TECHNICAL FIELD

In various embodiments, the present invention relates to the formation and processing of superconducting wires that are reinforced for additional mechanical strength.

BACKGROUND

A superconducting material exhibits no electrical resistance when cooled below its characteristic critical temperature. Although high-temperature superconductor materials, which have critical temperatures higher than the 77K boiling point of nitrogen, have been identified, these materials are often exotic (e.g., perovskite ceramics), difficult to process, and unsuitable for high-field applications. Thus, for practical superconducting applications requiring wires and coils and bundles thereof, the metallic superconductors Nb—Ti and Nb3Sn are most often utilized. While these materials have critical temperatures below 77K, the relative ease of processing these materials (e.g., drawing into wires) when compared to ceramic-based solutions, as well as their ability to operate at high currents and high magnetic fields, have resulted in their widespread use.

Typical metallic superconducting wires feature multiple strands (or “filaments”) of the superconducting phase embedded within a copper (Cu) conductive matrix. While this has resulted in the successful fabrication of metallic superconducting wires utilized for a host of different applications, the resulting wires often exhibit insufficient mechanical strength. While the copper matrix surrounding the superconducting filaments does provide some mechanical stability, copper is a very ductile, easily deformed material. Thus, there is a need for improved metallic superconducting wires incorporating a mechanical stabilizer that is sufficiently ductile (and thus drawable into wire) and that does not excessively diffuse into the copper (or Cu-based) wire matrix (and thus compromise its conductivity) during elevated heat treatments.

SUMMARY

In accordance with various embodiments of the present invention, a superconducting wire and/or precursor thereof (e.g., a composite filament utilized to form the wire) features one or more stabilizing elements including, consisting essentially of, or consisting of one or more metals having one or more mechanical properties (e.g., strength, yield strength, tensile strength, stiffness, Young's modulus, etc.) superior to that of the wire matrix (which is typically based on Cu to facilitate drawability into wire) and/or of the monofilaments (typically Nb-based) that are superconducting or that will subsequently react with one or more other species (e.g., Sn) to produce a superconducting phase. Exemplary stabilizing elements in accordance with embodiments of the invention may include, consist essentially of, or consist of tantalum (Ta) or a Ta alloy. As mentioned above, the stabilizing element is typically disposed within a Cu-based wire matrix along with multiple monofilaments and/or composite filaments that contain Nb. One or more stabilizing elements may be disposed substantially at the center of the composite filament or the superconducting wire, and/or one or more stabilizing elements may be disposed away from the core (e.g., proximate the periphery) of the composite filament or the superconducting wire. The composite filaments (and, in various embodiments, the stabilizing element) may have a cross-sectional shape facilitating efficient stacking of the various elements within the wire (e.g., hexagonal, square, rectangular, triangular). In accordance with embodiments, of the invention, monofilaments may each include, consist essentially of, or consist of a Nb-based core within a Cu-based matrix, and stacked assemblies of the monofilaments may be disposed within a Cu-based matrix and drawn down to form composite filaments. Thus, composite filaments may each include, consist essentially of, or consist of multiple Nb-based monofilaments within a Cu-based matrix. Like the composite filaments, the monofilaments may also have a cross-sectional shape facilitating efficient stacking within the composite filament (e.g., hexagonal, square, rectangular), and this cross-sectional shape may be the same as or different from the cross-sectional shape of the composite filaments.

In various embodiments, composite filaments are disposed within a Cu-based matrix (e.g., a Cu-based tube) and drawn down into the superconducting wire (or precursor thereof) and heat treated. One or more of the composite filaments may themselves be stabilized with a stabilizing element therein, and/or one or more stabilizing elements may be disposed within the Cu-based matrix of the superconducting wire in addition to the composite filaments. In various embodiments, the stabilizing element includes, consists essentially of, or consists of a Ta—W alloy including, for example, approximately 3% W (i.e., Ta-3W). In various other elements, the stabilizing element includes, consists essentially of, or consists of an alloy of Ta with nitrogen, e.g., tantalum nitride, and/or with carbon, e.g., tantalum carbide.

The superior mechanical properties of stabilizing elements in accordance with embodiments of the present invention provide improved mechanical strength to the final superconducting wires without making the wires excessively large. (In contrast, the use of various other metallic stabilizers with lesser mechanical properties would require the use of larger cores that would deleteriously impact the ductility and various other properties of the final wire.) Wires in accordance with embodiments of the present invention exhibit superior mechanical strength while retaining good high-field, high-current superconducting properties below their critical temperatures.

