EXPLOSIVE WELDING OF MULTIFILAMENTARY NbTi50-Cu COMPOSITE SUPERCONDUCTOR

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EXPLOSIVE WELDING OF MULTIFILAMENTARY NbTi50-Cu COMPOSITE SUPERCONDUCTOR

Zhang Xudong, Peng Wenan, Xiong Shougao, Ye Yongcai

To cite this version:

Zhang Xudong, Peng Wenan, Xiong Shougao, Ye Yongcai. EXPLOSIVE WELDING OF MULTI- FILAMENTARY NbTi50-Cu COMPOSITE SUPERCONDUCTOR. Journal de Physique Colloques, 1984, 45 (C1), pp.C1-611-C1-614. �10.1051/jphyscol:19841124�. �jpa-00223594�

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Colloque C1, supplbment a u no 1, Tome 45, janvier 1984 page C1-611

EXPLOSIVE WELDING OF MULTIFILAMENTARY NbTi50-Cu COMPOSITE SUPERCONDU.CTOR

Zhang Xudong, Peng Wenan, Xiong Shougao and Y e Yongcai Baoji I n s t i t u t e for Non-ferrous P4e'etaZ Research, P.O. Box 7 1 , Baoji, Shaanxi, China

Rssumg- Cet article dscrit le procgd6 de soudure par explosif de supraconducteurs multifilamentaires et les proprigtgs Slec- triques et mscaniques des liaisons rsalisges. Ces liaisons of- frent un excellent contact mEtallurqique du cuivre aussi bien que des filaments Nb Ti et prgsentent d'excellentes proprietes en flexion et une haute tenue a la traction (100 % de la rgsistance du supraconducteur ) . Des liaisons de section 3 , 6 x 1,8 mm2 posssdent un courant critique de 1801 A (5T 2 4,2K), soit 90 % du su raconducteur, et une rgsistance glectrique de 9.5 x 10-lg n a ^{4,2X et 5}, 5T. Ces resultats sont utiles pour la jonction de supraconducteurs de grande section ainsi que pour les amenges de courant des aimants supraconducteurs.

Abstract

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The explosive welding technique of multifilamen- t a r y superconductor, t h e mechanical and superconducting pro- p e r t i e s of j o i n t s a r e presented i n t h i s paper. Excellent m e t a l l u r g i c a l bonding i s found both i n Cu and i n NbTi f i l a - ments of t h e j o i n t s . The j o i n t s have excellent bending pro- p e r t y and high t e n s i l e s t r e n g t h (corresponding t o 100% of the s t r e n g t h of the superconductor). The supe conductive 5

j o i n t s with t h e cross s e c t i o n of 3.6 X 1.8 mm have a c r i t i - c a l current of 1801A (51 a t 4.2K), corresponding t o 90% of t h a t of t h e superconductor a t t h e same cond tions. The elec- t r i c r e s i s t a n c e of t h e j o i n t s i s 9.5 X 10-1

&

^{a t}^4.2K, ^5.5T.

The research r e s u l t s can be used f o r joining of long superconductors with l a r g e cross s e c t i o n a s well a s t h e current l e a d s of the superconducting magnet.

INTRODUCTION

I n a p p l i c a t i o n mf l a r g e p r a c t i c a l superconducting magnets, long conductors with l a r g e cross s e c t i o n a r e required. Limited by equipments and techniques, i t i s d i f f i c u l t t o provide conductors with s u f f i c i e n t length. However, welding process i s a t t a i n a b l e t o be an e f f e c t i v e approach.

