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

Abstract

A gamma prime precipitation-strengthened nickel-base superalloy and method of forging an article from the superalloy to promote a low cycle fatigue resistance and high temperature dwell behavior of the article. The superalloy has a composition of, by weight, 16.0-22.4% cobalt, 6.6-14.3% chromium, 2.6-4.8% aluminum, 2.4-4.6% titanium, 1.4-3.5% tantalum, 0.9-3.0% niobium, 1.9-4.0% tungsten, 1.9-3.9% molybdenum, 0.0-2.5% rhenium, greater than 0.05% carbon, at least 0.1% hafnium, 0.02-0.10% boron, 0.03-0.10% zirconium, the balance nickel and incidental impurities. A billet is formed of the superalloy and worked at a temperature below the gamma prime solvus temperature of the superalloy so as to form a worked article, which is then heat treated above the gamma prime solvus temperature of the superalloy to uniformly coarsen the grains of the article, after which the article is cooled to reprecipitate gamma prime. The article has an average grain size of not coarser than ASTM 7 and is substantially free of critical grain growth.

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 have a composition of, 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, greater than 0.05% carbon, at least 0.1% hafnium, about 0.02-0.10% boron, about 0.03-0.10% zirconium, the balance nickel and incidental impurities;   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 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;   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 greater than 0.1 weight percent carbon. 
     
     
         5 . The method according to  claim 1 , wherein the superalloy contains greater than 0.1 weight percent up to about 0.125 weight percent carbon. 
     
     
         6 . The method according to  claim 1 , wherein the superalloy contains 0.1 to 0.6 weight percent hafnium. 
     
     
         7 . The worked article formed by the method of  claim 1 , wherein the worked article is a component chosen from the group consisting of turbine disks and compressor disks and blisks of gas turbine engines. 
     
     
         8 . The method according to  claim 1 , wherein the maximum strain rate is at least 0.003 per second. 
     
     
         9 . The method according to  claim 8 , wherein the worked article has an average grain size of not coarser than ASTM 8. 
     
     
         10 . The worked article formed by the method of  claim 9 , wherein the worked article is a component chosen from the group consisting of turbine disks and compressor disks and blisks of gas turbine engines. 
     
     
         11 . The method according to  claim 1 , wherein the maximum strain rate is at least 0.03 per second. 
     
     
         12 . The method according to  claim 11 , wherein the worked article has an average grain size of not coarser than ASTM 8. 
     
     
         13 . The worked article formed by the method of  claim 12 , wherein the worked article is a component chosen from the group consisting of turbine disks and compressor disks and blisks of gas turbine engines. 
     
     
         14 . 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 have a composition of, 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, greater than 0.05% to about 0.125% carbon, about 0.1-0.6% hafnium, about 0.02-0.10% boron, about 0.03-0.10% zirconium, 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 working step being performed so that the billet undergoes non-superplastic deformation and achieves 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 0.03 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.   
     
     
         15 . The method according to  claim 14 , wherein the superalloy contains greater than 0.10 weight percent carbon. 
     
     
         16 . The method according to  claim 14 , wherein the worked article has an average grain size of not coarser than ASTM 8. 
     
     
         17 . The worked article formed by the method of  claim 16 , wherein the worked article is a component chosen from the group consisting of turbine disks and compressor disks and blisks of gas turbine engines. 
     
     
         18 . The method according to  claim 14 , wherein the maximum strain rate is at least 0.03 to about 0.3 per second. 
     
     
         19 . The method according to  claim 18 , wherein the worked article has an average grain size of not coarser than ASTM 8. 
     
     
         20 . The worked article formed by the method of  claim 19 , wherein the worked article is a component chosen from the group consisting of turbine disks and compressor disks and blisks of gas turbine engines.