PRESENT STATUS OF A15 COMPOUNDS

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PRESENT STATUS OF A15 COMPOUNDS

H. Hirabayashi

To cite this version:

H. Hirabayashi. PRESENT STATUS OF A15 COMPOUNDS. Journal de Physique Colloques, 1984,

45 (C1), pp.C1-359-C1-364. �10.1051/jphyscol:1984173�. �jpa-00223729�

JOURNAL DE PHYSIQUE

Colloque C l , supplément au n° 1, Tome *5, janvier 198* page Cl-359

PRESENT STATUS OF A15 COMPOUNDS

H. Hirabayashi

KEK, National Laboratory for High Energy Physics, Oho-maehi, Tsukuba-gun, Ibaraki-ken, SO5, Japan

Résumé - Une revue du développement des supraconducteurs A15 est présentée du point de vue pratique de l'utilisateur. Les procédés de fabrication et les caractéristiques des ttt^Sn, V3Sn et Nbg (Al, Ge) sont présentés brièvement, avec les améliorations récemment apportées. Ce rapport présente également les problèmes que pose l'application de composés supraconducteurs aux aimants.

Abstract - A review on the development of A15 compound superconductors is given from the practical point of view of a user. The manufacturing processes, characteristics of Nb.Sn, V,Ga and Nb_(Al,Ge) are briefly discussed together with their recent improvements. The problems in the applications of the compound conductors for magnets are also discussed.

Since the pioneering work on the practical use of V_Ga at Japanese National Research Institute for Metal (NRIM)/1/, the increased demands for high T , H „ and J in the laboratory, fusion and accelerator magnets, have promoted the development or stabilized A15 superconductors in Europe, Japan and the United States. As is well known, A15 intermetallic compounds are very hard and brittle, therefore, it is impossible to fabricate these materials into the wire conductors by a simple extruding and drawing technique as used in NbTi alloy superconductors. The fabrication of A15 compounds requires complicated techniques to realize their excellent characteristics. Some reviews on the superconductors, including A15 compounds, have been already written by other authors./2,3/ In this paper, therefore, a brief up-to-date description of the practical A15 compounds is given from the view point of practical applications.

I - MATERIALS AND STABILIZED CONDUCTORS

As the results of long term basic studies on A15 intermetallic compounds at many laboratories and industries, now we can utilize the following compound materials:

V_Ga, Nb Sn, Nb,(Al,Ge), Nb.Al, Nb Ge etc. These materials are fabricated to the stabilized superconductors By the various processes as described in the paragraph II. The critical temperatures (T ) and the upper critical fields (H .) at 4.2 K of the typical A15 compounds are summarized in Table 1. The materials xn Table 1 are represented according to the present practical availabilities for the magnet applications. Other A15 compounds, unlisted here, are still under basic studies, therefore, these materials are not mentioned in this paper.

There are several cross-sectional structures of A15 superconductors: tape, round

wire^ rectangular conductor, compacted strands, hollow conductor etc. To obtain the

excellent stability conditions, A15 compound superconductors are usually fabricated

in the forms of stabilized multifilamentary conductors even in the form of tape

conductor. Each A15 compound filament has a very small diameter of a few urn and

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984173

(21-360 JOURNAL DE PHYSIQUE

quite many filaments are twisted in the stabilizing material. In most cases, the stabilizing material is oxygen free high purity copper. The medium and large current capacity superconductors can be made of the small current capacity

conductors by the stranding technique, therefore, the fabrication technique of the multifilamentary A15 compound wire of a diameter around 1

is the essential problem for the industrial production.

Material Tc (K) Hc2 (T) at 4.2 K

Table 1. Critical parameters of typical A15 compounds.

I1 - FABRICATION PROCESSES

Several processes of the fabrication of A15 compounds have been developed:

composite/4/, in situ/5/, liquid quenching/6/, deposition/7/, powder metallurgy and infiltration/8,9/. These processes are as follows.

The composite process is a general term for the conventional bronze/lO/, external tin diffusion/ll/, internal tin diffusion/l2,13,14/ and modified jelly ro11/15/

methods. The conventional bronze method is the most established process in which the core material (Nb or V) reacts with the diffusing material (Sn or Ga) in the bronze matrix. This method is widely used in the industries to produce

multifilamentary A15 compound superconductors. The large current capacity A15 Nb Sn stabilized conductor, used in the large coils till 1982, were the products of the 3 conventional bronze process. /16,17/

The external tin diffusion method was developed to avoid the intermediate annealings in the conventional bronze method. Tin is plated on the surface of final size Cu-Nb composite and then reacted. There are some difficulties in this method associated with the so-called Kirkendall effect.

