Hydrogen induced cold cracking (HICC) and hydrogen embrittlement (HE) are influenced by the microstructural evolution, residual plastic strain (i.e. local misorientation), recrystallization of grains and the resultant grain boundary characteristic distribution (GBCD) brought about by welding processes. HICC and HE are known to cause failures in aerospace components and it is vitally important to quantify the microstructural evolution, degree of residual plastic strain and determine the GBCD across dissimilar weld joints in order to assess the susceptibility of the weld joint to these phenomena. In this investigation a full a microstructural characterization study was carried out at various locations within and around a dissimilar weld joint of Pulse-plated Nickel (PP-Ni) and Inconel 718 (IN718), taken from an aerospace component. Areas examined included the base metals, weld fusion zone and heat affected zones on both sides of the weld joint, formed via electron beam welding. Scanning electron microscopy (SEM) in combination with electron backscatter diffraction (EBSD) was employed to measure the residual plastic strain, grain structure, grain size distribution, crystal orientation distribution, grain boundary misorientation distribution and GBCD of the dissimilar metal weld joint. Finally a metallurgical examination was carried out using SEM on the IN718 HAZ in order to investigate the secondary phase precipitation arising from the welding process. The results shows large variety of GBCD, crystallographic orientation distribution, local plastic strain distribution and grain size, shape and structure distribution across dissimilar weld joint. And these localized microstructural characterized data sets need to be carefully transferred using data-driven approach in order to develop predictive multiscale material modelling for hydrogen induced cracking and hydrogen embrittlement.

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to that, superior tensile properties of AM 316L were also obtained at temperatures of 250 [7] and 800 C. [8] For long time exposures under high temperatures, however, unstable dislocation cells can deteriorate the creep properties. [9,10] Saeidi et al. [8] also observed the propagation of Luders bands, which are closely related to dynamic strain aging (DSA), at 800 C. However, no systematic study on the influence of the SLM microstructure on the mechanical properties over the entire temperature regime from room temperature to 900 C has been conducted yet. This is surprising, as AISI 316L is a widely used austenitic stainless steel for applications at elevated temperatures, and it is known from the conventionally produced material that DSA occurs at elevated temperatures. The improvement of the process parameters in recent years with respect to the laser power, hatch distance, scan strategy, etc. allows nowadays the manufacturing of geometrically accurate parts with high strength. [11] The high thermal gradients and high solidification rates in the SLM process lead to a fine columnar dendritic solidification with microsegregation. Rapid local heating and cooling introduce significant stresses in accordance with the temperature gradient mechanism (TGM). [12] Recent results of Bertsch et al. [13] showed that these stresses and strains contribute strongly to the formation of dislocations. Mainly due to the high dislocation density, networks are formed. These dislocation cells typically overlap the microsegregations. Dendritic segregations and dislocation cells are known to be beneficial for the mechanical properties. [1][2][3]5] The main strengthening mechanisms of the austenitic steel 316L are solid solution and Hall-Petch strengthening. In the case of SLM-processed 316L, additional strengthening by the dendritic substructure has to be considered. These substructures consist of segregated elements and entangled dislocations contributing to the strength of the material. [1,14,15] One model to understand the fundamentals of strengthening by cellular dislocation structures was established by Mughrabi. [16][17][18] The socalled composite model describes the stress distribution in the soft cell and hard wall regions and enables the calculation of the total strengthening effect by a modified Taylor equation, using a geometric constant for the heterogeneous composite, α het , depending on the wall thickness and cell diameter. [18] It was also found by Blum and Reppich, [19,20] for cellular dislocation networks developed under static creep loads, that the

Choosing a properly optimized rotating scan strategy during the selective laser melting (SLM) process is essential to reduce residual stresses and thus to obtain homogeneous properties. Surprisingly, anisotropic material properties are found in several materials that are built with the often applied rotating stripes scan strategy of Electro‐Optical Systems (EOS) because the scan strategy avoids possible interactions of the laser beam with process by‐products and therefore excludes a range of scanning directions. Herein, the alloys Hastelloy X, Inconel 718, and stainless steel 316L are investigated. Vertically built specimens with a cylindrical gauge geometry show an oval deformation during tensile testing, indicating a mechanical anisotropy in the horizontal x‐ and y‐direction. Tensile tests along the x‐ and y‐direction reveal a deviation of the yield strength of 7% for Hastelloy X. Analyses of the microstructures show differences in the grain morphology, size, and texture in all three coordinate planes of the three materials. This anisotropic behavior can be explained by a detailed study of the texture and the calculated Schmid factors. Heat treatments can reduce the textural and mechanical anisotropy due to recrystallization of grains but requires annealing at sufficiently high temperatures and long times.

The potential of the Additive Manufacturing technologies is impeded by the surface finish obtained on the as-manufactured material. Therefore, the influence of various surface treatments, commonly applied to space hardware, on the mechanical properties of three selected metallic alloys (SS316L, AlSi10Mg, Ti6Al4V) prepared by using Selective Laser Melting (SLM) and Electron Beam Melting (EBM) additive manufacturing processes have been investigated. Within this study, SLM using EOS M400 and EOS M280 equipment and in addition EBM using an ARCAM Q20 machine have been applied for sample manufacturing. A half-automated shot-peening process followed by a chemical and/or electrochemical polishing or Hirtisation® process has been applied in order to obtain lower surface roughness compared to their as-received states. Special emphasize has been taken on their tensile, fatigue, and fracture toughness properties. In addition, their stress corrosion cracking (SCC) behaviour including microstructural analysis using HR-SEM have been investigated.