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

镍基高温合金广泛应用于航空航天和发电厂工业，因为它们在高工作温度下具有优异的抗氧化性和抗腐蚀性。对于由具有非常复杂的几何形状的镍基超合金制成的部件的生产和加工，传统的铸造技术是不合适的，因此新的制造工艺如选择性激光熔化（SLM）已经成为研究的焦点。SLM允许小批量和单个组件的经济生产。然而，与铸造部件相比，SLM加工的部件的机械性能较差，阻止了SLM材料的广泛应用。初步结果显示，由SLM制造的镍基高温合金在热等静压（HIP）后显示出改善的机械性能。然而，迄今为止，还没有对Inconel 718合金的高温疲劳性能进行详细的研究，因此，本课题的主要研究目标有三个：提高SLM生产的Inconel 718合金的高温性能。该项目的第一个目标是确定以不同方式后处理的SLMed镍基高温合金在微观结构水平上的主导机制。由于SLM材料中的孔隙将对疲劳性能产生负面影响，因此必须在疲劳加载之前消除这些材料不均匀性，即通过HIP。因此，该项目的第二部分将侧重于热等静压对SLM材料的影响。除了详细的表面表征外，还将基于计算机断层扫描对整个组件体积进行调查。最后，该项目的第三个目标是开发一种新型的热等静压试样盒，该试样盒具有通过物理气相沉积施加的不同涂层。这种创新方法不仅可以通过覆盖部件表面的开放孔隙来增加HIP过程中的压实效果，而且还可以使部件功能化。

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.