Age-hardenable, nickel-base superalloy with improved notch ductility

Abstract

A precipitation hardenable nickel base alloy that provides a novel combination of elevated temperature strength, ductility, and reduced notch sensitivity at temperatures up to about 1300° F. is described. The alloy contains, in weight percent, about Carbon 0.10 max. Manganese 0.35 max. Silicon 0.2-0.7 Phosphorus 0.03 max. Sulfur 0.015 max. Chromium 12-20 Molybdenum 4 max. Tungsten 6 max. Cobalt 5-12 Iron 14 max. Titanium 0.4-1.4 Aluminum 0.6-2.6 Niobium 3-7 Boron 0.003-0.015 the balance being nickel and usual impurities. An article made from the alloy and a method of making the alloy are also disclosed.

1. A method of making a precipitation hardenable nickel base alloy comprising the steps of:
 providing charge materials in a vacuum melting furnace, said charge materials being selected to provide a precipitation hardenable nickel base alloy;  
 adding to said charge materials an amount of silicon effective to provide precipitation of a globular intermetallic phase in the alloy during elevated temperature processing thereof;  
 melting said charge materials and additions to form said alloy; and then  
 casting the molten alloy to form an ingot.  
 
     
     
       2. A method as set forth in  claim 1  wherein the step of providing the charge materials comprises the step of providing charge materials selected to provide a composition containing, in weight percent, about
                                       Carbon   0.10   max.         Manganese   0.35   max.         Phosphorus   0.03   max.         Sulfur   0.015   max.         Chromium   12-20         Molybdenum   4   max.         Tungsten   6   max.         Cobalt   5-12         Iron   14   max.         Titanium   0.4-1.4         Aluminum   0.6-2.6         Niobium   3-7         Boron   0.003-0.015                                           
 
       the balance being nickel and usual impurities. 
     
     
       3. A method as set forth in  claim 2  wherein the step of adding silicon comprises adding sufficient silicon to provide a retained amount of about 0.2% to about 0.7% silicon in the ingot. 
     
     
       4. A method as set forth in  claim 1  or  claim 2  comprising the steps of:
 forming said ingot into an article;  
 solution treating said article at a temperature of about 1750-1850° F.; and then age hardening said article.  
 
     
     
       5. A precipitation hardenable nickel base alloy that provides a unique combination of elevated temperature strength and ductility with reduced notch sensitivity at temperatures up to about 1300° F., said alloy comprising, in weight percent, about
                                       Carbon   0.10   max.         Manganese   0.35   max.         Silicon   0.4-0.7         Phosphorus   0.03   max.         Sulfur   0.015   max.         Chromium   12-20         Molybdenum   4   max.         Tungsten   6   max.         Cobalt   5-12         Iron   14   max.         Titanium   0.4-1.4         Aluminum   0.6-2.6         Niobium   3-7         Boron   0.003-0.015                                            
 
       the balance being nickel and usual impurities. 
     
     
       6. An alloy as set forth in  claim 5  which contains at least about 4% niobium. 
     
     
       7. An alloy as set forth in  claim 5  or  claim 6  which contains not more than about 0.6% silicon. 
     
     
       8. An alloy as set forth in  claim 7  which contains not more than about 6% niobium. 
     
     
       9. An alloy set forth in  claim 8  wherein the sum of molybdenum and tungsten is at least about 2% and not more than about 8%. 
     
     
       10. An article formed of a precipitation hardenable nickel base alloy as claimed in  claim 5  comprising a matrix formed of a nickel base alloy, a strengthening precipitate dispersed in said matrix, and a globular intermetallic precipitate dispersed at grain boundaries of said matrix material, such that the globular intermetallic precipitate restricts grain growth during elevated temperature processing of the alloy. 
     
     
       11. An article as set forth in  claim 10  wherein the globular intermetallic precipitate contains one or more of Si, Fe, Ni, Co and Cr, or a combination thereof, in combination with one or more of Nb, Mo, W, and Ti, or a combination thereof. 
     
     
       12. An article as set forth in  claim 10  which has been solution treated at a temperature of about 1750-1850° F. and age hardened. 
     
     
       13. An article as set forth in  claim 10  which has been solution treated at a temperature of about 1800-1850° F. and age hardened.