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Finished Research Projects

<p style="text-align: justify;">Scandium-containing aluminium alloys are currently attracting interest as candidates for high-performance aerospace structural materials due to their outstanding combination of strength, ductility and corrosion resistance. Strengthening is achieved by precipitation of Al<sub>3</sub>Sc-particles upon ageing heat treatment. </p>

Characterisation of the defects and precipitates in an SLM-produced Al-Mg-Sc alloy

Scandium-containing aluminium alloys are currently attracting interest as candidates for high-performance aerospace structural materials due to their outstanding combination of strength, ductility and corrosion resistance. Strengthening is achieved by precipitation of Al3Sc-particles upon ageing heat treatment.

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<p style="text-align: justify;">In this project, we investigate the phase transformation and twinning mechanisms in a typical interstitial high-entropy alloy (iHEA) via in-situ and interrupted in-situ tensile testing ...</p>

Understanding the phase transformation and twinning mechanisms in an interstitial high-entropy alloy

In this project, we investigate the phase transformation and twinning mechanisms in a typical interstitial high-entropy alloy (iHEA) via in-situ and interrupted in-situ tensile testing ...

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<div style="text-align: justify;">Single crystalline copper beams with thicknesses between 0.7 and 5 μm are manufactured with a focused ion beam technique and bent in a nanoindenter. The yield strengths of the beams show a mechanical size effect (smaller-is-stronger).</div>

The mechanical size effect as a mean-field breakdown phenomenon: Example of microscale single crystal beam bending

Single crystalline copper beams with thicknesses between 0.7 and 5 μm are manufactured with a focused ion beam technique and bent in a nanoindenter. The yield strengths of the beams show a mechanical size effect (smaller-is-stronger).
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<div style="text-align: justify;">In this project, we develop a new class of high-entropy alloys (HEAs) which is interstitially alloyed and unifies all known metallic strengthening mechanisms in one material. This results in joint activation of twinning- and transformation-induced plasticity (TWIP and TRIP) by tuning the matrix phase’s instability in a metastable TRIP-assisted dual-phase HEA.</div>

Interstitial high-entropy alloys with joint activation of twinning and transformation

In this project, we develop a new class of high-entropy alloys (HEAs) which is interstitially alloyed and unifies all known metallic strengthening mechanisms in one material. This results in joint activation of twinning- and transformation-induced plasticity (TWIP and TRIP) by tuning the matrix phase’s instability in a metastable TRIP-assisted dual-phase HEA.
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<p>In this project, we employ a metastability-engineering strategy to design bulk high-entropy alloys (HEAs) with multiple compositionally equivalent high-entropy phases.</p>

Design of transformation-induced plasticity-assisted dual-phase high-entropy alloys

In this project, we employ a metastability-engineering strategy to design bulk high-entropy alloys (HEAs) with multiple compositionally equivalent high-entropy phases.

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We review microstructures and properties of metal matrix composites produced by severe plastic deformation of multiphase alloys. Typical processings are wire drawing, ball milling, roll bonding, equal-channel angular extrusion, and high-pressure torsion of multiphase materials.

Metallic composites processed via extreme deformation: Toward the limits of strength in bulk materials

We review microstructures and properties of metal matrix composites produced by severe plastic deformation of multiphase alloys. Typical processings are wire drawing, ball milling, roll bonding, equal-channel angular extrusion, and high-pressure torsion of multiphase materials. [more]
<p style="text-align: justify;">Among the high number of multi-principal-element alloys that are referred to as high-entropy alloys (HEAs) in the literature, only a limited number solidify as single-phase solid solutions.</p>

Decomposition of the single-phase high-entropy alloy CrMnFeCoNi after prolonged anneals

Among the high number of multi-principal-element alloys that are referred to as high-entropy alloys (HEAs) in the literature, only a limited number solidify as single-phase solid solutions.

