Corrosion fatigue crack growth behavior of oil-grade nickel-base alloy 718. Part 2: Effect of aging treatment

The influence of aging treatment on microstructure and corrosion fatigue crack growth (CFCG) behavior of oil-grade nickel-base alloy 718 is investigated. The average grain size of alloy 718 increases after aging treatment. Isolated platelet δ phases are precipitated at some of the grain boundaries in aged specimens. The one-step aged specimen shows a uniform distribution of fine spherical γ′ and elongated γ″ precipitates. However, the two-step aged sample shows much finer γ″ precipitates. Aging treatment leads to lower CFCG rates of alloy 718. Nevertheless, no visible difference of CFCG rates is observed between one-step aged and two-step aged specimens.