The use of Ta-alloy stabilizing elements advantageously enables less of the cross-section of the superconducting wire to be occupied by the stabilizing elements, and thus more of the cross-section may be occupied by current-carrying superconducting filaments. For example, a Ta—W alloy containing approximately 3% W may have a yield strength approximately 25% greater than pure Ta; thus, stabilizing cores in accordance with embodiments of the present invention may occupy approximately 25% less of the cross-sectional area of a superconducting wire than similar wires having, e.g., pure Ta cores. In various embodiments, the stabilizing element(s) may occupy less than 10% of the cross-section of the final wire (e.g., approximately 5% to approximately 8% of the cross-section), or may occupy approximately 8% to approximately 15% of the cross-section of the superconducting wire.

While exemplary stabilizing elements based on Ta and/or Ta alloys are detailed herein, stabilizing elements may include, consist essentially of, or consist of one or more other metals in accordance with embodiments of the invention. For example, stabilizing elements may include, consist essentially of, or consist of a Nb alloy having greater mechanical strength than substantially pure Nb. For example, stabilizing elements in accordance with embodiments of the invention may include, consist essentially of, or consist of an alloy of Nb with one or more of Hf, Ti, Zr, Ta, V, Y, Mo, or W. For example, stabilizing elements in accordance with embodiments of the invention may include, consist essentially of, or consist of Nb C103 alloy, which includes approximately 10% Hf, approximately 0.7%-1.3% Ti, approximately 0.7% Zr, approximately 0.5% Ta, approximately 0.5% W, and the balance Nb. In other embodiments, stabilizing elements may include, consist essentially of, or consist of a Nb B66 alloy and/or a Nb B77 alloy.

In an aspect, embodiments of the invention feature a method of forming a mechanically stabilized superconducting wire. A plurality of monofilaments is provided. One or more (or even all) of the monofilaments includes, consists essentially of, or consists of a core and a cladding at least partially surrounding the core. The core of at least one (or even all) of the monofilaments includes, consists essentially of, or consists of Nb. The cladding of at least one (or even all) of the monofilaments includes, consists essentially of, or consists of Cu. A stabilizing element is provided. The stabilizing element includes, consists essentially of, or consists of a core and a cladding at least partially surrounding the core. The core of the stabilizing element includes, consists essentially of, or consists of Ta and/or a Ta alloy. The cladding of the stabilizing element includes, consists essentially of, or consists of Cu. A plurality of composite filaments is fabricated by, for each composite filament, (i) assembling a plurality of the monofilaments into a monofilament stack, (ii) at least partially surrounding the monofilament stack with a cladding comprising Cu, and (iii) reducing a diameter of the clad monofilament stack. Optionally, a cross-sectional shape of the clad monofilament stack may be altered. A plurality of the composite filaments and the stabilizing element are assembled into a composite stack. The stabilizing element extends through a radial dimension of the composite stack. The composite stack is at least partially surrounded with a cladding. The cladding of the composite stack includes, consists essentially of, or consists of Cu. A diameter (or other radial or lateral dimension) of the clad composite stack is reduced to form a wire.

Embodiments of the invention may include one or more of the following in any of a variety of combinations. The stabilizing element may be disposed substantially at a radial center of the composite stack. One or more (or even each) of the monofilaments may be provided by a process including, consisting essentially of, or consisting of (i) disposing a rod including, consisting essentially of, or consisting of Nb into a tube including, consisting essentially of, or consisting of Cu to form a clad rod, (ii) reducing a diameter of the clad rod, and (iii) optionally, altering a cross-sectional shape of the clad rod. Altering the cross-sectional shape of the clad rod may include, consist essentially of, or consist of drawing the clad rod through a hexagonal die. Providing the stabilizing element may include, consist essentially of, or consist of (i) disposing a rod including, consisting essentially of, or consisting of Ta and/or a Ta alloy into a tube including, consisting essentially of, or consisting of Cu to form a clad rod, (ii) reducing a diameter of the clad rod, and (iii) optionally, altering a cross-sectional shape of the clad rod. Altering the cross-sectional shape of the clad rod may include, consist essentially of, or consist of drawing the clad rod through a hexagonal die. Altering the cross-sectional shape of the clad monofilament stack may include, consist essentially of, or consist of drawing the clad monofilament stack through a hexagonal die.

