Fatigue strength of by selective laser melting generated samples

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Additive manufacturing processes promise to be time and cost saving compared to conventional manufacturing processes, especially for components manufactured in small batches. During the Selective Laser Melting process, one-component metals and alloys in powder form are processed in layers. The process belongs to the class of completely melting additive manufacturing processes in which the powder is completely remelted, whereby a melting metallurgical bond is formed between the individual layers. An obvious criterion for the quality of a component manufactured by SLM is its density in comparison to the base material. A component which is free of pores and cracks is desired. Furthermore, the mechanical properties are of interest. There are only a few systematic investigations, especially for the mechanical properties at cyclic loading. The large number of influencing variables in the process and their interaction with each other complicate a priori estimation with regard to the process window and the resulting properties of the samples.The investigations carried out during the first funding phase on steels 1.4404 and 1.2344 have shown that the causes of failure of SLM-generated materials cannot be reduced to the existing residual porosity after an improvement of the surface quality. The specimens failed in the steel matrix itself as well. Thus high fatigue strength cannot be coupled exclusively to the avoidance of residual porosity. The aim of the project is to realize homogeneous mechanical properties of SLM-generated components of highest fatigue strength. By reliably detecting transient temperature fields and the melt pool characteristics, the influences and the reaction of parameter shifts in the process are to be quantified and used as a basis for the design of a control concept. Over a constant temperature history, homogeneous sample properties with maximized fatigue strength are to be achieved. Simultaneously, different heat treatments of the manufactured parts are to be carried out in order to remove undesirable residual stresses for austenitic steel 1.4404 and tool steel 1.2344. In addition, a new hardening process adapted to the initial state of the specimens is to be developed for tool steel 1.2344 to achieve a homogeneous microstructure in order to further improve its fatigue strength. Furthermore, the fatigue strength of SLM-manufactured specimens before and after heat treatment is to be modelled using different modelling approaches in order to enable the prediction of fatigue strength.