Bonding titanium to stainless steel

Abstract

Forming an implantable component assembly by bonding a stainless steel part to a titanium part by heating a component assembly comprised of the titanium part, the stainless steel part, and a compact filler layer of titanium-nickel particulate material placed between the two parts and heated at a temperature that is less than the melting point of either the stainless steel part or the titanium part. The component assembly is held in intimate contact at temperature in a non-reactive atmosphere for a sufficient time to develop a hermetic and strong bond between the stainless steel part and the titanium part. The bonded component assembly is optionally treated with acid to remove any residual free nickel and nickel salts, to assure a biocompatible component assembly, when implanted in a human body.

1 . A component assembly configured for implantation in living tissue, comprising
 a stainless steel part;   a titanium part; and   a compact filler, not an alloy, is a dense bonded compact layer of a primary alloy metallic particulate and a secondary alloy metallic particulate, where said primary alloy particulate is comprised of a nickel alloy and said secondary alloy particulate is comprised of a titanium alloy, said compact filler configured to form said component assembly by bonding said stainless steel part to said titanium part.   
     
     
         2 . The component assembly of  claim 1 , wherein said primary alloy particulate and said secondary alloy particulate are randomly dispersed in said compact filler. 
     
     
         3 . The component assembly of  claim 1 , wherein said stainless steel part is selected from the group consisting of 200, 300, and 400 series stainless steel. 
     
     
         4 . The component assembly of  claim 1 , wherein said stainless steel part is comprised of 316L stainless steel. 
     
     
         5 . The component assembly of  claim 1 , wherein said titanium part is selected from the group consisting of titanium and titanium alloys. 
     
     
         6 . The component assembly of  claim 1 , wherein said titanium part is comprised of Ti-6AI-4V. 
     
     
         7 . The component assembly of  claim 1 , wherein said compact filler reacts with said titanium part and said stainless steel part to bond between said titanium part and said stainless steel part together. 
     
     
         8 . The component assembly of  claim 1 , wherein:
 said compact filler has a thickness less than 0.010 inches; and   said component assembly is heated to a temperature less than the melting point of said titanium part or of said stainless steel part, but greater than the melting point of said compact filler, thereby forming a bond.   
     
     
         9 . A method of making a stainless steel and titanium component assembly for implantation in living tissue, comprising the steps of:
 selecting a stainless steel part having a melting point;   selecting a titanium part having a melting point;   selecting a primary alloy particulate discrete particles comprised of a nickel alloy;   selecting a secondary alloy particulate discrete particles comprised of a titanium alloy;   forming a compact filler by combining said selected primary alloy particulate and said secondary alloy particulate in a randomly oriented mixture comprised of a 22% to 98% nickel portion and a remaining titanium portion;   mechanically compacting said compact filler to form a compact filler layer less than 0.010 inches thick;   positioning said 0.010 inches thick compact filler layer between said stainless steel part and said titanium part forming a component assembly;   placing said component assembly in a non-reactive atmosphere;   applying a force to said stainless steel part and said titanium part to place said compact filler layer in compression, thereby creating intimate contact between said stainless steel part, said compact filler layer, and said titanium part;   heating said component assembly to a bonding temperature between said melting point of said compact filler layer and said melting point of said titanium part;   holding said component assembly at said bonding temperature for a predetermined time to form a bond between said stainless steel part and said titanium part forming a bonded component assembly;   cooling said bonded component assembly; and   implanting said component assembly in a human body.   
     
     
         10 . The method of  claim 9  wherein said step of applying a force creates compression between about 5 and 50 psi. 
     
     
         11 . The method of  claim 9  wherein said step of applying a force creates compression between about 5 and 7 psi. 
     
     
         12 . The method of  claim 9  wherein said step of selecting a stainless steel part is selecting from the group consisting of 200, 300, and 400 series stainless steel. 
     
     
         13 . The method of  claim 9  wherein said step of selecting a titanium part is selecting from the group consisting of substantially pure titanium and its alloys. 
     
     
         14 . The method of  claim 9  wherein said step of selecting a titanium part is selecting said part comprised of Ti-6AI-4V. 
     
     
         15 . The method of  claim 9  further comprising the step of placing the assembly in a non-reactive atmosphere is placing in a vacuum less than 10 −5  torr. 
     
     
         16 . The method of  claim 9  further comprising the step of placing the assembly in a non-reactive atmosphere is placing in argon gas. 
     
     
         17 . The method of  claim 9  wherein said bonding temperature is between approximately 940° and 1260° C. 
     
     
         18 . The method of  claim 9  wherein said predetermined time is between approximately 5 and 60 minutes. 
     
     
         19 . The method of  claim 9  additionally comprising the step of cleaning said component assembly after bonding to remove elemental nickel and nickel salts by placing it in an acid bath. 
     
     
         20 . A method of making a stainless steel part and a titanium part component assembly for implantation in living tissue in which a filler is placed between the two parts to be bonded, applying a compressive force of 5 to 50 psi to said stainless steel part and to said titanium part so as to place said filler material in compression to form intimate contact between said stainless steel part and said titanium part and in which said component assembly, comprising said stainless steel part, said titanium part and said filler, is placed at a bonding temperature, for a predetermined time, wherein the improvement comprises:
 selecting said filler to be a compact filler comprised of a primary alloy particulate discrete particles comprised of a nickel alloy and a secondary alloy particulate discrete particles comprised of a titanium alloy;   bonding said component assembly between 940° and 1260° C.; and   implanting said component assembly in a human body.