Nickel-titanium alloy with a non-alloyed dispersion and methods of making same

Abstract

An article having a nickel-titanium alloy and a homogeneous dispersion of discrete particles. The discrete particles are substantially free of nickel and titanium. A method of making the article includes melting a substantially equiatomic composition of nickel and titanium to form an alloy and dispersing a discrete particle in the alloy to form an ingot. The melting and dispersing are performed at a temperature above the alloying temperature of the composition and below the melting temperature of the discrete particle. The ingot is hot worked to form a processed ingot. The processed ingot is cold worked and annealed to form the article.

1 . An article comprising: 
 a nickel-titanium alloy; and    a homogeneous dispersion of discrete particles in the article, wherein the discrete particles are substantially free of nickel and titanium.    
   
   
       2 . An article according to  claim 1 , wherein the discrete particles are selected from the group consisting of iridium, platinum, gold, rhenium, tungsten, palladium, rhodium, tantalum, silver, ruthenium, and hafnium.  
   
   
       3 . An article according to  claim 1 , wherein the discrete particles comprise one or more alloys substantially free of nickel and titanium.  
   
   
       4 . An article according to  claim 3 , wherein the one or more alloys comprise one or more of iridium, platinum, gold, rhenium, tungsten, palladium, rhodium, tantalum, silver, ruthenium, and hafnium.  
   
   
       5 . An article according to  claim 1 , wherein the discrete particles are aligned perpendicular to the likely direction of fatigue crack propagation.  
   
   
       6 . An article according to  claim 1 , wherein the alloy comprises a binary alloy.  
   
   
       7 . An article according to  claim 1 , wherein the alloy comprises a ternary or higher alloy.  
   
   
       8 . An article according to  claim 1 , wherein the alloy is nitinol.  
   
   
       9 . An article according to  claim 1 , wherein the article is a medical device.  
   
   
       10 . An article according to  claim 9 , wherein the medical device is a stent.  
   
   
       11 . A method of making an article, the method comprising: 
 melting a substantially equiatomic composition of nickel and titanium to form an alloy and dispersing at least one type of discrete particle in the alloy to form an ingot, wherein the melting and dispersing are performed at a temperature above the alloying temperature of the composition and below the melting temperature of the discrete particles;    hot working the ingot to form a processed ingot; and    cold working and annealing the processed ingot to form the article.    
   
   
       12 . A method of making an article, the method comprising: 
 vacuum melting a substantially equiatomic composition of nickel and titanium to form a melted ingot, wherein the melting is performed at or above an alloying temperature for the composition;    pour stream injecting particles into the melted ingot during vacuum induction melting at a temperature below the melting point of the particles;    hot working the melted ingot to form a processed ingot; and    cold working and annealing the processed ingot to form the article, the article comprising a nickel-titanium alloy and a homogeneous dispersion of discrete particles substantially free of nickel and titanium.    
   
   
       13 . A method of making an article according to  claim 12 , wherein the substantially equiatomic composition has a nickel:titanium atomic ratio of about 50:50.  
   
   
       14 . A method according to  claim 12  wherein the particles are selected from the group consisting of iridium, platinum, gold, rhenium, tungsten, palladium, rhodium, tantalum, silver, ruthenium, and hafnium.  
   
   
       15 . A method according to  claim 12 , wherein the particles comprise an alloy comprising one or more of iridium, platinum, gold, rhenium, tungsten, palladium, rhodium, tantalum, silver, ruthenium, and hafnium.  
   
   
       16 . A method according to  claim 12 , wherein the vacuum melting comprises vacuum induction melting.  
   
   
       17 . A method according to  claim 12 , wherein the vacuum melting comprises vacuum skull melting.  
   
   
       18 . A method of making an article, the method comprising: 
 preparing an electrode having a hollow center, the electrode comprising a substantially equiatomic composition of nickel and titanium;    introducing particles into the hollow center;    vacuum arc melting the electrode and the particles at a temperature above the alloying temperature of the composition and below the melting point of the particles to form a melted ingot;    hot working the melted ingot to form a processed ingot; and    cold working and annealing the processed ingot to form the article, the article comprising a nickel-titanium alloy and a homogeneous dispersion of discrete particles substantially free of nickel and titanium.    
   
   
       19 . A method according to  claim 18 , wherein the particles are selected from the group consisting of iridium, platinum, gold, rhenium, tungsten, palladium, rhodium, tantalum, silver, ruthenium, and hafnium.  
   
   
       20 . A method according to  claim 18 , wherein the particles comprise an alloy comprising one or more of iridium, platinum, gold, rhenium, tungsten, palladium, rhodium, tantalum, silver, ruthenium, and hafnium.  
   
   
       21 . A method according to  claim 18 , wherein the particles are introduced by injecting the particle into the hollow center.  
   
   
       22 . A method according to  claim 18 , wherein the particles are introduced by packing a powdered particle into the hollow center.