Method of controlling and refining final grain size in supersolvus heat treated nickel-base superalloys

Abstract

A method of forming a component from a gamma prime precipitation-strengthened nickel-base superalloy. The method entails formulating the superalloy to have a sufficiently high carbon content and forging the superalloy at sufficiently high local strain rates so that, following a supersolvus heat treatment, the component is characterized by a fine and substantially uniform grain size distribution, preferably finer than ASTM 7 and more preferably in a range of about ASTM 8 to 10.

1 . A method of forming an article from a gamma prime precipitation-strengthened nickel-base superalloy having a gamma prime solvus temperature, the method comprising the steps of:
 formulating the gamma prime precipitation-strengthened nickel-base superalloy to contain greater than 0.060 weight percent carbon;   forming a billet of the superalloy;   working the billet at a temperature below the gamma prime solvus temperature of the superalloy so as to form a worked article, wherein the billet is worked to undergo non-superplastic deformation and to achieve a maximum strain rate that is below an upper strain rate limit to avoid critical grain growth yet sufficiently high to control average grain size, wherein the upper strain rate limit is greater than 0.008 per second;   heat treating the worked article at a temperature above the gamma prime solvus temperature of the superalloy for a duration sufficient to uniformly coarsen the grains of the worked article; and   cooling the worked article at a rate sufficient to reprecipitate gamma prime within the worked article, wherein the worked article has an average grain size of not coarser than ASTM 7 and is substantially free of grains in excess of three ASTM units coarser than the average grain size.   
   
   
       2 . The method according to  claim 1 , wherein the forming step comprises a process chosen from the group consisting of powder metallurgy, cast and wrought, and spraycast forming techniques. 
   
   
       3 . The method according to  claim 1 , wherein the forming step comprises hot isostatic pressing or extrusion consolidation of a powder of the superalloy to form the billet. 
   
   
       4 . The method according to  claim 1 , wherein the superalloy contains up to about 0.10% carbon. 
   
   
       5 . The method according to  claim 1 , wherein the superalloy contains 0.065% to 0.085% carbon. 
   
   
       6 . The method according to  claim 1 , wherein the superalloy contains 0.066% to 0.070% carbon. 
   
   
       7 . The method according to  claim 1 , wherein the maximum strain rate is at least 0.010 per second. 
   
   
       8 . The method according to  claim 1 , wherein the maximum strain rate is at least 0.032 per second. 
   
   
       9 . The method according to  claim 1 , wherein the upper strain rate limit is greater than 0.100 per second. 
   
   
       10 . The method according to  claim 1 , wherein the worked article has an average grain size in a range of about ASTM 7 to 10. 
   
   
       11 . The method according to  claim 1 , wherein the worked article has an average grain size of not coarser than ASTM 8. 
   
   
       12 . The method according to  claim 1 , wherein the worked article has an average grain size of about ASTM 8 to about ASTM 10. 
   
   
       13 . The method according to  claim 1 , wherein the billet working step is characterized by a minimum strain rate sensitivity of less than m=0.3. 
   
   
       14 . The method according to  claim 1 , wherein the billet is worked so that nominal strain within the billet is about 0.7. 
   
   
       15 . The method according to  claim 1 , wherein the superalloy contains, by weight, about 15.0-17.0% chromium, about 12.0-14.0% cobalt, about 3.5-4.5% molybdenum, about 3.5-4.5% tungsten, about 1.5-2.5% aluminum, about 3.2-4.2% titanium, about 0.5.0-1.0% niobium, at least 0.065-0.10% carbon, about 0.010-0.060% zirconium, about 0.010-0.040% boron, about 0.0-0.3% hafnium, about 0.0-0.01 vanadium, and about 0.0-0.01 yttrium, the balance essentially nickel and incidental impurities. 
   
   
       16 . The worked article formed by the method of  claim 15 , wherein the worked article is a turbine disk of a gas turbine engine, and after the cooling step the worked article has an average grain size of ASTM 8 to 10. 
   
