Research Topic

Non-iron based Metals

Non-Iron based Metals

<div style="text-align: justify;">Phase stabilities of multicomponent material systems are best simulated with CALPHAD. The underlying databases are mainly obtained from calorimetric measurements, but suffer often from the fact that for certain phases an experimental approach is not feasible or not conclusive. Here, ab initio calculations emerge as an alternative, which is carefully investigated for the Al-Mg-Si-Cu and Al-Sc system within this project.</div>

Alloy thermodynamics for Al-Mg-Si-Cu

Phase stabilities of multicomponent material systems are best simulated with CALPHAD. The underlying databases are mainly obtained from calorimetric measurements, but suffer often from the fact that for certain phases an experimental approach is not feasible or not conclusive. Here, ab initio calculations emerge as an alternative, which is carefully investigated for the Al-Mg-Si-Cu and Al-Sc system within this project.
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Ti alloys are widely used in industry due to their superior properties, such as high strength, corrosion resistance, biological compatibility. Here, we study the substitution energy of Nb in Ti and reveal important consequences for the stability of various (meta)stable phases.

Intrinsic electronic interactions in TiNb alloys

Ti alloys are widely used in industry due to their superior properties, such as high strength, corrosion resistance, biological compatibility. Here, we study the substitution energy of Nb in Ti and reveal important consequences for the stability of various (meta)stable phases. [more]
Ab initio methods based on DFT are now routinely used to investigate T=0 K properties. In contrast, finite temperature DFT studies are rare and, in particular, limited to approximations such as the quasiharmonic model. In the present study, we investigate the influence of anharmonic excitations—which correspond to phonon-phonon interactions beyond the simple quasiharmonic picture—on the thermodynamics of Ti and TiNb alloys.

High accuracy ab initio prediction of phase transitions in Ti and TiNb alloys

Ab initio methods based on DFT are now routinely used to investigate T=0 K properties. In contrast, finite temperature DFT studies are rare and, in particular, limited to approximations such as the quasiharmonic model. In the present study, we investigate the influence of anharmonic excitations—which correspond to phonon-phonon interactions beyond the simple quasiharmonic picture—on the thermodynamics of Ti and TiNb alloys. [more]
<p class="p1" style="text-align: justify;">Interstitial alloying can improve the mechanical properties of high-entropy alloys (HEAs). In some cases, the interstitial-alloying impact is very different from those in conventional alloys. We investigate the effect of interstitial alloying in the CrMnFeCoNi HEA, particularly focusing on the solution energies and the impact on the stacking fault energy, based on first-principles calculations. Our results clarity, e.g., that the interstitial solution energy in HEAs is no longer a single value but shows a substantial distribution due to the dependence on local chemical environments.</p>

Interstitial alloying and the stacking fault energies of CrMnFeCoNi high entropy alloys

Interstitial alloying can improve the mechanical properties of high-entropy alloys (HEAs). In some cases, the interstitial-alloying impact is very different from those in conventional alloys. We investigate the effect of interstitial alloying in the CrMnFeCoNi HEA, particularly focusing on the solution energies and the impact on the stacking fault energy, based on first-principles calculations. Our results clarity, e.g., that the interstitial solution energy in HEAs is no longer a single value but shows a substantial distribution due to the dependence on local chemical environments.

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<p class="p1" style="text-align: justify;">Local lattice distortion is one of the core effects in complex concentrated alloys (CCAs). It has been expected that the strength CCAs can be improved by inducing larger local lattice distortions. In collaboration with experimentalists, we demonstrated that VCoNi has larger local lattice distortions and indeed has much better strength than the prototypical CrCoNi CCA has.</p>

Local lattice distortion and strength of VCoNi complex concentrated alloys

Local lattice distortion is one of the core effects in complex concentrated alloys (CCAs). It has been expected that the strength CCAs can be improved by inducing larger local lattice distortions. In collaboration with experimentalists, we demonstrated that VCoNi has larger local lattice distortions and indeed has much better strength than the prototypical CrCoNi CCA has.

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The thermodynamic stability of computationally designed multicomponent compounds against decomposition into structures with less favorable properties is often unclear. In this project, we have used sophisticated finite temperature <em>ab initio</em> methods to determine the relative phase stabilities of promising Ce-Fe-Ti hard-magnetic materials.

