Patent ID: 7527702

Claim:
A method of heat treating a 718-type nickel-base alloy, comprising: selecting a 718-type nickel-base alloy; solution treating the 718-type nickel-base alloy at a solution heat treat temperature greater than or equal to about 100° F. less than a γ′ and γ″ phase solvus temperature of the 718-type nickel alloy, and less than a δ and η phase solvus temperature of the 718-type nickel alloy, and for a solution heat treatment time sufficient to retain an amount of at least one grain boundary precipitate; wherein the at least one grain boundary precipitate comprises a δ-phase precipitate, an η-phase precipitate, or mixtures thereof; cooling the 718-type nickel-base alloy at a first cooling rate after solution treating the 718-type nickel-base alloy, wherein the first cooling rate is sufficient to substantially suppress precipitation and coarsening of a γ′-phase precipitate and a γ″-phase precipitate; first step aging the solution treated 718-type nickel-base alloy for a first step aging time and a first step aging temperature; wherein the first step aging temperature is below the γ′ and γ″ phase solvus temperature of the 718-type nickel alloy so that during the first step aging time an amount of primary γ′-phase grain matrix precipitates and an amount of primary γ″-phase grain matrix precipitates are formed; and second step aging the 718-type nickel-base alloy for a second step aging time and a second step aging temperature to form a heat treated 718-type nickel-base alloy; wherein the second step aging temperature is sufficiently less than the first step aging temperature so that an amount of secondary γ′-phase grain matrix precipitates and an amount of secondary γ″-phase grain matrix precipitates are formed during the second step aging time that are generally finer than the primary γ′-phase grain matrix precipitates and the primary γ″ phase grain matrix precipitates; wherein the primary and secondary γ′-phase grain matrix precipitates and the primary and secondary γ″-phase grain matrix precipitates are the predominant strengthening precipitates in the heat treated 718-type nickel-base alloy; wherein the amount of at least one grain boundary precipitate in the heat treated 718-type nickel-base alloy comprises short, generally rod-shaped morphologies and is sufficient to pin a majority of grain boundaries in place; and wherein the heat treated 718-type nickel-base alloy comprises thermally stable mechanical properties.