Nickel-base superalloy, unidirectional-solidification process therefor, and castings formed therefrom

Abstract

An alloy composition and method by which the incidence of freckling can be reduced in castings produced with properties similar to the René N5 nickel-base superalloy. The casting has a unidirectional crystal structure and a composition consisting of, by weight, 6% to 8% chromium, 6% to 9% cobalt, 0% to 2% molybdenum, 4% to 6% tungsten, 6.4% to 6.9% tantalum, 0% to 2% titanium, 5% to 7% aluminum, 2.7% to 3.0% rhenium, 0.3% to 0.7% haffiium, 0.04% to 0.08% carbon, 0.002% to 0.006% boron, 0% to 0.075% yttrium, 0.002% to 0.004% zirconium, the balance being nickel and incidental impurities.

1 . A nickel-base superalloy having a composition consisting of, by weight:
 6% to 8% chromium;   6% to 9% cobalt;   0% to 2% molybdenum;   4% to 6% tungsten;   6.4% to 6.9% tantalum;   0% to 2% titanium;   5% to 7% aluminum;   2.7% to 3.0% rhenium;   0.3% to 0.7% hafnium;   0.04% to 0.08% carbon;   0.002% to 0.006% boron;   0% to 0.075% yttrium;   0.002% to 0.004% zirconium;   the balance being nickel and incidental impurities.   
   
   
       2 . The nickel-base superalloy according to  claim 1 , wherein the nickel-base superalloy is in the form of a casting. 
   
   
       3 . The nickel-base superalloy according to  claim 2 , wherein the casting is substantially free of freckle defects. 
   
   
       4 . The nickel-base superalloy according to  claim 2 , wherein the casting has a unidirectional crystal structure. 
   
   
       5 . The nickel-base superalloy according to  claim 4 , wherein the unidirectional crystal structure is a single crystal. 
   
   
       6 . The nickel-base superalloy according to  claim 4 , wherein the casting is a component for a gas turbine. 
   
   
       7 . The nickel-base superalloy according to  claim 1 , wherein the composition contains 6.5 to 6.8 weight percent tantalum. 
   
   
       8 . The nickel-base superalloy according to  claim 1 , wherein the composition contains about 6.7 weight percent tantalum. 
   
   
       9 . The nickel-base superalloy according to  claim 1 , wherein the composition contains 6.0 to 6.2 weight percent aluminum. 
   
   
       10 . The nickel-base superalloy according to  claim 1 , wherein the composition contains about 6.1 weight percent aluminum. 
   
   
       11 . The nickel-base superalloy according to  claim 1 , wherein the composition contains 2.75 to 2.9 weight percent rhenium. 
   
   
       12 . The nickel-base superalloy according to  claim 1 , wherein the composition contains about 2.8 weight percent rhenium. 
   
   
       13 . The nickel-base superalloy according to  claim 1 , wherein the composition contains 0.4 to 0.6 weight percent hafnium. 
   
   
       14 . The nickel-base superalloy according to  claim 1 , wherein the composition contains about 0.5 weight percent hafnium. 
   
   
       15 . The nickel-base superalloy according to  claim 1 , wherein the composition contains 0.002 to 0.003 weight percent zirconium. 
   
   
       16 . The nickel-base superalloy according to  claim 1 , wherein the composition contains about 0.0025 weight percent zirconium. 
   
   
       17 . The nickel-base superalloy according to  claim 1 , wherein the composition contains, by weight, less than 4.90% tungsten, more than 6.44% tantalum, less than 6.20% aluminum, and less than 2.91% rhenium. 
   
   
       18 . (canceled) 
   
   
       19 . A nickel-base superalloy in the form of a casting having a unidirectional crystal structure that is substantially free of freckle defects, the superalloy having a composition consisting of, by weight:
 6.75% to 7.25% chromium;   7% to 8% cobalt;   1.3% to 1.7% molybdenum;   4.5% to 5.0% tungsten;   6.5% to 6.8% tantalum;   0% to 0.05% titanium;   6.0% to 6.2% aluminum;   2.75% to 2.90 rhenium;   0.4% to 0.6% hafnium;   0.04% to 0.08% carbon;   0.003% to 0.005% boron;   0% to 0.075% yttrium;   0.002% to 0.003% zirconium;   the balance being nickel and incidental impurities.   
   
   
       20 . The nickel-base superalloy according to  claim 19 , wherein the composition consists of, by weight:
 about 7% chromium;   about 7.5% cobalt;   about 1.5% molybdenum;   about 4.75% tungsten;   about 6.7% tantalum;   about 0% to 0.02% titanium;   about 6.1 % aluminum;   about 2.8% rhenium;   about 0.5% hafnium;   about 0.06% carbon;   about 0.004% boron;   0% to 0.03% yttrium;   about 0.0025% zirconium;   the balance being nickel and incidental impurities.