Breakdown process for superconducting ceramic composite conductors

Abstract

A reduced coefficient of friction, preferably created by ideal lubrication conditions, may advantageously be employed in the breakdown deformation of a precursor to a multifilamentary superconducting composite, particularly in combination with one or more high reduction breakdown drafts, to improve composite homogeneity and significantly increase the range of deformation conditions over which dimensional tolerances and J e may be optimized. Precursor composites made by this method exhibit reduced microhardness variability and fewer and less serious transverse filament defects than composites made by prior art methods. The method comprises the steps of: first, providing a precursor article comprising a metal matrix surrounding a plurality of filaments extending along the length of the article and comprising precursors to a desired superconducting ceramic; next, roll working the precursor article during a breakdown stage at a predetermined pressure and a coefficient of friction less than about 0.2, preferably less than 0.01, and preferably less than about 0.001 during each roll working draft, and, then, sintering the rolled article to obtain the desired superconducting ceramic. The coefficient of friction is preferably obtained by interposing a lubricant between the precursor article and one or more rolls, most preferably under conditions which create ideal lubrication conditions.

What is claimed is:  
     
         1 . A rolled precursor article to a multifilamentary superconducting ceramic composite article comprising a plurality of filaments extending along the length of the article and containing precursors to a desired superconducting ceramic, and a metal matrix substantially surrounding each filament, the precursor article having an overall variation in average microhardness between the filaments and the matrix of less than about 40 Knf.  
     
     
         2 . A rolled precursor article according to  claim 1  having an overall variation in average microhardness between the filaments and the matrix of less than 25 Knf.  
     
     
         3 . A rolled precursor article according to  claim 1  having an elongated form.  
     
     
         4 . A rolled precursor article according to  claim 3  in the form of a tape.  
     
     
         5 . A rolled precursor article according to  claim 3  in the form of a wire.  
     
     
         6 . A rolled precursor article according to  claim 3  in the form of a cable.  
     
     
         7 . A rolled precursor article according to  claim 3  in the form of a current lead.  
     
     
         8 . A rolled precursor article to a multifilamentary superconducting ceramic composite article comprising a plurality of filaments extending along the length of the article and containing precursors to a desired superconducting ceramic, and a metal matrix substantially surrounding each filament, the average microhardness of the filaments ranging from about 100 Knf to about 160 Knf.  
     
     
         9 . A rolled precursor article according to  claim 8  having an elongated form.  
     
     
         10 . A rolled precursor article according to  claim 9  in the form of a tape.  
     
     
         11 . A rolled precursor article according to  claim 9  in the form of a wire.  
     
     
         12 . A rolled precursor article according to  claim 9  in the form of a cable.  
     
     
         13 . A rolled precursor article according to  claim 9  in the form of a current lead.  
     
     
         14 . A rolled precursor article to a multifilamentary superconducting ceramic composite article comprising a plurality of filaments extending along the length of the article and containing precursors to a desired superconducting ceramic, and a metal matrix substantially surrounding each filament, the precursor article having a plurality of deformation zones established by rolling and an overall variation in average microhardness between the filaments in the deformation regions with lowest hardness and the filaments in the deformation regions with highest hardness of less than about 40 Knf.  
     
     
         15 . A rolled precursor article according to  claim 14  having an overall variation in average microhardness between the filaments in the deformation regions with lowest hardness and the filaments in the deformation regions with highest hardness of less than about 25 Knf.  
     
     
         16 . A rolled precursor article according to  claim 15  having an elongated form.  
     
     
         17 . A rolled precursor article according to  claim 16  in the form of a tape.  
     
     
         18 . A rolled precursor article according to  claim 16  in the form of a wire.  
     
     
         19 . A rolled precursor article according to  claim 16  in the form of a cable.  
     
     
         20 . A rolled precursor article according to  claim 16  in the form of a current lead.  
     
     
         21 . A rolled precursor article to a multifilamentary superconducting ceramic composite article comprising a plurality of filaments extending along the length of the article and containing precursors to a desired superconducting ceramic, and a metal matrix substantially surrounding each filament, the aspect ratio of each filament being greater than about 3.  
     
     
         22 . A rolled precursor article according to  claim 21  wherein the aspect ratio of each filament is at least about 15% of the aspect ratio of the article.  
     
     
         23 . A rolled precursor article according to  claim 22  having an elongated form.  
     
     
         24 . A rolled precursor article according to  claim 23  in the form of a tape.  
     
     
         25 . A rolled precursor article according to  claim 23  in the form of a wire.  
     
     
         26 . A rolled precursor article according to  claim 23  in the form of a cable.  
     
     
         27 . A rolled precursor article according to  claim 23  in the form of a current lead.  
     
     
         28 . A rolled precursor article to a multifilamentary superconducting ceramic composite article comprising a plurality of filaments extending along the length of the article and containing precursors to a desired superconducting ceramic, and a metal matrix substantially surrounding each filament, the variation in the width and thickness of the article being less than about 1% of the average width and thickness of the article.  
     
     
         29 . A rolled precursor article according to  claim 28  wherein the variation in the thickness of the article is less than about 10 microns.  
     
     
         30 . A rolled precursor article according to  claim 28  wherein the variation in the width of the article is less than about 50 microns.  
     
     
         31 . A rolled precursor article according to  claim 28  having an elongated form.  
     
     
         32 . A rolled precursor article according to  claim 31  in the form of a tape.  
     
     
         33 . A rolled precursor article according to  claim 31  in the form of a wire.  
     
     
         34 . A rolled precursor article according to  claim 31  in the form of a cable.  
     
     
         35 . A rolled precursor article according to  claim 31  in the form of a current lead.