- Max-Planck Institut für Eisenforschung
Düsseldorf
Germany
- Electron Backscatter Diffraction (EBSD), Nanoindentation, Mechanical Behavior Of Materials, Micromechanics, Steel Metallurgy, Crystal Plasticity, and 22 morePlasticity of Crystals and Interfaces, Microstructure modelling, Multiscale modelling, Nanoindentation, Simulation, Scanning Electron Microscopy, Recrystallization, Article Related to Brewer's Spent Grain Effect on the Growth of Calves, Atom probe tomography, Steel, Maraging Steels, Steels, Atom Probe, TEM, Microstructure, Ferrite, Precipitation, Thermodynamics, Modeling and Simulation, Finite Element Methods, Cellular Automata, Computational Materials Science, Crystallographic Texture, and X-ray crystallography(Plasticity of Crystals and Interfaces, Microstructure modelling, Multiscale modelling, Nanoindentation, Simulation, Scanning Electron Microscopy, Recrystallization, Article Related to Brewer's Spent Grain Effect on the Growth of Calves, Atom probe tomography, Steel, Maraging Steels, Steels, Atom Probe, TEM, Microstructure, Ferrite, Precipitation, Thermodynamics, Modeling and Simulation, Finite Element Methods, Cellular Automata, Computational Materials Science, Crystallographic Texture, and X-ray crystallography)edit
- I am interested in the atomistic and mesoscopic structure, processing, and properties of alloys using simulation and ... moreI am interested in the atomistic and mesoscopic structure, processing, and properties of alloys using simulation and experiment. We combine atom probe tomography, electron microscopy and multiscale simulations. We design novel materials and predict their properties. Materials of interest are high entropy alloys, magnesium and aluminium alloys and steels. Microstructure evolution and structure-property simulations are made using the free simulation toolset DAMASK(I am interested in the atomistic and mesoscopic structure, processing, and properties of alloys using simulation and experiment. We combine atom probe tomography, electron microscopy and multiscale simulations. We design novel materials and predict their properties. Materials of interest are high entropy alloys, magnesium and aluminium alloys and steels. Microstructure evolution and structure-property simulations are made using the free simulation toolset DAMASK)edit
Ammonia is a promising alternative hydrogen carrier that can be utilized for the solid-state reduction of iron oxides for sustainable ironmaking due to its easy transportation and high energy density. The main challenge for its... more
Ammonia is a promising alternative hydrogen carrier that can be utilized for the solid-state reduction of iron oxides for sustainable ironmaking due to its easy transportation and high energy density. The main challenge for its utilization on an industrial scale is to understand the reaction kinetics under different process conditions and the associated nitrogen incorporation in the reduced material that originates from ammonia decomposition. In this work, the effect of temperature on the reduction efficiency and nitride formation is investigated through phase, local chemistry, and gas evolution analysis. The effects of inherent reactions and diffusion on phase formation and chemistry evolution are discussed in relation to the reduction temperature. The work also discusses nitrogen incorporation into the material through both spontaneous and in-process nitriding, which fundamentally affects the structure and chemistry of the reduced material. Finally, the effect of nitrogen incorporation on the reoxidation tendency of the ammonia-based reduced material is investigated and compared with that of the hydrogen-based reduced counterpart. The results provide a fundamental understanding of the reduction and nitriding for iron oxides exposed to ammonia at temperatures from 500 to 800°C, serving as a basis for exploitation and upscaling of ammonia-based direct reduction for future green steel production.
Research Interests:
Excellent castability, significantly refined microstructure, and good mechanical properties make eutectic high-entropy alloys (EHEAs) a natural fit for rapid solidification processes, e.g., additive manufacturing. Previous investigations... more
Excellent castability, significantly refined microstructure, and good mechanical properties make eutectic high-entropy alloys (EHEAs) a natural fit for rapid solidification processes, e.g., additive manufacturing. Previous investigations have focused on developing EHEAs through trial and error and mixing known binary eutectic materials. However, eutectic compositions obtained from near-equilibrium conditions do not guarantee a fully eutectic microstructure under rapid solidifications. In this work, a thermodynamically guided high-throughput framework is proposed to design EHEAs for rapid solidification. Empirical formulas derived from past experimental observations and thermodynamic computations are applied and considered phase growth kinetics under rapid solidification (skewed phase diagram). The designed alloy candidate, Co 25.6 Fe 17.9 Ni 22.4 Cr 19.1 Ta 8.9 Al 6.1 (wt.%), contains nanostructured eutectic lamellar and shows a high Vickers hardness of 675 Hv. In addition to this specific composition, the alloy design toolbox enables the development of new EHEAs for rapid solidification without the limitation of previous knowledge.
Research Interests:
The rates of atomic clustering and precipitation hardening are closely related to the diffusivity of solutes and the concentration of vacancies during the natural aging of aluminum alloys. The measurement of the diffusivity of solutes at... more
The rates of atomic clustering and precipitation hardening are closely related to the diffusivity of solutes and
the concentration of vacancies during the natural aging of aluminum alloys. The measurement of the diffusivity
of solutes at room temperature, especially in systems with an equilibrium vacancy concentration, is beneficial to
the design of the aging process. However, this measurement has long been challenging because of the extremely
low diffusion rates of solutes in aluminum at room temperature and the presence of supersaturated vacancies.
In this work, we propose a method to quantify the diffusivity of solutes based on the kinetic evaluation of
the spinodal decomposition process. This evaluation involves conducting atom probe tomography experiments,
analyzing the radial distribution function, and modeling the phase separation process using the Cahn–Hilliard
theory. The aging experiments were conducted on nanoscale samples, where excess vacancies can be eliminated
at free surfaces due to a high surface-to-volume ratio. The results yielded a diffusivity of Zn in the Al-12.5
at.% Zn alloy of (1.32 ± 0.46) × 10−25 m2/s at 295 K. This work introduces a novel approach to assess the
solute diffusivity under conditions of equilibrium vacancy concentration at room temperature and expands the
temperature range for measuring the diffusivity in systems with spinodal decomposition, particularly in cases
where kinetic data at low temperatures are scarce.
the concentration of vacancies during the natural aging of aluminum alloys. The measurement of the diffusivity
of solutes at room temperature, especially in systems with an equilibrium vacancy concentration, is beneficial to
the design of the aging process. However, this measurement has long been challenging because of the extremely
low diffusion rates of solutes in aluminum at room temperature and the presence of supersaturated vacancies.
In this work, we propose a method to quantify the diffusivity of solutes based on the kinetic evaluation of
the spinodal decomposition process. This evaluation involves conducting atom probe tomography experiments,
analyzing the radial distribution function, and modeling the phase separation process using the Cahn–Hilliard
theory. The aging experiments were conducted on nanoscale samples, where excess vacancies can be eliminated
at free surfaces due to a high surface-to-volume ratio. The results yielded a diffusivity of Zn in the Al-12.5
at.% Zn alloy of (1.32 ± 0.46) × 10−25 m2/s at 295 K. This work introduces a novel approach to assess the
solute diffusivity under conditions of equilibrium vacancy concentration at room temperature and expands the
temperature range for measuring the diffusivity in systems with spinodal decomposition, particularly in cases
where kinetic data at low temperatures are scarce.
Research Interests: Thermodynamics, Microstructure, Metallurgy, Aging, Metallurgy and Materials Engineering, and 11 moreHeat treatment of metals and alloys, Diffusion, Clustering, Aluminium Alloys, Atom probe tomography, Metallurgical and Materials Engineering, Vacancy, Spinodal Decomposition, Zinc Compounds, Aluminum Alloy, and Alloys
Steel production emits approximately 8% of global CO2 mainly due to the use of fossil fuels in ironmaking. Hydrogen-based reduction of iron oxide is an alternative for primary synthesis. However, to counteract global warming,... more
Steel production emits approximately 8% of global CO2 mainly due to the use of fossil fuels in ironmaking. Hydrogen-based reduction of iron oxide is an alternative for primary synthesis. However, to counteract global warming, decarbonization of the steel sector must proceed much faster than the ongoing transition kinetics in primary steelmaking. Realizing a higher fraction of secondary steelmaking thus is gaining momentum. Steel production from scrap is well established for long products, but it remains challenging for high-performance sheet steels. This is a serious obstacle because advanced products demand explicit low-tolerance specifications for safety-critical and high-strength steels, such as for electric vehicles, energy conversion, high-speed trains, and infrastructure. Therefore, we review the metallurgical and microstructural challenges and opportunities for producing high-performance sheet steels via secondary synthesis. Focus is placed on the thermodynamic, kinetic, chemical, and microstructural fundamentals as well as the effects of scrap-related impurities on steel properties.
Research Interests:
Red mud is the waste of bauxite refinement into alumina, the feedstock for aluminium production1. With about 180 million tonnes produced per year1, red mud has amassed to one of the largest environmentally hazardous waste products, with... more
Red mud is the waste of bauxite refinement into alumina, the feedstock for aluminium production1. With about 180 million tonnes produced per year1, red mud has amassed to one of the largest environmentally hazardous waste products, with the staggering amount of 4 billion tonnes accumulated on a global scale1. Here we present how this red mud can be turned into valuable and sustainable feedstock for ironmaking using fossil-free hydrogen-plasma-based reduction, thus mitigating a part of the steel-related carbon dioxide emissions by making it available for the production of several hundred million tonnes of green steel. The process proceeds through rapid liquid-state reduction, chemical partitioning, as well as density-driven and viscosity-driven separation between metal and oxides. We show the underlying chemical reactions, pH-neutralization processes and phase transformations during this surprisingly simple and fast reduction method. The approach establishes a sustainable toxic-waste treatment from aluminium production through using red mud as feedstock to mitigate greenhouse gas emissions from steelmaking.
Research Interests:
Soft magnetic materials (SMMs) serve in electrical applications and sustainable energy supply, allowing magnetic flux variation in response to changes in applied magnetic field, at low energy loss1. The electrification of transport,... more
Soft magnetic materials (SMMs) serve in electrical applications and sustainable energy supply, allowing magnetic flux variation in response to changes in applied magnetic field, at low energy loss1. The electrification of transport, households and manufacturing leads to an increase in energy consumption owing to hysteresis losses2. Therefore, minimizing coercivity, which scales these losses, is crucial3. Yet meeting this target alone is not enough: SMMs in electrical engines must withstand severe mechanical loads; that is, the alloys need high strength and ductility4. This is a fundamental design challenge, as most methods that enhance strength introduce stress fields that can pin magnetic domains, thus increasing coercivity and hysteresis losses5. Here we introduce an approach to overcome this dilemma. We have designed a Fe–Co–Ni–Ta–Al multicomponent alloy (MCA) with ferromagnetic matrix and paramagnetic coherent nanoparticles (about 91 nm in size and around 55% volume fraction). They impede dislocation motion, enhancing strength and ductility. Their small size, low coherency stress and small magnetostatic energy create an interaction volume below the magnetic domain wall width, leading to minimal domain wall pinning, thus maintaining the soft magnetic properties. The alloy has a tensile strength of 1,336 MPa at 54% tensile elongation, extremely low coercivity of 78 A m−1 (less than 1 Oe), moderate saturation magnetization of 100 A m2 kg−1 and high electrical resistivity of 103 μΩ cm.
Research Interests: Electrical Engineering, Manufacturing, Sustainable Development, Metallurgy, Magnetic Materials, and 15 moreNanomaterials, Heat treatment of metals and alloys, Electrification, Nanoscience, Mechanical Properties of Materials, Magnetic Properties, High Entropy Alloys, Ductility, Alloy Design, Atom probe tomography, Resistivity, Metals, Soft Magnetic Materials, Coercivity Mechanism, and High Entropy Alloy(Nanomaterials, Heat treatment of metals and alloys, Electrification, Nanoscience, Mechanical Properties of Materials, Magnetic Properties, High Entropy Alloys, Ductility, Alloy Design, Atom probe tomography, Resistivity, Metals, Soft Magnetic Materials, Coercivity Mechanism, and High Entropy Alloy)
(Nanomaterials, Heat treatment of metals and alloys, Electrification, Nanoscience, Mechanical Properties of Materials, Magnetic Properties, High Entropy Alloys, Ductility, Alloy Design, Atom probe tomography, Resistivity, Metals, Soft Magnetic Materials, Coercivity Mechanism, and High Entropy Alloy)
In the current work, Mn enrichment at dislocations in Fe-Mn alloys due to segregation and spinodal decomposition along the dislocation line is studied via modeling and experimental characterization. To model these phenomena, both... more
In the current work, Mn enrichment at dislocations in Fe-Mn alloys due to segregation and spinodal decomposition along the dislocation line is studied via modeling and experimental characterization. To model these phenomena, both finite-deformation microscopic phase-field chemomechanics (MPFCM) and Monte Carlo molecular dynamics (MCMD) are employed. MPFCM calibration is carried out with the same Fe-Mn MEAMbased potential used in MCMD, as well as CALPHAD data. Simulation results for Mn segregation to, and spinodal decomposition along, straight screw and edge dislocations as well as dislocation loops, are compared with characterization results from atom probe tomography (APT) for two Fe-Mn alloy compositions. In contrast to classical Volterra (linear elastic) dislocation theory, both MPFCM and MCMD predict a non-zero hydrostatic stress field in screw cores. Being of much smaller magnitude than the hydrostatic stress in straight edge cores, much less solute segregates to screw than to edge cores. In addition, the segregated amount in screw cores is below the critical concentration of 0.157 for the onset of spinodal decomposition along the line. On the other hand, results from MPFCM-based modeling imply that the concentration dependence of the solute misfit distortion and resulting dependence of the elastic energy density on concentration have the strongest effect. The maximum amount of Mn segregating to straight edge dislocations predicted by MPFCM agrees well with APT results. On the other hand, the current MPFCM model for Fe-Mn predicts little or no variation in Mn concentration along a straight dislocation line, in contrast to the APT results. As shown by the example of a dislocation loop in the current work, a change in the hydrostatic stress along the line due to changing character of dislocation does lead to a corresponding variation in Mn concentration. Such a variation in Mn concentration can also then be expected along a dislocation line with kinks or jogs.