Hard-magnetic materials

The thermodynamic stability of computationally designed multicomponent compounds against decomposition into structures with less favorable properties is often unclear. In this project, we have used sophisticated finite temperature ab initio methods to determine the relative phase stabilities of promising Ce-Fe-Ti hard-magnetic materials. [more]
<p style="text-align: justify;">Magnetic properties of magnetocaloric materials is of utmost importance for their functional applications. In this project, we study the magnetic properties of different materials with the final goal to discover new magnetocaloric materials more suited for practical applications.</p>

Ab initio investigation of magnetocaloric materials

Magnetic properties of magnetocaloric materials is of utmost importance for their functional applications. In this project, we study the magnetic properties of different materials with the final goal to discover new magnetocaloric materials more suited for practical applications.

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<p style="text-align: justify;">In order to explore the possibility of using high entropy alloys (HEAs) for functional applications such as magnetic refrigeration it is necessary to have an in-depth understanding of their magnetic properties. The main goal of this project is to understand and improve the magnetic properties (e.g., saturation magnetization, Curie temperature etc.) in different medium and HEAs.</p>

Magnetic properties in high entropy alloys

In order to explore the possibility of using high entropy alloys (HEAs) for functional applications such as magnetic refrigeration it is necessary to have an in-depth understanding of their magnetic properties. The main goal of this project is to understand and improve the magnetic properties (e.g., saturation magnetization, Curie temperature etc.) in different medium and HEAs.

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<div style="text-align: justify;">Al-based alloys are promising structural materials owing to their mechanical properties and high thermal stability complemented by their light weight. Their performance and stability, however, is largely governed by the properties of inherent second phase particles. Computationally designing technologically-relevant alloys with desired properties therefore requires a comprehensive knowledge of the underlying atomistic processes and the interplay of strain and chemistry. The aim of this project is to integrate theory and experiments in understanding the thermodynamic and kinetics aspects of thermo-mechano-chemical coupling during the precipitate formation in Al based alloys taking the example of Al-Sc and Al-Sc-Zr systems.</div>

Precipitation formation in Al

Al-based alloys are promising structural materials owing to their mechanical properties and high thermal stability complemented by their light weight. Their performance and stability, however, is largely governed by the properties of inherent second phase particles. Computationally designing technologically-relevant alloys with desired properties therefore requires a comprehensive knowledge of the underlying atomistic processes and the interplay of strain and chemistry. The aim of this project is to integrate theory and experiments in understanding the thermodynamic and kinetics aspects of thermo-mechano-chemical coupling during the precipitate formation in Al based alloys taking the example of Al-Sc and Al-Sc-Zr systems.
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<div style="text-align: justify;">The aim of this project is the development of a complete first-principles based methodology to study the magneto-caloric effect (MCE) close to the technologically and scientifically relevant regime of first order magneto-structural transitions.</div>

Magneto-caloric materials

The aim of this project is the development of a complete first-principles based methodology to study the magneto-caloric effect (MCE) close to the technologically and scientifically relevant regime of first order magneto-structural transitions.
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<p style="text-align: justify;">A high degree of configurational entropy is a key underlying assumption of many high entropy alloys (HEAs). However, for the vast majority of HEAs very little is known about the degree of short-range chemical order as well as potential decomposition. Due to slow diffusivity, characteristic for e.g. refractory HEAs, chemical ordering is hardly ever approached under typical experimental conditions but could potentially influence creep properties long-term applications. In this project we study the phase stability and short-range order of selected refractory HEAs computationally.</p>

Phase stability and short-range order of refractory high entropy alloys

A high degree of configurational entropy is a key underlying assumption of many high entropy alloys (HEAs). However, for the vast majority of HEAs very little is known about the degree of short-range chemical order as well as potential decomposition. Due to slow diffusivity, characteristic for e.g. refractory HEAs, chemical ordering is hardly ever approached under typical experimental conditions but could potentially influence creep properties long-term applications. In this project we study the phase stability and short-range order of selected refractory HEAs computationally.

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Self-healing metallic materials for the practical use are not properly developed despite of their numerous potential applications. We investigate the possibility of designing new self-healing metals by using a hierarchical modeling approach. The present study aims at examining the interaction between nano-cracks and shape memory nano-particles which is an important concept to realize self-heling metals. The knowledge gained from the present study will guide future experimental works.

Atomic scale investigation of self-healing mechanisms in metallic materials

Self-healing metallic materials for the practical use are not properly developed despite of their numerous potential applications. We investigate the possibility of designing new self-healing metals by using a hierarchical modeling approach. The present study aims at examining the interaction between nano-cracks and shape memory nano-particles which is an important concept to realize self-heling metals. The knowledge gained from the present study will guide future experimental works. [more]
 
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