Additive Manufacturing: A Tool for Engineering Microstructures and Mechanical Behaviour
Laser powder bed fusion (L-PBF) is one of most widespread metal additive manufacturing techniques. Putting aside its profound capability for producing intricate shapes and complex geometries, it is also a powerful tool for engineering and optimizing the microstructure of metallic parts. By precisely controlling the process parameters, L-PBF enables fine-tuning of crystallographic textures, grain orientations and microstructural features, allowing for unprecedented control over the materials properties. Additionally, the characteristic high resolution of the L-PBF process allows for the combination of different process parameters and build strategies within the same part, thus allowing to produce site-specifically controlled metallic microstructures. These capabilities transform L-PBF into a versatile method, not only for creating intricate parts but also for tailoring the microstructure and thus the mechanical properties of metals, in order to meet the ever increasing requirements of real-world engineering applications.
In the context of the present thesis, L-PBF is employed to produce austenitic stainless steels, with tailored crystallographic textures to specific load states, aiming to enhance their mechanical response. Austenitic stainless steels, namely the 304L and 316L grades, are some of the most widely used metallic alloys. Upon mechanical deformation, austenitic stainless steels exhibit different deformation mechanisms, namely the Transformation Induced Plasticity (TRIP) and the Twinning Induced Plasticity (TWIP) effects. It is well established that under certain stress states, specific crystallographic orientations either favor or suppress the TRIP and TWIP effects.
Taking into consideration the above observations, the proposed work aims at defining the required microstructures, pinpointing the L-PBF processing routes, that lead to metallic parts with well controlled crystallographic textures, and to study those tailored textured parts using state of the art characterization techniques. Special emphasis is placed on understanding the local microstructural changes introduced via modification of the L-PBF processing parameters and their impact on mechanical properties, including the enhancement of the TWIP and TRIP effects. In situ characterization techniques, such as neutron diffraction, are employed to correlate processing parameters, microstructure evolution and material performance. Ultimately, the obtained knowledge is leveraged to locally manipulate the crystallographic texture and produce site-specifically tailored parts that exhibit superior mechanical response under complex stress states than reference, conventionally processed materials.
Prof. Michele Ceriotti (président) ; Prof. Roland Logé, prof. Efthymios Polatidis (directeurs) ; Dr Jean-Marie Drezet, Prof. Matteo Seita, Prof. Christian Haase (rapporteurs)
2024
Lausanne
2024-12-16
11106
170