SUPERCONDUCTING PROPERTIES OF Nb-Ti-Ta CABLES WITH DIFFERENT CHEMICAL COMPOSITIONS

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SUPERCONDUCTING PROPERTIES OF Nb-Ti-Ta CABLES WITH DIFFERENT CHEMICAL

COMPOSITIONS

G. Rondelli, E. Olzi, G. Turisini, C. Ferdeghini

To cite this version:

G. Rondelli, E. Olzi, G. Turisini, C. Ferdeghini. SUPERCONDUCTING PROPERTIES OF Nb-Ti-Ta

CABLES WITH DIFFERENT CHEMICAL COMPOSITIONS. Journal de Physique Colloques, 1984,

45 (C1), pp.C1-433-C1-436. �10.1051/jphyscol:1984189�. �jpa-00223745�

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JOURNAL DE PHYSIQUE

Colloque C l , supplément au n° 1, Tome 45, janvier 1984 page Cl-433

SUPERCONDUCTING PROPERTIES OF N b - T i - T a CABLES WITH DIFFERENT CHEMICAL COMPOSITIONS

G. R o n d e l l i , E. O l z i , G . P . T u r i s i n i and C. F e r d e g h i n i *

C.N.R. - I.T.M., Via Induno 10, 20092 Cinisello Balsamo, Italy

*C.N.R. -G.N.S.M., Viale Benedetto XV 5 , 16151 Genova, Italy

Résumé - Les alliages ternaires Nb-43

w

/oTi-25

w

/oTa, Nb-38

w

/oTi-34

w

/oTa, Nb-51 /oTi-14,7 /oTa ont été obtenus au laboratoire. Les alliages pré- sentent une excellente ductilité, et n'ont pas posé de problèmes au cours de la production et de l'utilisation des cables. Comme pour les alliages binaires, une augmentation de 1'écrouissage intermédiaire sur les alliages ternaires améliore les propriétés superconductrices. Après optimisation, l'alliage Nb-38

w

/oTi34

w

/oTa présente les meilleures propriétés supercon- ductrices et, à 12 Tesla et 12,5K, on a pu obtenir un J = 6ûOA/mnr A b s t r a c t - Laboratory scale t e r n a r y a l l o y s Nb-43

w

/oTi-25

w

/oTa, Nb-38

w

/oTi- 34

w

/oTa, Nb-51

w

/oTi-14.7

w

/oTa were prepared. The a l l o y s e x h i b i t e x c e l l e n t d u c t i l i t y and thus no problems a r i s e during production and handling o f the c a b l e s . As f o r the Nb-Ti a l l o y s , an increase o f i n t e r m e d i a t e cold-work de- gree, also f o r ternary a l l o y s , leads t o b e t t e r superconducting p r o p e r t i e s . A f t e r adequate o p t i m i z a t i o n , t h e Nb-38

w

/oTi-34

w

/oTa a l l o y shows the best su- perconducting p r o p e r t i e s and, a t 12 Tesla and 2.15K, J

c

=600A/mm

2

can be reached.

1 - INTRODUCTION

I t i s known t h a t Nb-Ti superconducting a l l o y s are i n p r a c t i c e the most used because o f t h e i r f a b r i c a t i o n f e a s i b i l i t y and e x c e l l e n t mechanical p r o p e r t i e s and Nb-Ti cables are commonly used f o r magnetic f i e l d s up t o 8 Tesla.Nb-Ti cables are also proposed f o r a p p l i c a t i o n i n case o f magnetic f i e l d s higher than 8 Tesla provided t h a t working tem- peratures are below 4.2K. New a p p l i c a t i o n s o f superconducting cables f o r energy ac- c e l e r a t o r s and f o r nuclear f u s i o n p l a n t s d i r e c t e d the producers o f superconducting cables to push t h e i r i n t e r e s t t o magnetic f i e l d s o f 10-12 t e s l a ; so f a r i n such range only A-15 type compounds were used. Recent i n v e s t i g a t i o n s / 1 - 4 / suggest the u t i l i z a - t i o n o f Nb-Ti-Ta t e r n a r y a l l o y s f o r high f i e l d a p p l i c a t i o n cables.

