MULTI-FILAMENT SUPERCONDUCTOR WIRE PRODUCTION

Abstract: A superconductor wire (46) with multi-filaments is made by extrusion of a billet (10) formed by spiral wrapping a woven layer (20) of superconductor wires (22) and normal metal wires (24) to provide an extrusion billet which will maintain separation of component superconductor wires during extrusion and subsequent processing to ensure separation of superconductor filaments in the final product.

Description: M(LTI-FlLAMENT SUPERfONLuCTOR WIRE PRCDUCTION BACRGFDURD OF TRUE INVENTION The present invention relates to production of multifilament superconductive wires of the class comprising 5,000 - 35,000 of such filaments in a wire. The conventional technique of assembling copper-coated superconductors into a billet and extruding is unsuitable for such purpose. Generally these billets are made, under conventional practice by inserting Nb-Ti rods into copper tubes, bundling into a copper billet tube and extruding. Alternatively, a copper billet can be pre-drilled with longitudinal holes, each of which is filled by a Nb-Ti rod (per se or with a coat of copper) The technique is also used with niobium or vanadium rods which can be reacted later to form Nb3Sn or V3Ga. As the starting billet can be varied only slightly, this requires the manufacturer to make much smaller tubing, with concomitant problems related to straightness, twist and the cleanliness of the inner diameter. While other techniques have been suggested, they all have drawbacks that make their use questionable. One of the earliest suggestions was to assemble a billet with a moderate number of filaments, say 150, extrude and draw this to a size where it could be cut into 150 pieces and assembled into another billet, extruded and drawn to a wire with 150 x 150 or 22500 filaments. Unfortunately, copper and titanium from the Nb-Ti alloy filaments interdiffuse when heated for the second extrusion to an even greater extent than during the first extrusion, to form a deleterious layer around each filament. Even greater complexity is involved in Nb3Sn or V3Ga manufacture by this approach. Another prior art technique is the use of expanded Nb-Ti mesh in a "jelly roll" type billet. While this technique simplifies the manufacture of fine filaments, it has the drawback that there are periodic junctions between filaments which may limit use to d.c. coils. An additional drawback is that nonruniform filiaments are produced for very fine filaments of less than 3 microns size. Under a.c. or ramped conditions, the junctions would probably cause unacceptably high losses and magnetization effects. The expanded mesh jelly roll technique is described in U.S. patent 4,262,412 to McDonald (assigned to Teledyne Industries). It is an object of the invention to provide a means of producing fine filament superconductor overcoming the foregoing problems. It is a further object of the invention to provide a rmpercafi ductor wire with 5,000 - 35,000 filaments therein of high uniformity of cross section, with the filaments being spaced from each other. SUMMARY OF THE INVENTION The objects of the invention are met through a construction of composite superconductor which provides spread and uniformly spaced superconductor filaments. The filaments are within the range of 110 microns diameter and substantially uniform (within 2 microns) in such range. The average spacing between filaments is between 1 to 5 filament diameters. The avoidance of junctions enables usage of the composite for alternating current situations. The product is made by rolling up a spiral of a woven wire layer. The layer has x - and y - axis wires. The x-wires (substantially parallel to the axis of spiral winding) comprise, for the most part or entirely, superconductor or precursor (prior to later heating to form such superconductor) selected from the class consisting of niobium, titanium, zirconium, vanadium, alloys thereof, normal metal coated (e.g. by copper, silver, aluminum, gold, tin or indium or alloys thereof) versions, bronze (copper-tin, copper-gallium, copper-aluminum) coated or cored versions thereof (to produce, e.g. niobium stannide or vanadium gallium or niobium aluminide in later heating) and suitable forms of niobium stannide or the like (e.g. in thin layers trapped between refractory metal layers). The y-axis layers comprise a normal metal and the weave is preferrably tight enough to assure that x-wires do not slide together. In a loose weave, other means can be provided to avoid contact of wires. In rolling the woven layer into a spiral, normal metal is placed between the spiral layers -- by interleaved spiral winding therewith using