Understanding Residual Stress Evolution in Directed Energy Deposition With Interlayer Deformation

Control of residual stresses (RS), inherent to fusion-based additive manufacturing (AM), process is important for the satisfactory mechanical performance of components. Recent work has attempted to control the RS profiles in AM components by applying mechanical peening between built layers. During laser powder bed fusion (LPBF), it has been shown that subsequent layer building does not relieve all the peening-induced compressive stresses. In this work, a similar study has been performed on a directed energy deposition (DED) process. It is shown that owing to the vastly different thermal profile in DED compared to LPBF, the compressive RS induced by peening, is completely alleviated during subsequent layer deposition for 316L stainless steel. Irrespective of the magnitude and depth, the peening-induced compressive stresses were not present in the final part. Experimental and numerical analyses revealed that stress relief due to intrinsic heating was insufficient to explain stress relaxation. Rather, the localized heating and constrained expansion from surrounding cold material was the mechanism responsible for strain redistribution and hence stress relaxation.