An extensive i n v e s t i g a t i o n on the t e r n a r y a l l o y s Nb-Ti-Ta performed by Hawksworth/5/has shown some chemical compositions leading t o an important increase o f B

C

2 a t tempera- tures below 4.2K; the maximum value obtained i s 15.5 Tesla a t 2K, w i t h an increase o f 1.3 Tesla compared w i t h Nb-Ti b i n a r y a l l o y s . Segal / 6 / r e p o r t s t h a t J

c

values o f some t e r n a r y a l l o y s , a t 2K, are 50-70% higher than those r e l a t e d t o Nb-Ti binary a l - loys and thus t e r n a r y a l l o y base cables o f s u i t a b l e chemical compositions and prop- e r l y optimized can be used f o r high f i e l d a p p l i c a t i o n s .

The present paper i s d e a l i n g w i t h a research on the f a b r i c a t i o n and c h a r a c t e r i z a t i o n of m u l t i f i l a m e n t a r y cables Nb-Ti-Ta base w i t h 3 d i f f e r e n t chemical compositions. The i n f l u e n c e o f the adopted thermo mechanical working cycle on high f i e l d (up t o 12 Tesla) superconducting p r o p e r t i e s and a t temperatures 4.2K, 3K, 2.25K, 2.15K i s analyzed and discussed.

2 - MATERIALS

Three different Nb-Ti-Ta laboratory scale ingots (-v250g each) were produced by elec-

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984189

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C1-434 JOURNAL DE PHYSIQUE

tron-beam d r i p - m e l t i n g technique; s t a r t i n g m a t e r i a l s were t h e p u r e elements. Chemi- c a l a n a l y s i s o f t h e a l l o y s a r e g i v e n i n TAB. I.

The i n g o t s (d=24mm) were f i r s t c o l d r o l l e d up t o b12mm and vacuum annealed 3h a t 1000°C. A f t e r f u r t h e r r e d u c t i o n t o d 6 m , t h e r o d was imbedded i n an OFHC copper can, drawn and bonded 90 minutes a t 600°C. The composite monoelement was subsequently c o l d drawn t o dl.2mm and 61 monoelements were assembled i n an OFHC copper tube and deformed by d r a w i n g t o 81 .2mm.Optimization thermal t r e a t m e n t s a t 2.400°C were p e r f o r - med a t pre-determined d e f o r m a t i o n stages, s i m i l a r l y t o t h e w e l l known Nb-Ti m u l t i p l e stage o p t i m i z a t i o n , w i t h t h r e e d i f f e r e n t thermo-mechanical c y c l e s (c.w.A<c.w.B<c.w.C).

I t must be emphasized t h a t t h e t e r n a r y a l l o y s show e x t r e m e l y good d u c t i l i t y and be- have, i n t h i s r e s p e c t , i n s i m i l a r way l i k e N6-.Ti.

3 - EXPERIMENTAL PROCEDURES

cw/ 0

.006

<.006 C.010

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 4.2K as w e l l as 3K, 2.25K and 2.15K.

The s h o r t sample c h a r a c t e r i z a t i o n o f t h e specimen was performed f r o m 4 t o 12 Tesla w i t h a cryomagnetic t e s t f a c i l i t y . The c u r r e n t grow-rate was 4A/min; t h e 3cm samples were mounted p e r p e n d i c u l a r l y t o t h e magnetic f i e l d f l u x - 1 i n e s and, t h e t r a n s i t i o n p o i n t was assumed when luV/cm v o l t a g e drop appeared a t t h e ends o f t h e specimen.

