Hybrid Additive Manufacturing of metal parts with 3D control of internal stresses and microstructures

A new hybrid additive manufacturing process is introduced, combining Laser Shock Peening (LSP) with Selective Laser Melting (SLM), and called 3D LSP. LSP is a well-known surface treatment introducing plastic deformation and Compressive Residual Stresses (CRS) over a certain penetration depth into the material. By repeatedly applying LSP during the part fabrication, 3D LSP can efficiently strain harden a metal and convert SLM induced Tensile Residual Stresses (TRS) into CRS, in the bulk of the part. This strategy opens a range of new possibilities such as increased fatigue life or geometrical accuracy, 3D design of grain structures, and improved processability. Examples are provided for each of these effects, looking at fatigue life and grain structure design of 316L steel samples, geometrical accuracy of Ti-6Al-4V samples, and processability of a Ni-based superalloy. In the latter case, 3D LSP brings a new efficient crack healing mechanism.   ·        References :   -        N. Kalentics, E. Boillat, P. Peyre, S. Ćirić-Kostić, N. Bogojević, R.E. Logé (2017), “Tailoring residual stress profile of Selective Laser Melted parts by Laser Shock Peening”, Additive Manufacturing 16, 90-97. -        N. Kalentics, E. Boillat, P. Peyre, C. Gorny, C. Kenel, C. Leinenbach, J. Jhabvala, R. E. Logé (2017), 3D Laser Shock Peening – a new method for the 3D control of residual stresses in Selective Laser Melting, Materials & Design 130, 350–356. -        N. Kalentics, A. Burn, M. Cloots and R.E. Logé (2018), “3D laser shock peening as a way to improve geometrical accuracy in selective laser melting“, Int. J. Advanced Manufacturing Technology, https://doi.org/10.1007/s00170-018-3033-3. -        N. Kalentics, K. Huang, M. Ortega Varela de Seijas, A. Burn, V. Romano and R.E. Logé (2019), “Laser shock peening: A promising tool for tailoring metallic microstructures in selective laser melting”, J. Materials Processing Tech. 266, 612–618.

Bio: Roland Logé is an associate professor at EPFL, with a primary affiliation to the Materials Institute, and a secondary affiliation to the Microengineering Institute. He is the head of the Laboratory of Thermomechanical Metallurgy, and active in the field of processing of metals and alloys in the solid state, focusing on the ability to tailor microstructures, and the associated material properties. Thermal and mechanical paths and the resulting microstructures are analyzed and simulated both experimentally and numerically. While most of the activities were so far related to recrystallization, precipitation, grain growth, textures and grain boundary engineering,  extensions of the microstructure design approach progressively include phase transformations, internal stresses and cracking phenomena, with applications to bulk metal forming and additive manufacturing.