Iris De Graeve

Austenitic 316L suffers dissolution corrosion in liquid lead (Pb) as the selective leaching of nickel (Ni) results in a destabilized microstructure. We demonstrate a chemistry-based corrosion control approach in which sub-saturated Ni together with controlled oxygen additions co-inhibit dissolution and promote oxide formation. Tests at 500 °C for 500 hours spanned a 2×3 matrix (Oxygen: 5 · 10⁻⁸ and 5 · 10⁻⁷ wt.%; Ni: 0, 0.05, 0.1 wt.%). In-situ oxygen concentration and oxygen consumption monitoring, corrosion depth measurements, and microstructure measured by SEM/EDX were assessed. In Ni-free lead, uniform selective leaching of Ni from the stainless steel is observed. At 0.05 wt.% dissolved Ni the depth of dissolution is localized and reduced by a factor of 10. And with 0.1 wt.% Ni, oxidation of the steel dominated at both oxygen concentrations. Oxygen consumption at 5 · 10-7 wt.% was ~2 times that at 5 · 10-8 wt.%, consistent with ~2 times thicker oxide. This work indicates a coupled effect of dissolved Ni and O that reduces dissolution corrosion observed on stainless steel in high temperature lead.

FBG-WDM, FBG-FMCW and OFDR distributed strain monitoring techniques are benchmarked and compared to FEM results, in view of assessing the performance of SHM of complex high-value structures subject to intense stress concentration. The results reveal distinct performance trade-offs: OFDR provides the highest accuracy but fails at high gradients (>100 µε/mm), while FBG-based methods are more robust, but their accuracy is algorithm-dependent due to spectral chirp. The CFG-FMCW technique systematically underestimates peak strains due to spatial filtering, confirming that no single technology is universally optimal for highgradient monitoring.

Direct writing enables rapid prototyping of liquid metal‐based stretchable electronics. Challenges, such as printing on uneven surfaces, a limited understanding of the flow behavior, and interfacial issues between liquid metal and electronic terminals for reliable interconnections, remain. We innovatively utilize the kinematic bed of a 3D printer to dynamically control the stand‐off distance during direct writing. This enables reliable printing on irregular surfaces and 3D structures with slopes up to 10%. We discover that the thickness of printed liquid metal is affected by a pressure‐driven backflow, enabling tuning of thickness in a range of 100 . To solve interfacial challenges, we develop a novel solder‐based technique that forms a liquid metal interface on metal coatings, resulting in 100% print reliability between the LM meniscus and the electronic terminal. This interface reduces contact resistance by a factor of four, and improves electrical stability during cyclic strain, with negligible resistance change up to three million cycles. These innovations are demonstrated through the fabrication of large (order of 10 cm) stretchable devices, and stretchable devices featuring integrated electronic components. Our contributions address the limitations of direct writing of liquid metal, advancing the practical realization of reliable, scalable, and fully integrated stretchable electronic systems.

Stretchable electronics that combine mechanical compliance with reliable electrical performance are essential for applications in soft robotics, wearable systems, and healthcare monitoring. Among the available conductive materials, liquid metals (LMs) offer exceptional conductivity and intrinsic deformability when encapsulated in elastomers, yet the long‐term reliability remains a challenge. This work addresses the critical issue of robust interconnections between the LM and rigid or flexible components, where stress concentration leads to failure under repeated strain. Herein, the robustness of such interfaces is improved by first eliminating secondary failure modes, such as silicone rupture and short circuits, until connection failure is the final dominant mode. Targeted connector designs are introduced to improve connection stability. Through X‐Ray tomography, delamination between encapsulant and connector is identified as the primary failure mechanism, which is subsequently mitigated through material based strain relief around the LM‐solid interface. Devices incorporating this strategy withstand at least one million cycles at 50% strain, even when rigid components are integrated. Further, at 100% strain, the cyclic durability increases from 16% survival rate to 50% survival rate after 100 000 stretch cycles by applying strain relief. These findings establish a framework for reliable LM‐based stretchable interconnections in demanding applications.

This work analyses the microstructural defects and the corrosion behaviour of 316L stainless steel clads deposited by laser metal deposition on wrought conventional material, which is a highly relevant system for repair applications. The different defects and microstructural features found in these systems were identified and analysed from a perspective relevant to the corrosion performance of these materials. The role of these features and defects on the corrosion process was evaluated by exposure of the samples to corrosive media and further examination of the corrosion morphology. The heat-affected zone, located on the wrought base material in close vicinity of the deposited clad, was identified to be the primary contributor to the corrosion activity of the system due to the large depletion of alloying elements in this region, which significantly decreased its pitting resistance. Alongside the heat-affected zones, relatively small (<30 µm in diameter) partially un-melted powder particles scattered across the surface of the clad were systematically identified as corrosion initiation spots, possibly due to their relatively high surface energy and therefore high reactivity compared to larger powder particles. This work highlights the need for more investigations on as-built surfaces of additively manufactured parts to better explore/understand the performance of the materials closer to their final applications. It demonstrates that the surface defects resulting from the additive manufacturing process, rather than the presence of the refined sub-granular cellular structure (as highlighted in previous works), play the predominant role in the corrosion behaviour of the system.

