Influence of surface modifications on pitting corrosion behavior of nickel-base alloy 718. Part 2: Effect of aging treatment

• Aging applied to the alloy with mill finishing (MF) and machine hammer peening (MHP).
• Aging produced a Cr-enriched oxide layer on the surface and high fraction γ′/γ″ precipitation.
• Aging increased surface hardness and relaxed compressive residual stress induced by MHP and MF.
• Corrosion resistance of the MHP specimens decreased after aging, but still better than the MF condition.

A two-step aging treatment is applied to nickel-base alloy 718 that has been previously surface-treated by mill finishing (MF) and machine hammer peening (MHP). As a result, a Cr-enriched oxide layer is formed along with a nano-precipitates layer that consists of high precipitate fractions of γ′/γ″ on the top surface. Surface hardness increases after aging and the compressive residual stress is almost relaxed. The synergistic effects of MHP and aging on pitting corrosion behavior are studied. The results show that the corrosion resistance of the MHP specimens decreases after aging, although the corrosion resistance is still higher than the MF condition.