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  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.
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.
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 work on correlative atomic structural and compositional investigations on Co and CoNi-based superalloys as a part of SFB/Transregio 103 project “Superalloy Single Crystals”. The task is to image the boron segregation at grain boundaries in the Co-9Al-9W-0.005B alloy. [more]
Materials used in catalytic reactions are exposed to conditions that inevitably lead to microstructural and chemical changes in the bulk and on the surface. To understand their complex interplay and influence on the catalyst´s performance, one requires spatially resolved methods that encompass surface and bulk sensitivity on the nanoscale, ideally in-operando. [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]
Despite the immanent advantages of metals and alloys processed by additive manufacturing (e.g. design freedom for complex geometry) and unexpected merits (e.g. superior mechanical performance) of AM processes, there are several remaining issues that need to be addressed in order to practically apply AM alloys to various industries. One of the most important issues is the mechanical behavior of AM alloys under hydrogen environments, since it is easily encountered in the industrial fields and has generally detrimental effects on metals and alloys.
Usually, the only requirement for the chemistry of the process gas in Laser Additive Manufacturing is a low oxygen content, i.e. a completely inert atmosphere. However, often a low oxygen content remains, leading to oxide inclusions in the produced alloy. In this project, we ask the question if the process atmosphere can be used intentionally to react with the feedstock material to produce materials with improved properties. [more]
In AM, parts are built from layer by layer fusion of raw material (eg. wire, powder etc.). Such layer by layer application of heat results in a time-temperature profile which is fundamentally different from any of the contemporary heat treatments.
Previous work in the group has established that this unique thermal profile can be exploited for microstructural modifications (eg. clustering, precipitation) during manufacturing. The aim of this work is to develop a fundamental understanding of such a strongly non-linear, peak-like thermal history on the precipitation kinetics.
This project investigates if particle strengthening is a viable mechanism for compositionally complex alloys (CCA) showing exceptional mechanical properties. Whether precipitates form analogously to conventional alloys, and, if so, with similar precipitation kinetics, still needs to be studied. Extending the concept of CCA to intentionally particle strengthened CCA (p-CCA) in a systematic way requires full microstructure analyses down to the atomic level.
In this project, we directly image and characterize solute hydrogen and hydride by use of atom probe tomography combined with electron microscopy, with the aim to investigate H interaction with different phases and lattice defects (such as grain boundaries, dislocation, etc.) in a set of specimens of commercially pure Ti, model and commercial Ti-alloys. [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]
There is a high interest to understand the response of metallic (amorphous) glasses to rapid heating and plastic deformation. These two topics are addressed in this project using correlative electron microscopy and atom probe tomography. [more]
The interplay of mechanical loads and body fluids leads to local decomposition and surface alloying effects in the modular taper joints of hip implants. We are investigating this engineering problem with state-of-the art correlative atom probe tomography and electron microscopy techniques. [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 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]
This alloy is particularly interesting since white etching cracks (WECs), which lead to premature failures occurring at as early as 5-10% of L10 life of most bearings , have not yet been observed to form here. The outstanding failure resistance of X30CrMoN15-1 is attributed to its unique chemical composition and microstructure.
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.
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.
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 Fe49.5Mn30Co10Cr10C0.5 (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.
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.
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.
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 ...
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)...
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)...
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).
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.
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),...
Tooth enamel is the hardest and most highly mineralized tissue in the human body with a mineral phase consisting of calcium-deficient hydroxyapatite, Ca5(PO4)3(OH). In modern oral care, biomimetic concepts with hydroxyapatite as main active compound gain increasing attention.