continuous or discontinuous layers of normal metal foil or a normal metal woven layer or by casting low melting normal metal into a loose spiral of the main woven layer containing the xaxis superconductive wires. The spiral is wound around a normal metal core of solid or tube form. The spiral is solidified by isostatic press action or the like to form a billet, which is extruded to rod, tube or strip form. The extruded product, which is essentially completely densified, may be further worked to finer cross section. In the extrusion, through a diameter reduction ratio in the range of 5:1 to 20:1, the x-axis superconducting filaments are correspondingly reduced from typical diameter of millimeter range to final diameter of 1 to 50 microns (and through further working, after extrusion to 1 to 5 microns; 25 microns = .001 inch = 1 mil). The x-wires of superconducting material used in the original woven layer may, per se, be products of extrusion and drawing. Preferrably such wires have normal metal coatings. Other objects, features and advantages will be apparent from the following detailed description of preferred embodiments thereof taken in connection with the accompanying drawing. BRIEF DESCRIPTION OF THE DRAWING FIG,1 is an isometric sketch of billet preparation, a step in practice of a first preferred embodiment of the invention. FIG2 is cross-section view of the same billet after extrusion and further reduction; FIG.3 shows in cross-section the FIG.1 billet after extrusion into a tube and backfilling with a metal source (for later reaction with filaments, e.g. Sn for reaction with Nb, Ga for reacting with V, Al for reacting with Nb or V); FIG.4 shows, in cross-section, the FIG 3. product in multiples, hex formed and re-packed, to make a larger assembly which can be further reduced and eventually heat treated; and FIGS. 5, 5A, 5B and 6 are isometric sketches illustrating further embodiments of the invention. - DEEEILED DESCRIPTION OF PREFERRED EMEODIM#NTS FIG.1 shows that a billet 10 is made by wrapping several spiral turns of a woven metal fiber fabric 20 around a mandrel 30. The fabric can be in separate sheets for each one turn, or small groups of turns or in a single sheet spirally wound for dozens, or all of, the turns. In either case the fabric comprises superconductor wires 22 running in the length direction of mandrel 30 (i.e. essentially parallel to axis 32 of mandrel 30, the ultimate direction E of later extrusion), although a slight diagonal offset can be applied to introduce a twist into the wires 22. Crossing wires 24 of normal electrical conductivity, high thermal conductivity metal 24 are preferrably woven with wires 22. The wires 24 run essentially 90 degrees (plus or minus 30 degrees diagonal offset) with respect to longitudinal superconductor wires 22. The nature of the weave and its tightness are selected to maximize the number of superconductor wires 22, yet assure that adjacent super conductor wires do not touch (within a spiral fabric layer). Normal metal wires 26 can be interspersed in the longitudinal direction, optionally. The spiral fabric layers are interleaved with similar spiral layers of normal metal in foil form, e.g. as shown at 28, or fabric (woven or non-woven) form to assure spacing of superconductor wires in the radial direction when the spiral turns are formed. The "superconductor wire" 22 can be a Type II superconductive niobium-alloy or a precursor (e.g. niobium or vanadium) of a compound form Type II superconductive compound, e g. k3Sn or V3Ga formed by later high temperature reaction with a source of tin or gallium. Niobium aluminide and several other compounds can be formed, similarly. The alloy or compound can have two or more than two major components. Preferrably each such superconductor wire 22 is continuous for the length of billet 10. Each wire may have a normal metal coating to enhance, electrical isolation, subject to the drawback that coatings degrade smoothness over the course of working while bare metal (e.g. Nb) wires 22 would have greater tendency to smoothness and size uniformity in the course of working. The normal metal used in wires 24 (and 26, if provided) and/or in a coating, if provided, of wires 22, and in the spiral interleaving layer 28 is preferrably copper, but may be gold, silver, aluminum, or other elements or a bronze (e.g. a copper-tin or copper-gallium bronze). Combinations of normal metal can be used. Typically wires 22, 24 and 26 are 10-30 mil diameter and a woven fabric form of layers 20 would, therefore, have high spots of 20-60 mils. Coatings if employed are 1-3 mils. If copper foil is used instead of a fabric as layer 28, it would