Current Research Projects

In collaboration with Dr. Edgar Rauch, SIMAP laboratory, Grenoble, and Dr. Wolfgang Ludwig, MATEIS, INSA Lyon, we are developing a correlative scanning precession electron diffraction and atom probe tomography method to access the three-dimensional (3D) crystallographic character and compositional information of nanomaterials with unprecedented spatial and chemical resolution. [more]

Hydrogen embrittlement (HE) is one of the most dangerous embrittlement problems in metallic materials and  advanced high-strength steels (AHSS) are particularly prone to HE with the presence of only a few parts-per-million of H. However, the HE mechanisms in these materials remain elusive, especially for the lightweight steels where the composition and microstructure significantly differ from the traditional plain-carbon steels. Here we focus on a high-Mn and high-Al lightweight steel and unravel the effects of H-associated decohesion and localized plasticity on its H-induced catastrophic failure.

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Within this project, we will use an infra-red laser beam source based selective powder melting to fabricate copper alloy (CuCrZr) architectures. The focus will be on identifying the process parameter-microstructure-mechanical property relationships in 3-dimensional CuCrZr alloy lattice architectures, under both quasi-static and dynamic loading conditions.
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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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Replacing carbon by hydrogen as the reducing agent in ironmaking offers a pathway to massively reduce the associated CO₂ emissions. However, the production of hydrogen using renewable energy will remain as one of the bottlenecks at least in the next two decades. The underlying reasons are the low electrolysis productivity and the insufficient capacities in both renewable electricity and industrial infrastructures to produce sufficient amounts of green hydrogen, especially in view of the gigantic demand for currently 1.8 billion tons of steel being produced every year, with forecasts predicting 2.4 billion tons by the year 2040. We therefore demonstrate how the efficiency in hydrogen and energy consumption during iron ore reduction can be dramatically improved by the knowledge-based combination of two technologies: partially reducing the ore at low temperature via solid-state hydrogen-based direct reduction (HyDR) to a kinetically defined degree, and subsequently melting and completely transforming it to iron under a reducing plasma (i.e. via hydrogen plasma reduction, HPR) [more]

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 developed a phase-field model capable of describing multi-component and multi-sublattice ordered phases, by directly incorporating the compound energy CALPHAD formalism based on chemical potentials. We investigated the complex compositional pathway for the formation of the η-phase in Al-Zn-Mg-Cu alloys during commercial multi-stage artificial ageing treatments.
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In this project we study the degradation of hydrogen embrittlement resistivity of austenitic high-Mn and high-Al lightweight steels upon age hardening and discover ways to mitigate this deterioration. [more]

Iron- and steelmaking is the most staggering single source of CO₂ emissions on the planet, accounting for ~7% of the global emissions. This fact challenges the current technologies to achieve carbon-lean steel production and reduce CO₂ emissions by 80% until 2050. Among the sustainable alternatives for ironmaking, the hydrogen plasma reduction (HPR) is a promising route, as the associated by-product is water. In this process, a hydrogen plasma arc is ignited between an electrode and the ore in a conventional electrical arc furnace (EAF), Figure 1 (a). Thus, melting and reduction occur simultaneously, enabling the production of liquid iron in single step. The highly energetic hydrogen species existing in a reducing plasma also enable exothermic redox chemical reactions with enhanced kinetics, permitting energy savings.
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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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To successfully transition from fossil fuels to a sustainable carbon-free energy supply, a safe and stable energy storage technology is required. Recently, metallic powders, and particularly iron powder, have been proposed as a high energy density, easily storable, and commonly traded fuel. Energy production is obtained through the heat of oxidation, and the combusted products can then be reduced at the solid-state using hydrogen coming from sustainable energy sources, resulting in a complete CO₂-free energy cycle. While the combustion of iron powders seems very promising in this regard, hardly anything is known about its in-process morphological, microstructural, and chemical evolution, which are critical for the circularity of the concept and the subsequent reduction process.
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The main aspect of this project is to understand how hydrogen interacts with dislocations/ stacking faults at the stress concentrated crack tip. A three-point bending test has been employed for this work. [more]

The HYDRI project aims at disentangling the correlation between material micro-/nanostructures and the hydrogen-based direct reduction (HyDR) kinetics, to reveal the vital role of acquired defects in HyDR processes. A multiscale and time-resolved operando approach will be used to characterize micro-/nanostructures in HyDR. Gaining better insights into these effects enable improved access to the microstructure-based design of more efficient HyDR methods, with potentially high impact on the urgently needed decarbonization in the steel industry. [more]

