Patent Application: US-92618910-A

Abstract:
a hollow tube , for inserting superconductor precursor material such as superconductor precursor rods into its bore , wherein the tube extends along an axial direction , and wherein the tube comprises a matrix made of a first ductile material , is characterized in that a plurality of continuous filaments , extending along the axial direction of the tube , are distributed in the matrix , wherein the continuous filaments are made of a second ductile material . with the invention , a good quality mechanical reinforcement of superconductor wires , in particular which can be used without later hot extrusion , can be achieved .

Description:
the tube with reinforcing filament of this preferred embodiment has a cu matrix and continuous longitudinal filaments made of ta . the advantage of this combination of materials is that cu has a high electrical conductivity and that there is negligible diffusion of ta atoms in the cu matrix even at the high temperature at which they are exposed during the extrusion necessary to fabricate the tube or during the reaction heat treatments necessary to form the superconducting filaments in the final wire . this embodiment is particularly suitable for the fabrication of reinforced nb 3 sn superconductor wires by the internal sn route or by the powder in tube route . fig1 presents the cross - section of an inventive tube 1 of the preferred embodiment nr . 1 , with the cross - section taken in a plane perpendicular to the axial direction in which the tube 1 extends . the tube 1 has a tube wall 2 which surrounds a central bore ( hole ) 3 . the tube wall 2 comprises a matrix 4 of cu in which six ta filaments 5 are embedded . the external shape 4 b of the tube 1 is round whereas the internal bore ( hole ) 3 is shaped for receiving a number of 109 hexagonal subelements . in more detail , compare also fig2 , the tube 1 has a round exterior shape 4 b and the central hole 3 is of a special polygonal shape , able to receive a number of ( here ) 109 subelements 6 with just a small clearance 7 between the interior wall 4 a of the tube 1 and the subelement bundle 8 , enough to allow the insertion of all the subelements 6 during assembly . the six reinforcing filaments 5 in the wall 2 of the tube 1 have an ovalized shape given by the tube fabrication process ( tube extrusion followed by tube drawing ) when starting with round ta rods in a cu billet . in this preferred embodiment , the reinforcing filaments 5 occupy ˜ 39 % of the cross - sectional area of the wall 2 of the tube 1 , whereas the central hole 3 takes ˜ 57 % of the total cross - sectional area of the tube 1 ( including the bore 3 ). a superconductor wire will be prepared by fabricating 109 subelements 6 containing the precursor materials 9 a for the formation of a superconducting phase surrounded by a layer of cu 9 b and then assembling these subelements 6 in the described tube 1 ( fig2 ) and mechanically deforming them by wire drawing to form a round wire of a diameter suitable for the winding of magnet coils ( usually between 0 . 5 and 2 mm ). in the final wire , the reinforcing filaments 5 will occupy ˜ 17 % of the total cross - sectional area of the wire , the rest of the area being divided between the cu stabilizer and the 109 superconducting subelements 6 (˜ 45 % of total area when excluding the cu separating them ). the content of reinforcing material and stabilizer cu of the final wire can be adjusted by changing the size of the six filaments 5 in the wall 2 of tube 1 . for wires prepared using the tube 1 of this embodiment , the size of the superconducting subelements 6 in the final wire with a diameter of 0 . 80 mm ( the so - called effective diameter ) will be around 50 μm . a smaller effective diameter can be obtained if a larger number of subelements is assembled in a tube with the central hole reshaped to accept them . fig2 presents the cross - section of the tube 1 of the preferred embodiment nr . 1 , with 109 hexagonal subelements 6 assembled in the specially shaped central hole 3 of the tube 1 . the tube with reinforcing filaments of this preferred embodiment has a cu matrix 4 and continuous longitudinal filaments 5 made of ta , compare fig3 . this embodiment is also particularly suitable for the fabrication of reinforced nb 3 sn superconductors . fig3 presents the cross - section of the tube 1 of the preferred embodiment nr . 