The effect of post-processing heat treatment on the corrosion behavior of AISI 316L stainless steel manufactured by laser powder bed fusion (L-PBF) is investigated in this work. Produced stainless steel was heat treated in a broad temperature range (from 200 °C to 1100 °C) in order to evaluate the electrochemical behavior and morphology of corrosion. The electrochemical behavior was investigated by potentiodynamic and galvanostatic polarization in a neutral and acidic (pH 1.8) 3.5% NaCl solution. The microstructure modification after heat treatment and the morphology of attack of corroded samples were evaluated by optical and scanning electron microscopy. The fine cellular/columnar microstructure typically observed for additive-manufactured stainless steel evolves into a fine equiaxed austenitic structure after thermal treatment at high temperatures (above 800 °C). The post-processing thermal treatment does not negatively affect the electrochemical behavior of additive-manufactured stainless steel even after prolonged heat treatment at 1100 °C for 8 h and 24 h. This indicates that the excellent barrier properties of the native oxide film are retained after heat treatment.

In this study, the corrosion susceptibility of powder‐coated Al6060 alloys with increasing Cu and Zn content is evaluated in a benchmark test. Although higher Cu and Zn limits would enable the industry to increase the use of end‐of‐life scrap and thus produce eco‐friendlier aluminum profiles, such alloys are often disregarded due to concerns of corrosion, especially filiform corrosion. Our results suggest that this concern is ungrounded as long as typical quality specifications for the pretreatment and coating process are followed and the alloy composition is kept within the limits of the European norm AW6060. Furthermore, we point out that the variation of the results due to processing at different coating production lines is larger than the difference between alloys of different Cu and Zn contents.

Additively manufactured (AM) AlSi10Mg is one of the most studied AM aluminium alloys to date. While several studies have focused on investigating its mechanical properties and corrosion performance, very little work has been dedicated to study corrosion protection mechanisms and surface treatments applicable for this material. This work presents for the first time an analysis of the mechanism of Zr electrochemical conversion on AM AlSi10Mg parts. A comparison with the conventional cast alloy was also conducted. An analysis of the specimens using SEM/EDS provided interesting insights concerning the effect of the microstructure on the deposition of the Zr conversion layer. This work demonstrates that due to the very fine microstructure and distribution of alloying elements in AM AlSi10Mg, a homogeneous deposition of the Zr conversion layer is promoted. Conversely, the cast alloy is characterized by a very heterogeneous deposition of the Zr conversion layer due to the presence of relatively large Fe-containing intermetallic particles. The influence of the conversion coating on the corrosion performance of these materials was also studied. The results show that while the conversion treatment has no impact on the corrosion resistance of the cast alloy, it greatly improves the passivity of the AM AlSi10Mg samples.

Metal additive manufacturing (MAM), also known as metal 3D printing, is a rapidly growing industry based on the fabrication of complex metal parts with improved functionalities. During MAM, metal parts are produced in a layer by layer fashion using 3D computer-aided design models. The advantages of using this technology include the reduction of materials waste, high efficiency for small production runs, near net shape manufacturing, ease of change or revision of versions of a product, support of lattice structures, and rapid prototyping. Numerous metals and alloys can nowadays be processed by additive manufacturing techniques. Among them, Al-based alloys are of great interest in the automotive and aeronautic industry due to their relatively high strength and stiffness to weight ratio, good wear and corrosion resistance, and recycling potential. The special conditions associated with the MAM processes are known to produce in these materials a fine microstructure with unique directional growth features far from equilibrium. This distinctive microstructure, together with other special features and microstructural defects originating from the additive manufacturing process, is known to greatly influence the corrosion behaviour of these materials. Several works have already been conducted in this direction. However, several issues concerning the corrosion and corrosion protection of these materials are still not well understood. This work reviews the main studies to date investigating the corrosion aspects of additively manufactured aluminium alloys. It also provides a summary and outlook of relevant directions to be explored in future research.

This work analyzes the galvanostatic anodizing behavior of additive manufactured (AM) Al-Si alloys. Two main factors were studied here: 1) the influence of Si content on the anodizing behavior and on the porous structure of the anodic oxide film, and 2) the effect of pre-existing internal pores on the anodizing behavior of these materials. Three different alloys were anodized in H₂SO₄ electrolyte, with 7%, 10%, and 12% Si. The voltage responses of the different samples during anodizing were compared and the formed oxide was analyzed. The amount of Si in the AM Al-Si alloys was found to have a great influence on the anodizing voltage and consequently on the porous structure of the anodic oxide layer. However, the anodic oxide growth rate was nearly independent of the Si content in the samples. Moreover, the effect of internal porosity resulting from the metal additive manufacturing process on the anodizing behavior of these specimens was also analyzed. An outer anodic oxide layer decorated the pre-existing internal pores that were reached by the anodic oxide front. These internal pores were also characterized by the systematic appearance of cracks resulting from the volume expansion of anodic oxide layers advancing in opposite directions.