Iron-manganese-silicon based shape memory alloys containing chromium and nitrogen

Abstract

Iron-manganese-silicon-based shape memory alloys comprising: (a) an effective amount of Mn greater than about 18%; (b) an effective amount of Si greater than about 5%; (c) from about 1% to about 8% Cr; (d) an effective amount of N; and (e) the balance of Fe. Preferably, the alloys comprise from about 20% to about 30% Mn, from about 5.5% to about 6% of Si, from about 2% to about 5% of Cr, from about 0.1% to about 0.5% N, and from about 61% to about 70% Fe. Preferred embodiments demonstrate about 100% shape recovery with one cycle of thermo-mechanical training with a prestrain of about 3%. Methods for training the alloys are provided, comprising the steps of tensile deforming samples by applying 3.0% or 3.5% prestrain at room temperature, heating each sample to approximately 600° C., and then cooling them after keeping them at this temperature for 10 minutes.

What is claimed is:  
     
         1 . A shape memory alloy, comprising 
 (a) an effective amount of Mn;    (b) an effective amount of Si;    (c) from about 1% to about 8% Cr;    (d) an effective amount of N; and    (e) the balance of Fe.    
     
     
         2 . A shape memory alloy of  claim 1 , comprising from about 18% to about 35% Mn.  
     
     
         3 . A shape memory alloy of  claim 2 , comprising from about 20% to about 30% Mn.  
     
     
         4 . A shape memory alloy of  claim 1 , comprising from about 5.2% to about 8% Si.  
     
     
         5 . A shape memory alloy of  claim 4 , comprising from about 5.5% to about 6% of Si.  
     
     
         6 . A shape memory alloy of  claim 1 , comprising from about 2% to about 5% of Cr.  
     
     
         7 . A shape memory alloy of  claim 1 , comprising from about 0.1% to about 0.5% N.  
     
     
         8 . A shape memory alloy of  claim 1 , comprising from about 55% to about 75% Fe.  
     
     
         9 . A shape memory alloy of  claim 8 , comprising from about 61% to about 70% Fe.  
     
     
         10 . A shape memory alloy of  claim 1 , wherein said alloy demonstrates about 100% shape recovery with one cycle of thermo-mechanical training with a prestrain of about 3%.  
     
     
         11 . A shape memory alloy comprising: 
 (a) from about 20% to about 30% of Mn;    (b) from about 5.5% to about 6% of Si;    (c) from about 1% to about 8% of Cr;    (d) from about 0.1% to about 0.5% N; and    (e) from about 60% to about 70% Fe.    
     
     
         12 . A shape memory alloy of  claim 11 , comprising from about 2% to about 5% of Cr.  
     
     
         13 . A shape memory alloy of  claim 11 , comprising from about 0.1% to about 0.3% N.  
     
     
         14 . A shape memory alloy of  claim 11 , wherein said alloy demonstrates about 100% shape recovery with one cycle of thermo-mechanical training with a prestrain of about 3%.  
     
     
         15 . A shape memory alloy of  claim 11 , comprising about 20% Mn, about 5.5% Si, about 5% Cr, about 0.16% N, and the balance Fe.  
     
     
         16 . A shape memory alloy of  claim 11 , comprising about 25% Mn, about 5% Si, about 5% Cr, about 0.13% N, and the balance Fe.  
     
     
         17 . A shape memory alloy of  claim 11 , comprising about 30% Mn, about 6% Si, about 2% Cr, about 0.10% N, and the balance Fe.  
     
     
         18 . A shape memory alloy according to  claim 1 , consisting essentially of: 
 (a) from about 18% to about 35% of Mn;    (b) from about 5% to about 8% of Si;    (c) from about 1% to about 8% of Cr;    (d) from about 0.08% to about 0.5% N; and    (e) the balance of Fe.    
     
     
         19 . A shape memory alloy according to  claim 18 , consisting essentially of: 
 (a) from about 20% to about 30% of Mn;    (b) from about 5.5% to about 6% of Si;    (c) from about 2% to about 5% of Cr;    (d) from about 0.1% to about 0.3% N; and    (e) from about 61% to about 70% Fe.    
     
     
         20 . In an iron-manganese-silicon-based shape memory alloy, the improvement comprising the addition to said alloy of from about 1% to about 8% Cr; and from about 0.1% to about 0.2% N.  
     
     
         21 . A iron-manganese-silicon-based shape memory alloy of  claim 20 , wherein said alloy comprises from about 18% to about 35% Mn; from about 5% to about 8% Si; and from about 55% to about 75% Fe.  
     
     
         22 . A iron-manganese-silicon-based shape memory alloy of  claim 21 , wherein said alloy comprises from about 20% to about 30% Mn; from about 5.5% to about 6% Si; from about 55% to about 75% Fe; from about 2% to about 5% of Cr; and from about 0.1% to about 0.16% N.  
     
     
         23 . A shape memory alloy of  claim 20 , wherein said alloy demonstrates about 100% shape recovery with one cycle of thermo-mechanical training with a prestrain of about 3%.  
     
     
         24 . A method of training a iron-manganese-silicon-based shape memory alloy containing Cr and N, comprising the steps of 
 (a) tensile deforming said alloy by applying from about 2.5% to about 4% prestrain at a temperature of from about 4° C. to about 45° C.;    (b) heating said alloy to a temperature of from about 500° C. to about 700° C. for at least about 2 minutes; and    (c) cooling said alloy.    
     
     
         25 . A method according to  claim 24 , wherein said tensile deforming step comprises applying from about 3.0% to about 3.5% prestrain at ambient temperature.  
     
     
         26 . A method according to  claim 24 , wherein said heating step is for from about 5 minutes to about 15 minutes, at a temperature of from about 550° C. to about 650° C.  
     
     
         27 . A method according to  claim 24 , wherein said heating step is for about 10 minutes at about 600° C.  
     
     
         28 . A method according to  claim 24 , additionally comprising repeating said steps (a), (b), and (c).  
     
     
         29 . A method according to  claim 28 , wherein said repeating is performed twice.  
     
     
         30 . A method according to  claim 24 , wherein said alloy comprises: 
 (a) from about 18% to about 35% of Mn;    (b) from about 5% to about 8% of Si;    (c) from about 1% to about 8% of Cr;    (d) from about 0.1% to about 0.5% N; and    (e) from about 55% to about 75% Fe.    
     
     
         31 . A method according to  claim 30 , wherein said alloy comprises: 
 (a) from about 20% to about 30% Mn;    (b) from about 5.5% to about 6% of Si;    (c) from about 2% to about 5% of Cr;    (d) 0.1% to about 0.4% N; and    (e) 61% to about 70% Fe.    
     
     
         32 . A method according to  claim 31 , wherein said alloy comprises about 20% Mn, about 5.5% Si, about 5% Cr, about 0.16% N, and the balance Fe.  
     
     
         33 . A method according to  claim 31 , wherein said alloy comprises about 25% Mn, about 5% Si, about 5% Cr, about 0.13% N, and the balance Fe.  
     
     
         34 . A method according to  claim 31 , wherein said alloy comprises about 30% Mn, about 6% Si, about 2% Cr, about 0.10% N, and the balance Fe.  
     
     
         35 . A method according to  claim 24 , wherein said alloy demonstrates about 100% shape recovery with a prestrain of about 3%.  
     
     
         36 . A iron-manganese-silicon-based shape memory alloy trained by the method of  claim 24.