Processing of magnesium-boride superconductor wires

Abstract

A method of making a high density Mg—B superconducting article includes providing a packed powder sheath, said powder comprising a source of magnesium and boron, subjecting the packed powder sheath to a symmetric deformation, said deformation selected to elongate the packed powder sheath to form a wire while retaining the free flow of particles within the powder core, subjecting the wire to high reduction rolling, said high reduction rolling selected to reduce the wire thickness by 40 to 95% and heating the rolled article to improve the superconducting properties of the article. A superconducting article comprised of one or more elongated metal matrix regions containing one or more embedded elongated superconducting Mg—B regions running the full length of the article is disclosed, wherein the superconducting Mg—B regions have a density greater than 95% of the theoretical density, and a transition temperature in zero field of 30 K.

1 . A method of making a high density Mg—B superconducting article, comprising the steps of: 
 providing a packed powder sheath, said powder comprising a source of magnesium and boron;    subjecting the packed powder sheath to a symmetric deformation, said deformation selected to elongate the packed powder sheath to form a wire while retaining the free flow of particles within the powder core;    subjecting the wire to high reduction rolling, said high reduction rolling selected to reduce the wire thickness by 40 to 95%; and    heating the rolled article to improve the superconducting properties of the article.    
     
     
         2 . The method of  claim 1 , wherein the powder of the packed powder sheath comprises a mechanically alloyed Mg+B powder.  
     
     
         3 . The method of  claim 1 , wherein the powder of the packed powder sheath comprises a mixture of boron and magnesium.  
     
     
         4 . The method of  claim 1 , wherein the powder of the packed powder sheath comprises MgB 2 .  
     
     
         5 . The method of  claim 1 , wherein the particle size of the powder is in the range of 10 nm to 1 micron.  
     
     
         6 . The method of  claim 1 , wherein the Mg—B superconductor further comprises flux pinning sites.  
     
     
         7 . The method of  claim 1 , wherein the sheath is comprised of copper or a copper alloy.  
     
     
         8 . The method of  claim 1 , wherein the packing density of the packed powder sheath is in the range of 35 to 80%.  
     
     
         9 . The method of  claim 1 , wherein the symmetric elongating deformation is selected from the group consisting or wire drawing, extrusion and rod rolling.  
     
     
         10 . The method of  claim 9 , wherein wire drawing is conducted using a die having a total die angle greater than or equal to 14°.  
     
     
         11 . The method of  claim 10 , wherein wire drawing is conducted using a die having a total die angle in the range of 14° to 25°.  
     
     
         12 . The method of  claim 1 , wherein the high reduction rolling reduces thickness in the range of 50 to 75%.  
     
     
         13 . The method of  claim 1 , wherein the high reduction rolling is carried out using large diameter rolls that have a large contact area with the wire.  
     
     
         14 . The method of  claim 13 , wherein the large diameter rolls have a diameter greater than 2 inches.  
     
     
         15 . The method of  claim 13 , wherein the large diameter rolls have a diameter greater than or equal to about 4 inches.  
     
     
         16 . The method of  claim 1 , wherein a low reduction rolling is carried out before the large reduction rolling.  
     
     
         17 . The method of  claim 16 , wherein the low reduction rolling reduces the thickness of the wire by less than 20% per pass.  
     
     
         18 . The method of  claim 16 , wherein the low reduction rolling alters the shape of the wire to provide a geometry that has a larger contact area with the roll in the subsequent high reduction rolling operation.  
     
     
         19 . The method of  claim 1 , wherein the wire prior to high reduction rolling has a geometry is round, oval, square, rectangular or tape-like.  
     
     
         20 . The method of  claim 1 , wherein the heating is carried out to convert a precursor of the Mg—B superconductor into the Mg—B superconductor.  
     
     
         21 . The method of  claim 1 , wherein the heating is carried out to sinter the Mg—B superconductor.