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Microstructure Physics and Alloy Design

Research in the department 'Microstructure Physics and Alloy Design' is on the relationships between synthesis, microstructure and mechanical as well as functional properties of nanostructured materials. Focus is placed on metallic alloys such as steels, high and medium entropy alloys, superalloys, magnesium, titanium, Heusler phases and aluminium alloys. Composites, semi-metallic thermoelectrics and solar cell semiconductors are considered as well. We study the microstructures and properties using theory and advanced characterization methods from the single atom level up to the macroscopic scale.

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Mission Statement

Since the dawn of mankind, complex materials have been the backbone of human society. Today, they are indispensable in the fields of energy, industry, transportation, health, construction, safety and manufacturing. With >2 billion tons produced every year, particularly metals stand for massive economic growth, job safety and wealth increase. Due to the sheer quantities produced and used, they also play a central role in sustainability.

Currently, we enter from the age of linear industry into a circular and digitalized economy. This offers huge opportunities to revolutionize the way how production, transport and energy supply work. These changes affect the daily lives of billions of people. Advanced materials, their production and downstream use, also at large scales, are key to this transition, as they enable a carbon-free, digitalized and electrified industrial and urban future.

Therefore, we devote all our efforts to understand, invent and enable advanced materials for a sustainable and safe future.

Material Classes and Fields of Research

Our group works on the fundamentals of the relations between synthesis, microstructure and properties of complex, nanostructured materials. Focus is on metallic alloys such as aluminium, titanium, steels, high and medium entropy alloys, metallic glasses, nanoglasses, superalloys, magnesium, superalloys and Heusler phases. Magnetic alloys, biological materials, composites, semi-metallic thermoelectrics and solar cell semiconductors are considered as well. We also study how such materials behave in reactive and harsh environments such as high and cryogenic temperatures, high fields and mechanical loads, as well as under corrosive and hydrogen exposure. Our experiments aim at profound and general insights, based on theoretical concepts. We combine computational materials science, machine learning, synthesis, processing with characterization down to atomic and electronic scales. Many projects are pursued in close cooperation with other departments and extramural partners.

Specific Research Topics of High Interest

Topics of currently high interest are sustainability of materials; hydrogen-related material response; correlative atom probe tomography, field ion microscopy and electron microscopy probing methodsmachine-learning enhanced atom probe tomography; hydrogen based metallurgical reduction methods; nanoscale deformation and phase transformation mechanisms; thermodynamics and kinetics at low dimensions and confined states at lattice defects; coupled crystal plasticity, phase field and damage modeling and experiments; nanoscale segregation engineering; machine learning in materials science and engineering;  alloy design; materials for additive manufacturing; the physics of lattice defects; linear complexions.

A Few Concrete Project Examples

We develop and apply advanced characterization methods from the atomic level up to the macroscopic scale. Examples are chemically sensitive Field Ion Microscopy (FIM) which is based on the integration of atom probe tomography (APT), FIM and machine learning as well as correlative APT and scanning transmission electron microscopy (STEM) in concert with a reaction chamber and UHV-cryo transfer unit; Electron Channeling Contrast imaging under controlled diffraction conditions (ECCI); 3D electron backscatter diffraction (EBSD) and cross-correlation EBSD; in-situ micromechanical experiments correlated to local strain and hydrogen mapping; and standardized bulk high-throughput metallurgy and mechanical testing. Several of these techniques are developed and operated in collaboration with the groups of G. Dehm, C. Scheu, M. Rohwerder, J. Neugebauer, C. Freysold, R. Dunin-Borkowski(Ernst Ruska Centre in Jülich), J. Schneider (RWTH Aachen) and G. Eggeler (RU Bochum).

We design experiments based on theory-guidance and conduct them under well controlled boundary conditions: For example for better understanding, quantifying and improving our atomic scale APT and FIM probing methods we collaborate with the group of J. Neugebauer on the simulation of field evaporation and image gas ionization as well as on the use of machine learning for crystallographic pattern recognition in APT data sets. Regarding thermodynamics and structure–property relations we also collaborate with in-house ab initio experts for instance on phase equilibria for bulk and confined states and the thermodynamics of high entropy alloys. Concerning constitutive simulations we have developed further our in-house modular freeware simulation package DAMASK (Düsseldorf Advanced Material Simulation Kit). This is a hierarchically structured model of material point behaviour for the solution of elastoplastic boundary value problems along with damage and thermal effects.

As an example, one topic where many of these fields of interest overlap in the department, is the interplay of local chemical composition, phase metastability and transformations in confined regions, i.e. at decorated lattice defects. Correlative atomic-scale probing and thermodynamic theory show that in many alloys segregation to lattice imperfections is an ubiquitous phenomenon, yet, it is typically acquired through trapping of atoms to defects during tempering rather than being engineered in a purposeful and property-directed manner. This has motivated us to conduct systematic ‘Segregation Engineering’ experiments and develop from that corresponding alloy design and processing strategies where we utilize Gibbs and Fowler-Guggenheim – type decoration of lattice defects with the aim to turn these regions into chemo-structural entities that lead to beneficial mechanical and functional behaviour. This site specific manipulation of confined defect regions by chemistry has for example allowed us to tune lattice defects for improved local cohesion, confined phase transformation, scattering, fracture toughness and impurity trapping. Specific thermodynamic phenomena that we discovered in this context are composition-driven phase transformations of dislocation cores, complexion, confined hydrides, stacking faults, spinodals at grain boundaries and dislocations, and confined phase states and precursors phases preceding nucleation. With these approaches and topics we conduct materials engineering down to the atomic scale.

Department Structure and Research Groups

The department is under permanent construction, both, to rapidly establish new initiatives and to provide opportunities to young science leaders to pursue their own ideas. Many of these dynamic groups are non-permanent, usually extramurally funded (e.g. ERC, DFG, BMBF or VW Stiftung). Several other groups, mostly those  with long-term science visions and larger investment and development requirements are permanent, Fig. 1.

Fig. 1: Research Groups in the Department Microstructure Physics and Alloy Design and Interdepartmental & Partner Groups

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