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 aim to realize an optimal balance among the strength, ductility and soft magnetic properties in soft-magnetic high-entropy alloys. To this end, we introduce a high-volume fraction of coherent and ordered nanoprecipitates into the high-entropy alloy matrix. The good combination of strength and ductility derives from massive solid solution, nanoprecipitation and dynamic microband strengthening, yielding mechanical features beyond those reported before for soft magnetic materials. The full coherency of the ordered nanoprecipitates and the matrix contributes significantly to the strength with only a slight increase in coercivity. [more]

This project is a joint project of the De Magnete group and the Atom Probe Tomography group, and was initiated  by MPIE’s participation in the CRC TR 270 HOMMAGE. We also benefit from additional collaborations with the “Machine-learning based data extraction from APT” project and the Defect Chemistry and Spectroscopy group.  [more]

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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The structures of grain boundaries (GBs) have been investigated in great detail. However, much less is known about their chemical features, owing to the experimental difficulties to probe these features at the near-atomic scale inside bulk material specimens. Atom probe tomography (APT) is a tool capable of accomplishing this task, with an ability to quantify chemical characteristics at near-atomic scale. [more]

Here, we aim to develop machine-learning enhanced atom probe tomography approaches to reveal chemical short/long-range order (S/LRO) in a series of metallic materials. [more]

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]

This project targets hydrogen behaviour and hydride formation mechanisms in commercially pure titanium (CP-Ti). A particular focus is on the role of β-pockets. Additionally, knowledge on the deformation behaviour of hydrides and their interaction with the parent Ti matrix can help with design approaches to alleviate hydrogen embrittlement of these alloys.
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Many important phenomena occurring in polycrystalline materials under large plastic strain, like microstructure, deformation localization and in-grain texture evolution can be predicted by high-resolution modeling of crystals. Unfortunately, the simulation mesh gets distorted during the deformation because of the heterogeneity of the plastic deformation in polycrystals. After reaching high local strain levels, it is no longer possible to continue the simulation, because the mesh distortion reduces the accuracy of the results. In this project we introduce two different adaptive remeshing approaches for simulating large deformation of 3D polycrystals with high resolution under periodic boundary conditions.
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This project is led by Felipe Morgado and Leigh Stephenson, and targets the analysis of single vacancies in nickel, but also their chemical neighborhood with tantalum, using Atom Probe Tomography, Field Ion Microscopy in conjunction with Time-of-Flight Mass Spectrometry, and Density-Functional Theory. [more]

CALPHAD-informed phase field modeling, scanning transmission electron microscopy and atom probe tomography have been used to study the segregation, precipitation, and solute distribution in high strength Aluminium alloys (7xxx). [more]

Direct reduction of iron ores with hydrogen is an attractive alternative to the common reduction with carbon, to eliminate the CO₂ emissions in steel making. The kinetics of this process are not yet well understood, in particular during the wüstite reduction step. Microstructure, local chemistry and lattice defects are studied for better understanding the underlaying microscopic transport and reduction mechanisms and kinetics, aiming to open the perspective for a carbon-neutral iron production. [more]

In this project we develop new aluminium alloys specifically for L-PBF that have both high strength and high resistance to solidification cracking. Modifying the chemical composition of commercial high-strength aluminium alloys and developing new alloys based on L1₂-Al₃X-forming elements  are the two different strategies. [more]

In this project we study how Segregation Engineering can serve in the design of more robust and crack-free microstructures in Additive Manufacturing. More specific, we were able to reduce hot tearing in additive manufacturing of an Al x CoCrFeNi high-entropy alloy by grain boundary segregation engineering. [more]

Within this project we show that medium Mn steels can develop a pronounced discontinuous yielding when the austenite matrix fraction lies about 65 vol%. This phenomenon is investigated by a combination of multiple in situ characterization techniques covering the macroscopic down to the nanoscopic scale. [more]

In order to solve key challenges in lightweight transportation and safe infrastructures stronger steels with high ductility are urgently needed. In this work we introduce a new unique chemical boundary engineering (CBE) approach, which enables us to create a material with an ultrafine hierarchically heterogeneous microstructure even after heating to high temperatures. [more]

We introduce here a new approach in which we strengthen a low-density solid solution matrix simultaneously by a dual-nanoprecipitation system containing both kappa-carbides and B2 particles. Since the conventional thermodynamic working point is not accessible to realize this dual-precipitation strategy, we designed a low-density (6.6 g/cm3) steel-type alloy, which uses merits of the recently introduced multi–principal element approach referred to as compositionally complex alloys (CCAs) or high-entropy alloys (HEAs).