There are three methods of the internal tin diffusion process: Mitsubishi,IGC method, ETL-Sumitorno solid-liquid method and Holec-ECN mehtod. The former two methods are available for large scale productions, however, the latter is still in the semi-industrial scale.

The modified jelly roll (MJR) technique has been developed by Teledyne Wah Chang. A major advantage of the MJR technique is to leave out the procedures of rebundling, the second extrusion, drawing and annealing, which required in the conventional bronze solid diffusion techniques.

In the in situ process, the Nb(V) dendrites precipitated in the Cu-Nb(Cu-V) binary

alloy at the arc-melting process are used as the cores, and severely worked by

cold-rolling and cold-drawing. If the innumerable dendrites uniformly distributed

are drawn into the long fine filaments in the worked alley, Sn(Ga) can easily

diffuse from the outside into, the Nb(V) cores and resultantly the Nb3Sn(V3Ga)

compound fibers are produced in the alloy. After numerous studies on this process,

now the V Ga conductors are produced by the consumable electrode arc-melting

technique in the semi-industrial production scale./l8/ 3

The powder metallurgy process to produce Nb Sn and Nb A1 have been studied by several authors. A newly developed liquid quenching zechnique on a hot substrate is

applied to produce the bcc phase ternary Nb-Al-Ge alloys at NRIM./19/ The A15 Nb (A1,Ge) compounds, having very high H of 40 T at 4.2 K and large J in high fields, have been successfully produced

gy the transformation from the guctile supersaturated bcc solid solutions. A continuous plasma-CVD apparatus for producing Nb3Ge tape with large J in high magnetic field has been recently developed in NRIM.

These processes, howeve?, are still under development stages.

111 - IMPROVEMENTS IN PRACTICAL COMPOSITE CONDUCTORS

Recently some important improvements in the composite Nb Sn and V Ga conductors have

3 3

been made by additions of the third element to the core and/or to the matrix. The kinds of the third element are Ti, Ta, In, Mg, Hf, Zr,Al,Ga etc. The addition of the third element to the Nb Sn compound conductors was tried at BNL using Ta.1201 From the practical point of3view, the most important additional element seems to be Ti to the core and/or to the bronze matrix. There are many reports on the effects of Ti addition to the Nb Sn conductors./21,22/ In the case of Nb Sn conductors,

3 3

annexed Ti is easily incorporated into the Nb Sn phase, and the improvements in the Nb Sn formation rate, T , Hc2 and J in high lields are obtained. The optimum amounts of added Ti to fhe core andCthe bronze matrix are around 0.7 wt% and 0.2 3 wt%, respectively. The economic method, however, is not to add Ti to the Nb core but to add Ti to the bronze matrix. The critical parameters, Hc2 and J , of this type of improved Nb Sn conductor are very high; the is considered 80 be higher than 25 T at 4.2 K 3 and the overall J is near 35 A/mmyc2at 15 T. Although the reasons of such high Hc2 and J in tfie improved conductors are not studied in details, there are some specul$tions which produce a strong pinning mechanism. The improved performance of the Ti added Nb Sn conductors may exceed that of the V Ga conductors in the critical current denslty at the region of very high fields. 3 3 The Ti addition to the matrix also improved the mechanical properties of the bronze processed Nb Sn conductors. The strain tolerance were improved as shown in Figure 1.

The industrial productions of the Ti added Nb Sn conductors were recently initiated 3 in Japan under the leadership of NRIM. The TI and other element additions could be 3 applied to many kinds of composite conductors. In fact many authors are making the trial additions of the third element to various kinds of A15 conductors and some of them are obtaining good results.

pure

i,\;\

bronze I ... :::

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Maximum strain %

Figure 1 - Normalized critical current J versus strain curves of the Ti added Nb Sn

conductor (by courtesy of theC~urukawa Electric Co. Ltd.).

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IV - APPLICATIONS OF A15 SUPERCONDUCTORS

There are three typical magnets in which the A15 compound superconductors are required: high field laboratory magnets, fusion magnets and high energy accelerator magnets.

