Titanium-base alloy and method of improving creep properties

Abstract

A titanium-base alloy consisting by weight of about 5.5 to 6.5% aluminum, 1.7 to 2.3% tin, 0.7 to 5.0% zirconium, 0.7 to 3.0% molybdenum, 0.04 to 0.13% silicon, and the balance titanium. The addition of silicon to the otherwise known alloy produces a marked improvement in creep properties without significant detrimental effect to other properties.

We claim: 
     
       1. A titanium-base .[.alloy.]. .Iadd.product .Iaddend.consisting by weight of about 5.5 to 6.5% aluminum, 1.7 to 2.3% tin, 0.7 to 5.0% zirconium, 0.7 to 3.0% molybdenum, silicon in an amount of at least 0.04% but less than 0.10%, and the balance titanium and unavoidable impurities, said .[.alloy.]. .Iadd.product .Iaddend.having .Iadd.as a major portion an alpha-beta worked structure and .Iaddend.a minimum Charpy V-notch impact energy of 10 ft.-lbs. .Iadd.at -40° F., .Iaddend.and requiring a minimum time of 35 hours to reach 0.1% deformation when exposed to a stress of 35 Ksi at 950° F. 
     
     
       2. .[.An alloy.]. .Iadd.A product .Iaddend.as defined in claim 1 in which the silicon content is within the range of 0.08 to 0.09% by weight. 
     
     
       3. .[.An alloy.]. .Iadd.A product .Iaddend.as defined in claim 1 of a weight composition approximately 6% aluminum, 2% tin, 4% zirconium, 2% molybdenum, 0.08 to 0.09% silicon, balance titanium and unavoidable impurities. 
     
     
       4. A method of improving the creep properties of a titanium base alloy which otherwise consists by weight of about 5.5 to 6.5% aluminum, 1.7 to 2.3% tin, 0.7 to 5.0% zirconium, 0.7 to 3.0% molybdenum, balance titanium and unavoidable impurities, and which has a residual silicon content of about 0.02 to 0.03%, said method comprising adding silicon to said alloy in an amount to produce a silicon content therein of at least 0.04% but less than 0.10% including the residual, .Iadd.alpha-beta working said alloy to produce an alpha-beta worked structure .Iaddend.whereby the alloy attains sufficient creep strength that specimens thereof require a minimum time of 35 hours to reach 0.1% deformation when exposed to a stress of 35 Ksi at 950° F., yet retain sufficient notch toughness to have a minimum Charpy V-notch impact energy of 10 ft.-lbs. .Iadd.at -40° F. .Iaddend. 
     
     
       5. A method as defined in claim 4 in which silicon is added to the alloy in an amount to produce a silicon content therein of 0.08 to 0.09%. 
     
     
       6. A method as defined in claim 4 in which the alloy otherwise consists by weight of approximately 6% aluminum, 2% tin, 4% zirconium, 2% molybdenum, balance titanium and unavoidable impurities.