Abstract
The wire-arc-additive-manufacturing (WAAM) process, derivated from arc welding process, is acclaimed in particular because it allows the production of massive parts. However, it tends to produced textured macrostructures of columnar grains, leading to an anisotropic mechanical behaviour. Few studies have been carried out to date on the impact of the process parameters on the microstructures formed, as well as their mechanical behaviour, particularly in fatigue. In this context, the WAAM production, and the study of the metallurgical structures and the mechanical behaviours of the materials obtained, in particular the fatigue initiation phase, were conducted. The chosen base materials are the 316L stainless steel and the TA6V titanium alloy. At first, the manufacturing of specimens by stacking of welding beads was realised. The impact of the process parameters setting and its physical consequences (electrical characteristics of the arc, temperatures, size of the bath), measured by means of in-situ instrumentation, on the geometries obtained (beads size, wetting), were analysed. In a second step, the impact of the sets of parameters on the characteristics of the granular structures formed, as well as on the particularities of the substructures, was studied in connection with the physical data collected. The phenomena of solidification and evolution in the solid phase specific to the WAAM process, which are different for each of the two materials studied, were discussed. The application of heat treatments has permitted to obtain materials different from the as-welded states (phase proportions, sizes of the substructures, etc.). The mechanical behaviour of the structures manufactured by WAAM was then studied through tensile, staircase cycling, and finally fatigue tests. These tests are complementary, and make it possible to understand the phenomena of plastic deformation and initiation of fatigue cracks. These analyses were held in a thermo mechanical framework : strain energy fields and heat sources were estimated after processing CCD and infrared images. The evolution of the intrinsic dissipation testifies to irreversible damage phenomena. These analyses made it possible to reveal differences in behaviour according to the loading direction and the microstructures generated. Calculations of deformation and dissipation fields have permitted to identify the areas prone to deformation and fatigue damage within the specimens. They contribute to a better understanding of the behaviours of materials, and of the influence of microstructural characteristics induced by process settings.