Microstructure and Properties

The interplay of microstructure and properties is at the core of materials science and engineering and is key to design optimized – often multifunctional - materials. Fracture toughness, strength, ductility, thermal conductivity, thermal stability, corrosion resistance, electrical conductivity, magnetic coercivity, and magnetic hysteresis are prominent examples of material properties, which we tailor by the extrinsic and intrinsic “architecture” of materials. In contrast to ideal single crystals, advanced materials typically contain a complex microstructure. Examples of microstructure elements are stable or metastable phases (their alignment can be manipulated by synthesis and subsequent thermo-mechanical treatments), texture, stacking faults, interfaces (with and without enrichment of alloying additions), dislocations, and point defects; in addition, these “imperfections” contain themselves defects of lower dimensionality and can undergo phase transformations. Our research deals with resolving the interplay of microstructure components and material properties and to establish quantitative relationships based on length-scale bridging experiments and simulations: - Tuning stacking fault energy and/or electronic structure of materials to enhance strength and also toughness (steels, HEA/CCA alloys, metallic glasses) - Phase transformations of grain boundaries and dislocations and their impact on transport properties (pure metals, alloys, intermetallic materials, phase diagrams and defect phase diagrams) - Microstructure design for functional materials (thermoelectrics, photovoltaics, magnetic materials, …) - Traps for hydrogen to prevent embrittlement and enable materials for hydrogen economy (steels, alloys, barrier coatings, hydrides) - Experimental and computational tools to resolve microstructure details and properties with high spatial resolution
2D MXenes guided by 3D Atomic-Resolution Tomography

In order to develop more efficient catalysts for energy conversion, the relationship between the surface composition of MXene-based electrode materials and its behavior has to be understood in operando. Our group will demonstrate how APT combined with scanning photoemission electron microscopy can advance the understanding of complex relationships between surface structure, surface oxidation state, surface composition and sub-surface regions, and performance of 2D materials.
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Advanced Microstructural Characterization of in situ Alloyed Nickel-Based Alloys by Welding

Nickel-based alloys are a particularly interesting class of materials due to their specific properties such as high-temperature strength, low-temperature ductility and toughness, oxidation resistance, hot-corrosion resistance, and weldability, becoming potential candidates for high-performance components that require corrosion resistance and good mechanical properties. This unparalleled combination of properties is achieved by adding alloying elements and changes in microstructure. This research project blended Ni-based metal welds produced by in situ alloying using the tandem GMAW process in a previous research project developed by the Welding Research and Technology Laboratory team at the Federal University of Ceará, in Brazil.
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Tuning soft magnetic properties of nanostructured Fe-Co-Ti-X (X = Si, Ge, Sn) compositionally complex alloys through microstructure engineering

The aim of this project is to develop novel nanostructured Fe-Co-Ti-X (X = Si, Ge, Sn) compositionally complex alloys (CCAs) with adjustable magnetic properties by tailoring microstructure and phase constituents through compositional and process tuning. The key aspect of this work is to build a fundamental understanding of the correlation between microstructure and magnetic properties by length scale bridging characterization and property determination. The ultimate goal is to establish guidelines for designing alloys with high magnetization saturation (Ms) and low coercivity (Hc), to optimize the magnetic properties of CCAs for high frequency magnetic field applications. more

Dynamic mechanical properties of functional ceramic oxides

Within this project, we will investigate the micromechanical properties of STO materials with low and higher content of dislocations at a wide range of strain rates (0.001/s-1000/s). Oxide ceramics have increasing importance as superconductors and their dislocation-based electrical functionalities that will affect these electrical properties. Hence it is fundamental to understand the deformation limits to introduce dislocations for both the fabrication process and in-use performance.
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Strain rate, size and defect density interdependence on the deformation of 3D printed microparticles

Statistical significance in materials science is a challenge that has been trying to overcome by miniaturization. However, this process is still limited to 4-5 tests per parameter variance, i.e. Size, orientation, grain size, composition, etc. as the process of fabricating pillars and testing has to be done one by one. With this project, we aim to fabricate arrays of well-defined and located particles that can be tested in an automated manner. With a statistically significant amount of samples tested per parameter variance, we expect to apply more complex statistical models and implement machine learning techniques to analyze this complex problem. more

Local structure-property relationships in laser-processed materials

In this project, links are being established between local chemical variation and the mechanical response of laser-processed metallic alloys and advanced materials.