Research Interests:
Hydrogen-based reduction of iron ores is the key technology for future sustainable ironmaking, to mitigate the CO2 burden from the steel industry, accounting for ~7–8% of all global emissions. However, using hydrogen as a reductant... more
Hydrogen-based reduction of iron ores is the key technology for future sustainable ironmaking, to mitigate the CO2 burden from the steel industry, accounting for ~7–8% of all global emissions. However, using hydrogen as a reductant prompts concerns about hydrogen embrittlement in steel products. This raises the question of how much hydrogen remains from green ironmaking in the metal produced. We answer this question here by quantifying the amount of hydrogen in iron produced via two hydrogen-based ironmaking processes, namely, direct reduction and plasma smelting reduction. Results suggest no threat of hydrogen embrittlement resulting from using hydrogen in green steel production.
Research Interests:
Steels with medium manganese (Mn) content (3∼12 wt-%) have emerged as a new alloy class and received considerable attention during the last decade. The microstructure and mechanical response of such alloys show significant differences... more
Steels with medium manganese (Mn) content (3∼12 wt-%) have emerged as a new alloy class and received considerable attention during the last decade. The microstructure and mechanical response of such alloys show significant differences from those of established steel grades, especially pertaining to the microstructural variety that can be tuned and the associated micromechanisms activated during deformation. The interplay and tuning opportunities between composition and the many microstructural features allow to trigger almost all known strengthening and strain-hardening mechanisms, enabling excellent strength-ductility synergy, at relatively lean alloy content. Previous investigations have revealed a high degree of microstructure and deformation complexity in such steels, but the underlying mechanisms are not adequately discussed and acknowledged. This encourages us to critically review and discuss these materials, focusing on the progress in fundamental research, with the aim to obtain better understanding and enable further progress in this field. The review addresses the main phase transformation phenomena in these steels and their mechanical behaviour, covering the whole inelastic deformation regime including yielding, strain hardening, plastic instability and damage. Based on these insights, the relationships between processing, microstructure and mechanical properties are critically assessed and rationalized. Open questions and challenges with respect to both, fundamental studies and industrial production are also identified and discussed to guide future research efforts.
Research Interests: Phase Transformations, Microstructure, Hydrogen, Heat Treatment, Fracture Mechanics, and 12 moreManganese, Heat treatment of metals and alloys, Mechanical Behaviour of Materials, Steel, Annealing, Mechanical Properties of Materials, Alloy Design, High Strength Steel, Steel processing, Strength of materials, Rolling, and Tensile Strength
We propose strategies that couple natural language processing with deep learning to enhance machine capability for corrosion-resistant alloy design. First, accuracy of machine learning models for materials datasets is often limited by... more
We propose strategies that couple natural language processing with deep learning to enhance machine capability for corrosion-resistant alloy design. First, accuracy of machine learning models for materials datasets is often limited by their inability to incorporate textual data. Manual extraction of numerical parameters from descriptions of alloy processing or experimental methodology inevitably leads to a reduction in information density. To overcome this, we have developed a fully automated natural language processing approach to transform textual data into a form compatible for feeding into a deep neural network. This approach has resulted in a pitting potential prediction accuracy substantially beyond state of the art. Second, we have implemented a deep learning model with a transformed-input feature space, consisting of a set of elemental physical/chemical property-based numerical descriptors of alloys replacing alloy compositions. This helped identification of those descriptors that are most critical toward enhancing their pitting potential. In particular, configurational entropy, atomic packing efficiency, local electronegativity differences, and atomic radii differences proved to be the most critical.
Research Interests: Artificial Intelligence, Natural Language Processing, Machine Learning, Materials Science and Engineering, Corrosion, and 11 moreHeat treatment of metals and alloys, Artificial Neural Networks, Deep Learning, Aluminium Alloys, Stainless Steel, Alloy Design, Electrochemical, Electronegativity, Steels, Deep Neural Networks, and Pitting Corrosion
Hydrogen embrittlement jeopardizes the use of high-strength steels in critical load-bearing applications. However, uncertainty regarding how hydrogen affects dislocation motion, owing to the lack of quantitative experimental evidence,... more
Hydrogen embrittlement jeopardizes the use of high-strength steels in
critical load-bearing applications. However, uncertainty regarding how
hydrogen affects dislocation motion, owing to the lack of quantitative
experimental evidence, hinders our understanding of hydrogen
embrittlement. Here, by studying the well-controlled, cyclic, bow-out
motions of individual screw dislocations in α-iron, we find that the critical
stress for initiating dislocation motion in a 2 Pa electron-beam-excited H2
atmosphere is 27–43% lower than that in a vacuum environment, proving
that hydrogen enhances screw dislocation motion. Moreover, we find that
aside from vacuum degassing, cyclic loading and unloading facilitates
the de-trapping of hydrogen, allowing the dislocation to regain its
hydrogen-free behaviour. These findings at the individual dislocation level
can inform hydrogen embrittlement modelling and guide the design of
hydrogen-resistant steels.
critical load-bearing applications. However, uncertainty regarding how
hydrogen affects dislocation motion, owing to the lack of quantitative
experimental evidence, hinders our understanding of hydrogen
embrittlement. Here, by studying the well-controlled, cyclic, bow-out
motions of individual screw dislocations in α-iron, we find that the critical
stress for initiating dislocation motion in a 2 Pa electron-beam-excited H2
atmosphere is 27–43% lower than that in a vacuum environment, proving
that hydrogen enhances screw dislocation motion. Moreover, we find that
aside from vacuum degassing, cyclic loading and unloading facilitates
the de-trapping of hydrogen, allowing the dislocation to regain its
hydrogen-free behaviour. These findings at the individual dislocation level
can inform hydrogen embrittlement modelling and guide the design of
hydrogen-resistant steels.
Research Interests:
Iron making is the biggest single cause of global warming. The reduction of iron ores with carbon generates about 7% of the global carbon dioxide emissions to produce ≈1.85 billion tons of steel per year. This dramatic scenario fuels... more
Iron making is the biggest single cause of global warming. The reduction of iron ores with carbon generates about 7% of the global carbon dioxide emissions to produce ≈1.85 billion tons of steel per year. This dramatic scenario fuels efforts to re-invent this sector by using renewable and carbon-free reductants and electricity. Here, the authors show how to make sustainable steel by reducing solid iron oxides with hydrogen released from ammonia. Ammonia is an annually 180 million ton traded chemical energy carrier, with established transcontinental logistics and low liquefaction costs. It can be synthesized with green hydrogen and release hydrogen again through the reduction reaction. This advantage connects it with green iron making, for replacing fossil reductants. the authors show that ammonia-based reduction of iron oxide proceeds through an autocatalytic reaction, is kinetically as effective as hydrogen-based direct reduction, yields the same metallization, and can be industrially realized with existing technologies. The produced iron/iron nitride mixture can be subsequently melted in an electric arc furnace (or co-charged into a converter) to adjust the chemical composition to the target steel grades. A novel approach is thus presented to deploying intermittent renewable energy, mediated by green ammonia, for a disruptive technology transition toward sustainable iron making.
Research Interests:
The chemical space for designing materials is practically infinite. This makes disruptive progress by traditional physics-based modeling alone challenging. Yet, training data for identifying composition-structureproperty relations by... more
The chemical space for designing materials is practically infinite. This makes disruptive progress by traditional physics-based modeling alone challenging. Yet, training data for identifying composition-structureproperty relations by artificial intelligence are sparse. We discuss opportunities to discover new chemically complex materials by hybrid methods where physics laws are combined with artificial intelligence. New materials are crucial in two aspects. On the one hand, they enable disruptive leaps in civilization. Examples are early ceramics for pottery; bronze for agriculture; steels for machinery; cement for buildings; aluminium for aviation; titanium for spaceships; rare earth elements for magnets; semiconductors for computer chips; platinum-group metals for catalysts; and polymers for packaging and medicine. On the other hand, material production is the largest single source of greenhouse gas emissions, energy consumption and environmental pollution, a fact that forces us to entirely rethink the way we produce, use and recycle them 1,2. The drive towards ever-improving materials has led to their higher chemical complexity, as property improvement often requires tweaking the intrinsic and microstructure-dominated features by composition adjustment. Examples are chemically fine-tuned intermetallic phases in superalloys 3-5 , complex precipitation pathways in high-performance aluminium alloys 6-8 or interfaces in advanced magnets 9,10. Another challenge is the near atomic-scale blending of multiple elements in microelectronics, where the borders between product and material become blurred, such as in the 2 nm process in semiconductor manufacturing. Both trends enhance compositional complexity of materials and highly integrated systems: they are preconditions for advanced product properties and open doors to new solid-state phenomena 11-14. Yet, chemistry never comes alone: compositional complexity of materials translates to their microstructure 15. Changes in the chemical composition affect many defect features, often with an exponential dependence: examples include changes in the solute decoration state and energy of the defects, drag forces acting on them and the formation of new phases at defects. This means that changes in chemical complexity are linked to changes in microstructure complexity. The latter aspect is important because materials are practically never used in their thermodynamic equilibrium state, but in a transient state, equipped with a complex microstructure
Research Interests: Materials Engineering, Artificial Intelligence, Materials Science, Thermodynamics, Machine Learning, and 9 moreComputational Materials Science, Metallurgy, Modeling and Simulation, Materials Science and Engineering, Heat treatment of metals and alloys, Simulation, Alloy Design, Metallurgical and Materials Engineering, and Metals
Iron making is the biggest single cause of global warming. The reduction of iron ores with carbon generates about 7% of the global carbon dioxide emissions to produce ≈1.85 billion tons of steel per year. This dramatic scenario fuels... more
Iron making is the biggest single cause of global warming. The reduction of iron ores with carbon generates about 7% of the global carbon dioxide emissions to produce ≈1.85 billion tons of steel per year. This dramatic scenario fuels efforts to re-invent this sector by using renewable and carbon-free reductants and electricity. Here, the authors show how to make sustainable steel by reducing solid iron oxides with hydrogen released from ammonia. Ammonia is an annually 180 million ton traded chemical energy carrier, with established transcontinental logistics and low liquefaction costs. It can be synthesized with green hydrogen and release hydrogen again through the reduction reaction. This advantage connects it with green iron making, for replacing fossil reductants. the authors show that ammonia-based reduction of iron oxide proceeds through an autocatalytic reaction, is kinetically as effective as hydrogen-based direct reduction, yields the same metallization, and can be industrially realized with existing technologies. The produced iron/iron nitride mixture can be subsequently melted in an electric arc furnace (or co-charged into a converter) to adjust the chemical composition to the target steel grades. A novel approach is thus presented to deploying intermittent renewable energy, mediated by green ammonia, for a disruptive technology transition toward sustainable iron making.
Research Interests:
Production of metals stands for 40% of all industrial greenhouse gas emissions, 10% of the global energy consumption, 3.2 billion tonnes of minerals mined, and several billion tonnes of by-products every year. Therefore, metals must... more
Production of metals stands for 40% of all industrial greenhouse gas emissions, 10% of the global energy consumption, 3.2 billion tonnes of minerals mined, and several billion tonnes of by-products every year. Therefore, metals must become more sustainable. A circular economy model does not work, because market demand exceeds the available scrap currently by about twothirds. Even under optimal conditions, at least one-third of the metals will also in the future come from primary production, creating huge emissions. Although the influence of metals on global warming has been discussed with respect to mitigation strategies and socioeconomic factors, the fundamental materials science to make the metallurgical sector more sustainable has been less addressed. This may be attributed to the fact that the field of sustainable metals describes a global challenge, but not yet a homogeneous research field. However, the sheer magnitude of this challenge and its huge environmental effects, caused by more than 2 billion tonnes of metals produced every year, make its sustainability an essential research topic not only from a technological point of view but also from a basic materials research perspective. Therefore, this paper aims to identify and discuss the most pressing scientific bottleneck questions and key mechanisms, considering metal synthesis from primary (minerals), secondary (scrap), and tertiary (re-mined) sources as well as the energyintensive downstream processing. Focus is placed on materials science aspects, particularly on those that help reduce CO 2 emissions, and less on process engineering or economy. The paper does not describe the devastating influence of metal-related greenhouse gas emissions on climate, but scientific approaches how to solve this problem, through research that can render metallurgy fossil-free. The content is considering only direct measures to metallurgical sustainability (production) and not indirect measures that materials leverage through their properties (strength, weight, longevity, functionality).
