n d 2050

~/mm2(5T,4.2K),respectively. I t i s obvious from t h e r e s u l t s t h a t t h e

&-Ti p r e c i p i t a t i o n p l a y e d a c r u c i a l r o l e i n d e v e l o p i n g J c i n NbTI.

-

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CH661

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0 2 6 6 8 1 0 1 2

1 2 3 6 5 6 7 8 9 IOBrTI B t T ,

Fig.1 Jc-B c u r v e s a t 4.2K f o r Fig.2 The p i n n i n g f o r c e vs.

t h e samples s t u d i e d B c u r v e s a t 4.2 K

F l u x P i n n i n g F o r c e The c u r v e s o f p i n n i n g f o r c e v s . B i s c h a r a c t e r i - z e d by p i n n i n g s t r u c t u r e . The p i n n i n g f o r c e F (JcXB) c u r v e s , e x h i b i - t e d by t h e s a m p l e s s t u d i e d , a r e g i v e n i n Fig.!?. The sample CH661 h a s t h e h i g h e s t F v a l u e o f 18.5 G N l m 3 a t a b o u t 4T, which i s much more t h a n t h a t of i 2 . 8 and 10.5 ~ ~ / m 3 f o r t h e o t h e r two samples. A s de- s c r i b e d p r e v i o u s l y , t h i s a p p e a r s due t o s t r o n g e s t & - T i p r e c i p i t a t i o n s t r u c t u r e i n sample CH661.

According t o t h e f l u x p i n n i n g s c a l i n g l a w s u i t a b l e t o NbTi a l l o y / 4 5 / , JcXB s h o u l d be l i n e a r t o B i n h i g h f i e l d s . E x t r a p o l a t i n g JcXB v s . B c u r v e t o z e r o c r i t i c a l c u r r e n t , t h e r e f o r e , c o u l d o b t a i n bulk u p p e r c r i t i c a l f i e l d Bc2. It i s s e e n from Fig.2 t h a t t h e l i n e a r r e l a t i o n between F a n d B i s o n l y a t t h e f i e l d r a n g e o f 7 t o 9 T. The b u l k u p p e r c r i g i c a l f i e l d v a l u e e x t r a p o l a t e d f o r CH661 i s a b o u t 9 .DT , w h i l e i n f a c t i t s t i l l c a n t r a n s p o r t s u p e r c o n d u t i n g c u r r e n t i n t h e f i e l d s above 10 T, showing a h i g h f i e l d t a i l . A s t h e Bc2 i s approached, J c becomes more and more dominated by t h e Bc2 of m a t r i x . A s s e e n i n Fig.2, t h e Fp o f sample CH661 f a l l s o f f s t e e p l y i n h i g h f i e l d s . The Bc2 d e c r e a s e o f sample w i t h 6 t i m e s of h e a t t r e a t m e n t s r e f l e c t s a l i t t l e o v e r - e x h a u s t e d T i c o n t e n t i n m a t r i x a f t e r 4 - T i p r e c i p i t a t i o n .

A f u r t h e r o p t i m i z a t i o n f o r h i g h - t r o l l i n g T i c o n t e n t a f t e r oC-Ti p r e c i p i t a t i o n o r a d d i n g T a e l e - ment t o r a i s e t h e Bc2 of m a t r i x .

3 0

2 5

f i e l d J c i s n e c e s s a r y t h r o u g h con-

C H ~ ~ I I Z . ~ ~ K J / Y

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^{0 A A} N.~15TiT.(225 ^MF MF N a 3 S ( 1 2 1 0 ¹⁸¹⁰ K ) j l 121 ^/2/.

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I n o r d e r t o e s t i m a t e t h e poten- t i a l a p p l i c a t i o n of NbTi50 i n s u p e r f l u i d He, a c o m p a r i s i o n of J c a vs.B a t 4.2K and 2K f o r NbTi, NbTiTa a n d &IF Nb Sn i s g i v e n i n F i .3 .It i s obvgous t h a t sample CHf61 h a s a g r e a t margin i n J c up

. t o 10T.From a t e c h n i c a l and ecno-

mic p o i n t of view, t h e r e f o r e , i t i s b e n i f i c a l t o u s e NbTi a l l o y i n t h e magnet w i t h 10 T o r a b o v e , c o o l e d by s u p e r f l u i d He.

o 2 L 6 8 1 0 in 1 6 1 8 BcT1 ? ; i i c r o s t r u c t u r e The d i s l o c a t i o n c e l l a n d sub-band s t r u c t u r e o f F i g . 3 Fp vs.B c u r v e s f o r NbTi

,

sample ~ H 6 6 1 i s v i s i b l e i n Fig.4.

MF Nb3Sn a n d NbTiTa a t 4.2, 2K The s e l e c t e d a r e a d i f f r a c t i o n p a t t e r n s i n d i c a t e t h e p r e s e n t o f

& T i precipitates.Measurements show t h e a v e r a g e d i a . of sub-band f o r sample CH661 i s 380

A ,

a n d 410

h

f o r sample 807b. I n a c o m p a r i s i o n of sub-band s i z e between CH661 a n d 8 0 7 b , i t c a n be s e e n t h a t t h e m u l t i p l e h e a t t r e a t m e n t s n o t o n l y c o n t r o l L T i p r e c i p i t a t i o n , but a l s o i n t e n d t o d e c r e a s e t h e sub-band s i z e . T h i s a p p e a r s b e c a u s e t h a t t h e d - T i p r e c i p i t a t e s formed a t sub-band encourage t h e s u b s e q u e n t r e f i n e m e n t o f t h e sub-band s t r u c t u r e d u r i n g drawing/6/.