The core of the stabilizing element may include, consist essentially of, or consist of Ta. The core of the stabilizing element may include, consist essentially of, or consist of a Ta alloy, e.g., an alloy of Ta with at least one of W, C, or N. The core of the stabilizing element may include, consist essentially of, or consist of Ta-3W. Sn may be disposed within or on the wire. The wire may be annealed to form a Nb3Sn phase within the wire. The stabilizing element may occupy less than approximately 20% of a cross-section of the wire, less than approximately 10% of a cross-section of the wire, or less than approximately 5% of a cross-section of the wire. The stabilizing element may occupy more than approximately 1% of a cross-section of the wire, more than approximately 2% of a cross-section of the wire, more than approximately 5% of a cross-section of the wire, more than approximately 8% of a cross-section of the wire, or more than approximately 10% of a cross-section of the wire.

In another aspect, embodiments of the invention feature a method of forming a mechanically stabilized superconducting wire. A plurality of monofilaments is provided. One or more (or even each) of the monofilaments includes, consists essentially of, or consists of a core and a cladding at least partially surrounding the core. The core of one or more (or even each) of the monofilaments includes, consists essentially of, or consists of Nb. The cladding of one or more (or even each) of the monofilaments includes, consists essentially of, or consists of Cu. A plurality of stabilizing elements is provided. One or more (or even each) of the stabilizing elements includes, consists essentially of, or consists of a core and a cladding at least partially surrounding the core. The core of one or more (or even each) of the stabilizing elements includes, consists essentially of, or consists of Ta and/or a Ta alloy. The cladding of one or more (or even each) of the stabilizing elements includes, consists essentially of, or consists of Cu. A plurality of composite filaments is fabricated by, for each composite filament, (i) assembling a plurality of the monofilaments and a first one or more of the stabilizing elements into a monofilament stack, wherein the first one or more of the stabilizing elements extend through an axial dimension of the monofilament stack, (ii) at least partially surrounding the monofilament stack with a cladding including, consisting essentially of, or consisting of Cu, and (iii) reducing a diameter of the clad monofilament stack. Optionally, a cross-sectional shape of the clad monofilament stack may be altered. A plurality of the composite filaments is assembled into a composite stack. The composite stack is at least partially surrounded with a cladding including, consisting essentially of, or consisting of Cu. A diameter (or other radial or lateral dimension) of the clad composite stack is reduced to form a wire.

Embodiments of the invention may include one or more of the following in any of a variety of combinations. A second one or more of the stabilizing elements may be assembled with the plurality of composite filaments to form the composite stack. The second one or more stabilizing elements may extend through an axial dimension of the composite stack. The second one or more stabilizing elements may be disposed substantially at a radial center of the composite stack. The second one or more stabilizing elements may occupy less than approximately 20% of a cross-section of the wire, less than approximately 10% of a cross-section of the wire, or less than approximately 5% of a cross-section of the wire. The second one or more stabilizing elements may occupy more than approximately 1% of a cross-section of the wire, more than approximately 2% of a cross-section of the wire, more than approximately 5% of a cross-section of the wire, more than approximately 8% of a cross-section of the wire, or more than approximately 10% of a cross-section of the wire.

The first one or more stabilizing elements may be disposed substantially at a radial center of one or more (or even each) of the monofilament stacks. Less than approximately 20% of a cross-section of at least one (or even each) of the composite filaments may be occupied by the first one or more stabilizing elements. Less than approximately 10% of a cross-section of at least one (or even each) of the composite filaments may be occupied by the first one or more stabilizing elements. Less than approximately 5% of a cross-section of at least one (or even each) of the composite filaments may be occupied by the first one or more stabilizing elements. More than approximately 1% of a cross-section of at least one (or even each) of the composite filaments may be occupied by the first one or more stabilizing elements. More than approximately 2% of a cross-section of at least one (or even each) of the composite filaments may be occupied by the first one or more stabilizing elements. More than approximately 5% of a cross-section of at least one (or even each) of the composite filaments may be occupied by the first one or more stabilizing elements. More than approximately 8% of a cross-section of at least one (or even each) of the composite filaments may be occupied by the first one or more stabilizing elements. More than approximately 10% of a cross-section of at least one (or even each) of the composite filaments may be occupied by the first one or more stabilizing elements.