Research Interests: Hydrogen, Sustainable Development, Metallurgy, Extractive Metallurgy, Titanium, and 15 moreMaterials Science and Engineering, Metallurgy and Materials Engineering, Heat treatment of metals and alloys, Copper extraction and production, Steel, Aluminium Alloys, Greenhouse Gas Emissions, Red Mud, Iron and Steel Making Industry, Hydrogen Economy, Waste of Electrical and Electronic Equipment WEEE, Direct Reduction Iron, Steel Scrap, Sustainable Metallurgy, and sustainable metals(Materials Science and Engineering, Metallurgy and Materials Engineering, Heat treatment of metals and alloys, Copper extraction and production, Steel, Aluminium Alloys, Greenhouse Gas Emissions, Red Mud, Iron and Steel Making Industry, Hydrogen Economy, Waste of Electrical and Electronic Equipment WEEE, Direct Reduction Iron, Steel Scrap, Sustainable Metallurgy, and sustainable metals)
(Materials Science and Engineering, Metallurgy and Materials Engineering, Heat treatment of metals and alloys, Copper extraction and production, Steel, Aluminium Alloys, Greenhouse Gas Emissions, Red Mud, Iron and Steel Making Industry, Hydrogen Economy, Waste of Electrical and Electronic Equipment WEEE, Direct Reduction Iron, Steel Scrap, Sustainable Metallurgy, and sustainable metals)
Production of metals stands for 40% of all industrial greenhouse gas emissions, 10% of the global energy consumption, 3.2 billion tonnes of minerals mined, and several billion tonnes of by-products every year. Therefore, metals must... more
Production of metals stands for 40% of all industrial greenhouse gas emissions, 10% of the global energy consumption, 3.2 billion tonnes of minerals mined, and several billion tonnes of by-products every year. Therefore, metals must become more sustainable. A circular economy model does not work, because market demand exceeds the available scrap currently by about twothirds. Even under optimal conditions, at least one-third of the metals will also in the future come from primary production, creating huge emissions. Although the influence of metals on global warming has been discussed with respect to mitigation strategies and socioeconomic factors, the fundamental materials science to make the metallurgical sector more sustainable has been less addressed. This may be attributed to the fact that the field of sustainable metals describes a global challenge, but not yet a homogeneous research field. However, the sheer magnitude of this challenge and its huge environmental effects, caused by more than 2 billion tonnes of metals produced every year, make its sustainability an essential research topic not only from a technological point of view but also from a basic materials research perspective. Therefore, this paper aims to identify and discuss the most pressing scientific bottleneck questions and key mechanisms, considering metal synthesis from primary (minerals), secondary (scrap), and tertiary (re-mined) sources as well as the energyintensive downstream processing. Focus is placed on materials science aspects, particularly on those that help reduce CO 2 emissions, and less on process engineering or economy. The paper does not describe the devastating influence of metal-related greenhouse gas emissions on climate, but scientific approaches how to solve this problem, through research that can render metallurgy fossil-free. The content is considering only direct measures to metallurgical sustainability (production) and not indirect measures that materials leverage through their properties (strength, weight, longevity, functionality).
Research Interests: Sustainable Development, Recycling, Combustion, Hydrometallurgy, Metallurgy, and 15 moreSustainable Manufacturing, Environmental Sustainability, Solid Waste Management, Metallurgy and Materials Engineering, Heat treatment of metals and alloys, Lithium-Ion Battery, Metal Casting, Copper extraction and production, Steel, Aluminium Alloys, Alloy Design, Greenhouse Gas Emissions, Red Mud, Biometallurgy, and Pyrometallurgy(Sustainable Manufacturing, Environmental Sustainability, Solid Waste Management, Metallurgy and Materials Engineering, Heat treatment of metals and alloys, Lithium-Ion Battery, Metal Casting, Copper extraction and production, Steel, Aluminium Alloys, Alloy Design, Greenhouse Gas Emissions, Red Mud, Biometallurgy, and Pyrometallurgy)
(Sustainable Manufacturing, Environmental Sustainability, Solid Waste Management, Metallurgy and Materials Engineering, Heat treatment of metals and alloys, Lithium-Ion Battery, Metal Casting, Copper extraction and production, Steel, Aluminium Alloys, Alloy Design, Greenhouse Gas Emissions, Red Mud, Biometallurgy, and Pyrometallurgy)
Steels with medium manganese (Mn) content (3∼12 wt-%) have emerged as a new alloy class and received considerable attention during the last decade. The microstructure and mechanical response of such alloys show significant differences... more
Steels with medium manganese (Mn) content (3∼12 wt-%) have emerged as a new alloy class and received considerable attention during the last decade. The microstructure and mechanical response of such alloys show significant differences from those of established steel grades, especially pertaining to the microstructural variety that can be tuned and the associated micromechanisms activated during deformation. The interplay and tuning opportunities between composition and the many microstructural features allow to trigger almost all known strengthening and strain-hardening mechanisms, enabling excellent strength-ductility synergy, at relatively lean alloy content. Previous investigations have revealed a high degree of microstructure and deformation complexity in such steels, but the underlying mechanisms are not adequately discussed and acknowledged. This encourages us to critically review and discuss these materials, focusing on the progress in fundamental research, with the aim to obtain better understanding and enable further progress in this field. The review addresses the main phase transformation phenomena in these steels and their mechanical behaviour, covering the whole inelastic deformation regime including yielding, strain hardening, plastic instability and damage. Based on these insights, the relationships between processing, microstructure and mechanical properties are critically assessed and rationalized. Open questions and challenges with respect to both, fundamental studies and industrial production are also identified and discussed to guide future research efforts.
Research Interests: Microstructure, Plasticity, Deformation and strain, Manganese, Heat treatment of metals and alloys, and 10 moreSteel, Crystal Plasticity, Microstructure and Grain Boundary Engineering, Strength of materials, Strengthening, Impact Strength, Tensile Strength, Twinning-induced Plasticity, Strain Hardening, and Transformation Induced Plasticity
Ultrafine austenite-ferrite duplex medium Mn steels often show a discontinuous yielding phenomenon, which is not commonly observed in other composite-like multiphase materials. The underlying dislocation-based mechanisms are not... more
Ultrafine austenite-ferrite duplex medium Mn steels often show a discontinuous yielding phenomenon, which is not commonly observed in other composite-like multiphase materials. The underlying dislocation-based mechanisms are not understood. Here 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. We observe that both austenite and ferrite are plastically deformed before the macroscopic yield point. In this microplastic regime, plastic deformation starts in the austenite phase before ferrite yields. The austenite-ferrite interfaces act as preferable nucleation sites for new partial dislocations in austenite and for full dislocations in ferrite. The large total interface area, caused by the submicron grain size, can provide a high density of dislocation sources and lead to a rapid increase of mobile dislocations, which is believed to be the major reason accounting for discontinuous yielding in such steels. We simultaneously study the Lüders banding behavior and the local deformation-induced martensite forming inside the Lüders bands. We find that grain size and the austenite stability against deformation-driven martensite formation are two important microstructural factors controlling the Lüders band characteristics in terms of the number of band nucleation sites and their propagation velocity. These factors thus govern the early yielding stages of medium Mn steels, due to their crucial influence on mobile dislocation generations and local work hardening.
Research Interests: Microstructure, Mechanical Properties of Materials, Dislocations, Microstructure and Grain Boundary Engineering, Microstructure characterization via XRD and TEM, and 11 moreMicrostructures, Plastic deformation, Steels, Developement of ultrafine-grained and nanostructured steels, Prior Austenite Grain, Martensite, Mechancial Engineering, Ultrafine-grained materials, Multiphase Alloys, Lüders instability , and Medium manganese steels
Metallic alloy design for room temperature applications typically aims at avoiding undesired brittle intermetallic phases. In transition metal alloys, the sigma phase is particularly known as a harmful phase leading to serious... more
Metallic alloy design for room temperature applications typically aims at avoiding undesired brittle intermetallic phases. In transition metal alloys, the sigma phase is particularly known as a harmful phase leading to serious embrittlement. Here, we develop a novel strategy that utilizes displacive transformation and heterogeneous structures to mitigate the embrittlement of sigma phase particles in high-entropy alloys (HEAs). A careful study of the deformation behavior reveals that the displacive transformation from face-centered cubic (FCC) to hexagonal close packed (HCP) phase can effectively suppress the propagation of microcracks originated in these brittle sigma particles (310±52 nm) and contributes to high work hardening behavior during tensile deformation. This is achieved by tuning the stacking fault energy of the FCC matrix by reducing the Ni content to promote transformation induce plasticity (TRIP) around the sigma phase in a non-equiatomic Fe 34 Mn 20 Co 20 Cr 20 Ni 6 (at. %) HEA. Such TRIP effect can be optimized in various heterogeneous structures with bimodal grain sizes via simple cold-rolling (~60%) and subsequent annealing (30 min at 700 or 800 • C). The heterogeneously structured HEAs containing brittle sigma particles exhibit ultimate tensile strengths as high as ~1.2 GPa while maintaining a ductility up to ~50%. This is mainly attributed to the transformation induced stress-relaxation around the regions containing brittle sigma particles. The insights provide a new design strategy of combining TRIP effect and heterogeneous structures for developing strong and ductile alloys.
Research Interests:
Research Interests:
Large strain warm deformation at different temperatures and subsequent intercritical annealing has been applied to obtain fine grained (FG, 2.4 µm) and ultrafine grained (UFG, 1.2 µm) ferrite/martensite dual-phase (DP) steels. Their... more
Large strain warm deformation at different temperatures and subsequent intercritical annealing has been applied to obtain fine grained (FG, 2.4 µm) and ultrafine grained (UFG, 1.2 µm) ferrite/martensite dual-phase (DP) steels. Their mechanical properties were tested under tensile conditions and compared to a hot deformed coarse grained (CG, 12.4 µm) counterpart. Both yield strength and tensile strength follow a Hall-Petch type linear relationship, whereas uniform elongation and total elongation are hardly affected by grain refinement. The initial strain hardening rate as well as the reduction in area increase with decreasing grain size. The deformation and fracture behavior of the steels were analyzed using scanning electron microscopy (SEM) combined with electron backscatter diffraction (EBSD). Slip band evolution was studied by multistep tensile tests. The increase in strength at improved ductility is explained with the enhanced martensite plasticity as a result of plastic constraints in UFG ferrite and the delayed formation of voids and martensite particle cracks due to the more homogeneous distribution and more spherical shape of UFG martensite particles.
Research Interests:
High temperature compression deformation studies of Ti-6Al-2Zr-1Mo-1V titanium alloy in full  phase region with different strains/strain rates and then with subsequent varied cooling rates were performed to understand the microstructure... more
High temperature compression deformation studies of Ti-6Al-2Zr-1Mo-1V titanium alloy in full  phase region with different strains/strain rates and then with subsequent varied cooling rates were performed to understand the microstructure evolution. Crystal orientation information and microstructure morphology of all tested samples were investigated by electron backscatter diffraction (EBSD) measurements. The crystal orientations of prior high temperature  grains were estimated by reconstructing the retained  phase at room temperature. The theoretical crystal orientations of all possible ␣ variants within an investigated prior  grain were calculated according to the Burgers orientation relationship (OR) between parent and product phase. The calculated and experimental results were then compared and analyzed. The influences of deformation strain, strain rate and cooling rate on the Burgers OR between prior  matrix and precipitated ␣ phase were investigated. Full discussions have been conducted by combination of crystal plasticity finite element method (CP-FEM) grain-scale simulation results. The results indicate that external factors (such as deformation strain, strain rate and cooling rate) have a slight influence on the obeying of Burgers OR rule during  → ␣ phase transformation. However, strain rate and cooling rate have a significant effect on the morphology of precipitated ␣ phase.
Research Interests:
Metallic alloy design for room temperature applications typically aims at avoiding undesired brittle intermetallic phases. In transition metal alloys, the sigma phase is particularly known as a harmful phase leading to serious... more
Metallic alloy design for room temperature applications typically aims at avoiding undesired brittle intermetallic phases. In transition metal alloys, the sigma phase is particularly known as a harmful phase leading to serious embrittlement. Here, we develop a novel strategy that utilizes displacive transformation and heterogeneous structures to mitigate the embrittlement of sigma phase particles in high-entropy alloys (HEAs). A careful study of the deformation behavior reveals that the displacive transformation from face-centered cubic (FCC) to hexagonal close packed (HCP) phase can effectively suppress the propagation of microcracks originated in these brittle sigma particles (310±52 nm) and contributes to high work hardening behavior during tensile deformation. This is achieved by tuning the stacking fault energy of the FCC matrix by reducing the Ni content to promote transformation induce plasticity (TRIP) around the sigma phase in a non-equiatomic Fe 34 Mn 20 Co 20 Cr 20 Ni 6 (at. %) HEA. Such TRIP effect can be optimized in various heterogeneous structures with bimodal grain sizes via simple cold-rolling (~60%) and subsequent annealing (30 min at 700 or 800 • C). The heterogeneously structured HEAs containing brittle sigma particles exhibit ultimate tensile strengths as high as ~1.2 GPa while maintaining a ductility up to ~50%. This is mainly attributed to the transformation induced stress-relaxation around the regions containing brittle sigma particles. The insights provide a new design strategy of combining TRIP effect and heterogeneous structures for developing strong and ductile alloys.
Research Interests:
In human-made malleable materials, microdamage such as cracking usually limits material lifetime. Some biological composites, such as bone, have hierarchical microstructures that tolerate cracks but cannot withstand high elongation. We... more
In human-made malleable materials, microdamage such as cracking usually limits material lifetime. Some biological composites, such as bone, have hierarchical microstructures that tolerate cracks but cannot withstand high elongation. We demonstrate a directionally solidified eutectic high-entropy alloy (EHEA) that successfully reconciles crack tolerance and high elongation. The solidified alloy has a hierarchically organized herringbone structure that enables bionic-inspired hierarchical crack buffering. This effect guides stable, persistent crystallographic nucleation and growth of multiple microcracks in abundant poor-deformability microstructures. Hierarchical buffering by adjacent dynamic strainhardened features helps the cracks to avoid catastrophic growth and percolation. Our self-buffering herringbone material yields an ultrahigh uniform tensile elongation (~50%), three times that of conventional nonbuffering EHEAs, without sacrificing strength.