The h i g h J c o b t a i n a b l e i n NbTi composite a r e c o n s i d e r e d t o be extrem- l y dependent o n two m i c r o s t r u c t u r a l f e a t u r e s

-

f i n e s c a l e sub-band a n d d - T i p r e c i p i t a t e s , a s d e m o n s t r a t e d by a number of w o r k e r s / 7 , 8 , 9 / The sub-band s i z e o f sample CH661 i s c l o s e t o t h a t of 807b and b o t h have a small d e v i r a t i o n . The CH66l h a s , however, a l a r g e m a r g i n i n J c

. O u r r e s u l t s a r e a f u r t h e r e v i d e n c e f o r t h e most i m p o r t a n t r o l e of d - T i p r e c i p i t a t e i n d e v e l o p i n g h i g h J c i n NbTi, a l t h o u g h a f i n e sub- band s t r u c t u r e i s a p r e r e q u i s i t e because i t p r o v i d e s t h e n u c l e a t i o n s i t e s f o r &-Ti p r e c i p i t a t i o n .

The TEM s t u d i e s of o u r sample C ~ 6 6 1 c a r r i e d on by D r . West and P r o f . L a r b a l e s t i e r / l O / have shown t h e p r e s e n t of p l a t e - l i k e &-Ti p r e c i p i -

CI-440 JOURNAL DE PHYSIQUE

Fig.4 F l e c t r o n m i c r o g r a p h ( A ) , a n d s e l e c t e d a r e a d i f f r a c t i o n p a t t e r n ( B f o r sample CH661

t a t e s w i t h a t h i c k n e e s o f 7 nm a n d p a r t i c l e s p a c e up t o 32 nm. I t c o u l d be supposed t h a t t h e a p p r o p r i a t e thicket-Ti p r e c i p i t a t e s a r e t h e most e f f e c t i v e and s t r o n g f l u x p i n n i n g s t r u c t u r e .

CONCLUSION

NbTi50 m u l t i f i l a m e n t a r y w i r e o p t i m i z e d w i t h m u l t i p l e h e a t t r e a t m e n t a n d p r o c e s s i n g c y c l e s have h i g h J c v a l u e s , e s p e c i a l l y e x c e l l e n t mid- f i e l d J c . Its 51-Jc(4.2K), f o r example, a t t a i n e d t o 3460 ~/mm2 a t 5 1 a n d 4.2 K.

Well o p t i m i z e d NbTi50 h a s v e r y h i g h volume p i n n i n g f o r c e Fpmax v a l u e s

.

I n comparison w i t h NbTiTa a l l o y and MF Nb Sn, NbTi h a s t e c h n i c a l and ecnomical a d v a n t a g e i n 10 T(1.8~)-magneZ u s e . A f u r t h e r o p t i m i - z a t i o n f o r h i g h - f i e l d J c i s n e c e s s a r y t h r o u g h c o n t r o l l i n g o f T i con- t e n t a f t e r d - T i p r e c i p i t a t i o n .

Taking a f i n e - s c a l e sub-band s t r c t u r e a s p r e c o n d i t i o n , m u l t i p l e h e a t t r e a t m e n t s produced i n NbTi50 a l l o y a c o n t r o l l e d d - T i p r e c i p i t a t i o n , and a l s o t r e n d e d t o d e c r e a s e sub-band s i z e . Both t h e f i n e - s c a l e sub- band a n d & - T i p r e c i p i t a t e s d e t e r m i n e t h e h i g h J c of NbTi a l l o y . I t i s , however, b e l i e v e d t h a t t h e p l a t e - l i k e d - T i p r e c i p i t a t e s p l a y e d a c r u - c i a l r o l e i n d e v e l o p i n g J c , p a r t i c u l a r l y t h e v e r y h i g h m i d - f i e l d J c .

ACKNOWLEDGEtvIJZNTS

One o f t h e a u t h e r s (Zhou L i a n ) w i s h e s t o thank D r s . V a l l i e r , P i c o c h e and Marty of t h e t N a t i o n a l High Magnetic F i e l d L a b . l i n Grenoble f o r t h e i r v a l u a b l e h e l p i n c a r r i n g o u t c r i t i c a l c u r r e n t measurements. He i s a l s o g r e a t l y i n d e b t e d t o D r . R.Tournier f o r h i s encouragement a n d a c c e p t i n g t h e a u t h e r l s s t a y i n his l a b .

REFERENCES

1

.

L i Chengren, WLL Xiaozu, Zhou Nong a t 1982 ASC ,IEEE Trans .on Mag- n e t i c s , (1983)

2. Zhou Lian, Tang Xiande,J.Marty, O.Larborde, IEEE Trans. MAG-17 (1981)

3 . L a r b a l e s t i e r D.C. a t 1983 P a r t i c l e A c c e l e r a t o r Conf. IEEE T r a n s . on Nuclear S c i e n c e (1983)

4. Hawkworth D.C. L a r b a l e s t i e r D.C. IEEE P u b l i c a t i o n 79 CH1441-5 NPS, (1980)

5. Hampshire R.G. T a y l o r M.T. J.Phys. F:Metal Phys. 2 (1972) 8 9 6 , West A.V. L a r b a l e s t i e r D.C. IEEE Trans. MAG-17, (1981)65 7. P f e i f f e r I. Hillman H. Acta Met. 1 6 , (1968) 1429

8. W i l l b r a n d J . Schlump \V. Z.Metallkunde 6 6 , (1975) 714

9. L a r b a l e s t i e r D.C. S u p e r c o n d u c t i n g M a t e r i a l s S c i e n c e , E d i t o r s , S.Foner, B.B. Schwartz, Plenum P r e s s , (1981) 133-197

10. L a r b a l e s t i e r D.C. P r i v a t e communication