Fatigue-resistant nickel-base superalloys and method

Claim 1

A forged body of predetermined shape made of nickel-base superalloy consisting essentially of: ______________________________________ Element Composition (wt %) ______________________________________ Cr about 14 to about 18 Co about 10 to about 14 Mo about 3.0 to about 5.0 W about 3.0 to about 5.0 Al about 2.0 to about 3.0 Ti about 2.0 to about 3.0 Nb about 2.0 to about 3.0 Ta 0.0 to about 3.0 Ti + Nb/2 + Ta/4 about 3.5 to about 5.0 Zr about .02 to about .08 B about .01 to about .05 C less than about 0.10 ______________________________________ and having present therein γ' precipitate phase in an amount from about 42 to about 48% by volume; the grain structure of said superalloy being predominantly equiaxed; said superalloy exhibiting fatigue crack growth rates substantially independent of the waveform and frequency of fatigue stress intensity cyclically applied thereto at elevated temperatures.

Claim 12

The method of preparing a forged nickel-base superalloy body having its grain structure substantially all equiaxed with the grain size being about ASTM 5-6, said superalloy exhibiting fatigue crack growth rates at elevated temperatures largely independent of the waveform and frequency of fatigue stress intensity cyclically applied thereto, said method comprising the steps of: (a) preparing an initial alloy consisting essentially of a mass having a composition in the range defined by the following table with the balance essentially nickel: ______________________________________ Element Composition (wt %) ______________________________________ Cr about 14 to about 18 Co about 10 to about 14 Mo about 3.0 to about 5.0 W about 3.0 to about 5.0 Al about 2.0 to about 3.0 Ti about 2.0 to about 3.0 Nb about 2.0 to about 3.0 Ta 0.0 to about 3.0 Ti + Nb/2 + Ta/4 about 3.5 to about 5.0 Zr about .02 to about .08 B about .01 to about .05 C less than about 0.10 ______________________________________ (b) forging said initial alloy mass to produce an alloy body of predetermined shape, said forging being initiated at a temperature in the range of from about 5° to about 25° C. higher than the γ' precipitate solvus temperature, (c) solution annealing said alloy body for a period ranging from about 1 to about 4 hours at a temperature in the range of from about 5° to about 15° C. above the recrystallization temperature of the forged alloy, (d) cooling said alloy body at a rate in the range of from about 80° to 150° C. per minute to a temperature below which further thermal reaction will not occur and (e) aging said alloy body for a period ranging from about 8 to about 24 hours at one or more temperatures in the range of from about 600° to about 800° C.

Claim 13

The method of preparing a forged nickel-base superalloy body having its grain structure substantially all equiaxed with the grain size being about ASTM 5-6, said superalloy exhibiting fatigue crack growth rates at elevated temperatures largely independent of the waveform and frequency of fatigue stress intensity cyclically applied thereto, said method comprising the steps of: (a) preparing an initial alloy consisting essentially of a mass having a composition in the range defined by the following table with the balance essentially nickel: ______________________________________ Element Composition (wt %) ______________________________________ Cr about 14 to about 18 Co about 10 to about 14 Mo about 3.0 to about 5.0 W about 3.0 to about 5.0 Al about 2.0 to about 3.0 Ti about 2.0 to about 3.0 Nb about 2.0 to about 3.0 Ta 0.0 to about 3.0 Ti + Nb/2 + Ta/4 about 3.5 to about 5.0 Zr about .02 to about .08 B about .01 to about .05 C less than about 0.10 ______________________________________ (b) forging said initial alloy mass to produce an alloy body of predetermined shape, said forging being initiated at a temperature in the range of from about 5° to about 25° C. higher than the γ' precipitate solvus temperature, (c) solution annealing said alloy body for a period ranging from about 1 to about 4 hours at a temperature in the range of from about 5° to about 15° C. above the recrystallization temperature of the forged alloy, (d) cooling said alloy body at a rate in the range of from about 80° to 150° C. per minute to a temperature below which further thermal reaction will not occur and (e) aging said alloy body for a period ranging from about 8 to about 24 hours at one or more temperatures in the range of from about 600° to about 800° C.