Modified advanced high strength single crystal superalloy composition

Abstract

The present invention relates to an improved single crystal nickel base superalloy and a process for making same. The single crystal nickel base superalloy has a composition comprising 3 to 12 wt % chromium, up to 3 wt % molybdenum, 3 to 10 wt % tungsten, up to 5 wt % rhenium, 6 to 12 wt % tantalum, 4 to 7 wt % aluminum, up to 15 wt % cobalt, up to 0.05 wt % carbon, up to 0.02 wt % boron, up to 0.1 wt % zirconium, up to 0.8 wt % hafnium, up to 2.0 wt % niobium, up to 1.0 wt % vanadium, up to 0.7 wt % titanium, up to 10 wt % of at least one element selected from the group consisting of ruthenium, rhodium, palladium, osmium, iridium, platinum, and mixtures thereof, and the balance essentially nickel. The single crystal nickel base superalloy has a microstructure which is pore-free and eutectic γ-γ′ free and which has a gamma prime morphology with a bimodal γ′ distribution.

1 - 11 . (canceled)  
   
   
       12 . A process for forming an improved nickel base superalloy comprising the steps of: 
 casting an object formed from a single crystal nickel base superalloy having a microstructure;    said casting step comprising casting a single crystal nickel base superalloy having a composition consisting of 3.0 to 12 wt % chromium, up to 3.0 wt % molybdenum, 3.0 to 10 wt % tungsten, less than 5.0 wt % rhenium, 6.0 to 12 wt % tantalum, 4.0 to 7.0 wt % aluminum, up to 15 wt % cobalt, up to 0.05 wt % carbon, up to 0.02 wt % boron, up to 0.1 wt % zirconium, up to 0.8 wt % hafnium, up to 2.0 wt % niobium, up to 1.0 wt % vanadium, up to 0.7 wt % titanium, up to 10 wt % of at least one element selected from the group consisting of ruthenium, rhodium, palladium, osmium, iridium, platinum, and mixtures thereof, and the balance nickel;    closing any as-cast microporosity and partially solutioning eutectic γ-γ′ phase islands in the microstructure of said single crystal nickel base superalloy;    fully solutioning any eutectic γ-γ′ phase and precipitating a uniform distribution of large γ′ particles in the microstructure; and    forming fine γ′ particles in the microstructure to improve the strength of the nickel base superalloy.    
   
   
       13 . (canceled)  
   
   
       14 . A process according to  claim 12 , wherein said closing and partially solutioning step comprises subjecting said cast object to hot isostatic processing at a final temperature in the range of from 2145° F. to 2625° F. for a time period in the range of from 3.5 hours to 4.5 hours at a final pressure in the range of from 13 ksi to 16.5 ksi.  
   
   
       15 . A process according to  claim 14 , wherein said hot isostatic processing step is carried out at a final temperature in the range of 2195° F. to 2565° F. and at a final pressure in the range of from 14 ksi to 16 ksi.  
   
   
       16 - 18 . (canceled)  
   
   
       19 . A process according to  claim 12 , wherein said fully solutioning and precipitating step comprises subjecting the cast object to a solution heat treatment step.  
   
   
       20 - 21 . (canceled)  
   
   
       22 . A process according to  claim 12 , wherein said forming fine γ′ particles step comprises precipitation heat treating the cast object by heating the cast object to a treatment temperature in the range of from 1175° F. to 1450° F., holding the cast object at said treatment temperature for a time period in the range of 20 hours to 30 hours, and then air cooling the cast object.  
   
   
       23 . A process according to  claim 22 , wherein said heat treating step comprises heating the cast object to a temperature in the range of from 1200° F. to 1400° F. and holding the cast object at said treatment temperature for a time period in the range of 22 hours to 26 hours.  
   
   
       24 - 26 . (canceled)