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<div style="text-align: justify;">For this project three ferrite/martensite dual-phase steels varying in the ferrite grain size (12.4, 2.4 and 1.2 um) but with the same martensite content (30 vol.%) were produced by large-strain warm deformation at different deformation temperatures, followed by intercritical annealing.</div>

Deformation and fracture in fine- and ultrafine-grained ferrite-martensite dual-phase steels

For this project three ferrite/martensite dual-phase steels varying in the ferrite grain size (12.4, 2.4 and 1.2 um) but with the same martensite content (30 vol.%) were produced by large-strain warm deformation at different deformation temperatures, followed by intercritical annealing.
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<div style="text-align: justify;">In this project we investigate the hydrogen distribution and desorption behavior in an electrochemically hydrogen-charged binary Ni-Nb model alloy. The aim is to study the role of the delta phase in hydrogen embrittlement of the Ni-base alloy 718.</div>

Study of hydrogen embrittlement by using multi-scale and spatially resolved hydrogen mapping in a Ni-Nb model alloy and in alloy 718

In this project we investigate the hydrogen distribution and desorption behavior in an electrochemically hydrogen-charged binary Ni-Nb model alloy. The aim is to study the role of the delta phase in hydrogen embrittlement of the Ni-base alloy 718.
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<div style="text-align: justify;">For this project two plain carbon steels with varying manganese content (0.87 wt pct and 1.63 wt pct) were refined to approximately 1 um by large strain warm deformation and subsequently subjected to intercritical annealing to produce an ultrafine grained ferrite/martensite dual-phase steel. The influence of the Mn content on microstructure evolution is studied by scanning electron microscopy (SEM).</div>

Effect of Manganese on Grain Size Stability and Hardenability in Ultrafine-Grained Dual-Phase Steels

For this project two plain carbon steels with varying manganese content (0.87 wt pct and 1.63 wt pct) were refined to approximately 1 um by large strain warm deformation and subsequently subjected to intercritical annealing to produce an ultrafine grained ferrite/martensite dual-phase steel. The influence of the Mn content on microstructure evolution is studied by scanning electron microscopy (SEM).
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<p style="text-align: justify;">The potential of high-entropy alloys (HEAs) to exhibit an extraordinary combination of properties by shifting the compositional regime from the corners towards the centers of phase diagrams has ledto worldwide attention by material scientists.</p>

High strength and ductility in a friction stir processing engineered dual phase high entropy alloy

The potential of high-entropy alloys (HEAs) to exhibit an extraordinary combination of properties by shifting the compositional regime from the corners towards the centers of phase diagrams has ledto worldwide attention by material scientists.

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<div style="text-align: justify;">In this project we conduct together with Dr. Sandlöbes at RWTH Aachen and the department of Prof. Neugebauer ab initio calculations for designing new Mg – Li alloys. Ab initio calculations can accurately predict basic structural, mechanical, and functional properties using only the atomic composition as a basis.</div>

Ab Initio Guided Design of bcc Ternary Mg–Li–X Alloys for Ultra-Lightweight Applications

In this project we conduct together with Dr. Sandlöbes at RWTH Aachen and the department of Prof. Neugebauer ab initio calculations for designing new Mg – Li alloys. Ab initio calculations can accurately predict basic structural, mechanical, and functional properties using only the atomic composition as a basis.
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<div style="text-align: justify;">In this project nanoprecipitates are designed via elastic misfit stabilization in Fe–Mn maraging steels by combining transmission electron microscopy (TEM) correlated atom probe tomography (APT) with ab initio simulations. Guided by these predictions, the Al content of the alloys is systematically varied...</div>

Designing Heusler nanoprecipitates by elastic misfit stabilization in Fe–Mn maraging steels

