Heat treatment of alloys having elements for improving grain boundary strength

Abstract

Heat treatment of alloys having elements for improving grain boundary strength is disclosed. Components directly after castings often reveal low or no transverse grain boundary strength, so that cracks do appear and decrease the yield rate. The provided measures do not lead to low transverse grain boundary strength but maintains efficient grain boundary strength, so that the yield rate of components without cracks is increased.

1 . A method of heat treating a directionally solidified columnar grain nickel base alloy casting to improve grain boundary strength, comprising casting the alloy such that it has a secondary phase after casting which is only partially solved in the matrix of the alloy at a solution temperature, the alloy comprising Boron present in an amount effective to substantially improve transverse stress rupture strength of the casting.  
   
   
       2 . A method of  claim 1 , wherein B is present in the range of about 0.003% to about 0.018% by weight.  
   
   
       3 . A method of  claim 1 , wherein after the heat treatment the alloy has a stress rupture life of at least about 100 hours and elongation to fracture of at least about 2.5% when tested at a temperature of 750 degrees C. (1382 degrees F.) and stress of 660 MPa (95.7 Ksi) applied in a direction perpendicular to a <001> crystal axis of the casting.  
   
   
       4 . A method of  claim 1 , wherein the alloy consists essentially of, in weight %: 
 about 11.6% to 12.70% Cr,    about 8.5% to 9.5% Co,    about 1.65% to 2.15% Mo,    about 3.5% to 4.10% W,    about 4.8% to 5.20% Ta,    about 3.4% to 3.80% Al,    about 3.9% to 4.25% Ti,    about 0.05% to 0.11% C,    about 0.003% to 0.0175% B,    balance essentially Ni and having substantially improved transverse stress rupture strength as compared to a similar casting without boron present.    
   
   
       5 . A method of  claim 1 , wherein the alloy consists essentially of, in weight %: 
 about 12.00% Cr,    about 9.00% Co,    about 1.85% Mo,    about 3.70% W,    about 5.10% Ta,    about 3.60% Al,    about 4.00% Ti,    about 0.0125% B,    about 0.09% C, balance essentially Ni and    having a stress rupture life of at least about 100 hours and elongation to fracture of at least about 2.5% when tested at a temperature of 750 degrees C. (1382 degrees F.) and stress of 660 MPa (95.7 Ksi) applied perpendicular to a <001> crystal axis of said casting.    
   
   
       6 . The method of  claim 1 , wherein the heat treatment is performed after casting.  
   
   
       7 . The method of  claim 6 , wherein a fully solution temperature is used.  
   
   
       8 . The method of  claim 1 , wherein the alloy is formed into a hollow component selected from the group consisting of vanes, blades and liners.  
   
   
       9 . The method of  claim 1 , wherein the alloy further comprises an addition selected from the group consisting of Zirconium, Silicon, Hafnium.  
   
   
       10 . The method of  claim 9 , wherein the Zirconium does not exceed 0.0075wt % of the alloy.  
   
   
       11 . The method of  claim 9 , wherein the Hafnium does not exceed 0.0075wt % of the alloy.