TAB I - Chemical a n a l y s i s o f t h e specimens

4 - RESULTS

Ow/o . I 1 0 .097 . I 2 0 TaW/o

25.0 34.0 14.7 ALLOY

A l l o y 1 A l l o y 2 A l l o y 3

Jc values measured a t d i f f e r e n t magnetic f i e l d s and d i f f e r e n t temperatures i n t h e t h r e e a l l o y s w i t h t h e same w o r k i n g c c l e and c o l d - w o r k A a r e summarized i n TAB. 11, 8

which evidences t h a t t h e a l l o y Nb-38 /o~i-34'/oTa, due t o t h e l o w e r s c a t t e r o f Jc betkeen l o w and h i g h f i e l d , seems t h e most p r o m i s i n g f o r t h e h i g h f i e l d s u t i l i z a t i o n s . D i f f e r e n t w o r k i n g c y c l e s were s t u d i e d on t h i s a l l o y s i n o r d e r t o improve t h e h i g h f i e l d s s u p e r c o n d u c t i n g p r o p e r t i e s .

NW/o

< .005 .003 .004 NbW/o

b a l .

TAB I 1 - Jc values of t h e 3 a l l o y s s t u d i e d a t d i f f e r e n t f i e l d s and tempe- r a t u r e s . c.w.A ( J c i n 105A/cm2)

T i W / o 43.0 38.0 51 .O

ALLOY A l l o y 1 A l l o y 2 A l l o y 3

-

I n t h e case o f t h e t h r e e a l l o y s t u d i e d , an i n c r e a s e o f t h e i n t e r m e d i a t e cold-work degree g i v e s b e t t e r s u p e r c o n d u c t i n g p r o p e r t i e s as shown i n f i g . 1 where t h e improve- ment o f t h e s u p e r c o n d u c t i n g p r o p e r t i e s i n a l l o y 2 i s a p p a r e n t .

6 T e s l a 4.2K 2.25K 1.34 2.39 1.14 2.03 1.03 2.05

12 T e s l a 4.2K 2.25K

- - .40

- - .43

-- --

8 T e s l a 4.2K 2.25K

.60 1.62

.60 1.46

.39 1.26

10 T e s l a 4.2K 2.25K

.10 1.04

.14 .89

.02 --

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f i g . 1 - JcvsB o f a l l o y 2 a t d i f f e r e n t f i g . 2 - JcvsT o f a l l o y 2 a t d i f f e r e n t temperatures f o r d i f f e r e n t thermo-me- magnetic f i e l d s f o r d i f f e r e n t t h e r m - c h a n i c a l c y c l e s . mechanical c y c l e s .

- I n f i g . 2 J c values measured i n a l -

rn

l o y ~ b - 3 8 ~ / o T i - 3 4 ~ / o T a a t c o n s t a n t

I E

1 4 - f i e l d a r e p l o t t e d versus T. When

z - 2.25K t h e temperature i s lowered, t h e in

0,

o - _- ^{1 2 -} a l l o y 2 crease o f J c values i s m r e e v i d e n t a t h i g h e r values o f t h e a p p l i e d

7

- magnetic f i e l d . Furthermore f i g . 2

0

1 0 - confirms t h a t h i g h e r c o l d-work de-

t.P grees l e a d t o b e t t e r superconduc-

t i n g p r o p e r t i e s o f t h e a l l o y . I n f i g . 3 FpvsB curves a t d i f f e r e n t temperatures o f t h e a l l o y 2 w i t h t h e o p t i m a l t h e r m - m e c h a n i c a l c y c l e a r e r e l a t e d and compared w i t h t h e

~ 6 - 4 7 ~ / o T i a l l o y s t u d i e d i n a p r e -

4 v i o u s work / 7 / . The f i g u r e e x h i b i t s

t h a t a l l o y 2 possesses b e t t e r super c o n d u c t i n g p r o p e r t i e s t h a n Nb-47W/oli

2 p a r t i c u l a r l y a t low temperature

(2.25K); i n such c o n d i t i o n Bma, occurs a t 7.5 T e s l a f o r t h e t e r n a r y a1 l o y w i t h an i n c r e a s e o f 1 Tesla 4 6 8 10 1 2 B ( T ) compared w i t h t h e b i n a r y a1 l o y .