   
       17 . The method according to  claim 1 , wherein the superalloy contains, by weight, about 16.0-22.4% cobalt, about 6.6-14.3% chromium, about 2.6-4.8% aluminum, about 2.4-4.6% titanium, about 1.4-3.5% tantalum, about 0.9-3.0% niobium, about 1.9-4.0% tungsten, about 1.9-3.9% molybdenum, about 0.0-2.5% rhenium, about 0.02-0.10% carbon, about 0.02-0.10% boron, about 0.03-0.10% zirconium, the balance essentially nickel and incidental impurities. 
   
   
       18 . The worked article formed by the method of  claim 17 , wherein the worked article is a turbine disk of a gas turbine engine, and after the cooling step the worked article has an average grain size of ASTM 8 to 10. 
   
   
       19 . The method according to  claim 1 , wherein the superalloy contains, by weight, about 16.0-20.0 percent cobalt, about 8.5-12.5 percent chromium, about 1.5-3.5 percent tantalum, about 2.0-4.0 percent tungsten, about 1.9-3.9 percent molybdenum, about 0.04-0.06 percent zirconium, about 1.0-3.0 percent niobium, about 2.6-4.6 percent titanium, about 2.6-4.6 percent aluminum, about 0.02-0.04 percent carbon, about 0.02-0.04 percent boron, the balance essentially nickel and incidental impurities. 
   
   
       20 . The worked article formed by the method of  claim 19 , wherein the worked article is a turbine disk of a gas turbine engine, and after the cooling step the worked article has an average grain size of ASTM 8 to 10. 
   
   
       21 . The worked article formed by the method of  claim 1 , wherein the worked article is a turbine disk of a gas turbine engine, and after the cooling step the worked article has an average grain size of ASTM 8 to 10. 
   
   
       22 . A method of forming an article from a gamma prime precipitation-strengthened nickel-base superalloy having a gamma prime solvus temperature, the method comprising the steps of:
 formulating the superalloy to consist of, by weight, about 15.0-17.0% chromium, about 12.0-14.0% cobalt, about 3.5-4.5% molybdenum, about 3.5-4.5% tungsten, about 1.5-2.5% aluminum, about 3.2-4.2% titanium, about 0.5.0-1.0% niobium, at least 0.065% to about 0.10% carbon, about 0.010-0.060% zirconium, about 0.010-0.040% boron, about 0.0-0.3% hafnium, about 0.0-0.01 vanadium, and about 0.0-0.01 yttrium, the balance nickel and incidental impurities;   forming a billet of the superalloy to have a fine grain size;   working the billet at a temperature below the gamma prime solvus temperature of the superalloy so as to form a worked article, the billet working step being characterized by a minimum strain rate sensitivity of less than m=0.3 so as not to be fully superplastic during the working step, the working step being performed to achieve a maximum strain rate that is below an upper strain rate limit to avoid critical grain growth yet sufficiently high to control average grain size, wherein the maximum strain rate is at least 0.010 per second and the upper strain rate limit is greater than 0.1 per second;   heat treating the worked article at a temperature above the gamma prime solvus temperature of the superalloy for a duration sufficient to uniformly coarsen the grains of the worked article; and   cooling the worked article at a rate sufficient to reprecipitate gamma prime within the worked article, wherein the worked article has an average grain size of not coarser than ASTM 7 and is substantially free of grains in excess of two ASTM units coarser than the average grain size.   
   
   
       23 . The method according to  claim 22 , wherein the maximum strain rate is at least 0.032 per second. 
   
   
       24 . The method according to  claim 22 , wherein the superalloy contains 0.065% to 0.085% carbon. 
   
   
       25 . The method according to  claim 22 , wherein the superalloy contains 0.066% to 0.070% carbon. 
   
   
       26 . The worked article formed by the method of  claim 22 , wherein the worked article is a turbine disk of a gas turbine engine, and after the cooling step the worked article has an average grain size of about ASTM 8 to 10.