Effects of the thermal history on the microstructural and the mechanical properties of stainless steel 316L parts produced by wire-based laser metal deposition

Laser metal deposition with coaxial wire feeding is a novel technology for additively manufacturing near-net-shape metal parts, as well as for repairing and modifying existing components. The microstructure and, thus, the mechanical properties of the deposited material significantly depend on the thermal history of the part, which is influenced by the process parameters and the amount of dissipated heat energy. In order to investigate these correlations, stainless steel 316L samples were produced under different thermal conditions and thoroughly characterized. Solid cuboids were built on a substrate plate at room temperature as well as on a preheated substrate plate. Subsequently, the influence of the different thermal conditions on the melt pool temperatures was evaluated, and the microstructures, the microhardness, and the tensile properties were analyzed. It was found that the mean melt pool temperatures and the primary dendrite arm spacing (PDAS) increased with the build height, while the cooling rates showed an inverse relationship with the build height. The determined PDAS values were correlated with the microhardness profile of the specimens using a Hall-Petch type relationship. An increased heat accumulation in the parts was thereby associated with a coarser microstructure and diminished mechanical properties. The presented results pave the way for tailoring the properties of additively manufactured components to specific requirements.