At least one (or even each) of the monofilaments may be provided by a process including, consisting essentially of, or consisting of (i) disposing a rod including, consisting essentially of, or consisting of Nb into a tube including, consisting essentially of, or consisting of Cu to form a clad rod, (ii) reducing a diameter of the clad rod, and (iii) optionally, altering a cross-sectional shape of the clad rod. Altering the cross-sectional shape of the clad rod may include, consist essentially of, or consist of drawing the clad rod through a hexagonal die. At least one (or even each) of the stabilizing elements may be provided by a process including, consisting essentially of, or consisting of (i) disposing a rod including, consisting essentially of, or consisting of Ta and/or a Ta alloy into a tube including, consisting essentially of, or consisting of Cu to form a clad rod, (ii) reducing a diameter of the clad rod, and (iii) optionally, altering a cross-sectional shape of the clad rod. Altering the cross-sectional shape of the clad rod may include, consist essentially of, or consist of drawing the clad rod through a hexagonal die. Altering the cross-sectional shape of the clad monofilament stack may include, consist essentially of, or consist of drawing the clad rod through a hexagonal die.

The core of one or more (or even each) of the stabilizing elements may include, consist essentially of, or consist of Ta. The core of one or more (or even each) of the stabilizing elements may include, consist essentially of, or consist of a Ta alloy, e.g., an alloy of Ta with at least one of W, C, or N. The core of one or more (or even each) of the stabilizing elements may include, consist essentially of, or consist of Ta-3W. Sn may be disposed within or on the wire. The wire may be annealed to form a Nb3Sn phase within the wire.

In yet another aspect, embodiments of the invention feature a superconducting wire that includes, consists essentially of, or consists of a wire matrix, a stabilizing element, and a plurality of composite filaments. The wire matrix includes, consists essentially of, or consists of Cu. The stabilizing element is embedded within the wire matrix. The stabilizing element includes, consists essentially of, or consists of a core and a cladding at least partially surrounding the core. The core of the stabilizing element includes, consists essentially of, or consists of Ta and/or a Ta alloy. The cladding of the stabilizing element includes, consists essentially of, or consists of Cu. The composite filaments are embedded within the wire matrix and at least partially surround the stabilizing element. One or more (or even each) of the composite filaments includes, consists essentially of, or consists of a plurality of monofilaments and a cladding at least partially surrounding the plurality of monofilaments. The cladding of one or more (or even each) of the composite filaments includes, consists essentially of, or consists of Cu. One or more (or even each) of the monofilaments includes, consists essentially of, or consists of a core and a cladding at least partially surrounding the core. The core of one or more (or even each) of the monofilaments includes, consists essentially of, or consists of Nb. The cladding of one or more (or even each) of the monofilaments includes, consists essentially of, or consists of Cu. The stabilizing element extends through an axial dimension of the wire.

Embodiments of the invention may include one or more of the following in any of a variety of combinations. The core of one or more (or even each) of the monofilaments may include, consist essentially of, or consist of Nb—Ti. The core of one or more (or even each) of the monofilaments may include, consist essentially of, or consist of Nb3Sn. The core of the stabilizing element may include, consist essentially of, or consist of Ta. The core of the stabilizing element may include, consist essentially of, or consist of a Ta alloy, e.g., an alloy of Ta with at least one of W, C, or N. The core of the stabilizing element may include, consist essentially of, or consist of Ta-3W. The stabilizing element may occupy less than approximately 20% of a cross-section of the wire, less than approximately 10% of a cross-section of the wire, or less than approximately 5% of a cross-section of the wire. The stabilizing element may occupy more than approximately 1% of a cross-section of the wire, more than approximately 2% of a cross-section of the wire, more than approximately 5% of a cross-section of the wire, more than approximately 8% of a cross-section of the wire, or more than approximately 10% of a cross-section of the wire. One or more (or even each) of the composite filaments may have a substantially hexagonal cross-sectional shape. One or more (or even each) of the monofilaments may have a substantially hexagonal cross-sectional shape. The stabilizing element may have a substantially hexagonal cross-sectional shape. The stabilizing element may be disposed proximate a radial center of the wire.