Research Interests: Microstructure, Nanoindentation, Transmission Electron Microscopy, Stress corrosion cracking, Fatigue crack growth, and 13 moreDamage Mechanics, Crack propagation, Solidification, Mechanical Properties of Materials, High Entropy Alloys, Nucleation and Growth, Microstructure and Grain Boundary Engineering, Microstructure characterization via XRD and TEM, Microdamage, Microcracks, Rapid solidification, Eutectic Alloys, and High Entropy Alloy(Damage Mechanics, Crack propagation, Solidification, Mechanical Properties of Materials, High Entropy Alloys, Nucleation and Growth, Microstructure and Grain Boundary Engineering, Microstructure characterization via XRD and TEM, Microdamage, Microcracks, Rapid solidification, Eutectic Alloys, and High Entropy Alloy)
(Damage Mechanics, Crack propagation, Solidification, Mechanical Properties of Materials, High Entropy Alloys, Nucleation and Growth, Microstructure and Grain Boundary Engineering, Microstructure characterization via XRD and TEM, Microdamage, Microcracks, Rapid solidification, Eutectic Alloys, and High Entropy Alloy)
Steels with medium manganese (Mn) content (3∼12 wt-%) have emerged as a new alloy class and received considerable attention during the last decade. The microstructure and mechanical response of such alloys show significant differences... more
Steels with medium manganese (Mn) content (3∼12 wt-%) have emerged as a new alloy class and received considerable attention during the last decade. The microstructure and mechanical response of such alloys show significant differences from those of established steel grades, especially pertaining to the microstructural variety that can be tuned and the associated micromechanisms activated during deformation. The interplay and tuning opportunities between composition and the many microstructural features allow to trigger almost all known strengthening and strain-hardening mechanisms, enabling excellent strength-ductility synergy, at relatively lean alloy content. Previous investigations have revealed a high degree of microstructure and deformation complexity in such steels, but the underlying mechanisms are not adequately discussed and acknowledged. This encourages us to critically review and discuss these materials, focusing on the progress in fundamental research, with the aim to obtain better understanding and enable further progress in this field. The review addresses the main phase transformation phenomena in these steels and their mechanical behaviour, covering the whole inelastic deformation regime including yielding, strain hardening, plastic instability and damage. Based on these insights, the relationships between processing, microstructure and mechanical properties are critically assessed and rationalized. Open questions and challenges with respect to both, fundamental studies and industrial production are also identified and discussed to guide future research efforts.
Research Interests: Mechanical Engineering, Phase Transformations, Microstructure, Deformation and strain, Steel Structure, and 15 moreHeat treatment of metals and alloys, Advanced high strength steels, Steel, Thermomechanical Processing, Microstructure and Grain Boundary Engineering, Strength of materials, Deformation Mechanisms, Dislocations Theory, Deformation and Fracture Mechanisms, Strengthening, Microstructures, Material Damage, Tensile Strength, Damage Tolerance, Twinning-induced Plasticity, and Transformation Induced Plasticity(Heat treatment of metals and alloys, Advanced high strength steels, Steel, Thermomechanical Processing, Microstructure and Grain Boundary Engineering, Strength of materials, Deformation Mechanisms, Dislocations Theory, Deformation and Fracture Mechanisms, Strengthening, Microstructures, Material Damage, Tensile Strength, Damage Tolerance, Twinning-induced Plasticity, and Transformation Induced Plasticity)
(Heat treatment of metals and alloys, Advanced high strength steels, Steel, Thermomechanical Processing, Microstructure and Grain Boundary Engineering, Strength of materials, Deformation Mechanisms, Dislocations Theory, Deformation and Fracture Mechanisms, Strengthening, Microstructures, Material Damage, Tensile Strength, Damage Tolerance, Twinning-induced Plasticity, and Transformation Induced Plasticity)
Mechanically strong and ductile load-carrying materials are needed in all sectors, from transportation to lightweight design to safe infrastructure. Yet, a grand challenge is to unify both features in one material. We show that a plain... more
Mechanically strong and ductile load-carrying materials are needed in all sectors, from transportation to lightweight design to safe infrastructure. Yet, a grand challenge is to unify both features in one material. We show that a plain medium-manganese steel can be processed to have a tensile strength >2.2 gigapascals at a uniform elongation >20%. This requires a combination of multiple transversal forging, cryogenic treatment, and tempering steps. A hierarchical microstructure that consists of laminated and twofold topologically aligned martensite with finely dispersed retained austenite simultaneously activates multiple micromechanisms to strengthen and ductilize the material. The dislocation slip in the well-organized martensite and the gradual deformation-stimulated phase transformation synergistically produce the high ductility. Our nanostructure design strategy produces 2 gigapascal-strength and yet ductile steels that have attractive composition and the potential to be produced at large industrial scales.
Research Interests: Microstructure, Mechanical Behavior Of Materials, Micromechanics, Advanced high strength steels, Steel, and 13 moreProcessing, Hot forging, Micromechanics of Deformation, Ductility, Alloy Design, High Strength Steel, Strength of materials, Metals, Forging, Tensile Strength, Martensite, Austenite, and Medium manganese steels
While age-hardened austenitic high-Mn and high-Al lightweight steels exhibit excellent strength-ductility combinations, their properties are strongly degraded when mechanically loaded under harsh environments, e.g. with the presence of... more
While age-hardened austenitic high-Mn and high-Al lightweight steels exhibit excellent strength-ductility combinations, their properties are strongly degraded when mechanically loaded under harsh environments, e.g. with the presence of hydrogen (H). The H embrittlement in this type of materials, especially pertaining to the effect of κ-carbide precipitation, has been scarcely studied. Here we focus on this subject, using a Fe-28.4Mn-8.3Al-1.3C (wt%) steel in different microstructure conditions, namely, solute solution treated and age-hardened. Contrary to the reports that grain boundary (GB) κ-carbides precipitate only during overaging, site-specific atom probe tomography and scanning transmission electron microscopy (STEM) reveal the existence of nanosized GB κ-carbides at early stages of aging. We correlate this observation with the deterioration of H embrittlement resistance in aged samples. While H precharged solution-treated samples fail by intergranular fracture at depths consistent with the H ingress depth (∼20 μm), age-hardened samples show intergranular fracture features at a much larger depth of above 500 μm, despite similar amount of H introduced into the material. This difference is explained in terms of the facile H-induced decohesion of GB κ-carbides/matrix interfaces where H can be continuously supplied through internal short-distance diffusion to the propagating crack tips. The H-associated decohesion mechanisms are supported by a comparison with the fracture behavior in samples loaded under the cryogenic temperature and can be explained based on dislocation pileups and elastic misfit at the GB κ-carbide/matrix interfaces. The roles of other plasticity-associated H embrittlement mechanisms are also discussed in this work based on careful investigations of the dislocation activities near the H-induced cracks. Possible alloying and microstructure design strategies for the enhancement of the H embrittlement resistance in this alloy family are also suggested.
Research Interests: Mechanical properties, Steel, Mechanical Properties of Materials, Grain Boundaries and Interfaces in Crystalline materials, Atom probe tomography, and 7 moreMicrostructure and Grain Boundary Engineering, Cracking, Hydrogen Embrittlement, Spinodal Decomposition, Hydrogen Economy, Tensile Strength, and Lightweight steels
Refractory high-entropy alloys are of interest due to the potential of compositionally complex alloys to achieve combinations of mechanical properties such as room-temperature ductility and high-temperature strength rarely found in... more
Refractory high-entropy alloys are of interest due to the potential of compositionally complex alloys to achieve combinations of mechanical properties such as room-temperature ductility and high-temperature strength rarely found in simpler alloys. To study a large compositional range of the system Nb-Mo-Ta-W, thin-film materials libraries were fabricated by combinatorial sputtering. High-throughput characterization methods were used to systematically determine composition-dependent properties: (I) the extent and stability of the complex solid solution range and (II) the mechanical properties (Young's modulus, hardness). The whole investigated composition range of Nb 20-59 Mo 9-31 Ta 10-42 W 12-32 crystallized in a bcc phase, independent of annealing temperatures ranging from 300 to 900 °C. Mechanical strength values of the Nb-Mo-Ta-W compositions were calculated using the Maresca-Curtin analytical model parameterized with experimental data. A strong positive correlation with measured hardness was observed that allows using this analytical model for optimization of the mechanical strength. We predict that compositions with high Mo contents provide the highest hardness values.
Research Interests:
High-entropy alloys are solid solutions of multiple principal elements that are capable of reaching composition and property regimes inaccessible for dilute materials. Discovering those with valuable properties, however, too often relies... more
High-entropy alloys are solid solutions of multiple principal elements that are capable of reaching composition and property regimes inaccessible for dilute materials. Discovering those with valuable properties, however, too often relies on serendipity, because thermodynamic alloy design rules alone often fail in high-dimensional composition spaces. We propose an active learning strategy to accelerate the design of high-entropy Invar alloys in a practically infinite compositional space based on very sparse data. Our approach works as a closed-loop, integrating machine learning with density-functional theory, thermodynamic calculations, and experiments. After processing and characterizing 17 new alloys out of millions of possible compositions, we identified two high-entropy Invar alloys with extremely low thermal expansion coefficients around 2 × 10 −6 per degree kelvin at 300 kelvin. We believe this to be a suitable pathway for the fast and automated discovery of high-entropy alloys with optimal thermal, magnetic, and electrical properties.
Research Interests: Artificial Intelligence, Thermodynamics, Machine Learning, Active Learning, Modeling and Simulation, and 10 moreDensity-functional theory, Heat treatment of metals and alloys, Alloy Design, Bayesian Optimization, Gradient Boosting, Metallic Alloys Materials, Thermal Expansion, High Entropy Alloy, Combinatorial Alloy Design, and multiple principal element alloys
Twin, dislocation, and grain boundary interaction in hexagonal materials, such as Mg, Ti, and Zr, has critical influence on the materials' mechanical properties. The development of a microstructure-sensitive constitutive model for these... more
Twin, dislocation, and grain boundary interaction in hexagonal materials, such as Mg, Ti, and Zr, has critical influence on the materials' mechanical properties. The development of a microstructure-sensitive constitutive model for these deformation mechanisms is the key to the design of high-strength and ductile alloys. In this work, we have developed a mechanical formulation within the finite strain framework for modeling dislocation slip-and deformation twinning-induced plasticity. A dislocation density-based crystal plasticity model was employed to describe the dislocation activities, and the stress and strain distributions. The model was coupled with a multi-phase-field model to predict twin formation and twin-twin interactions. The coupled model was then employed to study twin, dislocation, and grain boundary interactions in Mg single-and polycrystals during monotonic and cyclic deformation. The results show that twin-twin interactions can enhance the strength by impeding twin propagation and growth. The role of dislocation accommodation on twin-twin interactions was twofold. Dislocation slip diminished twin-twin hardening by relieving the development of back-stresses, while it effectively relaxed the stress concentration near twin-twin intersections and thus may alleviate crack nucleation. The plastic anisotropy in each grain and the constraints imposed by the local boundary conditions resulted in stress variations among grains. This stress heterogeneity was responsible for the observed anomalous twinning behaviour. That is, low Schmid factor twins were activated to relax local stresses and accommodate the strain incompatibility, whereas the absence of high Schmid factor twins was associated with slip band-induced stress relaxation.
Research Interests: Materials Science, Modeling and Simulation, Dislocation Dynamics Simulations, Magnesium, Crystallographic Texture, and 8 moreCrystal Plasticity, Mechanical Properties of Materials, Plasticity of Crystals and Interfaces, Dislocations, Mechanical twinning, Damask, Polycrystal Mechanics, and Crystal Plasticity Modeling
The reduction of iron ore with carbon-carriers is one of the largest sources of greenhouse gas emissions in the industry, motivating global activities to replace the coke-based blast furnace reduction by hydrogenbased direct reduction... more
The reduction of iron ore with carbon-carriers is one of the largest sources of greenhouse gas emissions in the industry, motivating global activities to replace the coke-based blast furnace reduction by hydrogenbased direct reduction (HyDR). Iron oxide reduction with hydrogen has been widely investigated both experimentally and theoretically. The HyDR process includes multiple types of chemical reactions, solid state and defect-mediated diffusion (of oxygen and hydrogen species), several phase transformations, as well as massive volume shrinkage and mechanical stress buildup. However, studies focusing on the chemo-mechanical interplay during the reduction reaction influenced by microstructure are sparse. In this work, a chemo-mechanically coupled phase-field (PF) model has been developed to explore the interplay between phase transformation, chemical reaction, species diffusion, large elasto-plastic deformation and microstructure evolution. Energetic constitutive relations of the model are based on the system free energy which is calibrated with the help of a thermodynamic database. The model has been first applied to the classical core-shell (wüstite-iron) structure. Simulations show that the phase transformation from wüstite to α-iron can result in high stresses and rapidly decelerating reaction kinetics. Mechanical stresses create elastic energy in the system, an effect which can negatively influence the phase transformations, thus causing slow reaction kinetics and low metallization. However, if the elastic stress becomes comparatively high, it can shift the shape of the free energy from a double-well to a single-well case, speed up the transformation and result in a higher reduction degree compared to the low-stress doublewell case. The model has been applied to simulate an experimentally characterized iron oxide specimen with its complex microstructure. The observed microstructure evolution during reduction is well predicted by the model. The simulation results also show that isolated pores in the microstructure are filled with water vapor during reduction, which can influence the local reaction atmosphere and dynamics.
Research Interests:
We present a virtual laboratory to investigate the anisotropic yield behavior of polycrystalline materials by using high resolution crystal plasticity simulations. Employing a fast spectral method solver enables us to conduct a large... more
We present a virtual laboratory to investigate the anisotropic yield behavior of polycrystalline materials by using high resolution crystal plasticity simulations. Employing a fast spectral method solver enables us to conduct a large number of full-field virtual experiments with different stress states to accurately identify the yield surface of the probed materials. Based on the simulated yield stress points, the parameters for many commonly used yield functions are acquired simultaneously with a nonlinear least square fitting procedure. Exemplarily, the parameters of four yield functions frequently used in sheet metal forming, namely Yld91, Yld2000-2D, Yld2004-18p, and Yld2004-27p are adjusted to accurately describe the yield behavior of an AA3014 aluminum alloy at two material states, namely with a recrystallization texture and a cold rolling texture. The comparison to experimental results proves that the methodology presented, combining accuracy with efficiency, is a promising micromechanics-based tool for probing the mechanical anisotropy of polycrystalline metals and for identifying the parameters of advanced yield functions.
