The wire and arc additive manufacturing (WAAM) technique can be used for manufacturing of large-scale metallic components. During the WAAM process, using a wire as feedstock, new material is deposited in the local melt pool, which is created with an electric arc as the heat source. Thereby a new bead of solid metal is formed after the melt pool solidifies. To take optimal benefit of the geometrical freedom for WAAM printed parts, a rigorous understanding of the effect of micro-structural characteristics on the resulting mechanical properties is required. These aspects are directly related to the manufacturing process, which determines the thermal-mechanical history of each material point. The influence of process parameters on the microstructure and thereby on the mechanical properties has been investigated in various empirical studies. This work aims to quantitatively characterize the WAAM-specific microstructure and to model its effect on the anisotropic mechanical properties.

The microstructure of 316L material manufactured with the WAAM technique is experimentally characterized using a range of microscopic techniques. For this material, a pronounced anisotropic grain morphology and texture is obtained. A full field model in the form of a three-dimensional periodic representative volume element (RVE) having the size of a single bead, and an efficient mean-field micromechanical model of this experimentally observed microstructure are constructed. Process-related characteristics, such as morphology and orientation of grains, are included in the crystal plasticity-based models. The anisotropic mechanical properties for products made with this large-scale deposition technique using different printing strategies are investigated with a combined experimental-numerical approach. This way, the relation between the processing-induced microstructure and the three-dimensional anisotropic yield behaviour is established. This relationship can be used to optimise the printing process as well as the designed product geometry in order to take benefit of this orientation dependence.