In another aspect, embodiments of the invention feature a superconducting wire that includes, consists essentially of, or consists of a wire matrix and a plurality of composite filaments embedded within the wire matrix. The wire matrix includes, consists essentially of, or consists of Cu. One or more (or even each) of the composite filaments includes, consists essentially of, or consists of (i) a first stabilizing element extending through an axial dimension of the composite filament, (ii) a plurality of monofilaments radially surrounding the first stabilizing element, and (iii) a cladding at least partially surrounding the plurality of monofilaments and the first stabilizing element. The cladding of one or more (or even each) of the composite filaments includes, consists essentially of, or consists of Cu. One or more (or even each) of the monofilaments includes, consists essentially of, or consists of a core and a cladding at least partially surrounding the core. The core of one or more (or even each) of the monofilaments includes, consists essentially of, or consists of Nb. The cladding of one or more (or even each) of the monofilaments includes, consists essentially of, or consists of Cu. One or more (or even each) of the first stabilizing elements includes, consists essentially of, or consists of a core and a cladding at least partially surrounding the core. The core of one or more (or even each) of the first stabilizing elements includes, consists essentially of, or consists of Ta and/or a Ta alloy. The cladding of one or more (or even each) of the first stabilizing elements includes, consists essentially of, or consists of Cu.

Embodiments of the invention may include one or more of the following in any of a variety of combinations. The wire may include a second stabilizing element embedded within the wire matrix and/or at least partially surrounded by the plurality of composite filaments. The second stabilizing element may extend through an axial dimension of the wire. The second stabilizing element may include, consist essentially of, or consist of a core and a cladding at least partially surrounding the core. The core of the second stabilizing element may include, consist essentially of, or consist of Ta and/or a Ta alloy. The cladding of the second stabilizing element may include, consist essentially of, or consist of Cu. The second stabilizing element may be disposed proximate a radial center of the wire. The core of the second stabilizing element may include, consist essentially of, or consist of Ta. The core of the second stabilizing element may include, consist essentially of, or consist of a Ta alloy, e.g., an alloy of Ta with at least one of W, C, or N. The core of the second stabilizing element may include, consist essentially of, or consist of Ta-3W. The second stabilizing element may occupy less than approximately 20% of a cross-section of the wire, less than approximately 10% of a cross-section of the wire, or less than approximately 5% of a cross-section of the wire. The second stabilizing element may occupy more than approximately 1% of a cross-section of the wire, more than approximately 2% of a cross-section of the wire, more than approximately 5% of a cross-section of the wire, more than approximately 8% of a cross-section of the wire, or more than approximately 10% of a cross-section of the wire.

The core of one or more (or even each) of the monofilaments may include, consist essentially of, or consist of Nb—Ti. The core of one or more (or even each) of the monofilaments may include, consist essentially of, or consist of Nb3Sn. The core of one or more (or even each) of the first stabilizing elements may include, consist essentially of, or consist of Ta. The core of one or more (or even each) of the first stabilizing elements may include, consist essentially of, or consist of a Ta alloy, e.g., an alloy of Ta with at least one of W, C, or N. The core of one or more (or even each) of the first stabilizing elements may include, consist essentially of, or consist of Ta-3W. One or more (or even each) of the composite filaments may have a hexagonal cross-sectional shape. One or more (or even each) of the monofilaments may have a hexagonal cross-sectional shape. One or more (or even each) of the first stabilizing elements may have a hexagonal cross-sectional shape. For one or more (or even each) of the composite filaments, the first stabilizing element may be disposed proximate a radial center of the composite filament. For one or more (or even each) of the composite filaments, the first stabilizing element may occupy less than approximately 20% of a cross-section of the composite filament, less than approximately 10% of a cross-section of the composite filament, or less than approximately 5% of a cross-section of the composite filament. For one or more (or even each) of the composite filaments, the first stabilizing element may occupy more than approximately 1% of a cross-section of the composite filament, more than approximately 2% of a cross-section of the composite filament, more than approximately 5% of a cross-section of the composite filament, more than approximately 8% of a cross-section of the composite filament, or more than approximately 10% of a cross-section of the composite filament.

These and other objects, along with advantages and features of the present invention herein disclosed, will become more apparent through reference to the following description, the accompanying drawings, and the claims. Furthermore, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and may exist in various combinations and permutations. As used herein, the terms “approximately” and “substantially” mean±10%, and in some embodiments, ±5%. The term “consists essentially of” means excluding other materials that contribute to function, unless otherwise defined herein. Nonetheless, such other materials may be present, collectively or individually, in trace amounts. For example, a structure consisting essentially of multiple metals will generally include only those metals and only unintentional impurities (which may be metallic or non-metallic) that may be detectable via chemical analysis but do not contribute to function. As used herein, “consisting essentially of at least one metal” refers to a metal or a mixture of two or more metals but not compounds between a metal and a non-metallic element or chemical species such as oxygen, silicon, or nitrogen (e.g., metal nitrides, metal silicides, or metal oxides); such non-metallic elements or chemical species may be present, collectively or individually, in trace amounts, e.g., as impurities.