In this project nanoprecipitates are designed via elastic misfit stabilization in Fe–Mn maraging steels by combining transmission electron microscopy (TEM) correlated atom probe tomography (APT) with ab initio simulations. Guided by these predictions, the Al content of the alloys is systematically varied...
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<div style="text-align: justify;">Carbon partitioning between ferritic and austenitic phases is essential for austenite stabilization in the most advanced steels such as those produced by the quenching and partitioning (Q&amp;P) process.</div>

 Atomic-scale analysis of carbon partitioning in quench-partioning  steels

Carbon partitioning between ferritic and austenitic phases is essential for austenite stabilization in the most advanced steels such as those produced by the quenching and partitioning (Q&P) process.
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<div style="text-align: justify;">In this project we study a new strategy for the theory-guided bottom up design of <strong>beta-Ti alloys</strong> for <strong>biomedical applications</strong> using a quantum mechanical approach in conjunction with experiments. Parameter-free <strong>density functional theory</strong> calculations are used to provide theoretical guidance in selecting and optimizing Ti-based alloys...</div>

Theory-guided bottom-up design of b-titanium alloys as biomaterials based on first principles calculations: Theory and experiments

In this project we study a new strategy for the theory-guided bottom up design of beta-Ti alloys for biomedical applications using a quantum mechanical approach in conjunction with experiments. Parameter-free density functional theory calculations are used to provide theoretical guidance in selecting and optimizing Ti-based alloys...
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<div style="text-align: justify;">In this project we investigate the kinetics of the deformation structure evolution and its contribution to the strain hardening of a Fe–30.5Mn–2.1Al–1.2C (wt.%) steel during tensile deformation by means of transmission electron microscopy and electron channeling contrast imaging combined with electron backscatter diffraction.</div>

Multistage strain hardening through dislocation substructure and twinning in a high strength and ductile low-density Fe–Mn–Al–C steel

In this project we investigate the kinetics of the deformation structure evolution and its contribution to the strain hardening of a Fe–30.5Mn–2.1Al–1.2C (wt.%) steel during tensile deformation by means of transmission electron microscopy and electron channeling contrast imaging combined with electron backscatter diffraction.
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<div style="text-align: justify;">Quench and Partioning (Q&amp;P) steels are 3rd generation advanced high strengths (AHS) steels. They consist of a martensite-austenite microstructure created during a quenching process. However, due to the subsequent partitioning treatment the martensite is relatively soft and the austenite relatively stable against phase transformation which makes the alloy strong (tensile strength up to 1000 MPa) and ductile (uniform tensile elongation up to 20 %) at the same time. We aim at improving the microstructure by obtaining finer austenite dispersion.</div>

Optimization of Q&P steels

Quench and Partioning (Q&P) steels are 3rd generation advanced high strengths (AHS) steels. They consist of a martensite-austenite microstructure created during a quenching process. However, due to the subsequent partitioning treatment the martensite is relatively soft and the austenite relatively stable against phase transformation which makes the alloy strong (tensile strength up to 1000 MPa) and ductile (uniform tensile elongation up to 20 %) at the same time. We aim at improving the microstructure by obtaining finer austenite dispersion.
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<div style="text-align: justify;">This project is about the understanding and optimization of the microstructure and properties of thin strip cast austenitic stainless steel (AISI 304, 1.4301). Concerning the processing steps the relevance of different thin strip casting parameters, in-line forming operations, and heat treatments for optimizing microstructure and properties have been studied.</div>

Advances in the Optimization of Thin Strip Cast Stainless Steels

This project is about the understanding and optimization of the microstructure and properties of thin strip cast austenitic stainless steel (AISI 304, 1.4301). Concerning the processing steps the relevance of different thin strip casting parameters, in-line forming operations, and heat treatments for optimizing microstructure and properties have been studied.
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<div style="text-align: justify;">In this project an integrated simulation strategy for studying primary static recrystallization was developed and applied to a single-crystal nickel-base superalloy. By using a crystal plasticity finite element approach, the driving force for nucleation and grain growth around a Brinell-type indent was modeled. </div>

