Due to the increasing use of the different composite materials in lightweight applications, such as in aerospace, it becomes crucial to understand the different damages occurring within them during life cycle and their possible inspection with different inspection techniques in different life cycle stages. A comprehensive classification of these damage patterns, measuring signals, and analysis methods using a taxonomical approach can help in this direction. In conjunction with the taxonomy, this work addresses damage diagnostics in hybrid and composite materials, such as fibre metal laminates (FMLs). A novel unified taxonomy atlas of damage patterns, measuring signals, and analysis methods is introduced. Analysis methods based on advanced supervised and unsupervised machine learning algorithms, such as autoencoders, self-organising maps, and convolutional neural networks, and a novel z-profiling method, are implemented. Besides formal aspects, an extended use case demonstrating damage identification in FML plates using X-ray computer tomography (X-ray CT) data is used to elaborate different data analysis techniques to amplify or detect damages and to show challenges.

Medium manganese steels can exhibit both high strength and ductility due to transformation-induced plasticity (TRIP), caused by metastable retained austenite, which in turn can be adjusted by intercritical annealing. This study addresses the laser additive processability and mechanical properties of the third-generation advanced high strength steels (AHSS) on the basis of medium manganese steel using Laser Powder Bed Fusion (LPBF). For the investigations, an alloy with a manganese concentration of 5 wt.% was gas atomized and processed by LPBF. Intercritical annealing was subsequently performed at different temperatures (630 and 770 °C) and three annealing times (3, 10 and 60 min) to adjust the stability of the retained austenite. Higher annealing temperatures lead to lower yield strength but an increase in tensile strength due to a stronger work-hardening. The maximum elongation at fracture was approximately in the middle of the examined temperature field. The microstructure and properties of the alloy were further investigated by scanning electron microscopy (SEM), hardness measurements, X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and element mapping.

Parts of vehicles, such as landing gear components of aircrafts, are subject to growing demands in terms of sustainability via lightweight design and durability. To fulfill these requirements, the development of thermochemical processes is auspicious. Titanium alloys allow a heat treatment in hydrogen-containing atmosphere for temporary hydrogen alloying, often called thermohydrogen treatment (THT). The investigation presented intends to realize a local microstructure modification of Ti-6Al-4V by means of THT. The study aims to use hydrogen (H) as a promoter for changing the local distribution and morphology of strengthening precipitates during THT as well as the local grain size (microstructural gradient). Both shall improve the fatigue properties of the material after hydrogen degassing. To derive suitable thermohydrogen treatment process parameters, the resulting fatigue crack propagation resistance and fracture toughness after different solution heat treatments are determined experimentally and compared to each other. Moreover, various graded microstructures are evaluated after hydrogen uptake (hydrogenation) and hydrogen degassing (dehydrogenation) using numerically simulated hydrogen concentration profiles, observed hardness curves, metallographically determined microstructure gradients and the corresponding results of the phase analysis by means of X-ray diffraction. The study shows that hydrogenation at 500 °C and dehydrogenation at 750 °C enables the generation of a promising microstructural gradient.

Powder bed fusion using a laser beam (PBF-LB/M) is a widely utilized additive manufacturing technique known for its ability to produce complex geometries with high precision. However, there are numerous factors that can influence the properties of components manufactured by this process. One scarcely investigated factor is the laser incidence angle, which refers to the orientation and positioning of a component relative to the direction from which the laser interacts with the layer to be melted. This study examines the effect of the laser incidence angle on surface roughness and fatigue properties of 316L components. Although the laser incidence angle varies during layer-by-layer deposition, two initial part orientations were investigated. IA specimens were oriented toward the laser, while IT specimens were oriented away from it. This initial orientation establishes a trend in the effective incidence angle throughout the build. Results confirmed that the tendency of the laser incidence angle significantly affects surface roughness and can contribute to the formation or reduction of internal defects. Increased surface roughness and internal defects, particularly the latter, adversely impact fatigue strength, with internal defects playing a primary role in crack initiation in this study. Given that the initial part orientation establishes the effective laser incidence angle trend, careful positioning of components on the build plate is crucial for optimizing surface quality and fatigue properties of additively manufactured parts.

Laser Powder Bed Fusion (LPBF) research on aluminum alloys has predominantly focused on commercial Al–Si–Mg systems with modest Mg ₂ Si contents, leaving the heat-treatment response of Mg ₂ Si-rich compositions largely unexplored. This study investigates, for the first time, the hardness response of an LPBF-tailored aluminum alloy containing 3.94 ma% Mg ₂ Si—over twice the equilibrium solid-state solubility limit—and identifies an optimized post-processing route to enhance mechanical performance. Three heat-treatment conditions were investigated: direct aging, solution annealing (SA), and combined solution annealing plus artificial aging (SA + A). Hardness mapping revealed that direct aging at 190 °C for 330 min achieved the highest hardness of 164 HBW2.5/67.5. The as-built and direct aged conditions were investigated using SEM, EBSD, and TEM to provide a comparative perspective of the microstructural changes that explain the increase in specimen hardness between the two conditions. The as-built state revealed a highly supersaturated α-Al matrix concentrated with early stage Al-, Mg- rich clusters and a refined Si network. In the direct aged condition, nanoscale precipitates were observed, consistent with the precipitation of Mg- and Si-rich phases responsible for the hardening response. The results indicate that the supersaturated solid solution generated during LPBF processing renders a solution-annealing step unnecessary, offering significant reductions in energy consumption. By correlating the heat-treatment routes with the resulting hardness and investigating the increase in hardness by microstructural investigations, this work provides a comprehensive comparison of post-processing routes and offers new insights into designing efficient, and sustainable thermal treatments for high performance aluminum alloys.

Technical components should be produced sustainably and are subject to growing demands in terms of durability and reliability. To meet these expectations, the development of thermochemical processes is auspicious. Titanium alloys, which have a comparatively high gas solubility, allow temporary hydrogen (H) loading, often called thermo hydrogen treatment (THT). THT causes lattice deformation and reduces the β transformation temperature. These effects enable an adjustment of the microstructure, which improves the mechanical properties as compared to those produced conventionally. Furthermore, the process is applicable to complex geometries that cannot be surface hardened by mechanical surface treatment techniques. The investigation presented intends to realize a local microstructure gradient in additively via laser-powder bed fusion (L-PBF) manufactured cylindrical Ti–6Al–4V specimens by changing the distribution and morphology of strengthening precipitates as well as the β grain size depending on the distance to the surface, which should improve the material fatigue properties. To evaluate the mechanical properties of such THT-induced microstructure gradients, the resulting change in fatigue life in the LCF and HCF range was determined by stress-controlled cyclic deformation tests. Besides, the resulting microstructure was characterized by means of XRD and TEM. In addition to the additively manufactured and thermo hydrogen treated cylindrical specimens, conventionally produced tube-like specimens were thermo hydrogen treated and examined. For the THT-induced microstructure gradients, numerically simulated H concentration profiles as well as experimentally determined hardness profiles were used for the evaluation of the THT process. The study shows that H-loading at 500°C and H-degassing at 750°C, followed by aging at 550°C, allows the establishment of a microstructure gradient that shows an 8% improvement in fatigue properties compared to a reference condition without THT. The reason for this improvement is an increased volume fraction secondary alpha phase in the near-surface area of the specimens. Moreover, the results show that the process is applicable a tube-like specimen with varying wall thicknesses.