There a r e many joining methods f o r superconductors. For l a r g e and medium s i z e d magnets, Brazin / I / , Cold welding/2.3/ explosive welding/4/ and d i f f u s i o n welding$5/ etc. a r e a l l common techniques. Ex- plosive welding i s one of t h e e f f e c t i v e mens. A magnet c o i l was wound by Imperial Metal I n d u s t r i e s Ltd. using MbTi-Cu conductor with many explosive by welded joints/4/. The s i z e of the conductor w a s 10 X 1.8 mm. The current capacity of t h e j o i n t wa 8 ¹⁵²⁰^{A ,} ^g^k

4.2 K , 6T. The low-lemperature r e s i s t a n c e i s 2 X 10- R . I n order Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19841124

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C1-612 JOURNAL DE PHYSIQUE

to prepare maximum length conductors for Yin-Yang shaped large coil applied in controlled thermonuclear fusion reactors, the multicore WbTi-Cu conductor of 6 X 6 mm was explosively welded by lawxence livermore laboratory in U.S.A./4/, At 4.2 K , 6T. The critical current of the joints was 800 A, and its low-temperature resistance was 3 X l0'l%2.

In the explosive welding process, shapes of joints are a decisive factor. According to the feature of the explosive welding, the scarf lap, a correct approach, has been adopted. It not only eliminates the disadvantages of the over lapping, but also benefits energy transmission on the interface during the joining, thus formingmetal jet and attaining the joining of each component including superconducting filaments.

The aim of the present study is providing welding techniques for the superconductors applied in partical accelerators and superconducting generators

.

EXPERLMEItTAL PROCEDURE

The materials used in our experRments are multifilamentary NbTi50-Cu composite conductors of 7 X 3.6 mm ( Cu / NbTi = 10, filament number 204, diameter of filament 11Ofim ) snd 3.6 X 1.8 mm ( Cu / NbTi = 5, filament number 174, diameter of filament 94Hm ), The distribution of NbTi filaments is toroidal.

The arrangement of the conductor during the welding is shown in Fig.

1, welding was done with Nitramon. The explosion velosity is 2000- 2400 m / sec., Copper plates are used as driver and base plates in the test. The tapers of the ends were prepared by a special tool. To obtain an optimum welding,tapersshould be kept clean and dry. The disposition of the conductors has an direct effect on welding results, therefore, one should operate carefully before welding and try hard to get a perfect coincidence of the tapers.

RESULTS AND ANALYSIS

1. Joinin condition of oints. A good joining in the joint arts of each compfnent INbTi wit: NbTi, NbTi with Cu, and Cu with Cu? can be clearly seen from Fig. 2, 3, 4., 5, and 6. it is shown in Fig. 4 that an authentic solid (state) joxning between NbTi has been gained.

After observing many cross-sections of joints, we found that it is no problem to join NbTi filaments of the upper conductor collided with that of the lower conductor. However, it is impossible to join a11 NbTi filaments. The only thing we could do is to join filaments as many as possible.

2. lechanical properties of joints. The mehanical properties of the joints at room temperature are shown in Table 1. It is obvious that the tensile strength for the specimens with joints and without joints is about the same. A11 fractures are far from the joints. When the welded samples wers subjected to bend deformation w i t h radius 1.5 mm and bend angle 180 , no crack has been found.

3. Superconductina properties of joint. The critical current and low-temperature resistance of the oint are measured by induction and inductive attenuation methods

?

see Fig. 7, 8 1. The critical current at 5Td 4.2 K is 1801 A and the low-temperature resistance is 9.5 X 10- Asat 4.2 K, 5.5 T. The critical current of joints is 1wo less than that of the base conductor under the same condition.

4. Joining technique. A better explosive joining technique is obtairr ed in the experiment. (see Table 2) The desposition of the conductor is of key importance in the explosive welding. In accordance with

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a t Room Temperature

specimen c o n d i t i o n r u p t u r i n t e n s i l e f r a c t u r e number l o a d (kg? s t r e n g t h p o s i t i o n

( kg/mm2 >

SB 8201 Ann. 241 .5 37.2

SB 8202' o 241 - 2 37.2

SB 8203 ^{t t} 242.0 37.3

EWB 8220 ^st 242.0 37.3 o u t s i d e t h e j o i n t

EWB 8221 ^{t t} 268.0 40.2 ¹¹

EWE 8222 ^O 240.0 37.0 $1

SB-indicates non-joint conductor. EWB-3.6 x 1.8 supr. conductor.

t h e e x p l o s i v e welding parameters provided by t h e p r e s e n t s t u d y , more p e r f e c t j o i n t s of superconductor can be gained. T h i s approach can a l s o be a p p l i e d i n j o i n i n g conventional conductors with similar cross-section.