2 , with 144 ta filaments 5 in the cu wall 2 of the tube 1 . the external shape 4 b of the tube 1 is round , whereas the internal bore ( hole ) 3 is shaped for receiving a number of ( here ) 109 hexagonal subelements . in more detail , the tube 1 has a round exterior shape 4 b and the central hole 3 is of a special polygonal shape able to receive a number of 109 subelements 6 , compare also fig4 , with just a small clearance 7 between the interior wall 4 a of the tube 1 and the subelement bundle 8 , enough to allow the insertion of all the subelements 6 during assembly . the 144 reinforcing filaments 5 in the wall 2 of the tube 1 are distributed in 12 groups separated by cu - only areas . in the final superconducting wire , the cu - only areas separating the ta filaments 5 ( in addition to the cu between the filaments 5 of each group ) will serve at the fast removal of any electrical or thermal disturbances from the superconducting subelements 6 in the center . in this preferred embodiment the reinforcing filaments 5 occupy ˜ 45 % of the cross - sectional area of the wall 2 of the tube 1 , whereas the central hole 3 takes ˜ 38 % of the total cross - sectional area of the tube 1 ( including the bore 3 ). a superconductor wire will be prepared by ( here ) fabricating 109 subelements 6 containing the precursor materials 9 a for the formation of a superconducting phase surrounded by a layer of cu 9 b and then assembling these subelements 6 in the described tube 1 ( fig4 ) and mechanically deforming them by wire drawing to form a round wire of a diameter suitable for the winding of magnet coils ( usually between 0 . 5 and 2 mm ). in the final wire , the reinforcing filaments 5 will occupy ˜ 28 % of the total cross - sectional area of the wire , the rest of the area being divided between the cu stabilizer and the 109 superconducting subelements 6 ( excluding the cu separating them , a maximum of ˜ 30 % of total area ). the content of reinforcing material and stabilizer cu of the final wire can be adjusted by changing the size or the number of filaments 5 in the wall 2 of tube 1 , for example by removing the outer layer of filaments 5 and reducing the external diameter of the tube 1 while keeping the rest of the filaments 5 and the central hole 3 unchanged . for wires prepared using the tube 1 of this embodiment , the size of the superconducting subelements 6 in the final wire with a diameter of 0 . 80 mm ( the so - called effective diameter ) will be around 50 μm . as lower values of this parameter lead to improved stability of the wire at low magnetic fields and reduced power dissipation under alternating magnetic fields , a configuration with a higher number of subelements is also proposed ( see embodiment nr . 3 below ). at the same final wire diameter the subelements 6 will end up having smaller effective diameters . fig4 presents the cross - section of the tube 1 of the preferred embodiment nr . 2 , with 109 hexagonal subelements 6 assembled in the specially shaped central hole 3 of the tube 1 . in another preferred embodiment , for applications where a lower level of reinforcement is needed , the reinforcing filaments 5 in the wall 2 of the tube 1 are shaped as annular sectors 5 a and are made of oxide dispersion strengthened ( ods ) cu , compare fig5 . significantly stronger than cu , this material has a relatively high electrical and thermal conductivity when compared with other materials of comparable strength . in a typical configuration , six annular segments 5 a made of ods - cu would occupy two thirds of an annulus in the tube wall 2 . the remainder of the annular segments , i . e . the matrix 4 , will be made of high purity cu ensuring an excellent electrical and thermal conductance along specific radial paths . this embodiment is also particularly suitable for the fabrication of nb 3 sn superconductors . fig5 presents the cross - section of the tube 1 of the preferred embodiment nr . 3 , with six ods cu filaments 5 in the cu wall 2 of the tube 1 . the external shape 4 b of the tube 1 is round whereas the internal bore ( hole ) 3 is shaped for receiving a number of ( here ) 253 hexagonal subelements . the ods - cu reinforcement occupies between 40 and 50 % of the cross - sectional area of the wall 2 of the tube 1 , but higher ratios can be also used , in particular if the radial high conductance cu paths are reduced in size . when the tube 1 is provided with a polygonal hole 3 able to receive 253 hexagonal subelements 6 , 10 ( compare fig6 ) and taking ˜ 67 % of the overall cross - sectional area of the tube 1 ( including the bore 3 ), it can be used to fabricate reinforced internal sn or powder in tube type nb 3 sn superconductors with relatively low subelement effective diameter . for a final wire diameter of 0 . 80 mm , the estimated subelement effective diameter will be just above 40 μm . the reinforcement of such superconductor would occupy 13 - 17 % of the total cross - sectional area of the wire , whereas the superconducting cores 9 a of the subelements 6 will occupy 50 - 55 %. if more stabilizer cu of high conductivity is needed for stability and / or mechanical deformation reasons , some of the central subelements 6 , 10 assembled in the tube 1 can be made of pure cu ( as exemplified in fig6 with the seven hexagonal subelements 10 in the center ). fig6 presents the cross - section of the tube 1 of the preferred embodiment nr . 