Advanced Materials

Nickel-based alloys are a particularly interesting class of materials due to their specific properties such as high-temperature strength, low-temperature ductility and toughness, oxidation resistance, hot-corrosion resistance, and weldability, becoming potential candidates for high-performance components that require corrosion resistance and good mechanical properties. This unparalleled combination of properties is achieved by adding alloying elements and changes in microstructure. This research project blended Ni-based metal welds produced by in situ alloying using the tandem GMAW process in a previous research project developed by the Welding Research and Technology Laboratory team at the Federal University of Ceará, in Brazil.
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The aim of this project is to develop novel nanostructured Fe-Co-Ti-X (X = Si, Ge, Sn) compositionally complex alloys (CCAs) with adjustable magnetic properties by tailoring microstructure and phase constituents through compositional and process tuning. The key aspect of this work is to build a fundamental understanding of the correlation between microstructure and magnetic properties by length scale bridging characterization and property determination. The ultimate goal is to establish guidelines for designing alloys with high magnetization saturation (Ms) and low coercivity (Hc), to optimize the magnetic properties of CCAs for high frequency magnetic field applications. more

In this project, links are being established between local chemical variation and the mechanical response of laser-processed metallic alloys and advanced materials.

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About 90% of all mechanical service failures are caused by fatigue. Avoiding fatigue failure requires addressing the wide knowledge gap regarding the micromechanical processes governing damage under cyclic loading, which may be fundamentally different from that under static loading. This is particularly true for deformation-induced martensitic transformation (DIMT), one of the most common strengthening mechanisms for alloys. Here, we identify two antagonistic mechanisms mediated by martensitic transformation during the fatigue process through in situ observations and demonstrate the dual role of DIMT in fatigue crack growth and its strong crack-size dependence. Our findings open up avenues for designing fatigue-resistant alloys through optimal use of DIMT. They also enable the development of physically based lifetime prediction models with higher fidelity.
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Oxides find broad applications as catalysts or in electronic components, however are generally brittle materials where dislocations are difficult to activate in the covalent rigid lattice. Here, the link between plasticity and fracture is critical for wide-scale application of functional oxide materials. more

Enabling a ‘hydrogen economy’ requires developing fuel cells satisfying economic constraints, reasonable operating costs and long-term stability. The fuel cell is an electrochemical device that converts chemical energy into electricity by recombining water from H₂ and O₂, allowing to generate environmentally-friendly power for e.g. cars or houses. However, upscaling anion-exchange membrane fuel cells (AEMFCs) is hindered by the slow kinetics of hydrogen oxidation reaction (HOR) at the anode.
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The worldwide developments of electric vehicles, as well as large-scale or grid-scale energy storage to compensate the intermittent nature of renewable energy generation has generated a surge of interest in battery technology. Understanding the factors controlling battery capacity and, critically, their degradation mechanisms to ensure long-term, sustainable and safe operation requires detailed knowledge of their microstructure and chemistry, and their evolution under operating conditions, on the nanoscale.
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In this project, we work on a generic solution to design advanced high-entropy alloys (HEAs) with enhanced magnetic properties. By overturning the concept of stabilizing solid solutions in HEAs, we propose to render the massive solid solutions metastable and trigger spinodal decomposition. The motivation for starting from the HEA for this approach is to provide the chemical degrees of freedom required to tailor spinodal behaviour using multiple components.
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In this project, we work on the use of a combinatorial experimental approach to design advanced multicomponent multi-functional alloys with rapid alloy prototyping. We use rapid alloy prototyping to investigate five multicomponent Invar alloys with 5 at.% addition of Al, Cr, Cu, Mn and Si to a super Invar alloy (Fe₆₃Ni₃₂Co₅; at.%), respectively. All the new alloys show a typical Invar effect with low TEC around room temperature.
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Laser Powder Bed Fusion (LPBF) is the most commonly used Additive Manufacturing processes. One of its biggest advantages it offers is to exploit its inherent specific process characteristics, namely the decoupling the solidification rate from the parts´volume, for novel materials with superior physical and mechanical properties. One prominet example are so called High Modulus Steels, where the combination of strong, ductile and tough metallic matrices with stiff ceramic particles allows the specific modulus (E/ρ) to be increased compared to conventional materials such as aluminum or steel, thereby reducing weight. The aim of this project is to elucidate the synthesis/microstructure/property causalities of high modulus steel fabricated with the LPBF process. more

Electro-responsive interfaces alter their properties in response to an electric potential trigger. Hence, such 'smart' interfaces offer exciting possibilities for applications in, for instance, microfluidics, separation systems, biosensors and -analytics. more

Water electrolysis has the potential to become the major technology for the production of the high amount of green hydrogen that is necessary for its widespread application in a decarbonized economy. The bottleneck of this electrochemical reaction is the anodic partial reaction, the oxygen evolution reaction (OER), which is sluggish and hence requires efficient catalysts. We use electrochemical in situ spectroscopy techniques to study this reaction in detail. more

The structure of solvent at solid-liquid interfaces influences the interactions and reactions occurring on it, which has strong impacts for applications in diverse fields, such as wetting phenomena, electrochemistry or biotechnology. We particularly try to understand the influence of nanoscale structures formed on functional interfaces on the interfacial solvent structure. more

The promising mechanical properties of metallic glasses (MG) such as high hardness, yield strength, and toughness [1] are desirable to exploit for structural applications. Monolithic MGs lack grains and grain boundaries; thus, the mechanical properties of MGs are depending on the chemistry as well as processing and testing conditions. However, despite the promising properties, catastrophic failure is often observed, especially under uniaxial tension.
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Wear-related energy loss and component damage, including friction and remanufacturing of components that failed by surface contacts, has an incredible cost. While high-strength materials generally have low wear rates, homogeneous deformation behaviour and the accommodation of plastic strain without cracking or localised brittle fracture are also crucial for wear-resistant metals. more

The exploration of high dimensional composition alloy spaces, where five or more alloying elements are added at near equal concentration, triggered the development of so-called high entropy (HEAs) or compositionally complex alloys (CCAs). This new design approach opened vast phase and composition spaces for the design of new materials with advanced mechanical and functional properties. more

Interstitial alloying in high-entropy alloys (HEAs) is an important strategy for tuning and improving their mechanical properties. Strength can be increased due to interstitial solid-solution hardening, while interstitial alloying can simultaneously affect, e.g., stacking fault energies (SFEs) and thus trigger different deformation mechanisms. While this provides a variety of opportunities, it introduces at the same time a further degree of complexity. An understanding of the fundamental mechanisms on the atomic scale is therefore crucial. more

The aim of this project is to correlate the point defect structure of Fe_1-xO to its mechanical, electrical and catalytic properties. Systematic stoichiometric variation of magnetron-sputtered Fe_1-xO thin films are investigated regarding structural analysis by transition electron microscopy (TEM) and spectroscopy methods, which can reveal the defect point defect structure caused by chemical variation. Following this, the defect structure can be correlated to mechanical properties such as fracture toughness, electrical resistivity, and the catalytic properties for possible future water-splitting applications.
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3D copper microarchitectures will be fabricated using a localized electrodeposition-based microscale additive manufacturing process and mechanically tested under extreme strain rates. Structures to be tested range from simple micropillars to complex microlattices. The suitability of such full-metal architectures towards energy absorption and mechanical band-gap engineering applications will be investigated. more

Femtosecond laser pulse sequences offer a way to explore the ultrafast dynamics of charge density waves. Designing specific pulse sequences may allow us to guide the system's trajectory through the potential energy surface and achieve precise control over processes at surfaces. more