Carburization of ferrous-based shape memory alloys

Abstract

The shape memory effect of an article made from a ferrous-based shape memory alloy is enhanced by carburizing the article's surfaces.

1 . The process comprising carburizing at least a portion of the surface of a shaped article formed from a carbon-enhanceable ferrous-based shape memory alloy in the austenitic phase to produce a concentration of interstitial carbon in the carburized surface portion greater than in the body of the article.  
   
   
       2 . The process of  claim 1 , wherein carburization is continued until the concentration of interstitial carbon in the carburized surface portion provides a noticeable improvement in the shape memory effect exhibited by the article.  
   
   
       3 . The process of  claim 1 , wherein carburization is continued until the concentration of interstitial carbon in the carburized surface portion is at least 2 atomic %.  
   
   
       4 . The process of  claim 3 , wherein carburization is continued until the concentration of interstitial carbon in the carburized surface portion is at least about 4 atomic %.  
   
   
       5 . The process of  claim 4 , wherein carburization is continued until the concentration of interstitial carbon in the carburized surface portion is at least about 6 atomic %.  
   
   
       6 . The process of  claim 1 , wherein carburization is accomplish by low temperature carburization.  
   
   
       7 . The process of  claim 6 , wherein the alloy is a stainless steel.  
   
   
       8 . The process of  claim 7 , wherein all surfaces of the shaped article are carburized.  
   
   
       9 . A shaped article formed from a carbon-enhanceable ferrous-based shape memory alloy, at least a portion of the surface of the article carrying a carburized surface layer having a concentration of interstitial carbon greater than in the body of the article.  
   
   
       10 . The shaped article of  claim 9 , wherein the concentration of interstitial carbon in the carburized surface portion is sufficient to provide a noticeable improvement in the shape memory effect exhibited by the article.  
   
   
       11 . The process of  claim 9 , wherein the concentration of interstitial carbon in the carburized surface portion is at least 2 atomic %.  
   
   
       12 . The shaped article of  claim 11 , wherein the concentration of interstitial carbon in the carburized surface portion is at least about 4 atomic %.  
   
   
       13 . The shaped article of  claim 12 , wherein the concentration of interstitial carbon in the carburized surface portion is at least about 6 atomic %.  
   
   
       14 . The shaped article of  claim 9 , wherein the carburized surface portion is substantially free of carbide precipitates.  
   
   
       15 . The shaped article of  claim 14 , wherein the alloy is a stainless steel.  
   
   
       16 . The shaped article of  claim 9 , wherein all surfaces of the shaped article are carburized.  
   
   
       17 . The shaped article of  claim 9 , wherein the carbon-enhanceable ferrous-based shape memory alloy is in the austenitic phase.