866 IEEE TRANSACTIONS ON MAGNETICS, VOL. 28, NO.l, JANUARY 1992

THE INVEEXIGATION OF PROWXION PROCES FEATUFSS AND PROPERTIES 1 OF N B , S WITH EXENDED 1- TIN XJURCES- '

Pantsyrny V. I., Nikulin A.D., Shikov A. K., Parno A . V . , kel jakov N. A. , Potapenko I. I.

A. A. Bochvar's A l l Union Scientlf IC Research Institute of Inorganic Materials. 123060, Moscow, USSR.

Rbstract - The p a t t e r n s of p r o d u c t i o n of ex tended i n t e r n a l t i n s o u r c e s u p e r c o n d u c t o r s are considered. lt is shown t h a t t h e applica-

( S ) to tin base alloy volume (V), that deter- mines the change of tin concentration in ac-

t i o n of d i f f e r e n t p a t t e r n s of s u p e r c o n d u c t o r cordance with t h e law C21: p r o d u c t i o n makes it p o s s i b l e t o va ry ove r a wide r a n g e t h e c o n t e n t of s t a b i l i z i n g coppe r i n a f i n i s h e d w i r e . Supe rconduc to r s B 0.5 - ,1.5 mm w i t h volume f r a c t i o n s t a b i l i z i n g coppe r 30-60 % a r e manufactured.The d a t a on supe rcon-

dC/dt = - D / S x S/V( Cu-CO) , where:

, d u c t i n g p r o p e r t i e s of wires produced de- D - dlff'uslon factor; pending upon h e a t t r e a t m e n t f o r 20-72 hour s -4 i n t h e t e m p e r a t u r e r a n g e of 600-75OoC are - thickness of boundary layer (8-10 m); g i v e n . O v e r a l l c u r r e n t d e n s i t y ( w i t h o u t s ta- CU - ultimate concentration of' solid b i l i z i p g coppe r ) made up 2 . 0 ~ 1 0 A / c m 2 and 3.7~10 A/cmein magnet ic f i e l d s 8 and 15 T substance at a given temperature; c o r r e s p o n d i n g l y . Comparing of t h e r e s u l t s CO - zrlltlal concentrat1on of 501 ld o b t a i n e d w i t h t h e d a t a t h a t a r e c h a r a c t e r i s - t i c f o r s u p e r c o n d u c t o r s w i th c e n t r a l t i n substance at a given temperature. s o u r c e is c a r r i e f o u t . The Jk v a l u e ( w i t h o u t Prospect production of superconductors' copper ) of 2.3~10 A/cmein magnet ic f i e l d 10 T is shown to be achieved on samples with cent- with extended %in sources IS in m y ways r a l t i n s o u r c e . confirmed by the results of investigations

known E3-61, where the process of such super- conductors production is not described in de- tails. The aim of this work is to investigate

I. I NTRODUCT I ON and develop different patterns of production : of stabi 1 ized mult ifi lamentary superconduc- kltifilmntary superconductors tors with extended tin sources, that make it

produced by the internal tin method ensure possible to vary over wide range the content the achievement of high current-carrying abi- of stabilizing copper, in a wire, and to esti- lity UP to 2x10 A/cmg in magnetic fields of mate their superconducting properties depen- 10 T at 4.2 K arid 5.1x104A/cme in 16 T Ell. ding upon heat treatment regime as well..

