High strength alpha/beta titanium alloy fasteners and fastener stock

Abstract

An article of manufacture selected from a titanium alloy fastener and a titanium alloy fastener stock including an alpha/beta titanium alloy comprising, in percent by weight: 3.9 to 4.5 aluminum; 2.2 to 3.0 vanadium; 1.2 to 1.8 iron; 0.24 to 0.3 oxygen; up to 0.08 carbon; up to 0.05 nitrogen; titanium; and up to a total of 0.3 of other elements. In certain embodiments, article of manufacture has an ultimate tensile strength of at least 170 ksi (1,172 MPa) and a double shear strength of at least 103 ksi (710.2 MPa). A method of manufacturing a titanium alloy fastener and a titanium alloy fastener stock comprising the alpha/beta alloy is disclosed.

I claim: 
     
         1 . A method for producing a titanium alloy fastener stock, the method comprising:
 providing an alpha/beta titanium alloy comprising, in percent by weight:
 3.9 to 4.5 aluminum; 
 2.2 to 3.0 vanadium; 
 1.2 to 1.8 iron; 
 0.24 to 0.3 oxygen; 
 up to 0.08 carbon; 
 up to 0.05 nitrogen; 
 titanium; and 
 up to a total of 0.3 of other elements; 
   hot rolling the titanium alloy in an alpha/beta phase of the titanium alloy;   annealing the titanium alloy at an annealing temperature in a range of 1,200° F. (648.9° C.) to 1,400° F. (760° C.) for an annealing time in a range of 1 hour to 2 hours;   air cooling the titanium alloy;   machining the titanium alloy to a predetermined dimension;   solution treating the titanium alloy in a solution treatment range of 1,500° F. (815.6° C.) to 1,700° F. (926.7° C.) for a solution treating time in a range of 0.5 hours to 2 hours;   cooling the titanium alloy at a cooling rate that is at least equivalent to air cooling,   aging the titanium alloy at an aging treatment temperature in a range of 800° F. (426.7° C.) to 1,000° F. (537.8° C.) for an aging time in a range of 4 hours to 16 hours; and   air cooling the titanium alloy.   
     
     
         2 . The method of  claim 1 , wherein the other elements of the alpha/beta titanium alloy consist essentially of one or more of tin, zirconium, molybdenum, chromium, nickel, silicon, copper, niobium, tantalum, manganese, and cobalt, wherein the weight percent of each such element is 0.1 or less, and boron and yttrium, wherein the weight percent of each such element is less than 0.005. 
     
     
         3 . The method of  claim 1 , wherein the hot rolling is conducted at a temperature in the range of 50° F. (27.8° C.) below a beta transus temperature of the titanium alloy to 600° F. (333.3° C.) below the beta transus temperature of the titanium alloy. 
     
     
         4 . The method of  claim 1 , further comprising after hot rolling and before annealing the titanium alloy, cold drawing the titanium alloy to a reduction in cross-sectional area less than 10% and annealing. 
     
     
         5 . The method of  claim 4 , further comprising coating the titanium alloy with a solid lubricant before cold drawing. 
     
     
         6 . The method of  claim 5 , wherein the solid lubricant is molybdenum disulfide. 
     
     
         7 . The method of  claim 1 , wherein the annealing temperature is 1,275° F. (690.6° C.) and the annealing time is 1 hour. 
     
     
         8 . The method of  claim 1 , wherein the titanium alloy is coated prior to machining the titanium alloy. 
     
     
         9 . The method of  claim 1 , wherein cooling after the solution treating step comprises one of air cooling, water cooling, and water quenching. 
     
     
         10 . The method of  claim 1 , wherein the solution treatment temperature is 1,610° F. (876.7° C.) and cooling the titanium alloy comprises water quenching. 
     
     
         11 . The method of  claim 1 , wherein the aging the titanium alloy comprises aging at 850° F. (454.4° C.) for 10 hours.