Nickel-titanium-yttrium alloys with reduced oxide inclusions

Abstract

A nickel-titanium alloy is made to be wholly or substantially free of titanium-rich oxide inclusions by including yttrium in an amount up to 0.15 wt. %, with the balance of the alloy being nickel and titanium in approximately equal proportion. For example, a NiTiY alloy may have a composition including, in weight percent based on total alloy weight: between 50 and 60 wt. % nickel; between 40 and 50 wt. % titanium; and between 0.01 and 0.15 wt. % yttrium. The resulting alloy is capable of being drawn into various forms, e.g., fine medical-grade wire, without exhibiting an unacceptable tendency to develop surface defects or to fracture or crack during cold drawing or forging. The resulting final forms exhibit favorable fatigue strength and fatigue-resistant characteristics.

1 - 6 . (canceled) 
     
     
         7 . A nickel-titanium (NiTi) alloy, comprising:
 at least 20 wt. % nickel;   between 35 wt. % titanium and 55 wt. % titanium;   between 0.01 wt. % yttrium and 0.15 wt. % yttrium; and   at least one of:
 copper between 1 wt. % and 10 wt. %, in lieu of an equal amount of nickel; 
 niobium between 1 wt. % and 15 wt. %, in lieu of an equal amount of titanium; 
 hafnium between 0.5 wt. % and 50 wt. %, in lieu of an equal amount of titanium; 
 zirconium between 0.5 wt. % and 35 wt. %, in lieu of an equal amount of titanium; 
 cobalt between 0.1 wt. % and 5 wt. %, in lieu of an equal amount of titanium, nickel, or a combination of titanium and nickel; 
 chromium between 0.1 wt. % and 1 wt. %, in lieu of an equal amount of titanium; and 
 iron between 0.1 wt. % and 10 wt. %, in lieu of an equal amount of titanium, nickel, or a combination of titanium and nickel. 
   
     
     
         8 - 11 . (canceled) 
     
     
         12 . A method of making a nickel-titanium (NiTi) alloy, comprising:
 providing at least 20 wt. % nickel;   providing between 35 wt. % titanium and 55 wt. % titanium;   providing between 0.01 wt. % yttrium and 0.15 wt. % yttrium;   providing at least one of:
 copper between 1 wt. % and 10 wt. %, in lieu of an equal amount of nickel; 
 niobium between 1 wt. % and 15 wt. %, in lieu of an equal amount of titanium; 
 hafnium between 0.5 wt. % and 50 wt. %, in lieu of an equal amount of titanium; 
 zirconium between 0.5 wt. % and 35 wt. %, in lieu of an equal amount of titanium; 
 cobalt between 0.1 wt. % and 5 wt. %, in lieu of an equal amount of titanium, nickel, or a combination of titanium and nickel; 
 chromium between 0.1 wt. % and 1 wt. %, in lieu of an equal amount of titanium; and 
 iron between 0.1 wt. % and 10 wt. %, in lieu of an equal amount of titanium, nickel, or a combination of titanium and nickel; and 
   forming an ingot including the nickel, the titanium and the yttrium, the ingot further including at least one of the copper, the niobium, the hafnium, the zirconium, the cobalt, the chromium and the iron.   
     
     
         13 . The method of  claim 12 , further comprising forming the ingot into a fine wire having a diameter of up to 1 mm. 
     
     
         14 . The method of  claim 12 , further comprising forming the ingot into an intermediate construct comprising one of a rod, wire, tube, sheet or plate by repetitive cold-forming and annealing cycles. 
     
     
         15 . The method of  claim 14 , further comprising forming the intermediate construct into a fine wire having a diameter of up to 1 mm.