Table 2. E x ~ l o s i v e j o i n i n g parameter f o r superconductors .. - -

conduct OF- t a p e r of d e p o s i t i o n i n i t i a l amount of e x p l o s i v e workpiece a n g l e d i s t a n c e (mm) charge (g/cm2 )

7 X 3.6 5 ^O o0 2.6

-

^3.5 ³- ^3.5

3.6 X 1.8

- 5 ^O o0 ^1.6

-

^2.5 ²

-

^2.5 ^-

CONCLUSIONS

1. Explosive welding i s a f e a s i b l e method f o r j o i n i n g of t h e m u l t i - f i l a m e n t a r y NbTi-Cu composite conductor. T h i s technique i s charc- t e r i z e d b y i t s h i g h e r r e p e a t a b i l i t y and s t a b i l i t y , as w e l l as simple o p e r a t i o n and lower c o s t .

2. The supercon.ducting j o i n t s provided by p r e s e n t s t u d y p o s s e s s sa- t i s f a c t o r y mechanical and e l e c t r i c a l p r o p e r t i e s .

The a u t h o r s wish t o thank Zhou L i a n , Xu P e i f e i , and Wan J i n , f o r t h e i r h e l p i n t h e prepa.ration of t h e manuscript and t h e measurement of t h e sample.

REFERENCES

( 1 ) A. J. Moorhead, J. J. Woodhouse and D. S. Easton "Welding of NbTi-coating copper superconductorsw ^~4Welding>), Vol. 56 ( 1 0 )

1977

( 2 ) P: ' W. Rackov, C. D. Henning llSuperconduct o r j o i n i n g method f o r l a r g e CTR magnetst1 i n proceding 6 t h symp. En g. B o b . of Fusion Reseach, s a n , Diego 1975 (IEEB, New York 1 9 7 8 593-6

( 3 ) D. N. Cornish, D. W. D e i s , and J. J. Zbasnik "Cold

-

P r e s s u r e welded j o i n t i n l a r g e m u l t i f i l a m e n t a r y NbTi superconductors"

Enginering prob. of f u s i o n Reseach proc. symp.6th San, Diego c a l i f . Nov 18

-

21 1975OIO6

( 4 ) D. N. Cornish and J. P. Zbasnick "Explosive j o i n t s i n Wb-Ti / cU composite superconductors" i n proceeding 6 t h symp. Engs

.

^probe

of Fusion Reseach. San Diego, 1975 (XBEE, New York ,9767 P106-110 ( 5 ) Charles E. Withercu t l D i f f u s i o n Welding mult'ifilamentary super-

conducting compositen <<Weldings) , Vol. 57, No. 6. June 1978

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C1-614 JOURNAL DE PHYSIQUE

I -8ectric debutor 5 ~ncbinatvn

2 -Dr,vrr plate 6 - in.tial 6~stcncc

3 LOWLT c o d u d o ~ 7 -uppar cmn4uclor

4 Base piae 8 fxplosive charso

Fig. 1. The arrangement of the conduct o r

Fig. 3. Cross-section of j o i n t X 200

Pig. 5. L o n g i t u d i n a l s e c t i o n

o f j o i n t X 10

CIIWQENT - A

Fig. 7, R e s i s t a n c e of j o i n t (4.2K)

Fig. 2. Welded NbTi f i l a m e n t s (Cu surrounding t h e f i l a m e n t s w a s d i s s o l v e d away)

Fig. 4. Welding wave of j o i n i n g

NbTi filament X 960

Fig. 6 . A welded NbTi f i l a m e n t X 96

5

F I E L D - T

Fig. 8. C r i t i c a l c u r r e n t (4.2K)