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Steels are backbone materials of civilization since more than 3000 years. They retrieve their properties not from expensive chemical compositions but rather from complex nano- and microstructures. They cover a wider spectrum of properties than any other material. [more]

Stainless steels, invented more than 100 years ago, enable many sustainable applications: 1) they are among the most corrosion-resistant commodity alloys (corrosion being one of the biggest sustainability problems, destroying annually about 3.4% of the GDP (2.5 trillion Euros )).
2) they have with about 75% one of the highest end-of-life recycling rates of all mass-produced materials is use, averaged over all stainless steel grades.
However, there are 2 drawbacks: (a) high and expensive alloying content. (b) high weight.
We tackled both challenges: In a team effort we developed a new family of low-density stainless steels with ultra-high strength (> 1 GPa) and high ductility (> 35%). [more]

We are working on understanding the underlying mechanism of hydrogen embrittlement susceptibility in a Fe 28Mn 0.3C (Wt.%) alloy on the micro and nano scale by  exploring differentt hydrogen charging routes, for instance cathodic charging, gas charging and plasma charging. The defect behavior (dislocation density and arrangement, stacking faults, twins, ε-martensite, residual stresses) is investigated using deformation experiments coupled with electron channeling contrast imaging (ECCI) technique in both charged and uncharged conditions.Local residual stresses are measured with cross-correlation EBSD.In order to investigate the role of grain boundaries and stacking faults as hydrogen trapping sites, we also perform site-specific atom probe tomography (APT) studiesafter charging the samples with hydrogen/deuterium. [more]

 In this project, we reveal the subtle yet important interplay between the faceting of grain boundaries and their chemical decoration with solutes in an engineering Al-Zn-Mg-Cu alloy. Previously, the interplay of chemistry and faceting was revealed for specific grain boundaries in well-defined bicrystals, which are realistically not encountered in engineering alloys. [more]

In this project we investigate tensile fracture mechanisms of medium Mn steels with two typical types of microstructures. One group consists of ferrite (α) plus austenite (γ) and the other one of a layered structure with an austenite-ferrite constituent and δ-ferrite. [more]

In this project we show that medium Mn steels with an austenite matrix (austenite fraction ~65 vol%) can exhibit pronounced discontinuous yielding. A combination of multiple in situ characterization techniques from macroscopic (a few millimeters) down to nanoscopic scale (below 100 nm) is utilized to investigate this phenomenon. [more]

Severe plastic deformation leads to cementite decomposition in pearlitic and martensitic alloys, resulting in high-strength nanocrystalline ferrite. This effect can be employed to strengthen pearlitic wires but it can also be associated with material failure by white etching cracks (WECs) [more]

The phase-field method is particularly well-suited to model coupled mechanical-thermal-chemical microstructure evolution and structure-property relations.
It has been successfully applied to model multiple thermo-chemo-mechanical processes including solidification, precipitation, fracture and dislocation motion. [more]

One purpose of metallurgical and materials science is the theory-guided tailoring of materials, including elasto-plastic mechanical response, chemical composition and microstructure, in order to obtain improved properties for a sustainable technological development. [more]

In this project, we successfully developed a crystal-glass high-entropy nanocomposite in CrFeCoNi-based system. The microstructure, composition and deformation mechanism of the novel crystal-glass high-entropy nanocomposite was comprehensively studied using probe-corrected scanning transmission electron microscope and atom probe tomography. This crystal-glass nanocomposite design provides a route to develop advanced structural materials with an outstanding combination of strength and ductility. [more]

To reach highest quality of microstructure and mechanical properties, adjustment of downstream processing parameters are often required along the process chain, dependent on exact chemical composition of the batch and the preceding casting, deformation and annealing processing steps. [more]

The focus of this project is the investigation of the kinetics of the deformation structure evolution and its influence on the strain hardening of a Fe-30.5Mn-2.1Al-1.2 (wt.%) steel. The observations are carried out during tensile deformation by transmission electron microscopy and electron channeling contrast imaging combined with electron backscatter diffraction. [more]