Recrystallization studied with indentation tests and coupled crystal plasticity and cellular automaton simulations

In this project an integrated simulation strategy for studying primary static recrystallization was developed and applied to a single-crystal nickel-base superalloy. By using a crystal plasticity finite element approach, the driving force for nucleation and grain growth around a Brinell-type indent was modeled.
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<div style="text-align: justify;">In this project we study - together with the department of Prof. Neugebauer and Dr. Sandlöbes at RWTH Aachen - the underlying mechanisms that are responsible for the improved room-temperature ductility in Mg–Y alloys compared to pure Mg.</div>

Ductility and stacking fault energies in Mg and Mg-Y alloys

In this project we study - together with the department of Prof. Neugebauer and Dr. Sandlöbes at RWTH Aachen - the underlying mechanisms that are responsible for the improved room-temperature ductility in Mg–Y alloys compared to pure Mg.
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Mapping Hydrogen in TWIP Steels

Hydrogen embrittlement of austenitic steels is of high interest because of the potential use of these materials in hydrogen-energy related infrastructures. In order to elucidate the associated hydrogen embrittlement mechanisms, the mapping of heterogeneities in strain, damage (crack/void), and hydrogen and their relation to the underlying microstructures is a key assignment in this field.
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Austenite reversion during tempering of a Fe-13.6Cr-0.44C (wt.%) martensite results in an ultra-high strength ferritic stainless steel with excellent ductility.

Advanced design of a ductile 2 GPa Fe-Cr-C martensitic-austenitic steel by nanoscale austenite reversion through partitioning, segregation, and kinetic freezing

Austenite reversion during tempering of a Fe-13.6Cr-0.44C (wt.%) martensite results in an ultra-high strength ferritic stainless steel with excellent ductility. [more]
<div style="text-align: justify;">We have studied a nanocrystalline AlCrCuFeNiZn high-entropy alloy synthesized by ball milling followed by hot compaction at 600°C for 15 min at 650 MPa. X-ray diffraction reveals that the mechanically alloyed powder consists of a solid-solution body-centered cubic (bcc) matrix containing 12 vol.% face-centered cubic (fcc) phase. After hot compaction, it consists of 60 vol.% bcc and 40 vol.% fcc. Composition analysis by atom probe tomography shows that the material is not a homogeneous fcc–bcc solid solution</div>

Atomic-scale compositional characterization of a nanocrystalline AlCrCuFeNiZn high-entropy alloy using atom probe tomography

We have studied a nanocrystalline AlCrCuFeNiZn high-entropy alloy synthesized by ball milling followed by hot compaction at 600°C for 15 min at 650 MPa. X-ray diffraction reveals that the mechanically alloyed powder consists of a solid-solution body-centered cubic (bcc) matrix containing 12 vol.% face-centered cubic (fcc) phase. After hot compaction, it consists of 60 vol.% bcc and 40 vol.% fcc. Composition analysis by atom probe tomography shows that the material is not a homogeneous fcc–bcc solid solution
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In this project we pursue recent developments in the field of austenitic steels with up to 18% reduced mass density. The alloys are based on the Fe-Mn-Al-C system.

Alloy Design, Combinatorial Synthesis, and Microstructure– Property Relations for Low-Density Fe-Mn-Al-C Austenitic Steels

In this project we pursue recent developments in the field of austenitic steels with up to 18% reduced mass density. The alloys are based on the Fe-Mn-Al-C system. [more]
<div style="text-align: justify;">Carbon partitioning from martensite into austenite in the quenching and partitioning (Q&amp;P) process has been suggested to be controlled by the constrained carbon equilibrium (CCE) criterion.</div>

Carbon partitioning during quenching and partitioning heat treatment accompanied by carbide precipitation

Carbon partitioning from martensite into austenite in the quenching and partitioning (Q&P) process has been suggested to be controlled by the constrained carbon equilibrium (CCE) criterion.
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