be provided in 5-20 mil thickness and fabric forms of layer 28 would be made of 5-10 mil copper wire with high spots (at fabric cross-overs) of 10-20 mils. The normal metal "wires" 24 layer 20 can be of ribbon form or of round, but lower diameter than 22 so that the fabric layer 20 comprises its component wires 22 essentially in the same (spiralled) plane. The rolled up billet 10 is initially 55-65% of theoretical density. It is isostatically pressed in accordance with preferred practice of the invention to 95-99% theoretical density then extruded and drawn to a rod form in a 100 to 1 reduction (area to area reduction, 10 to 1 on a diameter basis) to correspondingly reduce contained wires 22' (of twenty mils diameter, originally) to filaments (of two mils diameter) in a normal metal matrix derived from the normal metal wires and foil of the original billet, as shown in FIG.2. In some instances, it will be desirable to, extrude billet 10 to a tube rather than rod form, backfill the tube hole with tin or gallium or aluminum or an alloy thereof as indicated in FIG. The resultant rod can be hex formed and packed together with other similarly formed rods as shown in FIG.4, and cold worked as a group. In this way thousands or tens of thousands of filaments of the necessary 1-10 micron diameter range can be provided in a single composite conductor with only a single extrusion heating of copper in contact with niobium, or the like in its processing history, to avoid undesired diffusion (that results from prior art dual heating steps). In most embodiments it is desirable to provide an outer copper layer 42 (FIG.2) separated from the copper matrix 32 by an inert (e.g. tantalum) sheath 44, to form a final rod product 46. containing the core 34 (derived from mandrel 30 of FIG.1 or alternately a substitute core 34' as in FIG.3) surrounded by a copper matrix containing filaments 22' (derived from wires 22) in the copper matrix 32. The filaments 22' have essentially no tangential contact with each other --i.e. essentially all of the filaments being separated from each other by at least half of average filament diameter throughout 90% or more of length of rod 40, derived from billet 10 via the extrusion, and at least a micron apart, but not necessarily over 4 micron spacing, in any event. The product 46 comprising rod 40 (with its jacket 42 and barrier layer 44, applied before or after extrusion) can further reduced if desired by hot or cold swaging, drawing, rolling or other common metallurgical working techniques with associated heat treatments to optimize size and physical and electrical properties of the end product and its components. For instance the 1-2 mii filaments can be reduced further to a .02 mil size (5 microns) or less. The assemblage of FIG.4 may include interspersed kinds of component hex rods, eg, some comprising products of spiral winding and extrusion and having superconductor and a residual bronze therein and others having pure copper protected from diffusion by a tantalum layer. FIGS. 5 - 6 show two further embodiments of the invention comprising respectively, for FIG. 5, a spiral wrap 110 of a weave of wires 122 (longitudinal or x-axis) with ribbons 124 (lateral or yaxis) and for FIG. 6 a spiral 210 of a lateral series of wires 222 overlaid (or underlaid) with a foil 224. The wires 122 and 222 comprise niobium-titanium alloy with a copper coating and an interweaving diffusion barrier layer of niobium or tantalum between the alloy core and the copper coat (to prevent adverse reaction of copper with the titanium component of the alloy). The spiral may be formed as a rod or tube and processed similarly to processing of the spiral in connection with FIGS. 1 - 4 and related text above. The wires 122 and 222 are in the range of 5 - 20 mil diameter (typically 10 mils each, of which 8 - 9 mils is alloy and 1 - 2 mils is barrier layer double thicknesses -- i.e. 0.5 - 1 mil layer thicknesses appearing twice on a cross section diameter), with spacing being 1 4 mils (usually 2) between wires in FIG. 5. In FIG. 6 the wires are preferrably soldered or brazed to each other aiwor the foil using the copper coat of the wire as all or part of a soldering or brazing medium effectively made at low heats (100 - 200 C) which do not appreciably advance oxidation of the alloy or at room temperature with pressure or ultrasonic vibration. Such bonding facilitates handling of the assemblage. The ribbons 124 of FIG. 5 are typically 5 - 10 wire diameters in width, i.e. 0.05 - 0.1 inches. The spirals 110 and/or 210 can be continuous or segmented (endto-end in the lateral direction with end joints or overlaps). There may be as