Thermoelectric materials can be used to generate electricity from a heat source through the Seebeck effect, whereby a temperature difference leads to a difference in voltage for power generation. The opposite effect, known as the Peltier effect, is exploited for heating and cooling for instance. The efficiency of the conversion can be increased by introducing defects that efficiently scatter phonons, i.e. the carriers of lattice vibrations and hence heat, but do not affect much the movement of electrons so as to maintain good electrical conductivity.
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This project targets to exploit or develop new methodologies to not only visualize the 3D morphology but also measure chemical distribution of as-synthesized nanostructures using atom probe tomography. [more]

This research focuses on studying the segregation behavior of solute atoms at defects like dislocations and grain boundaries (GBs). We aim at generating a connection between defect-related observations to mechanical properties. The outcome will provide input into the design of advanced alloys.
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By using the DAMASK simulation package we developed a new approach to predict the evolution of anisotropic yield functions by coupling large scale forming simulations directly with crystal plasticity-spectral based virtual experiments, realizing a multi-scale model for metal forming. [more]

A wide range of steels is nowadays used in Additive Manufacturing (AM). The different matrix microstructure components and phases such as austenite, ferrite, and martensite as well as the various precipitation phases such as intermetallic precipitates and carbides generally equip steels with a huge variability in microstructure and properties. [more]

New product development in the steel industry nowadays requires faster development of the new alloys with increased complexity. Moreover, for these complex new steel grades, it is more challenging to control their properties during the process chain. This leads to more experimental testing, more plant trials and also higher rejections due to unmatched requirements. Therefore, the steel companies wish to have a sophisticated offline through process model to capture the microstructure and engineering property evolution during manufacturing. [more]

Crystal Plasticity (CP) modeling [1] is a powerful and well established computational materials science tool to investigate mechanical structure–property relations in crystalline materials. It has been successfully applied to study diverse micromechanical phenomena ranging from strain hardening in single crystals to texture evolution in polycrystalline aggregates. [more]

Thermo-chemo-mechanical interactions due to thermally activated and/or mechanically induced processes govern the constitutive behaviour of metallic alloys during production and in service. Understanding these mechanisms and their influence on the material behaviour is of very high relevance for designing new alloys and corresponding thermomechanical processing routes. [more]

The Atom Probe Tomography group in the Microstructure Physics and Alloy Design department is developing integrated protocols for ultra-high vacuum cryogenic specimen transfer between platforms without exposure to atmospheric contamination. [more]

Advanced microscopy and spectroscopy offer unique opportunities to study the structure, composition, and bonding state of individual atoms from within complex, engineering materials. Such information can be collected at a spatial resolution of as small as 0.1 nm with the help of aberration correction. [more]

The project focuses on development and design of workflows, which enable advanced processing and analyses of various data obtained from different field ion emission microscope techniques such as field ion microscope (FIM), atom probe tomography (APT), electronic FIM (e-FIM) and time of flight enabled FIM (tof-FIM). [more]

In this project we try to expand the possibilities of using atom probe tomography (APT) to investigate proteins, their structures and binding to ligands. The project is funded by Volkswagenstiftung "Experiment" (Seeing atoms in biological materials - a new frontier for atomic-scale tomography) [more]

This project is part of Correlative atomic structural and compositional investigations on Co and CoNi-based superalloys as a part of SFB/Transregio 103 project “Superalloy Single Crystals”. This project deals with the identifying the local atomic diffusional mechanisms occurring during creep of new Co and Co/Ni based superalloys by correlative techniques. [more]

The objective of the project is to investigate grain boundary precipitation in comparison to bulk precipitation in a model Al-Zn-Mg-Cu alloy during aging. [more]

Understanding the deformation mechanisms observed in high performance materials, such as superalloys, allows us to design strategies for the development of materials exhibiting enhanced performance. In this project, we focus on the combination of structural information gained from electron microscopy and compositional measurements from atom probe tomography (APT). [more]

In this project we study the development of a maraging steel alloy consisting of Fe, Ni and Al, that shows pronounced response to the intrinsic heat treatment imposed during Laser Additive Manufacturing (LAM). Without any further heat treatment, it was possible to produce a maraging steel that is intrinsically precipitation strengthened by an extremely high number density of 1.2x10²⁵ m^-3 NiAl nanoparticles of 2‑4 nm size. The high number density is related to the low lattice mismatch between the martensitic matrix and the NiAl phase. [more]