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However, the given parameters of criti-

ry superconductors with central tin source. It seem advantageous for resons of reliali- Vacuummelted copper and high purity bility to use extended tin source wires for !niobium of electron-beam melting, were used practical application in magnetic systems, as initial materials. 19-cored hexagonal rods being manufactured by the wind-and-react me- were used as starting copper-niobium precur- thod. The reduction of tin source diameter sors. They were cut to lengths and built up resulted from this, improves the conditions in a tube assembly, that containes niobium of diffusion processes of tin redistribution diffusion barrier in peripherycal part and from the alloy on its base into the copper high pure copper external cladding. The as- matrix, containing Nb filaments. It occurs as 'sembly with outside diameter 100 mm was a result of increase of the ratio: tin source avacuated and hot extruded on the mandrel. /alloy with copper matrix interaction surface :The extruded tube was deformed by drawing

Manuscript received June 24. 1991 gonal rod was cut to lengths and heat treated.

cal current were achieved for mult if ilamenta- I I. RESULTS AND DISCUSSION

I ;up to hollow hexagonal rod production. Hexa-

0018-9464/92$03.00 0 1992 IEEE

Then 7 rods were c o l l e c t e d i n a copper tube and only a f te r t h a t , t h e hexagonal e l e m n t channels were f i l l e d with a t in-base a l loy . So, i t becomes possible t o g e t a precursor where mechanical p r o p e r t i e s of ex te rna l clad- ding and co res are considerably closer t o each o the r than those in known p a t t e r n s of product ion of superconductors with extended t i n sources. A t t he same time t h e prob<&ility o f N b f i l amen t s brealtage in t h e process of. deformation up t o t h e f i n a l d i m e t e r is a l s o considerably diminished. Fig. 1 arid 2 show the cross s e c t i o n of wire at d i f f e r e n t stages of its production.

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t ioris, f'or example, i n solenoid windings, de- slgried ror achievements of extremly s t r o n g m g n e t i c f i e l d s , t he content of s t a b i l i z i n g copper in a wire should be reduced up t o 302. TO produce conductors with t h e indicated small amount of' copper the l a t t e r wras remved from hexagonal subelerrents bef'os-e t h e i r a.;sern- blying i n t o ex te rna l copper tube by e t ch ing i n HN133. Then t h e wire w a s produced by t h e <above merit ioried pa t t s rn . Fig. 3 shows t h e CT'OSC: s e c t i o n o f t h e wire with 30% of copper.

P ig . 1. Cross s e c t i o n of t h e p r e c u r s o r b e f o r e t h e o p e r a t i o n of c h a n n e l s f i l l i ~ g w i t h t i n a l l o y . h'ig. 3 . Cross sec t . i on of wire w i t . 1 1 'i t i n

sources and -30% Cu.

E' ip.2. C r o s s s e c t i o n of wire w i t h 'i t i n s o u r - ces and ti0 X of s t a b i l i z i n g copper .

The proposed p a t t e r n of wire production presumes t o o b t a i n 50-80% of stabilizing cop- per i n t he conductor cross s e c t l o n without considerable d i s t o r t i o n of geometry of Nb f i - lmnts. However, f o r a number of appl ica-

The wires produced by t h e two proposed p a t t e r n s had a good workabi l i ty t h a t made i t possible t o produce up t o 0.3 mm diameter w i - r e s without breakage. An add i t iorial evidence of t he f a c t t h a t 1 .0 mm wires have enough re- sourse of p l a s t i c i t y is that t h e wire w i t k i - s t and without breakage a 1% d t w i s t i n g opera- t ion. As it has been shown bef'ore C l I , con- ductors be ing produced by t h e in t e rna l t i n method, e x i b i t a considerably mre s t r o n g dependence o r current-ccurying ab i 1 i t y upon heat t reatment regimf;.s, than the wires, pro- duced by "brorize'l method. Thir; is coririected with prevalence of' 1 iquid phase processes of wire components d i f f u s i o n i n t e r a c t ion at d i f f e r e n t stages of heat treatment. To deter- mine a heat t r e a t m n t regime prel iminary i w e s t i gat i oris were conducted on samples, t h a t were i n f.act_ e l e m n t s of. conductors w i t h '7' t i n sources. Fig. 4 shows the c r o s s s e c t i o n of this elerrwit..

