Assessment of residual strain in laser shock peened additive manufactured Inconel 718 using synchrotron X-ray diffraction

The through-thickness residual strain profile due to laser shock peening (LSP) of an additively-manufactured IN718 sample is shown for the first time. The results provide tantalising insight into the potential of fatigue life extension of additive-manufactured samples using LSP. Residual strains were measured in as-manufactured and peened samples using state-of-the-art synchrotron radiation. Significant beneficial compressive in-plane residual strains, extending to 1.0 mm depth, were observed due to the peening process. No phase changes were observed due to LSP. A periodic strain variation was observed arising from the layer-by-layer manufacturing strategy of the samples. The peened sample showed no increase in diffraction peak width in the near-surface regions. This is contrary to reported studies using wrought laser shock peened alloys and suggests less grain disruption in additively-manufactured peened samples. The results are timely given a current drive to adopt additive-manufacturing for a step-change in efficiency of aero-engine component production.