3 , with 253 hexagonal subelements 6 , 10 assembled in the specially shaped central hole 3 of the tube 1 . some of the subelements 6 , 10 in the center of the assembly ( seven in this case ) may be replaced with cu hexagonal rods 10 if more stabilizer is needed or to improve the drawing of the wire . for the fabrication of mgb 2 powder in tube type superconductors it is desirable to use tubes of materials that do not react significantly with mg , b or mgb 2 during the reaction heat treatment . the formation of the intermetallic compound mgcu 2 eliminates cu as a material coming in contact with the precursor powders of mgb 2 superconductors . fe , ni , nb , ta or ti will not react significantly with the mgb 2 precursors and hence these metals are the usual materials for such applications , either in the form of a tube or as a barrier separating the mgb 2 precursor powders from the rest of the tube that contains the powders . in the case of a barrier , the tube material can be of any metal that has the proper combination of yield strength and deformability to allow the successful deformation into an elongated rod for future restacking to form a multifilament wire . even in the presence of a barrier , cu is often too soft to be material of the tube containing the mgb 2 precursor powders , and the assembly cannot be successfully deformed to the desired size . as a solution to this problem , the invention proposes a tube that combines the good electrical and thermal properties of cu with the strength of fe or ni by embedding cu filaments in the wall of a tube made of fe or ni . the material in contact with the mgb 2 precursor powders would then be compatible ( i . e . non - reactive with respect to mgb 2 ), whereas the cu filaments would provide paths of high electrical and thermal conductivity that will improve the stability of the wire . the relatively high strength of the tube wall will allow the successful deformation of the precursor . in the round tube 1 exemplified in fig7 , the sixteen cu filaments 5 occupy ˜ 30 % of the cross - sectional area of the wall 2 of the tube 1 . the cross - sectional area of the wall 2 of the tube 1 is roughly equal to the cross - sectional area of the round central bore ( hole ) 3 of the tube 1 . depending on the method of fabrication , the filaments 5 may be round as presented in fig7 or have other shapes , like oval or sector of annular region . fig7 . presents the cross - section of a variant of the tube 1 of the preferred embodiment nr . 4 , with sixteen cu filaments 5 in the wall 2 of the tube 1 made of fe or ni . a further improvement of the electrical and thermal properties of the tube 1 of this embodiment can be achieved by exposing part of the cu filaments 5 at the outer surface 4 b of a tube 1 , see fig8 , wherein the tube 1 was initially fabricated as the tube 1 in fig7 . to expose the cu filaments 5 , a mechanical or chemical process for removing a layer of material at the outside 4 b of tube 1 will be employed during the fabrication of the tube 1 or at some stage during the deformation of the assembled precursor . the cu filaments 5 in such a design can typically occupy 40 % of the cross - sectional area of the tube wall 2 . fig8 presents the cross - section of a variant of the tube 1 of the preferred embodiment nr . 4 , with sixteen cu filaments 5 in the wall 2 of the tube 1 , with the matrix 4 made of fe or ni , wherein the cu filaments 5 were exposed at the outer surface 4 b of the tube 1 . fig9 illustrates in a cross - section of a fifth embodiment of an inventive tube 1 , wherein the filaments 5 are sheathed with a barrier 11 each ( made of nb or ta for example ). the sheathed filaments 5 are embedded in the matrix 4 of the tube wall 2 . the materials of the filaments 5 , the barrier 11 and the matrix 4 are all different from each other . by means of the barrier 11 , unwanted reactions or interdiffusion of the matrix material and the filament material can be prevented . fig1 illustrates the fabrication of a compound 12 in accordance with the invention . in a step a ), an inventive tube 1 with reinforcing filaments 5 in the tube wall 2 is provided . typically , each filament 5 extends through the complete axial length axl of the tube 1 . in a step b ), superconducting material or superconductor precursor material is inserted into the bore 3 of the tube 1 . in the example shown , a bundle of superconductor precursor rods 13 is inserted into the bore 3 . afterwards , in step c ), the tube 1 including the superconductor precursor rods 13 is mechanically deformed . the resulting component 12 has an increased axial length , but a reduced diameter as compared to the tube 1 . the component 12 is subjected to a heat treatment afterwards , in order to react the precursor material on the precursor rods 13 into superconducting material . then the component 12 may be used as a superconducting wire , e . g . in a magnet coil . note that the dimensions in fig1 are not drawn to scale . t . luhman , c . j . klamut , m . suenaga , and d . welch , “ superconducting wire with improved strain characteristics ,” u . s . pat . no . 4 , 343 , 867 , aug . 10 , 1982 . e . gregory , l . r . motowidlo , g . m . ozeryansky , and l . t . summers , “ high strength nb 3 sn conductors for high magnetic field applications ,” ieee trans . magn ., vol . 27 , pp . 2033 - 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