3D laser shock peening – A new method for improving fatigue properties of selective laser melted parts

Abstract

Although Selective Laser Melting (SLM) currently revolutionizes the way parts are being manufactured, certain process inherent limitations such as accumulation of residual stresses and increased porosity content can lead to a decrease in fatigue life of produced parts. 3D Laser Shock Peening is a new hybrid additive manufacturing process whereby a periodic Laser Shock Peening (LSP) treatment is added to the standard SLM process. LSP can be applied selectively in the 3D volume of metallic parts, and is shown to influence the bulk internal stress state and hardness, as well as the distribution of porosities in the material. Here, a decoupled 3D LSP process was used, i.e. LSP treatments were applied during the SLM process, by removing the sample from the SLM chamber whenever needed. We report fatigue lives of 316 L stainless steel multiplied by more than 15 times compared to standard SLM parts, and more than 57 times compared to conventional manufacturing, with a significant improvement over other state-of-the art methods. The effect of the 3D LSP treatment on SLM parts and the consequence on crack initiation and propagation is investigated by measuring the near surface residual stresses, imaging the fractured surface, measuring the porosity content and analyzing the microstructure and microhardness.