IMX Talks - Towards defect-free and 3D architected microstructures in additive manufacturing of metals and alloys

Additive Manufacturing (AM) is often mentioned as a source of renewal in the metallurgy community. There is indeed a long-standing “dream” of fabricating metallic parts with full spatial control of defect content, microstructure, and chemical composition. Processes from past centuries have shown multiple ways of designing properties of final products based on partial control of thermo-mechanical processes. However, the spatial resolution at which microstructures could be designed, and the available degrees of freedom to achieve such design, were limited. In the AM context, the developments of monitoring approaches and numerical modelling at the relevant space and time scales provide the opportunity of a bottom-up manufacture, which may even include multiple materials. While the literature has focused most of the attention on the minimization of defects, the last few years have shown increasing trends in controlling microstructures, typically from tuned heat source (laser, electron beam) parameters, or beam profile (i.e. beam shaping). Considering the partly stochastic nature of AM, the vision consists in optimizing the processing conditions, while keeping the option of corrective actions whenever undesired events are detected.

In this presentation, I will discuss our recent advances in the 3D control of defects and microstructures with the Laser Powder Bed Fusion (LPBF) process. A first part will describe the invention of a new hybrid process, combining traditional LPBF with periodic Laser Shock Peening (LSP) treatments. This approach proved effective in controlling residual stresses in 3D (thereby increasing processability and/or fatigue life), healing cracks, tuning dislocation density, and improving geometrical accuracy. A second part will focus on operando experiments, to follow defect formation and microstructure changes during LPBF or upon local laser heat treatment. The experiments are monitored with high energy X-Rays (at the PSI Synchrotron) as well as with acoustic emission, and promote the development of advanced monitoring methods that could be implemented in commercial LPBF machines. Combined with multiscale LPBF thermal models, they help defining optimal time-dependent laser parameters. Examples will include the detection and healing of porosity through acoustic emission monitoring, laser induced martensite decomposition in Ti-6Al-4V, and selective recrystallization in 316L steel. They represent important milestones in the objective of building defect-free 3D architected materials.

Bio: Roland Logé is an associate professor at EPFL (Switzerland), holder of the PX Group Chair, with a primary affiliation to the Materials Institute, and a secondary affiliation to the Electrical and Microengineering Institute. He is the head of the Laboratory of Thermomechanical Metallurgy, and active in the field of processing of metals and alloys, focusing on the ability to tailor microstructures, and the associated material properties. Topics of interest include recrystallization, precipitation, grain growth, textures and grain boundary engineering, phase transformations, internal stresses and cracking phenomena, with applications to bulk metal forming and additive manufacturing. They are the subject of more than 150 academic papers.
Roland Logé received in 2008, with Yvan Chastel, the ALCAN award from the French Academy of Sciences; in 2019, the Materials Science best teacher award from EPFL; in 2021, the THERMEC Distinguished Award; and in 2022, the SF2M Albert Portevin Medal. He has been a member of the Editorial Board of Metals, of the Scientific Advisory Board of the SEAM laboratory of Excellence (France), of the Swiss Spallation Neutron Source Scientific Committee (PSI, Switzerland), of the THERMEC International Advisory Committee, of the CNRS National committee, of SF2M and TMS.