Silver and silver alloy articles

Abstract

A new method for fabricating silver or silver alloy tube stock is described. The method provides silver or silver alloy tube stock with a structure that is substantially free of defects, has a fine grain size, and is amenable to uniform deformation. The silver or silver alloy tube stock is used to make silver-superconductor monofilament or multifilament precursor articles and composites.

What is claimed is:  
     
         1 . A method of manufacturing a seamless metal tube comprising a fine-grained silver or silver alloy and having a desired inner diameter, a desired outer diameter, and a desired cross-sectional area determined by the desired outer diameter and the desired inner diameter, comprising the steps of: 
 providing an ingot of silver or a silver alloy having a long axis and a hole parallel to the long axis and having a diameter approximately equal to the desired inner diameter of the seamless metal tube, and an initial cross-sectional area at least 8 times greater than the desired cross-sectional area;    inserting a mandrel having a diameter approximately equal to the desired inner diameter of the seamless metal tube into the hole of the ingot prior to the pressing step; and    extruding the ingot through a die having a diameter approximately equal to the desired outer diameter of the seamless metal tube to produce the seamless metal tube and reduce the average and maximum grain size of the silver or silver alloy.    
     
     
         2 . The method of  claim 1 , wherein the initial cross-sectional area is at least 20 times greater than the desired cross-sectional area.  
     
     
         3 . The method of  claim 1 , further comprising the steps of: 
 heating the ingot to a temperature between about 200 to 450° C. prior to the extruding step; and    cooling the seamless metal tube to below nominally 200° C. within 5 minutes of the extruding step.    
     
     
         4 . The method of  claim 1 , wherein the average diameter of the ingot is greater than 100 millimeters.  
     
     
         5 . The method of  claim 1 , wherein the desired outer diameter of the seamless metal tube is between 25 and 100 millimeters.  
     
     
         6 . The method of  claim 1 , wherein the seamless metal tube is substantially free of major defects.  
     
     
         7 . The method of  claim 1 , wherein the average grain size of the fine-grained silver or silver alloy is less than 50 micrometers.  
     
     
         8 . The method of  claim 7 , wherein the average grain size is less than 20 micrometers.  
     
     
         9 . The method of  claim 1 , wherein the maximum grain size of the fine-grained silver or silver alloy is about 100 micrometers.  
     
     
         10 . The method of  claim 9 , wherein the maximum grain size is about 50 micrometers.  
     
     
         11 . The method of  claim 1 , wherein the step of providing the ingot comprises the steps of providing a silver or silver alloy casting having a diameter smaller than the average diameter of the ingot and upsetting the casting one or more time, in a press to produce the ingot at a desired diameter larger than the diameter of the casting.  
     
     
         12 . The method of  claim 11 , wherein the average diameter of the ingot is greater than 150 millimeters.  
     
     
         13 . A method of reducing the grain size of a silver or silver alloy article having a desired outer diameter and a desired cross-sectional area comprising the steps of: 
 providing an ingot of silver or a silver alloy having a long axis and an initial cross-sectional area at least 8 times greater than the desired cross-sectional area; and    extruding the ingot through a die having a diameter approximately equal to the desired outer diameter of the article to produce the article having a fine grain size.    
     
     
         14 . The method of  claim 13 , further comprising the steps of: 
 heating the ingot to a temperature between about 200 to 450° C. prior to the extruding step; and    cooling the article to below nominally 200° C. within 5 minutes of the extruding step.    
     
     
         15 . The method of  claim 14 , wherein the ingot further includes a hole parallel to the long axis and having a diameter approximately equal to a desired inner diameter of the article and the method further includes the step of inserting a mandrel having a diameter approximately equal to the desired inner diameter of the article.  
     
     
         16 . The method of  claim 15 , wherein the initial cross-sectional area is at least 20 times greater than the desired cross-sectional area.  
     
     
         17 . The method of  claim 13 , wherein the ingot has a first average grain size and the article has a second average grain size that is a factor of 100 smaller than the first grain size.  
     
     
         18 . The method of  claim 13 , wherein the silver or silver alloy of the article has a maximum grain size of about 100 micrometers.  
     
     
         19 . The method of  claim 18 , wherein the maximum grain size of about 50 micrometers.  
     
     
         20 . The method of  claim 13 , wherein the silver or silver alloy has an average grain size less than 50 micrometers.  
     
     
         21 . The method of  claim 20 , wherein the average grain size is less than 20 micrometers.  
     
     
         22 . A thick-walled, seamless metal tube comprising silver or a silver alloy having an average grain size that is less than 200 micrometers and a maximum grain size less than about 300 micrometers.  
     
     
         23 . The seamless metal tube of  claim 22 , wherein the tube has an outer diameter greater than 25 millimeters.  
     
     
         24 . The seamless metal tube of  claim 22 , wherein the seamless metal tube is substantially free of major defects.  
     
     
         25 . The seamless metal tube of  claim 24 , wherein the average grain size is less than 100 micrometers and the maximum grain size is less than about 200 micrometers.  
     
     
         26 . The seamless metal tube of  claim 25 , wherein the average grain size is less than 20 micrometers, and the maximum grain size is less than about 50 micrometers.  
     
     
         27 . A superconducting article precursor comprising a superconductor or superconductor precursor contained in a thick-walled, seamless metal tube comprising silver or a silver alloy.  
     
     
         28 . The superconducting article precursor of  claim 27 , wherein the thick-walled, seamless metal tube has an outer diameter greater than 25 millimeters.  
     
     
         29 . The superconducting article precursor of  claim 27 , wherein the seamless metal tube is substantially free of major defects.  
     
     
         30 . A method of manufacturing a composite superconducting article, comprising the steps of: 
 providing a precursor article including a superconductor or superconductor precursor contained in a seamless metal tube comprising fine-grained silver or silver alloy, the seamless metal tube having an outer diameter greater than 25 millimeters; and    treating the precursor article to obtain the superconducting article.    
     
     
         31 . A method of manufacturing a fine-grained silver or silver alloy article independent of initial grain size of the silver or silver alloy, the article having a desired outer diameter and a desired cross-sectional area, the method comprising the steps of: 
 providing an ingot of silver or a silver alloy having a long axis and an initial cross-sectional area at least 8 times greater than the desired cross-sectional area; and    extruding the ingot through a die having a diameter approximately equal to the desired outer diameter of the article to produce the article.    
     
     
         32 . The method of  claim 31 , further comprising the steps of: 
 heating the ingot to a temperature between about 200 to 450° C. prior to the extruding step; and    cooling the article to below nominally 200° C. within 5 minutes of the extruding step.    
     
     
         33 . The method of  claim 31 , wherein the initial cross-sectional area is at least 20 times greater than the desired cross-sectional area.  
     
     
         34 . The method of  claim 31 , wherein the article is substantially free of major defects.  
     
     
         35 . The method of  claim 31 , wherein the article has an average grain size is less than 100 micrometers.  
     
     
         36 . The method of  claim 35 , wherein the average grain size is less than 20 micrometers.  
     
     
         37 . The method of  claim 36 , wherein the article has a maximum grain size of about 100 micrometers.  
     
     
         38 . The method of  claim 37 , wherein the maximum grain size is about 50 micrometers.  
     
     
         39 . A metal article comprising fine-grained silver or silver alloy, wherein the metal article has a minimum cross-sectional area greater than about 100 square millimeters and is substantially free of major defects.