For high field laboratory magnets, very high upper critical fields (Hc2) and high critical current (J

are required. In general the required current capacities are not so large. The types of magnets are mostly solenoids, therefore, the structure is very simple. The superconductors in the solenoid are usually graded depending upon the magnetic field strength i.e. the inner superconductor requires the higher critical field. For example, the inner solenoids are some times wound with the V Ga tape conductors instead of the Nb Sn conductors, because the V Ga tape conductors 3 are having higher critical curren2 densities than that of the ib Sn conductors up to 20 T. This type of magnets is normally wound with the reacted superconductors, 3 therefore, the allowable bending strains in the inner layers are the important constraints. The application of multifilamentary tapes to the inner layers gives a solution for this problem.

For the fusion magnets, large current capacity superconductors working around 12 T are required. The current capacities are as large as 10 kA per superconductor. Due to the great electromagnetic forces in the magnet coils, the A15 compound

superconductors can not survive without the thick stabilizers and reinforcements.

The stabilization conditions of the fusion magnets are moderate, namely, cryostable.

These design conditions not always require high current densities of superconductors at high fields. The important problem is how to make the reliable large current capacity superconductors in large scale. This is the problem of industries. It seems that the industries are getting the solution for this problem. Another problem in the A15 superconductors for the fusion magnets is the allowable bending strain in the thick conductor. For improvement of the mechanical properties of Nb Sn conductors, the Ti addition is very attractive as mentioned above. Anyway the

~ 1 3 compound superconductors for the fusion magnets should to be designed in the close relation to the stabilizers and reinforcements. There are many varieties of the conductor designs.

In high energy physics, the high field magnets for the next generation of high energy accelerators are under development/23,24/. The special features of the accelerator magnets are the high current densities in the magnet coils. The coils are not designed with the cryogenic stabilization conditions but designed with the burn-out safety conditions to save the required materials. For instance, an average coil current density is as high as 300 A/mm at LO T. The high coil current density inevitably requires an extremely high critical current density in the A15

superconductor in the field region below 12 T. Without the extremely high critical current density in the superconductor, an excellent design of the accelerator magnet can not be advanced. The high field accelerator magnets beyond 10 T are not easily developed by the reason of the difficulties in the coil supporting structures.

V - SUMMARY OF CRITICAL CURRENT DENSITIES

As is well known, the critical current density is one of the most important

parameters in the practical application of the A15 compound conductors. The present relations between the critical current densities and the magnetic field for the A15 NbgSn superconductors produced by different processes are summarized in Figure 2.

These data are mostly taken with the industrial products.

As is seen in Figure 2, the internal tin processed superconductors have very high

current densities in the region below 12 T. On the other hand, the improved bronze

processed superconductors with the addition of Ti to the matrix have the high

critical current in the region above 13 T.

The in situ processed V Ga superconductor has the highest current density in the region up to 20 T. But the production scale is still in the semi-industrial stage 3 and the current capacity per conductor is small. The in situ processed Nb Sn superconductor has the higher critical current density than that of the composite 3 processed Nb Sn superconductors, however, the production technique is also still in the development stage. The addition of Ti to the in situ processed Nb Sn produces 3 an improvement of high field performance in analogy with bronze processed Nb Sn. 3

3

Holec (Internal Tin Tube)

I

10 6 8 10 12

14

Magnetic Field (TI

Figure 2 - Overall critical current density (J

without stabilizers versus magnetic field curves of the Nb Sn compound guperconductors produced by various

processes. 3

VI - CONCLUSIONS

Present status of the A15 compound superconductors could be summarized as follows.

1.

For the applications below 12 T, there are many kinds of the A15 superconductors.

If the higher current density is required, the use of the internal tin diffusion processed Nb Sn conductors is recommended, however, great care on the mechanical properties must be taken for the degradation with bending strains. 3

2. For the application above 12 T, the Ti added Nb Sn conductors are recommended, because of their high critical current densities and good mechanical properties 3 at high fields. Now this type of conductors are commercially available.

3. The in situ processed V Ga conductors are recommended for the application to the high field laboratory solenoids up to 3 18 T, because of their extremely high critical current densities and excellent mechanical properties. In situ processed Nb Sn conductors also should be quickly developed.

4. The new liqurd quenching and transformation process of Nb (A1,Ge) conductors 3

should be established for the next generation A15 compouna superconductor.

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5. As the brittle nature of the A15 compounds is essential, the stabilization and reinforcement methods in the practical uses of these compounds are must be further studied.

VII - ACKNOWLEDGEMENTS

The author wishes to express his gratitude to Dr. K. Tachikawa of NRIM for his valuable suggestions in preparation of this paper. The discussions with Dr. K.

