Titanium alloys

Abstract

Provided herein are titanium alloys that can achieve a combination of high strength and high toughness or elongation, and a method to produce the alloys. By tolerating iron, oxygen, and other incidental elements and impurities, the alloys enable the use of lower quality scrap as raw materials. The alloys are castable and can form α-phase laths in a basketweave morphology by a commercially feasible heat treatment that does not require hot-working or rapid cooling rates. The alloys comprise, by weight, about 3.0% to about 6.0% aluminum, 0% to about 1.5% tin, about 2.0% to about 4.0% vanadium, about 0.5% to about 4.5% molybdenum, about 1.0% to about 2.5% chromium, about 0.20% to about 0.55% iron, 0% to about 0.35% oxygen, 0% to about 0.007% boron, and 0% to about 0.60% other incidental elements and impurities, the balance of weight percent comprising titanium.

1 . A method for casting a titanium alloy article of manufacture comprising the steps of:
 (a) forming a melt comprising, by weight, about 3.0% to about 6.0% aluminum, 0% to about 1.5% tin, about 2.0% to about 4.0% vanadium, about 0.5% to about 4.5% molybdenum, about 1.0% to about 2.5% chromium, 0% to about 0.35% oxygen, 0% to about 0.007% boron, 0% to about 0.60%, other incidental elements and impurities, about 0.20% to about 0.55% iron, and the balance of weight percent comprising titanium;   (b) casting said melt; and   (c) cooling said casting.   
     
     
         2 . The method of  claim 1 , including initially forming the casting as said article without hot working. 
     
     
         3 . The method of  claim 1 , wherein said melt is comprised of starting material combined in said melt of at least 25% of a titanium based alloy that includes, by weight, about 6% aluminum and about 4% vanadium, the balance of weight percent comprising titanium, the said starting material further including, by weight, 0% to about 0.35% oxygen, 0% to about 0.55% iron, and other incidental elements and impurities. 
     
     
         4 . The method of  claim 1  further comprising the heat treatment of:
 subjecting the cast and formed alloy to a hot isostatic pressing at 900° C. and about 100 MPa Ar for 2 hours; 
 annealing the alloy to form a single-phase microstructure of β-phase; and 
 subsequently cooling the alloy from the β-phase to an α-phase at a cooling rate to form α-phase laths in a basketweave morphology. 
 
     
     
         5 . The method of  claim 4 , wherein the cooling step comprises cooling the casting with a gas pressurized to about 2 atm. 
     
     
         6 . The method of  claim 5 , wherein the annealing is at a temperature above 0-transus temperature of the alloy. 
     
     
         7 . The method of  claim 5  wherein annealing is at a temperature up to about 950° C. 
     
     
         8 . The method of  claim 5 , wherein the cooling rate is between about 0.03° C. per second to about 10° C. per second. 
     
     
         9 . The method of  claim 1 , wherein the titanium-based melt includes, by weight, about 4.0% to about 5.5% aluminum, 0% to about 1.0% tin, about 2.5% to about 3.5% vanadium, about 1.0% to about 2.0% molybdenum, about 1.0% to about 2.0% chromium, about 0.30% to about 0.55% iron, 0.25% to about 0.3% oxygen, 0% to about 0.005% boron, and 0% to about 0.2% other incidental elements and impurities, the balance of weight percent comprising titanium. 
     
     
         10 . The method of  claim 9 , further comprising:
 subjecting the cast alloy to a hot isostatic pressing at 900° C. and about 100 MPa Ar for 2 hours;   annealin g the alloy to form a single-phase microstructure of β-phase; and   cooling the alloy from the β-phase to an α-phase at a cooling rate to form α-phase laths in a basketweave morphology.   
     
     
         11 . The method of  claim 10 , wherein the annealing is at a temperature above the β-transus temperature of the alloy. 
     
     
         12 . The method of  claim 11 , wherein the cooling rate is between about 0.03° C. per second to about 10° C. per second. 
     
     
         13 . An article of manufacture by the process of  claim 1 . 
     
     
         14 . A titanium alloy comprising:
 about 3.0% to about 6.0% aluminum, 0% to about 1.5% tin, about 2.0% to about 4.0% vanadium, about 0.5% to about 4.5% molybdenum, about 1.0% to about 2.5% chromium, 0% to about 0.35% oxygen, 0% to about 0.007% boron, 0% to about 0.60% other incidental elements and impurities, about 0.20% to about 0.55% iron, and the balance of weight percent comprising titanium, said alloy characterized by a substantially basketweave α-phase lath structure, a tensile elongation of at least about 10% and a tensile strength greater than about 960 MPa.   
     
     
         15 . The alloy of  claim 14 , wherein the laths of the lath structure measure no more than about 100 microns in the longest dimension 
     
     
         16 . The alloy of  claim 14 , wherein the aluminum content is about 4.0% to about 5.5%, the tin content is 0% to about 1.0%, the vanadium content is about 2.5% to about 3.5%, the molybdenum content is about 1.0% to about 2.0%, the chromium content is about 1.0% to about 2.0%, the iron content is about 0.30% to about 0.55%, the oxygen content is 0% to about 0.20%, the boron content is 0% to about 0.005%, and the content of other incidental elements and impurities is 0% to about 0.20%. 
     
     
         17 . The alloy of  claim 14 , wherein the α-phase laths comprise a basketweave morphology. 
     
     
         18 . The method of  claim 1  wherein the iron content by weight consists of 0.20% to 0.55%.