High temperature fatigue behaviour of nickel base superalloys manufactured conventionally and via selective laser melting and hot isostatic pressing

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Nickel-based superalloys are used intensively in aerospace and power plant industries, as they show excellent oxidation- and corrosion-resistance at high service temperature. For the production and processing of components made from nickel-based superalloys with very complex geometries conventional casting techniques are not suitable and hence new manufacturing processes such as selective laser melting (SLM) have moved into the focus of research. SLM allows for economical production of small batches and single components. However, the inferior mechanical properties of parts processed by SLM as compared to cast components, prevent the broad application of SLM-material so far.Preliminary results revealed that nickel-based superalloys which were manufactured by SLM showed improved mechanical properties after hot isostatic pressing (HIP). However, a detailed study about the fatigue behaviour, especially at high temperature, has not been carried out so far.Consequently, the proposed research project basically pursues three aims, in order to improve the high temperature properties of Inconel 718 produced by SLM. The first goal of the project is to identify the dominating mechanisms at the microstructural level in SLMed nickel-based superalloys post treated in different ways. Since pores in the SLM-material will have a negative effect on the fatigue properties, these material inhomogeneities have to be eliminated prior to fatigue loading, i.e. by HIP. Thus, the second part of the project will focus on the effects of HIP on the SLM-material. In addition to a detailed surface characterization, investigation of the full component volume will be conducted, based on computer tomography. Finally, the third objective of the project is the development of a novel specimen capsule for HIP with different coatings applied by physical-vapour-deposition. This innovative method should not only increase the compaction effect during HIP by covering the open porosity of the surface of the components but can also serve to functionalize the component.