Superalloys based on nickel (e.g. Inconel® 718 and 738, MAR-M-247®) and cobalt (e.g., MAR-M-509®) are among the most commonly used materials in turbomachinery because they possess excellent thermo-mechanical properties even at extremely high temperatures. In the end, the properties of the component depend upon the material and its microstructure, the volume defects, the surface quality as well as the residual stresses.
These essential aspects are determined by the running process chain, i.e. by the combination of raw material, the SLM process and the thermal and mechanical post-treatment. Scientists at the Fraunhofer ILT, therefore, are investigating the cause-and-effect relationships along this process chain and working out selected measures to further develop the individual process steps, particularly those of the SLM process.
When crack-resistant materials such as Inconel® 718 or MAR-M-509® are used, one needs to consider the influence of the SLM process in combination with the thermal treatment upon the microstructure and the thermo-mechanical properties.
By contrast, when materials susceptible to cracking, such as Inconel® 738 are processed, the focus lies on the development of the SLM process for defect-free processing of these alloys. Here, approaches are being developed that, among others, reduce thermal gradients through global preheating or selectively control the solidification conditions by using additional local heat sources.
The experimental research is being assisted by the development of CFD- and FEM-models for the simulation of the process-related temperature-time cycles and solidification conditions.
In addition to developing customer-specific process chains, we are examining how individual process steps influence the economics of the overall process and quality of the components, such as how different SLM building strategies and finishing processes influence the achievable geometrical accuracy and surface quality.