Effects of Hammer Peening and Aging Treatment on Microstructure, Mechanical Properties and Corrosion Resistance of Oil‐Grade Alloy 718

The effects of hammer peening and aging treatment on the near surface microstructure, mechanical properties, and corrosion resistance of oil-grade alloy 718, were investigated. Milling and hammer peening treatments were performed on the surface of alloy 718, followed by a double aging treatment. It was found that after aging treatment there were three distinguishable layers near the hammer-peened surface that had significantly different microstructures than the bulk material. On the top of the hammerpeened surface was a Cr-enriched oxide film. The second layer was a thin layer with high amount of γ’/γ’’ nano-precipitations, and the one closest to the bulk material was a visible plastic deformation layer which was indicated by slip bands. It was also found that the micro-hardness significantly increased by hammer peening to the depth of about 1000 µm, however, aging treatment decreased the effective thickness to about 750 µm. Moreover, the surface compressive residual stresses were introduced by hammer peening but decreased after aging treatment. The effects of hammer peening and aging treatment on the corrosion resistance of oil-grade alloy 718 were also discussed in the final part of this paper.