Research Interests:
Deformation-induced martensitic transformation (DIMT) has been used for designing high-performance alloys to prevent structural failure under static loads. Its effectiveness against fatigue, however, is unclear. This limits the... more
Deformation-induced martensitic transformation (DIMT) has been
used for designing high-performance alloys to prevent structural
failure under static loads. Its effectiveness against fatigue, however,
is unclear. This limits the application of DIMT for parts that
are exposed to variable loads, although such scenarios are the rule
and not the exception for structural failure. Here we reveal the
dual role of DIMT in fatigue crack growth through in situ observations.
Two antagonistic fatigue mechanisms mediated by DIMT are
identified, namely, transformation-mediated crack arresting,
which prevents crack growth, and transformation-mediated crack
coalescence, which promotes crack growth. Both mechanisms are
due to the hardness and brittleness of martensite as a transformation
product, rather than to the actual transformation process
itself. In fatigue crack growth, the prevalence of one mechanism
over the other critically depends on the crack size and the mechanical
stability of the parent austenite phase. Elucidating the two
mechanisms and their interplay allows for the microstructure
design and safe use of metastable alloys that experience fatigue
loads. The findings also generally reveal how metastable alloy
microstructures must be designed for materials to be fatigue resistant.
used for designing high-performance alloys to prevent structural
failure under static loads. Its effectiveness against fatigue, however,
is unclear. This limits the application of DIMT for parts that
are exposed to variable loads, although such scenarios are the rule
and not the exception for structural failure. Here we reveal the
dual role of DIMT in fatigue crack growth through in situ observations.
Two antagonistic fatigue mechanisms mediated by DIMT are
identified, namely, transformation-mediated crack arresting,
which prevents crack growth, and transformation-mediated crack
coalescence, which promotes crack growth. Both mechanisms are
due to the hardness and brittleness of martensite as a transformation
product, rather than to the actual transformation process
itself. In fatigue crack growth, the prevalence of one mechanism
over the other critically depends on the crack size and the mechanical
stability of the parent austenite phase. Elucidating the two
mechanisms and their interplay allows for the microstructure
design and safe use of metastable alloys that experience fatigue
loads. The findings also generally reveal how metastable alloy
microstructures must be designed for materials to be fatigue resistant.
Research Interests:
Deformation-induced martensitic transformation (DIMT) has been used for designing high-performance alloys to prevent structural failure under static loads. Its effectiveness against fatigue, however, is unclear. This limits the... more
Deformation-induced martensitic transformation (DIMT) has been
used for designing high-performance alloys to prevent structural
failure under static loads. Its effectiveness against fatigue, however,
is unclear. This limits the application of DIMT for parts that
are exposed to variable loads, although such scenarios are the rule
and not the exception for structural failure. Here we reveal the
dual role of DIMT in fatigue crack growth through in situ observations.
Two antagonistic fatigue mechanisms mediated by DIMT are
identified, namely, transformation-mediated crack arresting,
which prevents crack growth, and transformation-mediated crack
coalescence, which promotes crack growth. Both mechanisms are
due to the hardness and brittleness of martensite as a transformation
product, rather than to the actual transformation process
itself. In fatigue crack growth, the prevalence of one mechanism
over the other critically depends on the crack size and the mechanical
stability of the parent austenite phase. Elucidating the two
mechanisms and their interplay allows for the microstructure
design and safe use of metastable alloys that experience fatigue
loads. The findings also generally reveal how metastable alloy
microstructures must be designed for materials to be fatigueresistant.
used for designing high-performance alloys to prevent structural
failure under static loads. Its effectiveness against fatigue, however,
is unclear. This limits the application of DIMT for parts that
are exposed to variable loads, although such scenarios are the rule
and not the exception for structural failure. Here we reveal the
dual role of DIMT in fatigue crack growth through in situ observations.
Two antagonistic fatigue mechanisms mediated by DIMT are
identified, namely, transformation-mediated crack arresting,
which prevents crack growth, and transformation-mediated crack
coalescence, which promotes crack growth. Both mechanisms are
due to the hardness and brittleness of martensite as a transformation
product, rather than to the actual transformation process
itself. In fatigue crack growth, the prevalence of one mechanism
over the other critically depends on the crack size and the mechanical
stability of the parent austenite phase. Elucidating the two
mechanisms and their interplay allows for the microstructure
design and safe use of metastable alloys that experience fatigue
loads. The findings also generally reveal how metastable alloy
microstructures must be designed for materials to be fatigueresistant.
Research Interests: Phase Transformations, Microstructure, Electron Backscatter Diffraction (EBSD), Fatigue, Fatigue crack growth, and 12 moreSteel Structures, Mechanical Properties of Materials, Microstructural Characterization, Microstructurally Small Crack, Crack Growth on Steel, Lifetime, Martensitic Transformation, Short Crack Growth, Failure Analysis (Materials Charaterization, Microstructural Investigation), Martensite, Mechancial, and TRIP effect(Steel Structures, Mechanical Properties of Materials, Microstructural Characterization, Microstructurally Small Crack, Crack Growth on Steel, Lifetime, Martensitic Transformation, Short Crack Growth, Failure Analysis (Materials Charaterization, Microstructural Investigation), Martensite, Mechancial, and TRIP effect)
(Steel Structures, Mechanical Properties of Materials, Microstructural Characterization, Microstructurally Small Crack, Crack Growth on Steel, Lifetime, Martensitic Transformation, Short Crack Growth, Failure Analysis (Materials Charaterization, Microstructural Investigation), Martensite, Mechancial, and TRIP effect)
Ever more stringent regulations on greenhouse gas emissions from transportation motivate efforts to revisit materials used for vehicles1. High-strength aluminium alloys often used in aircrafts could help reduce the weight of automobiles,... more
Ever more stringent regulations on greenhouse gas emissions from transportation
motivate efforts to revisit materials used for vehicles1. High-strength aluminium alloys
often used in aircrafts could help reduce the weight of automobiles, but are
susceptible to environmental degradation2,3. Hydrogen ‘embrittlement’ is often
indicated as the main culprit4; however, the exact mechanisms underpinning failure
are not precisely known: atomic-scale analysis of H inside an alloy remains a challenge,
and this prevents deploying alloy design strategies to enhance the durability of the
materials. Here we performed near-atomic-scale analysis of H trapped in
second-phase particles and at grain boundaries in a high-strength 7xxx Al alloy. We
used these observations to guide atomistic ab initio calculations, which show that the
co-segregation of alloying elements and H favours grain boundary decohesion, and
the strong partitioning of H into the second-phase particles removes solute H from
the matrix, hence preventing H embrittlement. Our insights further advance the
mechanistic understanding of H-assisted embrittlement in Al alloys, emphasizing the
role of H traps in minimizing cracking and guiding new alloy design.
motivate efforts to revisit materials used for vehicles1. High-strength aluminium alloys
often used in aircrafts could help reduce the weight of automobiles, but are
susceptible to environmental degradation2,3. Hydrogen ‘embrittlement’ is often
indicated as the main culprit4; however, the exact mechanisms underpinning failure
are not precisely known: atomic-scale analysis of H inside an alloy remains a challenge,
and this prevents deploying alloy design strategies to enhance the durability of the
materials. Here we performed near-atomic-scale analysis of H trapped in
second-phase particles and at grain boundaries in a high-strength 7xxx Al alloy. We
used these observations to guide atomistic ab initio calculations, which show that the
co-segregation of alloying elements and H favours grain boundary decohesion, and
the strong partitioning of H into the second-phase particles removes solute H from
the matrix, hence preventing H embrittlement. Our insights further advance the
mechanistic understanding of H-assisted embrittlement in Al alloys, emphasizing the
role of H traps in minimizing cracking and guiding new alloy design.
Research Interests:
Research Interests:
Capturing and converting waste heat into electrical power through thermoelectric generators based on the Seebeck effect is a promising alternative energy source. Among thermoelectric compounds, PbTe can be alloyed and form precipitates by... more
Capturing and converting waste heat into electrical power through thermoelectric generators based on the Seebeck effect is a promising alternative energy source. Among thermoelectric compounds, PbTe can be alloyed and form precipitates by aging at elevated temperatures, thus reducing thermal conductivity by phonon scattering. Here, PbTe is alloyed with Ag to form Ag-rich precipitates having a number density controlled by heat treatments. We employ complementary scanning transmission electron microscopy and atom probe tomography to analyze the precipitate number density and the PbTe-matrix composition. We measure the temperature-dependent transport coefficients and correlate them with the microstructure. The thermal and electrical conductivities, as well as the Seebeck coefficients, are found to be highly sensitive to the microstructure and its temporal evolution, e.g., the number density of Ag-rich precipitates increases by ca. 3 orders of magnitude and reaches (1.68 ± 0.92) × 10 m upon aging at 380 °C for 6 h, which is pronounced by reduction in thermal conductivity to a value as low as 0.85 W m K at 300 °C. Our findings will help to guide predictive tools for further design of materials for energy harvesting.
Research Interests:
Next-generation high-performance structural materials are required for lightweight design strategies and advanced energy applications. Maraging steels, combining a martensite matrix with nanoprecipitates, are a class of high-strength... more
Next-generation high-performance structural materials are required for lightweight design strategies and advanced energy applications. Maraging steels, combining a martensite matrix with nanoprecipitates, are a class of high-strength materials with the potential for matching these demands. Their outstanding strength originates from semi-coherent precipitates, which unavoidably exhibit a heterogeneous distribution that creates large coherency strains, which in turn may promote crack initiation under load. Here we report a counterintuitive strategy for the design of ultrastrong steel alloys by high-density nanoprecipitation with minimal lattice misfit. We found that these highly dispersed, fully coherent precipitates (that is, the crystal lattice of the precipitates is almost the same as that of the surrounding matrix), showing very low lattice misfit with the matrix and high anti-phase boundary energy, strengthen alloys without sacrificing ductility. Such low lattice misfit (0.03 ± 0...
Research Interests:
Thermoelectric materials are of utmost significance for conversion of heat flux into electrical power in the low-power regime. Their conversion efficiency depends strongly on the microstructure. AgSbTe2-based compounds are high-efficiency... more
Thermoelectric materials are of utmost significance for conversion of heat flux into electrical power in the low-power regime. Their conversion efficiency depends strongly on the microstructure. AgSbTe2-based compounds are high-efficiency thermoelectric materials suitable for the mid-temperature range. Herein, we explore a Ag16.7Sb30Te53.3 alloy (at. %) subjected to heat treatments at 380 °C for different durations aimed at nucleation and coarsening of Sb2Te3-precipitates. To characterize the Sb2Te3-precipitation, we use a set of methods combining thermal and electrical measurements in concert with transmission electron microscopy and atom probe tomography. We find correlations between the measured thermoelectric transport coefficients and the applied heat treatments. Specifically, the lowest electrical and thermal conductivity values are obtained for the as-quenched state, whereas the highest values are observed for alloys aged for 8 h. In turn, long term heat treatments result in intermediate values of transport coefficients. We explain these findings in terms of interplay between precipitate formation and variations of the matrix composition, highlighting the importance of material's thermal stability under service conditions.
Research Interests:
Atom-probe tomography is a materials characterization method ideally suited for the investigation of clustering and precipitation phenomena. To distinguish the clusters from the surrounding matrix, the maximum separation algorithm is... more
Atom-probe tomography is a materials characterization method ideally suited for the investigation of clustering and precipitation phenomena. To distinguish the clusters from the surrounding matrix, the maximum separation algorithm is widely employed. However, the results of the cluster analysis strongly depend on the parameters used in the algorithm and hence, a wrong choice of parameters leads to erroneous results, e.g., for the cluster number density, concentration, and size. Here, a new method to determine the optimum value of the parameter dmax is proposed, which relies only on information contained in the measured atom-probe data set. Atom-probe simulations are employed to verify the method and to determine the sensitivity of the maximum separation algorithm to other input parameters. In addition, simulations are used to assess the accuracy of cluster analysis in the presence of trajectory aberrations caused by the local magnification effect. In the case of Cu-rich precipitates...
Research Interests:
Research Interests:
Ab initio calculations are becoming increasingly useful to engineers interested in designing new alloys because these calculations are able to accurately predict basic material properties only knowing the atomic composition of the... more
Ab initio calculations are becoming increasingly useful to engineers interested in designing new alloys because these calculations are able to accurately predict basic material properties only knowing the atomic composition of the material. In this paper, fundamental physical properties (like formation energies and elastic constants) of 11 bcc Mg-Li compounds are calculated using density-functional theory (DFT) and compared with available experimental data. These DFT-determined properties are in turn used to calculate engineering parameters like (i) ...
Research Interests:
We present a design strategy for a new type of age hardenable ultrahigh strength TRIP-assisted steels with a good tensile elongation. The alloys have a low carbon content (below 0.02 mass% C), 9–15 mass% Mn and, in order to reduce costs,... more
We present a design strategy for a new type of age hardenable ultrahigh strength TRIP-assisted steels with a good tensile elongation. The alloys have a low carbon content (below 0.02 mass% C), 9–15 mass% Mn and, in order to reduce costs, only minor additions of Ni, Al, Ti, and Mo (of the order of 1–2 mass%). After quenching the microstructure of these steels comprises martensite and different amounts of retained austenite. During age hardening the strength and ductility can be increased simultaneously: The strength is increased by the ...
