Microstructure- and defect-controlled damage tolerance evaluation of lattice structures at room temperature and 650 °C based on the E-PBF processed Ni-based alloy Inconel 718

该项目的主要目标是建立对基于E-PBF处理的Inconel 718(IN718)合金的结构行为以及晶格结构的微观结构和力学性能的深刻理解。特别是，将调查材料特性和表面粗糙度在多大程度上可以通过工艺参数和随后的后处理(表面和热处理)来系统地调整。关于表面光洁度，由于传统的磨削和抛光仅部分适用于添加制造的晶格结构，因此重点讨论了替代方法。除了化学腐蚀或电化学抛光(ECP)等湿化学处理外，还考虑了振动抛光和球磨抛光等机械工艺。必须确保在试件的近表面和中心进行均匀的材料去除。为了评估不同的方法，将使用共焦显微镜和计算机层析成像(µ-CT)来测量所产生的表面粗糙度。除了2D/3D气孔分析外，还将通过扫描(SEM)和透射电子显微镜(TEM)以及近表面和中心区域的硬度测量来进行补充的微观结构研究，以量化后续热处理(固溶+淬火、热等静压+固溶+淬火)的影响。不同的材料条件将通过准静态和循环测试的方式进行研究，最长可达107个循环，使用面向应用的测量技术，如直流/交流电位降(DC-/AcPD)系统、红外相机和Optimizer4D传感器。除了室温(RT)测试外，还将进一步研究650°C的相关高温范围，以确定IN718晶格结构的高温性能。然而，特别是不同测量技术的适应是具有挑战性的。为了更深入地了解这种材料，将进行额外的损伤演化测试，以分别对额外制造的网格结构的损伤累积和扩展做出深入的结论。总之，微观结构、计算机断层扫描和力学研究将与疲劳试验结果相关联。基于这些相关性，将定性和定量地建立工艺-几何-组织-性能之间的关系。

The main objective of the project is the establishment of a profound understanding of the structural behavior as well as the microstructural and mechanical properties of lattice structures based on the E-PBF processed Inconel 718 (IN718) alloy. In particular, it will be investigated how far material properties and surface roughness can systematically be adjusted by process parameters and subsequent post-processing (surface and heat treatment). Regarding the surface finish, alternative approaches are focused, since conventional grinding and polishing are only partially suitable for additively manufactured lattice structures. Besides wet chemical treatments such as chemical etching or electrochemical polishing (ECP), mechanical processes such as vibratory finishing and ball-polishing are considered. It has to be ensured that uniform material removal takes place in the near-surface and in the center of the specimen. In order to evaluate the different approaches, resulting surface roughness will be measured using confocal microscope and computer tomography (µ-CT). In addition to 2D/3D pore analysis, supplementary mircostructural investigations will be carried out by means of scanning- (SEM) and transmission electron microscopy (TEM) as well as hardness measurements in the near-surface and the center area of the specimens in order to quantify the influence of subsequent heat treatments (solution annealing + quenching, HIP + solution annealing + quenching). The different material conditions will be investigated by means of quasi-static and cyclic tests up to 107 cycles, using application-oriented measurement techniques such as a direct/alternating current potential drop (DC-/ACPD) system, infrared camera and Optimizer4D sensor. In addition to the tests at room temperature (RT), the relevant high-temperature range of 650 °C will further be investigated in order to determine the high temperature properties of IN718 lattice structures. However, especially the adaption of the different measurement techniques is challenging. For a profound understanding of the material, additional damage evolution tests will be carried out to enable in-depth conclusions on the damage accumulation and propagation, respectively, in additively manufactured lattice structures. In summary, microstructural, computed tomographic as well as mechanical investigations will be correlated with the results of fatigue testing. Based on these correlations process-geometry-microstructure-property relationships will be qualitatively and quantitatively established.