E'ig.4. Cross s e c t i o n of wire w i t h c e n t r a l t i n s o u r c e

Wirg samples were heat t r e a t e d at 700-780 C for 24-170 h. SEM inves t iga t ion of Nb Sn l a y e r ' s structure v e r i f i e d the forma- t i o n of homgeneous s t r u c t u r e from equiaxed g ra ins all over t he completely reac ted fila- ments. The composition o f NgSn l aye r ac ross the fi lament s e c t i o n is homogeneous wi th in 1%. Long length (100 m) wire samples i n t h e form of solenoid inserts were measured i n the f i e l d s up t o 16 T ( t a b l e l ) .

TABLE 1 CURRENT-CARRYING ABILITY OF WIRES WITH

CENTRAL TIN CORE .

Wire d i a Critical cu r ren t ( A ) i n magnetic m f i e l d (T)

10 12 1 4 16

1.0 450 385 255 120 0. 8 335 212 120 7 0

With the aim of modelling t h e condi t ions of d i f f u s i o n process running in the wires with extended t i n sources , t h e wire with cen- tral t l n core w a s deformed t o 0 .4 m. As fol- lows from the d a t a of critical cu r ren t densi- t y measurements, t he value of J c i n magnetic f i e l d s up t o 15 T exceeds the u s u a l l y achie- vable i n 0.8-1.0 mrn wires ( f ig . 5).

Magnetic field , T

p i g . 5 . C u r r e n t - c a r r y i n g c a p a c i t y of s i n g l e c o r e s u p e r c o n d u c t o r s . Uiameter: 1 - 0 . 4 mm; 2 - 0 . 8 mm;

3 - 0 . 9 mm.

The cr i t i cal cu r ren t dens i t Y i n the f i e l d of' 10 T reaches 23x10 A/cm* f o r d 0.4 mm wire, t h a t is two times as l a rge as the corresponding value f o r JZ 0.8 m wire.

As i t has a l ready been noted, conductors with extended t in sources a r e charac te r ized by an i n c r e m x l value of S/V r a t i o , that s t rong ly e f ' fec t s t h e k i n e t i c s of' l i q u i d pha- s e in t e rac t ion of t in -base a l l o y with copper matrix, conta in ing niobium f i laments .

Taking the received r e s u l t s i n to account p re l imiriary inves t iga t ions on cur ren t -car - ry ing abi 1 i t y of' superconductors conta in ing 60 % of s t a b i l i z i n g copper, were conducted. Heat treatment w a s c a r r i e d out at 575-700'C. The masured values of hea t - t r ea t ed samples superconducting p rope r t i e s a r e given i n tab- l e 2.

SUPERCONDUCT ING F'ROPERT IES OF fl 1.0 MM WIRES WITH 60 % OF STABILIZING COPPER

TABLE 2

-5 2 Heat t r e a t . J k x10 A/cm Tc. 1-1. Tc.m. Tc. s.

regime, (by bronze) K K K ' C , h B - 8 T

600 24 0.5 14.6 11.5 9.1 650 48 , 1.69 17.8 16.6 15.9 6'75 48 1.74 17.7 15.1 12.2 700 48 1.82 17.2 14.6 9.8

Tc.n. , T c . m , Tcs. - normal, medium and superconduct irig temperatures of trans1 t ion inLo superconduct ing s t a t e .

869 Attention should be paid to the fact t h a t

unl i ke conductors w i th a central t in source,

treatment temperature of' 600 C a considerable formtion of' Nb3Sn lavers, takes place simul- taneously with the process of tin redistribu- tion into copper matrix. So. superconductors current-carrying ability even a f t e r t-iolding f'or 24 h at 600'C M e s up 5x10 Aicm2 in the f'ielrl of' 8 T.

And the composition of' Nb3Sn phase, judging by the Tc value mea.;ured by the in- duct ive method, dif'f'ers f'rom stoichiometric composition ( T c . ri = 14.6 K).

As it was expected, the processes of tin redistribution and of. Nb Sn layers f'ormtiori is running considerably faster. After heat treatment at 650OC for 48 ki a high value Jc = 1.EYx-10 A/cm in rragnetic field 8 T is achieved at a corresponding high value of Tc. n = 17. 8 K.

