Nitrogen-modified titanium and method of producing same

Abstract

A liquid-state reaction between a titanium molten pool and a fraction of gaseous nitrogen in an inert atmosphere creates an alloy with increased strength and hardness. A direct manufacturing technique involving rapid solidification processing is used rather than conventional casting techniques that require bulk melting of solid-state nitrided powder. By utilizing rapid solidification techniques, solubility levels can be increased resulting in alloys with unique mechanical and physical properties that are unattainable through conventional processing methods. Laser-powder deposition of titanium alloys in atmospheres of varying argon/nitrogen content produce significant strengthening without cracking in atmosphere concentrations as high as approximately 10% nitrogen. Very high hardness values indicate that this material has valuable applications as a hard face coating on titanium structures and in functionally graded materials.

1 . A method of forming an alloy, comprising: 
 (a) providing a heat source and a plurality of nozzles;    (b) mounting the heat source and the nozzles to a movable platform;    (c) delivering a metallic powder through the nozzles by entraining the metallic powder in an atmosphere comprising an inert gas and an gaseous alloying element for delivery into and through the nozzles;    (d) directing the metallic powder through the nozzles to a point where streams of the metallic powder converge with the heat source;    (e) melting the metallic powder with the heat source to form a molten pool on a substrate such that the metallic powder alloys with the gaseous alloying element; and    (f) moving the platform for the heat source and the nozzles away from the molten pool, such that the molten pool rapidly cools and solidifies to form a continuous line of deposited alloy to form a part.    
   
   
       2 . The method of  claim 1 , wherein step (c) comprises providing the atmosphere as approximately 90 to 99.9% inert gas, and approximately 0.1% to 10% gaseous alloying element.  
   
   
       3 . The method of  claim 1 , wherein step (c) comprises providing the gaseous alloying element as nitrogen.  
   
   
       4 . The method of  claim 1 , wherein step (a) comprises providing the heat source as a laser that is directed by fiber optics.  
   
   
       5 . The method of  claim 1 , wherein step (a) comprises providing the heat source as an electron beam.  
   
   
       6 . The method of  claim 1 , wherein step (a) comprises providing the heat source as an arc.  
   
   
       7 . The method of  claim 1 , further comprising the step of controlling the heat source with optics, the optics also being mounted to the movable platform, and wherein the movable platform is computer-controlled to position the heat source and the nozzles in a desired location for multiple sections and layers of the part being formed.  
   
   
       8 . The method of  claim 1 , further comprising the step of orienting the nozzles at 90° increments relative to each other in an array having a selected radius from, and being centered on the heat source.  
   
   
       9 . The method of  claim 1 , wherein step (f) comprises forming the part with adjacent, side-by-side layers to form a width of the part, and adjacent, stacked layers to form a height of the part.  
   
   
       10 . An alloy, comprising: 
 titanium; and    nitrogen having a weight percentage of approximately 0.05% to 3.0%.    
   
   
       11 . The alloy of  claim 10 , further comprising a hardness up to 55 HRC, and an ultimate tensile strength as high as 140 ksi.