Hosoyama of KEK and Dr. Y. Tanaka of Furukawa Electric Co., Ltd. on the A15 compounds are also appreciated.

VIII - REFERENCES

/I/ Tachikawa (K.), Proc. the 3rd Intern. Cryog. Eng. Conf., Iliffe Science and Tech., Surrey, 1970, 339.

/2/ Suenaga (M.) and Clark (A.F.), A15 Superconductors, Plenum Press, New York,

1980.

/3/ Hilman (H.), Superconductor material science, Ed. by Foner (S) and Schartz (B.B.), Plenum Pub., New York, 1981, 275.

/4/ Kaufman (A.R.) and Pickett (J.J.), Bull. Am. Phys. Soc., 1970, 15, 838.

/5/ Tsuei (C.C.), Science, 1973, 180, 57.

/6/ Togano (K.), Takeuchi (T.) and Tachikawa (K.), Appl. Phys. Lett., 1982, 41, 199.

/7/ Dahlgren (S.D.), Suenaga (M.) and Luhman (T.S.), J. Appl. Phys. Lett.., 1974, 45, 5462.

/8/ Thieme (C.L.H.), Zhang (H.), Otubo (J.), Pourrahimi (S.), Schwartz (B.B.) and Forner (S.), IEEE Trans. Mag., 1983, MAG-19, 567.

/9/ Hemachalam (K.) and Pickus (M.R.), IEEE Trans. Mag., 1977, MAG-13, 466.

/lo/ Hillmann (H.), Pfister (H.), Springer (E.), Wilhelm (M.), Wohlleben (K.), A15 Superconductors, Ed. by Sue~~aga (M.) and Clark (A.F.), Plenum Press, New York, 1980, 17.

1111 Suenaga (M.) and Sampson (W.B.), Appl. Phys. Lett., 1972, 20, 443.

/12/ Hashimoto (Y.), Yoshizaki (K.) and Tanaka (M.), Proc. of 5th 1ntern.Cryog. Eng.

Conf., Kyoto, Japan, 1974, 332.

/13/ Schwa11 (R.E.'), Ozeryansky (G.M.), Hazelton (D.W.), Cogan (S.F.) and Rose (R.M.), IEEE Trans. Mag., 1983, MAG-19, 1135.

1141 Okuda (S.), Nagata (M.), Yokota (M.), Watanabe (M.) and Kimura (Y.),

Filamentary A15 sSuperconductors, Ed. by Suenaga (M.) and Clark (A.F.), Plenum Press, New York, 1980, 81.

/15/ McDonald (W.K.), Composite superconductor construction by modified jelly roll method, Teledyne Wah Chang, patent pending.

1161 Sanger (P.A.) , Adam (E.), Grabinsky (G.), Gregory (E.), Ioriatti (E.) and Roemer (F.), Proc. of the 9th Fusion Symposium on Engineering Problems of Fusion Research, Chicago, 1981.

1171 Andow (T.), Shimamoto (S.), Hiyama (T.), Tsuji (H.), Takahashi (Y.), Nishi (M.), Yoshida (K.), Tada (E.), Okuno (K.), Koizumi (K.), Kato (T.), Nakajima (H.), Dresner (L.), Iida (F.), Sanada (Y.), Shimada (M.), Takahashi (0.) and Yasukochi (K.), IEEE Trans. Mag., 1983, MAG-19, 312.

/18/ Kumakura (H.), Togano (K.) and Tachikawa (K.), Adv. in Cryog. Eng., 1982, 28, 515.

/19/ Togano (K.), Kumakura (H.), Takeuchi (T.) and Tachikawa (K.), IEEE Trans. Mag., 1983, MAG-19, 414.

1201 Suenaga (M.), Aihara (K.), Kaiho (K.) and Luhman (T.S.), Adv. Cryog. Eng. 1980, 26.

/21/ Sekine (H.), Iij,ima (Y.), Itoh

Tachikawa (K.), Tanaka (K.) and Furuto (Y.), IEEE Trans. Mag., 1983, MAG-19, 1429.

/22/ Kamata (K.), Tada (N.), Itoh (K.) and Tachikawa

IEEE Trans. Mag., 1983, MAG-19, 1433.

/23/ H. Hirabaxashi, IEEE Trans. Mag., 1983, MAG-19, 198.

1241 Taylor (C.), Meuser ( R . ) , Caspi (S.), Gilbert (W.), Hassenzahl (W.), Peters

(C.), Schafer (R.) and Wolgast (R.), IEEE Trans. Mag., 1983, MAG-19, 1398.