A t the present, stage of investigation an opt imization of heat treatment regimes for conductors with 30 Z, of. stabilizing copper w a s not carried out. Nevertheless, current- carrying ability after heat treatment conduc- ted at 7OO0C for 48 h makes up

5 (1.8-2.0)x10 A/cmZ in the magnetic, f'ield of 8 T and 3 . 7 ~ 1 0 A/cm2 in the magnetic f ' i e l d of 15 T.

supel,i--- ,mductor-s be ing invest, igated at heat 0

4

5

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I I I. CONCLUS ION

The main stages of the process of' pro- duction of multifilmntmy stabilized Nb3Sn base superconductors with exterided tin sour- ces arid niobium l"i1aments size down to 1 rrcm are investigated. A posc;ibi 1 ity of production of superconductors with the ztabil izing cop- per content from 25 to 60 %, by the pattern suggested i s shown. On the G,se of the re- sults of' pre l imiriary investigations of. heat treatment pararwters interconnect ion with su- perconduct ing properties, .it w a s cs tabl ished that cr 1 t i cal current dens i ty w i thout copper) attains 2.0~10 A/cm2in the field of 8 T. 5

ACKNOkLEDGMENTS

The authors would I ike to t h a n k Kozlen- kova N. I. , Erokhina I. V. for conduct ing Tc meL=urementr;, Kl imenko E. Ju. . Kruclov V. S. , Davlatjan T. A. ( Institute of Atomic Energy) For conduct ing invest igat ions 01 developed superconductors current-carrying capac itv.

REFERENCES L 1 J V . i . f ' an t sy rny , A . K. Sh ikov , 1. 1. Uavydov, '

e t a l . "The s t u d y of s t r u c t u r e and pro- p e r t i e s o f Nb S n i a y e r v i n mui t i f i l amen- t a r y supe rconduc t .o r s , manufac tured by' t h e i n t e r n a l t i n method" P r e s e n t e d a t Appl ied S u p e r c o n d u c t i v i t y Confe rence , 6 o u l d e r , USA, 1 9 Y O .

L Z 1. V . Nikolaenko, G . 1. U a t a l i n , l z v e s t i y a H , M e t a i l y , N3, 1983 ( i n r u s s i a n ) .

L Y I U. H. Smat.hers, I-'. M. 0 Leary , M . M . S t e e v e s , M . 0. Koeiiig " P r o d u c t i o n of t i n c o r e modi-' t i e d j e i i y - r o l l c a b l e f o r t h e M l T m u l t i - purpose c o i l " P r e s e n t e d a t t h e Magnet Techno Logy Conference- 1 U . 80s t o n , Massa- c h u s e t s , S e p t . 1 9 8 ' f .

a l . 'Nb3Sn s u p e r c o n d u c t i n g c a b l e s p roces - s e d by i n t e r n a l t i n d i f f u s i o n " I T r a n s a c t i o n s on Magne t i c s , v . MAG- 1'3, 1 9 8 9 , 3 , p.1131.

L S I E . Gregory , G . M . Ozeryansky , H. M. S c h a d i e r e t . al. "An i n t e r n a l t i n conduc to r w i t h Nb-1 u t X T i f i l a m e n t s " P r e s e n t e d a t ICMC, Los-Angeles , J u l y , 1989.

L 6 i J . -Q. Xu, W. Speck ing , H . O b s t , E . S e i b t , k. F' lukiger "Supe rconduc t ing and m e - t a l l u r g i c a l p r o p e r t i e s of NbjSn wires p rocessed by. i n t e r n a l t i n r o u t e i n c l u - d i n g h y d r o s t a t i c e x t r u s i o n " Cryoge- n i c s , 1989, v . 2 9 , N 2 , p . 8 7 .

14.1 K. Yosh izak i , U. l ' aguchi , F. Fuj iwara e t