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Aufsatz
Design of novel materials for additive manufacturing - Isotropic microstructure and high defect tolerance
(2018-01-22)
Electron Beam Melting (EBM) is a powder-bed additive manufacturing technology enabling the production of complex metallic parts with generally good mechanical properties. However, the performance of powder-bed based additively manufactured materials is governed by multiple factors that are difficult to control. Alloys that solidify in cubic crystal structures are usually affected by strong anisotropy due to the formation of columnar grains of preferred orientation. Moreover, processing induced defects and porosity ...
Aufsatz
Shape memory effect and superelasticity in high-strength FeNiCoAlTi single crystals hardened by nanoparticles
(2019-11-19)
For [001]-oriented single crystals of Fe-28Ni-17Co-11.5Al-2.5Ti (at %) alloy in tension, it was shown that particles of the γ’-phase with a size of 4–6 nm lead to the appearance of superelasticity, with a strain of εSE=4.5% and a shape memory effect of εSME=5.9%. Increasing the particle size to 10–12 nm reduces εSE to 3.6% and εSME to 3.5%. The paper discusses the causes of the influence of particle size on the reversible strain.
Aufsatz
Excellent superelasticity in a Co-Ni-Ga high-temperature shape memory alloy processed by directed energy deposition
(2020-04-30)
A Co-Ni-Ga high-temperature shape memory alloy has been additively manufactured by directed energy deposition. Due to the highly anisotropic microstructure, i.e. columnar grains featuring a strong near-⟨001⟩ texture in build direction, the as-built material is characterized by a very low degree of constraints and, thus, shows excellent superelasticity without conducting a post-process heat treatment. As characterized by in situ deformation testing and post-mortem microstructural analysis, additive manufacturing ...
Dissertation
Untersuchung von Gussporen in einer Aluminium-Gusslegierung mit der Computertomographie
(2022-04)
In dieser Arbeit wird das Schädigungsverhalten einer Aluminium-Gusslegierung anhand von zweidimensionalen und dreidimensionalen Verfahren untersucht. Dabei liegt das Hauptaugenmerk auf innenliegenden Gussdefekten wie Gas- und Schrumpfungsporen. Die Schädigungsentwicklung unter schwingender Belastung, sowie der Einfluss auf die Mikrostruktur und die mechanischen Eigenschaften sowie die Wechselwirkung verschiedener Gussdefekte werden dabei untersucht. Insbesondere wird der beim Versagensverhalten entscheidende Einfluss ...
Aufsatz
Mechanics of colloidal supraparticles under compression
(2021-10-13)
Colloidal supraparticles are finite, spherical assemblies of many primary particles. To take advantage of their emergent functionalities, such supraparticles must retain their structural integrity. Here, we investigate their size-dependent mechanical properties via nanoindentation. We find that the deformation resistance inversely scales with the primary particle diameter, while the work of deformation is dependent on the supraparticle diameter. We adopt the Griffith theory to such particulate systems to provide a ...
Aufsatz
Hydrogen absorption of ultra-high strength aluminum-silicon coated 22MnB5 steels
(2022-12-30)
The hot forming process allows to produce safety-relevant structural components in the automotive industry with strengths of 1500 MPa and higher. Generally, high strengths make material sensitive to hydrogen embrittlement. The heat treatment in the hot forming process chain is a potential source of diffusible hydrogen for hot-dipped aluminum-silicon coated boron-manganese steels. In the present work, the influence of different process gases and furnace dwell times during the heat treatment was investigated. Humidified ...
Aufsatz
Exploring the mechanical properties of additively manufactured carbon-rich zirconia 3D microarchitectures
(2023-07-11)
Two-photon lithography (TPL) is a promising technique for manufacturing ceramic microstructures with nanoscale resolution. The process relies on tailor-made precursor resins rich in metal–organic and organic constituents, which can lead to carbon-based residues incorporated within the ceramic microstructures. While these are generally considered unwanted impurities, our study reveals that the presence of carbon-rich residues in the form of graphitic and disordered carbon in tetragonal (t-) ZrO₂ can benefit the ...
Aufsatz
Describing mechanical damage evolution through in situ electrical resistance measurements
(2023-02-27)
The fatigue properties of metallizations used as electrical conductors in flexible electronic devices have been thoroughly studied over the years. Most studies use time-intensive characterization methods to evaluate mechanical damage. For their ease of access, in situ electrical resistance measurements are often performed along with other characterization methods. However, the data are mostly used as an indicator of failure and a thorough analysis is usually missing. This work presents some deeper analysis methods ...
Aufsatz
Linking through-thickness cracks in metallic thin films to in-situ electrical resistance peak broadening
(2022-01-29)
Measurements of electrical resistance have been used extensively as a failure criterion in cyclically loaded conductive films. However, not much research has been performed on extracting additional information contained within such resistance data sets. This study shows that an increase in peak width evidences a transition from cracks bridging to through-thickness crack formation. A Au/Cr bilayer system on a polyimide substrate is used for data generation but the method is applicable to any material system where both ...
Aufsatz
Influence of Cu Addition and Microstructural Configuration on the Creep Resistance and Mechanical Properties of an Fe-Based α/α′/α″ Superalloy
(2023-01-14)
Introducing Cu nanoparticles is an effective mechanism for strengthening and toughening Fe-based materials such as ultra-high-strength steels. Herein, the effect of Cu on the mechanical properties of a novel Fe-based α/α′/α″ superalloy is studied. Compared to a Cu-free reference alloy, nanoindentation reveals an increase in hardness, which was associated with the formation of Cu nanoparticles. Both alloys show room temperature (RT) compressive plastic strain at maximum stress greater than 8%, irrespective of the ...