many as 35,000 wires 122 or 222 in the spirals of FIG. 5 or 6 (typically 20,000). A very high proportion, in the ending cross-section of the spiral after compaction and extrusion, is achieved compared to prior art systems. FIG. 5A shows a variant of the FIG. 5 construction wherein instead of using discrete ribbon foils 124, a single sheet 125 is slit with multiple through cuts 123 all parallel and lateral, for form component ribbons 124A including end ribbons a, k, and G Each of the ribbon components is corrugated and the corresponding corrugations are offset by one from adjacent ribbon component to adjacent ribbon component. Thus a wire 122-1 passes under corrugations a-l and c-l while wire 122-2 passes over ribbon components a and c but under corrugation b-l. FIG. 5B shows a further aspect of the use of FIG. 5 construction in that wires 122-M of a turn M nest with wires 122-N of the next adjacent turn N of a spiral. FIG. 6B shows a forward ribbon 124F and a rear ribbon 124R But the nesting advantage, for higher packing factor and ultimately high proportion of superconductive niobium alloy, is achieved also in the FIG. 5A and FIG 6A constructions as well, while gaining the benefits of round wire/filament form for components 122. In accordance with the present invention, bronze sources of tin, gallium or the like can be correlated with refractory metal for formation of compounds in accordance with state of the art knowledge, shown, e.g., in British patent 1,535,971 (Toshiba), J. Appl. Phys., 49:6020 (1978), U.S. patents 3,731,374 (Suenega) 3,838,503 (Suenega), 3,910,801 and 802 (Wong/Supercon,Inc.), 4,043,028 (Showa Electric). It is also contemplated that the extrusion can be supplemented or displaced by other forms of hot or cold working elongation including rolling swaging, and drawing. The spiral cylinder described above can be flattened - in some applications not requiring central axis symmetry -- to provide an elliptical (central plan symmetry) rather than a circular spiral. The spiral can be substituted by a fanfold in some instances. Further, the invention can be applied to plural superposed layers of fabric which are not part of a continuous layer. It will not be apparent to those skilled in the art that other embodiments, improvements, details, and uses can be made consistent with the letter and spirit of the foregoing disclosure and within the scope of this patent, which is limited only by the following claims, construed in accordance with the patent law, including the doctrine of equivalents. What is claimed is:

Claims: CLADSS 1. An elongated composite comprising a high conductivity normal metal matrix with dispersed continuous filaments thereof of 57ype II superconductor of a uniform diameter in the range of 1 to 10 microns and in a number in the range of 5,000 - 35,000 filaments, as made by elongating a spiral roll array of superconductor wires, which are radially and peripherally spaced. 2. Composite in accordance with claim 1 wherein the spacing is provided by multi-layer of superposed woven array of x-direction superconductive wires with y-direction normal metal elements substantially orthogonal thereto and the layers of such x and y wires being spirally wound. 3. Composite in accordance with claim 2 wherein the normal wires and matrix are made of copper. 4. Composite in accordance with claim 2 wherein the superconductive wire is niobium-titanium alloy. 5. Composite in accordance with claim 2 wherein the superconductive wire is Nb3Sn compound. 6. Composite in accordance with claim 2 wherein the superconductive wire is V3Ga compound and Nb3Al. 7. Composite in accordance with claim 2 wherein superconductive wire is a Nb3Al compound. 8. Composite in accordance with claim 2 wherein the superconductive wire composite comprises a bundle of component subcomposites, each of which has a spirally rolled up woven array of xdirection superconductive wires with y direction normal metal wires. 9. Method of making an elongated metal composite comprising filaments of a refractory metal in a matrix comprising the steps of spirally wrapping a sheet containing wires of the refractory metal extending essentially parallel to each other and substantially horizontal to the planes of spiral turning, maintaining the wires radially and peripherally spaced from each other in the spiral wrap, providing a matrix metal in the wrap, densifying and extruding the product to elongate the product and its component wires while maintaining the relative spacing of wires and reducing the crosssize thereof substantially uniformly. 10. Method in accordance with claim 9 and comprising the further step of cold work elongation of the extruded product. 