Method for enhancing fretting fatigue resistance of alloys

Abstract

A method for increasing the fretting fatigue resistance of an alloy by prehardened a surface of the alloy followed by laser shock peening the prehardened surface. In one exemplary embodiment, an orthopedic prosthesis is formed from a titanium alloy and subjected to surface nitriding followed by laser shock peening. By nitriding the titanium alloy, the hardness of the alloy's surface is increased. Then, by subjecting the nitrided surface of the alloy to laser shock peening, the fretting fatigue of the nitrided surface may be increased by more than 100%.

1 . A method of enhancing the fretting fatigue resistance of an alloy, comprising the steps of:
 forming an orthopedic component from an alloy, wherein the alloy has a melting point;   nitriding at least a portion of the orthopedic component to form a nitrided surface, the nitrided surface having a first fretting fatigue strength; and   laser shock peening at least a portion of the nitrided surface of the orthopedic component to form a laser shock peened surface, wherein the laser shock peened surface has a second fretting fatigue strength.   
   
   
       2 . The method of  claim 1 , wherein the second fretting fatigue strength is at least 100 percent greater than the first fretting fatigue strength. 
   
   
       3 . The method of  claim 1 , wherein the second fretting fatigue strength is at least 120 percent greater than the first fretting fatigue strength. 
   
   
       4 . The method of  claim 1 , wherein the second fretting fatigue strength is at least 140 percent greater than the first fretting fatigue strength. 
   
   
       5 . The method of  claim 1 , further comprising the step of heating the orthopedic component to a nitriding temperature, wherein the step of nitriding the orthopedic component is performed at the nitriding temperature. 
   
   
       6 . The method of  claim 1 , further comprising the step of heating the orthopedic component to a nitriding temperature, the nitriding temperature being less than the beta-transus temperature of the alloy, wherein the step of nitriding the orthopedic component is performed at the nitriding temperature. 
   
   
       7 . The method of  claim 1 , wherein the forming step further comprises forming the orthopedic component from a titanium alloy. 
   
   
       8 . The method of  claim 7 , wherein the titanium alloy is Ti-6Al-4V. 
   
   
       9 . The method of  claim 1 , wherein the forming step further comprises forming the orthopedic component from Co—Cr—Mo. 
   
   
       10 . A method of enhancing the fretting fatigue resistance of an alloy, comprising the steps of:
 forming a modular orthopedic component from an alloy having a melting point, the modular orthopedic component comprising:
 a first component defining a male tapered surface; and 
 a second component defining a female tapered surface, the male tapered surface of the first component configured to form a taper lock with the female tapered surface of the second component; 
   nitriding at least one of the male tapered surface of the first component and the female tapered surface of the second component to form a nitrided surface, the nitrided surface having a first fretting fatigue; and   laser shock peening at least a portion of the nitrided surface to form a laser shock peened surface, wherein the laser shock peened surface has a second fretting fatigued strength.   
   
   
       11 . The method of  claim 10 , wherein the first component defining a male tapered surface comprises a stem portion of a hip stem and the second component defining a female tapered portion comprises a neck portion of a hip stem. 
   
   
       12 . The method of  claim 10 , wherein the second fretting fatigue strength is at least 100 percent greater than the first fretting fatigue strength. 
   
   
       13 . The method of  claim 10 , wherein the second fretting fatigue strength is at least 120 percent greater than the first fretting fatigue strength. 
   
   
       14 . The method of  claim 10 , wherein the second fretting fatigue strength is at least 140 percent greater than the first fretting fatigue strength. 
   
   
       15 . The method of  claim 10 , wherein the nitriding step further comprises nitriding both the male tapered surface of the first component and the female tapered surface of the second component. 
   
   
       16 . The method of  claim 10 , wherein the nitriding step further comprises nitriding at least one of the male tapered surface of the first component and the female tapered surface of the second component at a nitriding temperature, the nitriding temperature being at least 1,000 degrees Fahrenheit and less than the melting point of the alloy. 
   
   
       17 . The method of  claim 10 , wherein the nitriding step further comprises nitriding at least one of the male tapered surface of the first component and the female tapered surface of the second component at a nitriding temperature that is less than the beta-transus temperature of the alloy. 
   
   
       18 . The method of  claim 10 , wherein the forming step further comprises forming the orthopedic component from a titanium alloy. 
   
   
       19 . The method of  claim 18 , wherein the titanium alloy is Ti-6Al-4V. 
   
   
       20 . The method of  claim 10 , wherein the forming step further comprises forming the orthopedic component from Co—Cr—Mo.