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is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. A B S T R A C TThis paper describes a hybrid additive manufacturing process -3D Laser Shock Peening (3D LSP), based on the integration of Laser Shock Peening (LSP) with selective laser melting (SLM). The well-known tensile residual stresses (TRS) in the as -built (AB) state of SLM parts in the subsurface region have a detrimental effect on their fatigue life. LSP is a relatively expensive surface post treatment method, known to generate deep CRS into the subsurface of the part, and used for high end applications (e.g. aerospace, nuclear) where fatigue life is crucial. The novel proposed 3D LSP process takes advantage of the possibility to repeatedly interrupt the part manufacturing, with cycles of a few SLM layers. This approach leads to higher and deeper CRS in the subsurface of the produced part, with expected improved fatigue properties. In this paper, 316L stainless steel samples were 3D LSP processed using a decoupled approach, i.e. by moving back and forth the baseplate from an SLM machine to an LSP station. A clear and significant increase in the magnitude and depth of CRS was observed, for all investigated process parameters, when compared to the AB SLM parts, or those traditionally LSP (surface) treated.

In the selective laser melting process, one has to strike a balance between power and scan speed. When a small scan speed is used, thermal gradients are important and local solidification can lead to cracks. On the other hand, when high speed is used, the power has to be huge and phenomena due to heat transfer, like delamination or balling, arise. In this paper, we study different possible scanning strategies and we indicate those that lead to homogeneous heating of the part until its melting point. The results are compared to numerical simulations.

Selective laser melting Laser shock peening 3D Laser shock peening Residual stress profile 15-5 PH stainless steel 316L stainless steel a b s t r a c t The paper describes a new approach in controlling and tailoring residual stress profile of parts made by Selective Laser Melting (SLM). SLM parts are well known for the high tensile stresses in the as -built state in the surface or subsurface region. These stresses have a detrimental effect on the mechanical properties and especially on the fatigue life. Laser Shock Peening (LSP) as a surface treatment method was applied on SLM parts and residual stress measurements with the hole -drilling method were performed. Two different grades of stainless steel were used: a martensitic 15-5 precipitation hardenable PH1 and an austenitic 316L. Different LSP parameters were used, varying laser energy, shot overlap, laser spot size and treatments with and without an ablative medium. For both materials the as-built (AB) residual stress state was changed to a more beneficial compressive state. The value and the depth of the compressive stress was analyzed and showed a clear dependence on the LSP processing parameters. Application of LSP on SLM parts showed promising results, and a novel method that would combine these two processes is proposed. The use of LSP during the building phase of SLM as a "3D LSP" method would possibly give the advantage of further increasing the depth and volume of compressive residual stresses, and selectively treating key areas of the part, thereby further increasing fatigue life.