The c r i t i c a l c u r r e n t values a t 12 Tes l a a t d i f f e r e n t temperatures f o r t h e FpvsB o f d i f f e r e n t a l l o y s a t 3 Nb-Ti-Ta a l l o y s a r e shown i n f i g . 4 .

df: ^'?i:rLnt temperatures. The a n a l y s i s o f t h i s f i g u r e i n d i -

c a t e s t h a t Nb-5lw/oTi-14. 7W/oTa

a1 1 oy possesses p o o r e r superconduc-

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JOURNAL DE PHYSIQUE

t i n g p r o p e r t i e s than t h e o t h e r a1 l o y s . The Nb-38W/oTi-34w/oTa

N

a l l o y w i t h t h e h i g h e s t cold-work

E

E 700 . degree w o r k i n g c y c l e e x h i b i t s

1

a a l l o y 2 c.w.C t h e b e s t superconducting p r o p e r -

U

t i e s w i t h c r i t i c a l c u r r e n t dens1

3

t i e s a t 12 T e s l a and 2.15K

h i g h e r than 600A/mm7.

From t h e p r e s e n t s t u d y i t can be observed t h a t t h e adopted o p t i - m i z a t i o n c y c l e s f o r t e r n a r y a l - l o y s ( p l a s t i c c o l d d e f o r m a t i o n w i t h i n t e r m e d i a t e thermal t r e a t - ments a t temperatures %400°C) a r e s i m i l a r t o those performed

I I I

i n the Nb-Ti b i n a r y a l l o y s . T h i s 2.15 3 T(K) b e h a v i o r seems t o i n d i c a t e t h a t

2.25 t h e p i n n i n g mechanism based upon

a - T i p r e c i p i t a t i o n s on g r a i n

f i g . 4 - JcvsT f o r t h e t h r e e a l l o y s s t u d i e d a t ~! ^~ ^~ ^d ^, ^~~~~~~s ^, ^, ^~ ^~ ^~ ^~ ^~ ^~ ^~ ^~ ^~

c.w.A compared w i t h a l l o y 2 a t c.w.C.

mations, as assumed f o r b i n a r y a l l o y s , operates a l s o i n Nb-Ti-Ta t e r n a r y a1 l o y s .

5 - CONCLUSIONS

The s u p e r c o n d u c t i n g p r o p e r t i e s o f t h r e e Nb-Ti-Ta a1 l o y s w i t h d i f f e r e n t chemical com- p o s i t i o n s were examined i n t h i s study. The Nb-Ti-Ta t e r n a r y a l l o y s possess an ex- t r e m e l y good d u c t i l i t y and t h a t w i t h t h e r e l a t e d c a b l e s no problems can a r i s e d u r i n g p r o d u c t i o n and h a n d l i n g i n magnet f a b r i c a t i o n . The a l l o y ~ b - 3 8 ~ / o ~ i - 3 4 ' / o ~ a which gave t h e b e s t r e s u l t s seems t h e most p r o m i s i n g f o r f a b r i c a t i o n o f superconducting c a b l e s o p e r a t i n g a t magnetic f i e l d s up t o 12 Tesla a t temperatures i n t h e range o f 2K. A p r o p e r l y o p t i m i z e d c a b l e w i t h such a l l o y shows a c r i t i c a l c u r r e n t d e n s i t y o f 600A/m2 a t 12 T e s l a and 2.15K. T h i s v a l u e i s 50% h i g h e r than f o r a Nb-4W/oTi c a b l e s t u d i e d i n a p r e v i o u s work.

REFERENCES

/ l / - L a r b a l e s t i e r D.C.-MT7 Conference - K a r l s r u h e 30/3-3/4-1981 - Paper C-2 /2/-Segal H.R., S t e k l y J.J., de W i n t e r T.A.-ibidem - paper 6-10