Research Interests:
Titanium alloys can suffer from halide-associated stress corrosion cracking at elevated temperatures e.g., in jet engines, where chlorides and Ti-oxide promote the cracking of water vapour in the gas stream, depositing embrittling species... more
Titanium alloys can suffer from halide-associated stress corrosion cracking at elevated temperatures e.g., in jet engines, where chlorides and Ti-oxide promote the cracking of water vapour in the gas stream, depositing embrittling species at the crack tip. Here we report, using isotopically-labelled experiments, that crack tips in an industrial Ti-6Al-2Sn-4Zr-6Mo alloy are strongly enriched (> 5 at.%) in oxygen from the water vapour, far greater than the amounts (0.25 at.%) required to embrittle the material. Surprisingly, relatively little hydrogen (deuterium) is measured, despite careful preparation and analysis. Therefore, we suggest that a combined effect of O and H leads to cracking, with O playing a vital role, since it is well-known to cause embrittlement of the alloy. In contrast it appears that in α + β Ti alloys, it may be that H may drain away into the bulk owing to its high solubility in β-Ti, rather than being retained in the stress field of the crack tip. Therefore, whilst hydrides may form on the fracture surface, hydrogen ingress might not be the only plausible mechanism of embrittlement of the underlying matrix. This possibility challenges decades of understanding of stress-corrosion cracking as being related solely to the hydrogen enhanced localised plasticity (HELP) mechanism, which explains why H-doped Ti alloys are embrittled. This would change the perspective on stress corrosion embrittlement away from a focus purely on hydrogen to also consider the ingress of O originating from the water vapour, insights critical for designing corrosion resistant materials.
Research Interests:
Grain boundaries (GBs) are planar lattice defects that govern the properties of many types of polycrystalline materials. Hence, their structures have been investigated in great detail. However, much less is known about their chemical... more
Grain boundaries (GBs) are planar lattice defects that govern the properties of many types of polycrystalline materials. Hence, their structures 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 atomic length 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. Using APT data sets, we present here a machine-learning-based approach for the automated quantification of chemical features of GBs. We trained a convolutional neural network (CNN) using twenty thousand synthesized images of grain interiors, GBs, or triple junctions. Such a trained CNN automatically detects the locations of GBs from APT data. Those GBs are then subjected to compositional mapping and analysis, including revealing their in-plane chemical decoration patterns. We applied this approach to experimentally obtained APT data sets pertaining to three case studies, namely, NiP , Pt-Au, and Al-Zn-Mg-Cu alloys. In the first case, we extracted GB specific segregation features as a function of misorientation and coincidence site lattice character. Secondly, we revealed interfacial excesses and in-plane chemical features that could not have been found by standard compositional analyses. Lastly, we tracked the temporal evolution of chemical decoration from early-stage solute GB segregation in the dilute limit to interfacial phase separation, characterized by the evolution of complex composition patterns. This machine-learningbased approach provides quantitative, unbiased, and automated access to GB chemical analyses, serving as an enabling tool for new discoveries related to interface thermodynamics, kinetics, and the associated chemistry-structure-property relations.
Research Interests:
Two approaches in materials physics have proven immensely successful in alloy design: First, thermodynamic and kinetic descriptions for tailoring and processing alloys to achieve a desired microstructure. Second, crystal defect... more
Two approaches in materials physics have proven immensely successful in alloy design: First, thermodynamic and kinetic descriptions for tailoring and processing alloys to achieve a desired microstructure. Second, crystal defect manipulation to control strength, formability and corrosion resistance. However, to date, the two concepts remain essentially decoupled. A bridge is needed between these powerful approaches to achieve a single conceptual framework. Considering defects and their thermodynamic state holistically as 'defect phases', provides a future materials design strategy by jointly treating the thermodynamic stability of both, the local crystalline structure and the distribution of elements at defects. Here, we suggest that these concepts are naturally linked by defect phase diagrams describing the coexistence and transitions of defect phases. Construction of these defect phase diagrams will require new quantitative descriptors. We believe such a framework will enable a paradigm shift in the description and design of future engineering materials.
Research Interests: Thermodynamics, Electron Microscopy, Surface Physics, Atomistic Simulation, Density-functional theory, and 8 moreGrain Boundaries, Phase Diagrams, Atomistic Simulation using MD and Ab Inition Method, Non-equilibrium thermodynamics, Mechanical Properties of Materials, Dislocations, Atom probe tomography, and Microstructure and Grain Boundary Engineering
Achieving high mechanical strength and ductility in age-hardenable Al7000 series (Al-Zn-Mg) alloys fabricated by selective laser melting (SLM) remains challenging. Here, we show that crack-free AlZnMgCuScZr alloys with an unprecedented... more
Achieving high mechanical strength and ductility in age-hardenable Al7000 series (Al-Zn-Mg) alloys fabricated by selective laser melting (SLM) remains challenging. Here, we show that crack-free AlZnMgCuScZr alloys with an unprecedented strength-ductility synergy can be fabricated via SLM and heat treatment. The as-built samples had an architectured microstructure consisting of a multimodal grain structure and a hierarchical phase morphology. It consisted of primary Al 3 (Sc x ,Zr 1Àx) particles which act as inoculants for ultrafine grains, preventing crack formation. The metastable Mg-, Zn-, and Cu-rich icosahedral quasicrystals (I-phase) ubiquitously dispersed inside the grains and aligned as a filigree skeleton along the grain boundaries. The heat treated SLM-produced AlZnMgCuScZr alloy exhibited tunable mechanical behaviors through trade-off among the hierarchical features, including the dual-nanoprecipitation, viz, g 0 phase, and secondary (Al,Zn) 3 (Sc 9 Zr), and grain coarsening. Less coarsening of grains and (Al,Zn) 3 (Sc 9 Zr) particles, due to a reduced solution treatment temperature and time, could overwhelm the more complete dissolution of I-phase (triggering more g 0 phase), resulting in higher yield strength. Optimal combination of the hierarchical features yields the highest yield strength ($647 MPa) among all reported SLM-produced Al alloys to date with appreciable ductility ($11.6%). The successful fabrication of high-strength Al7000 series alloys with an adjustable hierarchical microstructure paves the way for designing and fine-tuning SLM-produced aluminum engineering components exposed to high mechanical loads.
Research Interests: Microstructure, Electron Backscatter Diffraction (EBSD), Electron Diffraction, Mechanical Behavior Of Materials, Additive Manufacturing, and 13 moreHeat treatment of metals and alloys, Aluminium Alloys, Ductility, Alloy Design, Additive Manufacturing and 3D printing, Microstructure and Grain Boundary Engineering, Quasicrystals, Microstructures, Selective Laser Melting, Aluminum Alloy, Aluminium Age Hardening, Electron Channeling Contrast Imaging, and Nanoprecipitation(Heat treatment of metals and alloys, Aluminium Alloys, Ductility, Alloy Design, Additive Manufacturing and 3D printing, Microstructure and Grain Boundary Engineering, Quasicrystals, Microstructures, Selective Laser Melting, Aluminum Alloy, Aluminium Age Hardening, Electron Channeling Contrast Imaging, and Nanoprecipitation)
(Heat treatment of metals and alloys, Aluminium Alloys, Ductility, Alloy Design, Additive Manufacturing and 3D printing, Microstructure and Grain Boundary Engineering, Quasicrystals, Microstructures, Selective Laser Melting, Aluminum Alloy, Aluminium Age Hardening, Electron Channeling Contrast Imaging, and Nanoprecipitation)
Grain boundaries are intrinsic and omnipresent microstructural imperfections in polycrystalline and nanocrystalline materials. They are short-circuit diffusion paths and preferential locations for alloying elements, dopants, and... more
Grain boundaries are intrinsic and omnipresent microstructural imperfections in polycrystalline and nanocrystalline materials. They are short-circuit diffusion paths and preferential locations for alloying elements, dopants, and impurities segregation. They also facilitate heterogeneous nucleation and the growth of secondary phases. Therefore, grain boundaries strongly influence many materials' properties and their stabilities during application. Here, we propose an approach to measure diffusion, segregation, and segregation-induced precipitation at grain boundaries at a sub-nanometer scale by combining atom probe tomography and scanning transmission electron microscopy. Nanocrystalline multilayer thin films with columnar grain structure were used as a model system as they offer a large area of random highangle grain boundaries and inherent short diffusion distance. Our results show that the fast diffusion flux proceeds primarily through the core region of the grain boundary, which is around 1 nm. While the spatial range that the segregated solute atoms occupied is larger: below the saturation level, it is 1,2 nm; as the segregation saturates, it is 2-3.4 nm in most grain boundary areas. Above 3.4 nm, secondary phase nuclei seem to form. The observed distributions of the solutes at the matrix grain boundaries evidence that even at a single grain boundary, different regions accommodate different amounts of solute atoms and promote secondary phase nuclei with different compositions, which is caused by its complex threedimensional topology.
Research Interests:
In human-made malleable materials, microdamage such as cracking usually limits material lifetime. Some biological composites, such as bone, have hierarchical microstructures that tolerate cracks but cannot withstand high elongation. We... more
In human-made malleable materials, microdamage such as cracking usually limits material lifetime. Some biological composites, such as bone, have hierarchical microstructures that tolerate cracks but cannot withstand high elongation. We demonstrate a directionally solidified eutectic high-entropy alloy (EHEA) that successfully reconciles crack tolerance and high elongation. The solidified alloy has a hierarchically organized herringbone structure that enables bionic-inspired hierarchical crack buffering. This effect guides stable, persistent crystallographic nucleation and growth of multiple microcracks in abundant poor-deformability microstructures. Hierarchical buffering by adjacent dynamic strainhardened features helps the cracks to avoid catastrophic growth and percolation. Our self-buffering herringbone material yields an ultrahigh uniform tensile elongation (~50%), three times that of conventional nonbuffering EHEAs, without sacrificing strength.
Research Interests: Microstructure, Composites, Metallurgy, Bio-Inspired Systems, Fracture Mechanics, and 13 moreMetallurgy and Materials Engineering, Heat treatment of metals and alloys, Crack, Physical Metallurgy, Mechanical Properties of Materials, High Entropy Alloys, Alloy Design, Microstructure and Grain Boundary Engineering, Microdamage, Lifetime, Fracture Toughness, Tensile Strength, and Solidifcation(Metallurgy and Materials Engineering, Heat treatment of metals and alloys, Crack, Physical Metallurgy, Mechanical Properties of Materials, High Entropy Alloys, Alloy Design, Microstructure and Grain Boundary Engineering, Microdamage, Lifetime, Fracture Toughness, Tensile Strength, and Solidifcation)
(Metallurgy and Materials Engineering, Heat treatment of metals and alloys, Crack, Physical Metallurgy, Mechanical Properties of Materials, High Entropy Alloys, Alloy Design, Microstructure and Grain Boundary Engineering, Microdamage, Lifetime, Fracture Toughness, Tensile Strength, and Solidifcation)
The electrochemical properties of high strength 7xxx aluminium alloys strongly depend on the substitutional occupancy of Zn by Cu and Al in the strengthening η-phase with the two-sublattice structure, and its microstructural and... more
The electrochemical properties of high strength 7xxx aluminium alloys strongly depend on the substitutional occupancy of Zn by Cu and Al in the strengthening η-phase with the two-sublattice structure, and its microstructural and compositional prediction is the key to design of new generation corrosion resistant alloys. In this work, we have developed a chemical-potential-based phase-field model capable of describing multi-component and two-sublattice ordered phases, during commercial multi-stage artificial ageing treatments, by directly incorporating the compound energy CALPHAD formalism. The model developed has been employed to explore the complex compositional pathway for the formation of the η-phase in Al-Zn-Mg-Cu alloys during heat treatments. In particular, the influence of alloy composition, solute diffusivity, and heat treatment parameters on the microstructural and compositional evolution of η-phase precipitates, was systematically investigated from a thermodynamic and kinetic perspective and compared to electron probe microanalysis validation data. The simulated η-phase growth kinetics and the matrix residual solute evolution in the AA7050 alloy indicates that Zn depletion mainly controlled the η-phase growth process during the early stage of ageing, resulting in fast η-phase growth kinetics, enrichment of Zn in the η-phase, and an excess in residual Cu in the matrix. The gradual substitution of Zn by Cu atoms in the η-phase during the later ageing stage was in principle a kinetically controlled process, owing to the slower diffusivity of Cu relative to Zn in the matrix. It was also found that the higher nominal Zn content in alloys like the AA7085 alloy, compared to the AA7050 alloy, could significantly enhance the chemical potential of Zn, but this had a minor influence on Cu, which essentially led to the higher Zn content (and consequently lower Cu) seen in the η-phase. Finally, substantial depletion of Zn and supersaturation of Cu in the matrix of the AA7050 alloy was predicted after 24 h ageing at 120 • C , whereas the second higher-temperature ageing stage at 180 • C markedly enhanced the diffusion of Cu from the supersaturated matrix into the η-phase, while the matrix residual Zn content was only slightly affected.