11. Method in accordance with claim 9 wherein the matrix is provided at least in part by interleaving turns of spirally wound matrix metal layer with said sheet. 12. Method in accordance with claim 11 wherein the matrix metal layer is a foil. 13. Method in accordance with claim 9 wherein the sheet comprises matrix metal wires cross-woven with the refractory metal wires. 14. Method in accordance with claim 13 wherein the sheet comprises matrix metal wires running parallel to the refractory metal wires and interspersed therewith. 15. Method in accordance with claim 9 and further comprising insertion in the product of a source of further material which is capable of reacting with the refractory metal to form a compund thereof. 16. Method in accordance with claim 15 wherein the source of further material is an alloy of matrix and further material. 17. The process of forming a superconductor which comprises the steps of: a) weaving a fabric of a first metal wire and a second metal wire, the first metal wire being selected from the class of metals which are superconductors or which can be converted to superconductors by reaction with another material, the second metal wire being a normal metal; b) rolling said fabric into a spiral to form a tightly compacted billet, the first metal wires in the fabric spiral being generally parallel to the axis of the billet and being separated from each other by a normal metal through substantially all their length; c) elongating said billet in a direction parallel to its axis; d) further reducing said billet to reduce the diameter of the first wires to a size on the order of 1-10 microns. 18. Process in accordance with claim 17 and further comprising the step of compacting said spiral to produce a relatively solid billet. 19. Process in accordance with claim 17 and further comprising the step of compacting said billet to increase its density. 20. Process in accordance with claim 17 and further comprising the step of reducing the diameter of said billet by swaging, extruding or the like. 21. Process in accordance with claim 17 wherein the first wires are separated from each other throughout their length. 22. Process in accordance with claim 17 wherein the first metal wires are not superconductive as extruded but are reacted with a component in said normal metal to form a superconductor. 23. Process in accordance with claim 17 in which the said normal metal comprises a constituent which will react with the first metal to form a superconductor. 24. Process in accordance with claim 17 in which a multiplicity of said first wires is provided in a composite body and further comprising the step of reducing the body to provide a final product having at least 5000 individual superconducting wires therein. 25. Process in accordance with claim 17 in which the product is extruded into the form of a tube and the tube contains material which can react with the metal of the first wires for forming said final superconductor. 26. Process in accordance with claim 17 in which each layer of the fabric spiral is separated from the adjacent such fabric spiral layer by a layer of normal metal. 27. The process of forming a superconductor which comprises the steps of: a) providing a fabric comprising superconducting metal strands which extend in one direction and normal metal strands which extend in a transverse direction; b) forming an assembly of said fabric by superposing a plurality of layers of said fabric, each layer being separated from the adjacent layer so that a layer of normal metal separates each superconductor strand; c) compacting said assembly and elongating the assembly in the direction of the superconducting strands by one or more of the working steps of extruding, rolling, drawing, swaging and the like, to provide a final product having elongated superconducting strands with a thickness of 1 to 10 microns. 28. Process in accordance with claim 27 wherein each first metal strand is a niobium-titanium superconductive alloy coated with a normal metal of higher thermal conductivity and comprising an interweaving barrier in an aggregate wire form, the second strand is a ribbon of normal metal and the wires of adjacent superposed layers are nested. 29. Process in accordance with claim 28 wherein the ribbon strands are part of a continuous slit foil and comprise corrugations offset by one in adjacent ribbons. 30. A superconductor composite product as made by the process of claim 27.

Inventors: STOHLMAN KATHARINE M, WONG JAMES, STOHLMAN, KATHARINE, M., WONG, JAMES
Applicants: SUPERCON INC, SUPERCON, INC.
Application year: 1985
Main classification: H01B12
IPC codes: H01L39