Heat treatment of alloys having elements for improving grain boundary strength

Abstract

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

1 . A method of heat treating a directionally solidified or single crystal nickel based cast alloy comprising boron which improves grain boundary strength,
 wherein the alloy has a secondary phase after casting, which can be solved in the matrix of the alloy at a solution temperature,   wherein a heat treatment is performed in such a way that the secondary phase is only partly solved.   
   
   
       2 . A method of  claim 1 ,
 wherein at least one aging treatment is performed after the heat treatment.   
   
   
       3 . A method of  claim 1 ,
 wherein the temperature of the heat treatment is less than the fully solution temperature.   
   
   
       4 . A method of  claim 1 ,
 wherein the duration of the heat treatment is chosen in such a way, that the secondary is not completely solved.   
   
   
       5 . (canceled) 
   
   
       6 . A method of  claim 1 ,
 wherein the heat treatment is performed with hollow components.   
   
   
       7 . A method of  claim 6 ,
 wherein the heat treatment is performed with components having a length of about 20 centimeters to about 60 centimeters.   
   
   
       8 . A method of  claim 6 ,
 wherein the heat treatment is performed with hollow components having a thickness of an outer wall smaller than 8 mm.   
   
   
       9 . A method of  claim 5 ,
 wherein the secondary phase is the γ′-phase.   
   
   
       10 . (canceled) 
   
   
       11 . A method of  claim 1 ,
 wherein the heat treatment is performed with an alloy having carbon as an addition.   
   
   
       12 . A method of  claim 1 ,
 wherein the heat treatment is performed with an alloy having a directionally solidified columnar grains.   
   
   
       13 . A method of  claim 1 ,
 wherein the heat treatment is performed with an alloy having a single crystal structure.   
   
   
       14 . A method of  claim 1 ,
 wherein the parameters of the heat treatment is chosen in such a way that the amount of the secondary phase brought into solution is smaller than 90 vol %.   
   
   
       15 . A method of  claim 1 ,
 wherein the parameters of the heat treatment is chosen in such a way that the amount of the secondary phase brought into solution is smaller than 70 vol %.   
   
   
       16 . A method of  claim 1 ,
 wherein the parameters of the heat treatment is chosen in such a way that the amount of the secondary phase brought into solution is smaller than 50 vol %.   
   
   
       17 . A method of  claim 1 ,
 wherein the parameters of the heat treatment is chosen in such a way that the amount of the secondary phase brought into solution is smaller than 30 vol %.   
   
   
       18 . A method of  claim 1 ,
 wherein the heat treatment is performed with a directionally solidified columnar grain   nickel base alloy casting,   consisting essentially of, in weight % of   about 9.5% to 14% Cr,   about 7% to 11% Co,   about 1% to 2.5% Mo,   about 3% to 6% W,   about 1% to 6% Ta,   about 3% to 4% Al,   about 3% to 5% Ti,   about 0% to 1% Nb,   and balance essentially Ni   and B present in an amount effective to substantially improve transverse stress rupture strength of said casting as compared to a similar casting without boron present.   
   
   
       19 . A method of  claim 18 ,
 wherein the heat treatment is performed with an alloy,   wherein B is present in the range of about 0.003% to about 0.018% by weight.   
   
   
       20 . A method of  claim 18 ,
 wherein the alloy after the heat treatment 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 said casting.   
   
   
       21 . A method of  claim 1 ,
 wherein the heat treatment is performed with a directionally solidified columnar grain nickel base alloy casting consisting essentially of, in weight %, of   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,   about3.4% 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.   
   
   
       22 . A method of  claim 21 ,
 wherein the alloy after the heat treatment has a stress rupture life of at least about 120 hours and elongation 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.   
   
   
       23 . A method of  claim 1 ,
 wherein the heat treatment is performed with directionally solidified columnar grain nickel base alloy casting having a nominal composition consisting essentially of, in weight %, of   about 12.00% Cr,   about 9.00% Co,   about 1.85% Mo,   about 3.700% 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.   
   
   
       24 . A method of  claim 1 ,
 wherein the heat treatment is performed after casting.   
   
   
       25 . A method of  claim 4 ,
 wherein the fully solution temperature is used.   
   
   
       26 . A method of  claim 6 ,
 wherein the hollow components are chosen of the group consisting of vanes, blades and liners.   
   
   
       27 . A method of  claim 1 ,
 wherein the heat treatment is performed with massive components.   
   
   
       28 . A method of  claim 1 ,
 wherein the heat treatment is performed with an alloy having an addition selected from the group consisting of Zircon, Silicon, Hafnium.   
   
   
       29 . A method of  claim 3 ,
 wherein the duration of the heat treatment is chosen in such a way, that the secondary is not completely solved.