Research Interests: Computational Materials Science, Modeling, Heat treatment of metals and alloys, Simulation, Aluminium Alloys, and 7 moreMulti-Scale Modelling of Materials, Aluminium Alloy Development, Phase Field Modeling, Computational Thermodynamics, CALPHAD, Modeling of Precipitation, Aluminum Alloy, and Integrated Computational Materials Engineering
DP steel, TWIP steel, middle-Mn steel, weight reduced steel, maraging steels, bainite, ductile martensite, maraging-TRIP steels, TRIP steel, press hardening steels, cutting steels, superplastic steels
Research Interests:
The microstructure and texture development of a medium-carbon steel (0.36% C) during heavy warm deformation (HWD) was studied using scanning electron microscopy and electron back scattering diffraction. The spheroidization of pearlite is... more
The microstructure and texture development of a medium-carbon steel (0.36% C) during heavy warm deformation (HWD) was
studied using scanning electron microscopy and electron back scattering diffraction. The spheroidization of pearlite is accelerated due to the HWD, which leads to the formation of completely spheroidized cementite already after the deformation and coiling at 873 K (600°C). The homogeneity of the cementite distribution depends on the cooling rate and the coiling temperature. The cooling rate of about 10 K/s (ferrite–pearlite prior to HWD) and deformation/coiling at 943–973 K (670–700 °C) lead to a homogeneous cementite distribution with a cementite particle size of less than 1 lm. The ferrite softening can be attributed to continuous recrystallization. Even up to fairly high deformation/coiling temperatures of 983 K (710 C) the texture consists of typical deformation components. During the continuous recrystallization the amount of high angle grain boundaries can increase up to 70% with a ferrite grain size of 1–3 um. An increase of the cooling rate up to 20 K/s (ferrite–pearlite–bainite prior to HWD) deteriorates the
homogeneity of the cementite distribution and the softening of ferrite in the final microstructure.
studied using scanning electron microscopy and electron back scattering diffraction. The spheroidization of pearlite is accelerated due to the HWD, which leads to the formation of completely spheroidized cementite already after the deformation and coiling at 873 K (600°C). The homogeneity of the cementite distribution depends on the cooling rate and the coiling temperature. The cooling rate of about 10 K/s (ferrite–pearlite prior to HWD) and deformation/coiling at 943–973 K (670–700 °C) lead to a homogeneous cementite distribution with a cementite particle size of less than 1 lm. The ferrite softening can be attributed to continuous recrystallization. Even up to fairly high deformation/coiling temperatures of 983 K (710 C) the texture consists of typical deformation components. During the continuous recrystallization the amount of high angle grain boundaries can increase up to 70% with a ferrite grain size of 1–3 um. An increase of the cooling rate up to 20 K/s (ferrite–pearlite–bainite prior to HWD) deteriorates the
homogeneity of the cementite distribution and the softening of ferrite in the final microstructure.
Research Interests: Thermodynamics, Microstructure, Ferrite, High temperature corrosion, TEM, and 10 moreAtom probe tomography, Precipitation, Martensite and its reverse transformation in nanocrystalline bulk Co, Steels, Pearlite, Austenitic Mn Steels, High Chromium White Irons, High Temperature Wear Abrasion Resistant Alloys, High Temperature Wear, and Atom Probe
Developing strong, damage-tolerant, and functional steels shapes the backbone for industrial innovations in manufacturing, energy, transportation, and safety. Examples are Fe-Cr steels for emission-reduced turbines; weight reduced and... more
Developing strong, damage-tolerant, and functional steels shapes the backbone for industrial innovations in manufacturing, energy, transportation, and safety. Examples are Fe-Cr steels for emission-reduced turbines; weight reduced and ultra-high strength Fe-Mn steels for light-weight and safe mobility; magnetic Fe-Si steels for low-loss electrical motors and generators; or stainless steels for power plants. These examples document the necessity of developing improved high strength and yet ductile steels. Most traditional hardening mechanisms, however, such as enabled by solutes, dislocations, or precipitates, albeit leading to high strength, often reduce ductility rendering the material brittle and susceptible for failure. This phenomenon is sometimes referred to as the inverse strength-ductility problem.
The reduction of the grain size offers a pathway for increasing both, strength and toughness of steels. Here we develop this concept further in that we combine this strategy with the manipulation of individual interfaces by grain boundary segregation and local phase transformation. More specific, we enable grain boundaries in steels not only as barriers against dislocation motion but also as regions where segregation and nanoscale phase transformation occur. Such locally transformed regions can act as compliance layers impeding for instance crack penetration among lath martensite lamellae.
The reduction of the grain size offers a pathway for increasing both, strength and toughness of steels. Here we develop this concept further in that we combine this strategy with the manipulation of individual interfaces by grain boundary segregation and local phase transformation. More specific, we enable grain boundaries in steels not only as barriers against dislocation motion but also as regions where segregation and nanoscale phase transformation occur. Such locally transformed regions can act as compliance layers impeding for instance crack penetration among lath martensite lamellae.
Research Interests: Nanostructured materials, High temperature corrosion, Alloy Design, Atom probe tomography, Microstructure and Grain Boundary Engineering, and 6 moreSteel Design, Austenitic Mn Steels, High Chromium White Irons, High Temperature Wear Abrasion Resistant Alloys, High Temperature Wear, and Combinatorial Materials Science
Invited lecture, Royal Society International Seminar April 22nd-23rd 2013 on ‘Superalloys to Order' at the Kavli Royal Society International Centre, Royal Society, Chicheley Hall, England J. Millan, D. Ponge, I. Povstugar, S. Sandlöbes,... more
Invited lecture, Royal Society International Seminar April 22nd-23rd 2013 on ‘Superalloys to Order' at the Kavli Royal Society International Centre, Royal Society, Chicheley Hall, England
J. Millan, D. Ponge, I. Povstugar, S. Sandlöbes, P. Choi, S. Zaefferer, S.M. Hafez Haghighat, G. Eggeler, A. Nematollahi, M. Herbig, R. Kirchheim, G. Inden, J. Neugebauer, D. Raabe: Scale-hoping approaches in desiging complex alloys
J. Millan, D. Ponge, I. Povstugar, S. Sandlöbes, P. Choi, S. Zaefferer, S.M. Hafez Haghighat, G. Eggeler, A. Nematollahi, M. Herbig, R. Kirchheim, G. Inden, J. Neugebauer, D. Raabe: Scale-hoping approaches in desiging complex alloys
Invited lecture, German-Chinese High-level Workshop on “Microstructure-driven Design and Performance of Advanced Metals” held 12-16. April 2013 in the Institute of Metals Research (IMR) of the Chinese Academy of Science (CAS), Shenyang,... more
Invited lecture, German-Chinese High-level Workshop on “Microstructure-driven Design and Performance of Advanced Metals” held 12-16. April 2013 in the Institute of Metals Research (IMR) of the Chinese Academy of Science (CAS), Shenyang, China
D. Raabe, Y. Li, D. Ponge, S. Sandlöbes, P. Choi, T. Hickel, R. Kirchheim, J. Neugebauer
D. Raabe, Y. Li, D. Ponge, S. Sandlöbes, P. Choi, T. Hickel, R. Kirchheim, J. Neugebauer
Research Interests: Thermodynamics, Microstructure, Atom probe field ion microscopy, Modeling and Simulation, Ferrite, and 10 moreAdvanced high strength steels, High temperature corrosion, TEM, Precipitation, Steels, Austenitic Mn Steels, High Chromium White Irons, High Temperature Wear Abrasion Resistant Alloys, High Temperature Wear, and Atom Probe
The microstructure and texture development of a medium-carbon steel (0.36% C) during heavy warm deformation (HWD) was studied using scanning electron microscopy and electron back scattering diffraction. The spheroidization of pearlite is... more
The microstructure and texture development of a medium-carbon steel (0.36% C) during heavy warm deformation (HWD) was studied using scanning electron microscopy and electron back scattering diffraction. The spheroidization of pearlite is accelerated due to the HWD, which leads to the formation of completely spheroidized cementite already after the deformation and coiling at 873 K (600 C). The homogeneity of the cementite distribution depends on the cooling rate and the coiling temperature. The cooling rate of about 10 K/s (ferrite–pearlite prior to HWD) and deformation/coiling at 943–973 K (670–700 C) lead to a homogeneous cementite distribution with a cementite particle size of less than 1 lm. The ferrite softening can be attributed to continuous recrystallization. Even up to fairly high deformation/coiling temperatures of 983 K (710 C) the texture consists of typical deformation components. During the continuous recrystallization the amount of high angle grain boundaries can increase up to 70% with a ferrite grain size of 1–3 lm. An increase of the cooling rate up to 20 K/s (ferrite–pearlite–bainite prior to HWD) deteriorates the homogeneity of the cementite distribution and the softening of ferrite in the final microstructure.
Here we present cellular automaton models in materials science. It gives an introduction to the fundamentals of cellular automata and reviews applications, particularly for those that predict recrystallization phenomena. Cellular automata... more
Here we present cellular automaton models in materials science. It gives an introduction to the fundamentals of cellular automata and reviews applications, particularly for those that predict recrystallization phenomena. Cellular automata for recrystallization are typically discrete in time, physical space, and orientation space and often use quantities such as dislocation density and crystal orientation as state variables. Cellular automata can be defined on a regular or nonregular two- or three-dimensional lattice considering the first, second, and third neighbor shell for the calculation of the local driving forces. The kinetic transformation rules are usually formulated to map a linearized symmetric rate equation for sharp grain boundary segment motion. While deterministic cellular automata directly perform cell switches by sweeping the corresponding set of neighbor cells in accord with the underlying rate equation, probabilistic cellular automata calculate the switching probability of each lattice point and make the actual decision about a switching event by evaluating the local switching probability using a Monte Carlo step. Switches are in a cellular automaton algorithm generally performed as a function of the previous state of a lattice point and the state of the neighboring lattice points. The transformation rules can be scaled in terms of time and space using, for instance, the ratio of the local and the maximum possible grain boundary mobility, the local crystallographic texture, the ratio of the local and the maximum-occurring driving forces, or appropriate scaling measures derived from a real initial specimen. The cell state update in a cellular automaton is made in synchrony for all cells. The review deals, in particular, with the prediction of the kinetics, microstructure, and texture of recrystallization. Couplings between cellular automata and crystal plasticity finite element models are also discussed.
Research Interests: Microstructure, Computational Materials Science, Heat treatment of metals and alloys, EBSD, Texture, and 3 moreRecrystallization, Recrystallization Modeling, and Phase Transformation and Fatigue in nickel titanium (NiTi) Shape Memory Alloys and Development of High Temperature NiTi based Shape Memory Alloys
A Cu-8.2 wt% Ag-4 wt% Nb in situ metal matrix composite was manufactured by inductive melting, casting, swaging, and wire drawing. The ®nal wire ( ln
A0=A 10:5, A: wire cross section) had a strength of 1840 MPa and 46% of the... more
A Cu-8.2 wt% Ag-4 wt% Nb in situ metal matrix composite was manufactured by inductive melting, casting, swaging, and wire drawing. The ®nal wire ( ln
A0=A 10:5, A: wire cross section)
had a strength of 1840 MPa and 46% of the conductivity of pure Cu. The electrical resistivity of the composite wires was experimentally investigated as a function of wire strain and temperature. The microstructure was examined by means of optical and electron microscopy. The observed decrease in conductivity with increasing wire strain is interpreted in terms of inelastic electron scattering at internal phase boundaries. The experimental data are in very good accord with the predictions of an analytical size-effect model which takes into account the development of the filament spacing as a function of wire strain and the mean free path of the conduction electrons as a function of temperature. The experimentally obtained and calculated resistivity data are compared to those of the pure constituents.
had a strength of 1840 MPa and 46% of the conductivity of pure Cu. The electrical resistivity of the composite wires was experimentally investigated as a function of wire strain and temperature. The microstructure was examined by means of optical and electron microscopy. The observed decrease in conductivity with increasing wire strain is interpreted in terms of inelastic electron scattering at internal phase boundaries. The experimental data are in very good accord with the predictions of an analytical size-effect model which takes into account the development of the filament spacing as a function of wire strain and the mean free path of the conduction electrons as a function of temperature. The experimentally obtained and calculated resistivity data are compared to those of the pure constituents.
Research Interests: Nanocomposites, Metal matrix composite, Metallurgy and Materials Engineering, Shear bands, Copper, and 21 moreMetal Matrix Composites, Nanocomposite, Severe Plastic Deformation, Size Effects, Resistivity, Severe Plastic Deformation Methods, Metal Matrix Composite materials, processing and manufacturing, Electrical Resistivity, Wire Drawing, Metal Matrix Composite (MMC) Research in Electronics Materials, Severe Plastic Deformations, Finite Element, Severe Plastic Deformation, Metal Matrix Nanocomposites, Phase Boundary, Copper-niobium, Copper-silver, Nanocomposite Wire, High Strength Conductor, Conduction Electrons, Cu-Nb, and Cu-Ag(Metal Matrix Composites, Nanocomposite, Severe Plastic Deformation, Size Effects, Resistivity, Severe Plastic Deformation Methods, Metal Matrix Composite materials, processing and manufacturing, Electrical Resistivity, Wire Drawing, Metal Matrix Composite (MMC) Research in Electronics Materials, Severe Plastic Deformations, Finite Element, Severe Plastic Deformation, Metal Matrix Nanocomposites, Phase Boundary, Copper-niobium, Copper-silver, Nanocomposite Wire, High Strength Conductor, Conduction Electrons, Cu-Nb, and Cu-Ag)
(Metal Matrix Composites, Nanocomposite, Severe Plastic Deformation, Size Effects, Resistivity, Severe Plastic Deformation Methods, Metal Matrix Composite materials, processing and manufacturing, Electrical Resistivity, Wire Drawing, Metal Matrix Composite (MMC) Research in Electronics Materials, Severe Plastic Deformations, Finite Element, Severe Plastic Deformation, Metal Matrix Nanocomposites, Phase Boundary, Copper-niobium, Copper-silver, Nanocomposite Wire, High Strength Conductor, Conduction Electrons, Cu-Nb, and Cu-Ag)
Pearlitic steel can exhibit tensile strengths higher than 5 GPa after severe plastic deformation, where the deformation promotes a refinement of the lamellar structure and cementite decomposition. However, a convincing correlation between... more
Pearlitic steel can exhibit tensile strengths higher than 5 GPa after severe plastic deformation, where the deformation promotes a refinement of the lamellar structure and cementite decomposition. However, a convincing correlation between deformation and cementite decomposition in pearlite is still absent. In the present work, a local electrode atom probe was used to characterize the microstructural evolution of pearlitic steel, cold-drawn with progressive strains up to 5.4. Transmission electron microscopy was also employed to perform complementary analyses of the microstructure. Both methods yielded consistent results. The overall carbon content in the detected volumes as well as the carbon concentrations in ferrite and cementite were measured by atom probe. In addition, the thickness of the cementite filaments was determined. In ferrite, we found a correlation of carbon concentration with the strain, and in cementite, we found a correlation of carbon concentration with the lamella thickness. Direct evidence for the formation of cell/subgrain boundaries in ferrite and segregation of carbon atoms at these defects was found. Based on these findings, the mechanisms of cementite decomposition are discussed in terms of carbon–dislocation interaction.
