Method of improving the properties of a component of a medical device comprising a nickel-titanium-chromium alloy

Abstract

A method of improving the properties of a component of a medical device entails constraining the component, which comprises about 45-55 at. % Ni, about 45-55 at. % Ti, and about 0.3 at. % Cr, into a predetermined configuration. The component also includes at least about 35% cold work. The component is heated during the constraining at a temperature of between about 425° C. and about 500° C. for a time duration of between about 5 minutes and about 30 minutes, thereby improving the superelastic and mechanical properties of the component. A medical device includes a superelastic component for use in a body vessel that comprises about 45-55 at. % Ni, about 45-55 at. % Ti, and about 0.3 at. % Cr, where the component has an upper plateau strength of at least about 75 ksi, a residual elongation of about 0.1% or less, and an austenite finish temperature (Af) of about 30° C. or less.

1 . A method of improving the properties of a component of a medical device comprising a Ni—Ti—Cr alloy, the method comprising:
 constraining a component comprising about 45-55 at. % Ni, about 45-55 at. % Ti, and about 0.3 at. % Cr into a predetermined configuration, the component comprising at least about 35% cold work; 
 heating the component during the constraining at a temperature of between about 425° C. and about 500° C. for a time duration of between about 5 minutes and about 30 minutes, thereby improving the superelastic and mechanical properties of the component. 
 
     
     
         2 . The method of  claim 1  wherein the component includes about 0.25 at. % Cr. 
     
     
         3 . The method of  claim 1  wherein the temperature of the heating is between about 450° C. and about 475° C. 
     
     
         4 . The method of  claim 1  wherein the time duration of the heating is about 20 minutes. 
     
     
         5 . The method of  claim 1  wherein the component includes between about 35% and about 45% cold work. 
     
     
         6 . The method of  claim 5  wherein the component includes about 45% cold work. 
     
     
         7 . The method of  claim 1  further comprising, prior to constraining the component, drawing an elongate body having a first cross-sectional area to a second cross-sectional area at least about 35% smaller than the first cross-sectional area, thereby forming the component. 
     
     
         8 . The method of  claim 1  wherein the component is a wire. 
     
     
         9 . The method of  claim 1  wherein the component is a thin-walled cannula. 
     
     
         10 . The method of  claim 1  wherein the component includes about 0.25% Cr and between about 35% and about 45% cold work, and wherein the temperature of the heating is between about 450° C. and about 475° C. and the time duration of the heating is about 20 minutes. 
     
     
         11 . The method of  claim 10  wherein the component includes about 45% cold work and the temperature of the heating is about 450° C. 
     
     
         12 . A medical device comprising a superelastic component for use in a body vessel, the medical device comprising:
 a component comprising about 45-55 at. % Ni, about 45-55 at. % Ti, and about 0.3 at. % Cr, wherein the component has an upper plateau strength of at least about 75 ksi, a residual elongation of about 0.1% or less, and an austenite finish temperature (A f ) of about 30° C. or less.   
     
     
         13 . The medical device of  claim 12 , wherein the component further comprises an ultimate tensile strength of at least about 200 ksi. 
     
     
         14 . The medical device of  claim 12  wherein the component further comprises a lower plateau strength of at least about 40 ksi. 
     
     
         15 . The medical device of  claim 12  wherein the component further comprises a radial force per unit length exceeding that of a component comprising a binary Nitinol alloy. 
     
     
         16 . The medical device of  claim 12  wherein the austenite finish temperature (A f ) is about 25° C. or less. 
     
     
         17 . The medical device of  claim 12  wherein the upper plateau strength is at least about 90 ksi. 
     
     
         18 . The medical device of  claim 12 , wherein the component comprises an upper plateau strength of at least about 90 ksi, a lower plateau strength of at least about 40 ksi, an ultimate tensile strength of at least about 200 ksi, a residual elongation of about 0.1% or less, an austenite finish temperature (A f ) of about 25° C. or less, and a radial force per unit length exceeding that of a component comprising a binary Nitinol alloy.