In this project we work on the fabrication and the thermodynamic and metallurgical basics associated with the additive manufacturing of dense Mo-Si-B-based alloys. [more]

In this ongoing project, we investigate spinodal fluctuations at crystal defects such as grain boundaries and dislocations in Fe-Mn alloys using atom probe tomography, electron microscopy and thermodynamic modeling [1,2]. [more]

By characterizing the high N alloyed martensitic stainless bearing steel X30CrMoN15-1 in-depth, we rationalize the exceptional white etching crack resistance of this complex technical alloy in terms of the different grain boundary segregation behavior between nitrogen and carbon, the mechanical and thermodynamic stability of the precipitates, and the cleanliness of the steel. [more]

In this project, we aim to design novel NiCoCr-based medium entropy alloys (MEAs) and further enhance their mechanical properties by tuning the multiscale heterogeneous composite structures. This is being achieved by alloying of varying elements in the NiCoCr matrix and appropriate thermal-mechanical processing. [more]

The aim of the project is to elucidate the mechanism behind white etching crack (WEC) formation in bearing applications and to create materials that are resistant to this failure mechanism. The most prominent example for WEC failure are gear bearings of wind turbines. However, also many other applications from rails, over clutches to washing machines are concerned. [more]

This project studies the mechanical properties and microstructural evolution of a transformation-induced plasticity (TRIP)-assisted interstitial high-entropy alloy (iHEA) with a nominal composition of Fe_49.5Mn₃₀Co₁₀Cr₁₀C_0.5 (at. %) at cryogenic temperature (77 K). We aim to understand the hardening behavior of the iHEA at 77 K, and hence guide the future design of advanced HEA for cryogenic applications. [more]

In this project, we aim at significantly enhancing the strength-ductility combination of quinary high-entropy alloys (HEAs) with five principal elements by simultaneously introducing interstitial C/N and the transformation induced plasticity (TRIP) effect. Thus, a new class of alloys, namely, interstitially alloyed TRIP-assisted quinary (five-component) HEAs is being developed. [more]

In this project, we aim to understand the interstitial carbon effect on the recrystallization behavior of the equiatomic CoCrFeMnNi HEA and hence to tune the corresponding mechanical properties. [more]

In this project, we aim to enhance the mechanical properties of an equiatomic CoCrNi medium-entropy alloy (MEA) by interstitial alloying. Carbon and nitrogen with varying contents have been added into the face-centred cubic structured CoCrNi MEA. [more]

In this project, we aim to achieve an atomic scale understanding about the structure and phase transformation process in the dual-phase high-entropy alloys (HEAs) with transformation induced plasticity (TRIP) effect. Aberration-corrected scanning transmission electron microscopy (TEM) techniques are being applied ... [more]

In this project, a strategy of combining intermetallic phases and massive solid solutions is employed to design novel Refractory high-entropy alloys (RHEAs). [more]

In this project, we perform macro-/microscopic experiments and constitutive modelling to investigate the effects of stress amplitude and mean stress on the ratchetting strain and the overall cyclic behavior of interstitial high-entropy alloys (iHEAs)... [more]

In this project, we probe the invar effect in the high and medium entropy alloys over the huge unexplored compositional space. Combining experimental investigation (PPMS, EBSD, ECCI, APT and TEM) and theoretical calculation (DFT and Calphad)... [more]

In this project, we investigate the segregation behavior and complexions in the CoCrFeMnNi high-entropy alloys (HEAs). The structure and chemistry in the HEAs at varying conditions are being revealed systematically by combining multiple advanced techniques such as electron backscatter diffraction (EBSD) and atom probe tomography (APT). [more]

In this project, the electrochemical and corrosion behavior of high entropy alloys (HEAs) have been investigated by combining a micro-electrochemical scanning flow cell (SFC) and an inductively coupled plasma mass spectroscopy (ICP-MS) element analysis. [more]

In this project, the hydrogen embrittlement mechanisms in several types of high-entropy alloys (HEAs) have been investigated through combined techniques, e.g., low strain rate tensile testing under in-situ hydrogen charging, thermal desorption spectroscopy (TDS),... [more]

In a set of projects we study the field of strong and ductile non-equiatomic high-entropy alloys (HEAs). [more]

The unpredictable failure mechanism of White Etching Crack (WEC) formation in bearing steels urgently demands in-depth understanding of the underlying mechanisms in the microstructure. The first breakthrough was achieved by relating the formation of White Etching Areas (WEAs) to successive WEC movement. [more]