Research Interests:
See full lecture here: https://www.youtube.com/watch?v=1kihsaLSxv0 see reference here: https://www.nature.com/articles/s41586-019-1702-5 This is an introductory class about sustainable metals and metallurgy, a field that is also... more
See full lecture here:
https://www.youtube.com/watch?v=1kihsaLSxv0
see reference here:
https://www.nature.com/articles/s41586-019-1702-5
This is an introductory class about sustainable metals and metallurgy, a field that is also referred to as green metallurgy.
Engineering materials and particularly metallic alloys have enabled technological progress over millenia.
Metallic materials have a historic and enduring importance in our society. They have paved the path of human civilization with load-bearing applications that can be used under the harshest environmental conditions, from the Bronze Age onwards. Only metallic materials encompass such diverse features as strength, hardness, workability, damage tolerance, joinability, ductility and toughness, often combined with functional properties such as corrosion resistance, thermal and electric conductivity and magnetism.
The high and accelerating demand for load-bearing (structural) and functional metallic alloys in key sectors such as energy, construction, safety and transportation is resulting in predicted production growth rates of up to 200 per cent until 2050. Yet most of these metallic materials, specifically steel, aluminium, nickel and titanium, require a lot of energy when extracted and manufactured and these processes emit large amounts of greenhouse gases and pollution.
The huge success of metallic products and industries also means that they has an important role in addressing the current environmental crisis.
The availability of metals (most of the elements used in structural alloys are among the most abundant), efficient mass producibility, low price and amenability to large-scale industrial production (from extraction to the metal alloy) and manufacturing (downstream operations after solidification) have become a substantial environmental burden: worldwide production of metals leads to a total energy consumption of about 53 exajoules (10^18 J) (8% of the global energy used) and almost 30% of industrial CO2-equivalent emissions (4.4 gigatons of carbon dioxide equivalent, Gt CO2eq) when counting only steels and aluminium alloys (the largest fraction of metal use by volume)
This lecture gives an introductory overview of methods for improving the direct sustainability of structural metals, in areas including reduced-carbon-dioxide primary production, recycling, scrap-compatible alloy design, contaminant tolerance of alloys and improved alloy longevity, for instance throgh better corrosion resistance. The lecture also discusses the effectiveness and technological readiness of individual measures and also show how novel structural materials enable improved energy efficiency through their reduced mass, higher thermal stability and better mechanical properties than currently available alloys.
https://www.youtube.com/watch?v=1kihsaLSxv0
see reference here:
https://www.nature.com/articles/s41586-019-1702-5
This is an introductory class about sustainable metals and metallurgy, a field that is also referred to as green metallurgy.
Engineering materials and particularly metallic alloys have enabled technological progress over millenia.
Metallic materials have a historic and enduring importance in our society. They have paved the path of human civilization with load-bearing applications that can be used under the harshest environmental conditions, from the Bronze Age onwards. Only metallic materials encompass such diverse features as strength, hardness, workability, damage tolerance, joinability, ductility and toughness, often combined with functional properties such as corrosion resistance, thermal and electric conductivity and magnetism.
The high and accelerating demand for load-bearing (structural) and functional metallic alloys in key sectors such as energy, construction, safety and transportation is resulting in predicted production growth rates of up to 200 per cent until 2050. Yet most of these metallic materials, specifically steel, aluminium, nickel and titanium, require a lot of energy when extracted and manufactured and these processes emit large amounts of greenhouse gases and pollution.
The huge success of metallic products and industries also means that they has an important role in addressing the current environmental crisis.
The availability of metals (most of the elements used in structural alloys are among the most abundant), efficient mass producibility, low price and amenability to large-scale industrial production (from extraction to the metal alloy) and manufacturing (downstream operations after solidification) have become a substantial environmental burden: worldwide production of metals leads to a total energy consumption of about 53 exajoules (10^18 J) (8% of the global energy used) and almost 30% of industrial CO2-equivalent emissions (4.4 gigatons of carbon dioxide equivalent, Gt CO2eq) when counting only steels and aluminium alloys (the largest fraction of metal use by volume)
This lecture gives an introductory overview of methods for improving the direct sustainability of structural metals, in areas including reduced-carbon-dioxide primary production, recycling, scrap-compatible alloy design, contaminant tolerance of alloys and improved alloy longevity, for instance throgh better corrosion resistance. The lecture also discusses the effectiveness and technological readiness of individual measures and also show how novel structural materials enable improved energy efficiency through their reduced mass, higher thermal stability and better mechanical properties than currently available alloys.
Research Interests: Metallurgy, Life Cycle Assessment, Titanium, Environmental Sustainability, Metallurgy and Materials Engineering, and 12 moreSteel Making, Steel, Aluminium Alloys, Hydrogen Energy, Hydrogen Production, Green Manufacturing, Blast Furnace, Greenhouse Gas Emissions, Nickel, Hydrogen Economy, Green Process and Production Methods, and Sustainability
Research Interests:
The recent advance of numerical prediction methods in nearly all domains of materials science and engineering has established a new, exciting, interdisciplinary approach which is often referred to as “computational materials science”. It... more
The recent advance of numerical prediction methods in nearly all domains of materials science and engineering has established a new, exciting, interdisciplinary approach which is often referred to as “computational materials science”. It brings together elements from materials science, physics, computer science, mathematics, chemistry, and mechanical engineering. For instance, simulations in the field of materials physics concentrate on the investigation of lattice and defect dynamics at the atomic scale using molecular dynamics and Monte Carlo methods. Materials-related simulations in the field of mechanical engineering focus on large-scale construction problems, using finite element methods where the microstructure is incorporated by using averaging constitutive laws. In contrast to these examples, the classical domain of materials science can be seen in the investigation of lattice defects and their interactions at the mesoscale. Performing simulations on this particular scale is a great challenge, in that it must bridge enormous space and time scales and provide concepts to describe adequately complex many-body interaction phenomena. For this purpose a variety of new concepts has been developed which enables one to handle the interaction of many individual lattice defects in a more or less discrete manner at dimensions above the atomic scale and below the macroscopic scale. These so-called mesoscale simulation methods include deterministic and probabilistic cellular automata with global and local transformation rules, Ginzburg–Landau-type phase field kinetic methods, dislocation dynamics, polycrystal and non-linear crystal plasticity finite element models, geometrical and component models, topological network or vertex models, and multistate kinetic Potts-type Monte Carlo approaches. However, classical techniques such as molecular dynamics, Metropolis Monte Carlo, and conventional finite element simulations are also used extensively. Although an increasing body of excellent conference proceedings, monographs, and journals are available covering particular aspects of computational materials science, no comprehensive overview of that field exists (see General Reading). This contribution aims to fill that gap. It gives a review of modern approaches to the space- and time-discretized simulation of materials microstructures, together with the respective theoretical backgrounds, that currently prevail in materials science. Particular emphasis is placed on the fundamentals of space- and time-discretized simulations of materials microstructures at the mesoscale.
Research Interests:
The physical mechanisms that lead to the abnormal growth of Goss-oriented grains in grain-oriented electrical steel (GOES) are still not well understood, despite almost a century of research. The present paper reviews the existing... more
The physical mechanisms that lead to the abnormal growth of Goss-oriented grains in grain-oriented electrical steel (GOES) are still not well understood, despite almost a century of research. The present paper reviews the existing hypotheses on the formation of Goss-oriented grains by abnormal grain growth and provides more insights into the underlying mechanism for Goss texture formation by bnormally grown Goss-oriented grains in fully-processed industrial GOES samples are shown to contain a fine network of internal subgrain boundaries with very low angle (0.03°-0.18°) each consisting of regular arrays of dislocations. These subgrain boundaries form a branched ray-like pattern from the Goss grain center towards its perimeter, i.e. they seem to have evolved with the grain during its growth. Structural and compositional analysis of these dislocations by controlled electron channelling contrast imaging (cECCI) and atom probe tomography (APT) show that these dislocations are enriched with solutes such as Sn, Cu, C, and more importantly, with Al, N and Mn, which all build the composition of the inhibitor particles that assist the abnormal growth of Goss-oriented grains. Additionally, molecular statics (MS) calculations are employed to compare the segregation tendencies of Al atoms on dislocations and on 9 boundaries. It is found that Al prefers to segregate to dislocations rather than to the boundaries. The origin and the role of subgrain boundaries are discussed based on the experimental and simulation results. The results indicate that, after the dissolution of inhibitors along the grain boundaries, solutes are absorbed by the subgrain dislocations. As a result, grain boundaries surrounding Goss grains become less decorated by solutes and precipitates and more mobile compared to the boundaries of matrix grains.
Research Interests: Microstructure, Segregation, Magnetic Materials, Heat treatment of metals and alloys, Steel, and 6 moreGrain Boundaries and Interfaces in Crystalline materials, Microstructure and Grain Boundary Engineering, Grain Boundary, Magnetism and Magnetic Materials, Metallic Alloys Materials, and Soft Magnetic Materials
Soft magnetic materials (SMMs) serve in electrical applications and sustainable energy supply, allowing magnetic flux variation in response to changes in applied magnetic field, at low energy loss1. The electrification of transport,... more
Soft magnetic materials (SMMs) serve in electrical applications and sustainable energy supply, allowing magnetic flux variation in response to changes in applied magnetic field, at low energy loss1. The electrification of transport, households and manufacturing leads to an increase in energy consumption due to hysteresis losses2. Therefore, minimizing coercivity, which scales these losses, is crucial3. Yet, meeting this target alone is not enough: SMMs in electrical engines must withstand severe mechanical loads, i.e., the alloys need high strength and ductility4. This is a fundamental design challenge, as most methods that enhance strength introduce stress fields that can pin magnetic domains, thus increasing coercivity and hysteretic losses5. Here, we introduce an approach to overcome this dilemma. We have designed a Fe-Co-Ni-Ta-Al multicomponent alloy with ferromagnetic matrix and paramagnetic coherent nanoparticles (~91 nm size, ~55% volume fraction). They impede dislocation motion, enhancing strength and ductility. Their small size, low coherency and small magnetostatic energy create an interaction volume below the magnetic domain wall width, leading to minimal domain wall pinning, thus maintaining the soft magnetic properties. The alloy has a tensile strength of 1336 MPa at 54% tensile elongation, extremely low coercivity of 78 A/m (<1 Oe), moderate saturation magnetization of 100 Am2/kg, and high electrical resistivity of 103 μΩ·cm.
Research Interests:
There are several facets of aluminum when it comes to sustainability. While it helps to save fuel due to its low density, producing it from ores is very energy-intensive. Recycling it shifts the balance towards higher sustainability,... more
There are several facets of aluminum when it comes to sustainability. While it helps to save
fuel due to its low density, producing it from ores is very energy-intensive. Recycling it shifts
the balance towards higher sustainability, because the energy needed to melt aluminum from
scrap is only about 5% of that consumed in ore reduction. The amount of aluminum available
for recycling is estimated to double by 2050. This offers an opportunity to bring the
metallurgical sector closer to a circular economy. A challenge is that large amounts of scrap
are post-consumer scrap, containing high levels of elemental contamination. This has to be
taken into account in more sustainable alloy design strategies. A “green aluminum” trend has
already triggered a new trading platform for low-carbon aluminum at the London Metal
Exchange (2020). The trend may lead to limits on the use of less-sustainable materials in
future products. The shift from primary synthesis (ore reduction) to secondary synthesis
(scrap melting) requires to gain better understanding of how multiple scrap-related
contaminant elements act on aluminum alloys and how future alloys can be designed upfront
to become scrap-compatible and composition-tolerant. The paper therefore discusses the
influence of scrap-related impurities on the thermodynamics and kinetics of precipitation
reactions and their mechanical and electrochemical effects; impurity effects on precipitationfree
zones around grain boundaries; their effects on casting microstructures; and the
possibilities presented by adjusting processing parameters and the associated mechanical,
functional and chemical properties. The objective is to foster the design and production of
aluminum alloys with the highest possible scrap fractions, using even low-quality scrap and
scrap types which match only a few target alloys when recycled.
fuel due to its low density, producing it from ores is very energy-intensive. Recycling it shifts
the balance towards higher sustainability, because the energy needed to melt aluminum from
scrap is only about 5% of that consumed in ore reduction. The amount of aluminum available
for recycling is estimated to double by 2050. This offers an opportunity to bring the
metallurgical sector closer to a circular economy. A challenge is that large amounts of scrap
are post-consumer scrap, containing high levels of elemental contamination. This has to be
taken into account in more sustainable alloy design strategies. A “green aluminum” trend has
already triggered a new trading platform for low-carbon aluminum at the London Metal
Exchange (2020). The trend may lead to limits on the use of less-sustainable materials in
future products. The shift from primary synthesis (ore reduction) to secondary synthesis
(scrap melting) requires to gain better understanding of how multiple scrap-related
contaminant elements act on aluminum alloys and how future alloys can be designed upfront
to become scrap-compatible and composition-tolerant. The paper therefore discusses the
influence of scrap-related impurities on the thermodynamics and kinetics of precipitation
reactions and their mechanical and electrochemical effects; impurity effects on precipitationfree
zones around grain boundaries; their effects on casting microstructures; and the
possibilities presented by adjusting processing parameters and the associated mechanical,
functional and chemical properties. The objective is to foster the design and production of
aluminum alloys with the highest possible scrap fractions, using even low-quality scrap and
scrap types which match only a few target alloys when recycled.