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Correlative orientation (TEM) and compositional mapping (APT) in 3-dimensions with high spatial and chemical resolution

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

Hydrogen-associated decohesion and localized plasticity in a high-Mn two-phase lightweight steel

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

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The dual role of martensitic transformation in fatigue crack growth

About 90% of all mechanical service failures are caused by fatigue. Avoiding fatigue failure requires addressing the wide knowledge gap regarding the micromechanical processes governing damage under cyclic loading, which may be fundamentally different from that under static loading. This is particularly true for deformation-induced martensitic transformation (DIMT), one of the most common strengthening mechanisms for alloys. Here, we identify two antagonistic mechanisms mediated by martensitic transformation during the fatigue process through in situ observations and demonstrate the dual role of DIMT in fatigue crack growth and its strong crack-size dependence. Our findings open up avenues for designing fatigue-resistant alloys through optimal use of DIMT. They also enable the development of physically based lifetime prediction models with higher fidelity.
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Laser powder bed fusion based CuCrZr alloy lattices: fabrication and characterization

Within this project, we will use an infra-red laser beam source based selective powder melting to fabricate copper alloy (CuCrZr) architectures. The focus will be on identifying the process parameter-microstructure-mechanical property relationships in 3-dimensional CuCrZr alloy lattice architectures, under both quasi-static and dynamic loading conditions.
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Nano-/microscale deformation of functional oxides

Oxides find broad applications as catalysts or in electronic components, however are generally brittle materials where dislocations are difficult to activate in the covalent rigid lattice. Here, the link between plasticity and fracture is critical for wide-scale application of functional oxide materials. more

CALPHAD-informed phase-field model for two-sublattice phases: η-phase precipitation in Al-Zn-Mg-Cu alloys

In this project we developed a phase-field model capable of describing multi-component and multi-sublattice ordered phases, by directly incorporating the compound energy CALPHAD formalism based on chemical potentials. We investigated the complex compositional pathway for the formation of the η-phase in Al-Zn-Mg-Cu alloys during commercial multi-stage artificial ageing treatments.
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Ultrastrong and Ductile Soft Magnetic High-Entropy Alloys via Coherent Ordered Nanoprecipitates

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

In-situ investigation of H interaction with stacking faults (SFs) at the stress concentrated crack tip

The main aspect of this project is to understand how hydrogen interacts with dislocations/ stacking faults at the stress concentrated crack tip. A three-point bending test has been employed for this work. more

Modulus

Laser Powder Bed Fusion (LPBF) is the most commonly used Additive Manufacturing processes. One of its biggest advantages it offers is to exploit its inherent specific process characteristics, namely the decoupling the solidification rate from the parts´volume, for novel materials with superior physical and mechanical properties. One prominet example are so called High Modulus Steels, where the combination of strong, ductile and tough metallic matrices with stiff ceramic particles allows the specific modulus (E/ρ) to be increased compared to conventional materials such as aluminum or steel, thereby reducing weight. The aim of this project is to elucidate the synthesis/microstructure/property causalities of high modulus steel fabricated with the LPBF process. more

Atom probe tomography to advance understanding of magnetic materials

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

Modelling of grain boundary phases in fcc metals and their properties

Grain boundaries (GBs) affect many macroscopic properties of materials. In the case of metals grain growth, Hall–Petch hardening, diffusion, and electrical conductivity, for example, are influenced or caused by GBs. The goal of this project is to investigate the different GB phases (also called complexions) that can occur in tilt boundaries of fcc metals. We aim to investigate possible atomic structures and their thermodynamic description and connect them to mechanical properties.
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Influence of grain boundary segregation on microscale strengthening of Cu bicrystals

This project studies the influence of grain boundary chemistry on mechanical behaviour using state-of-the-art micromechanical testing systems. For this purpose, we use Cu-Ag as a model system and compare the mechanical response/deformation behaviour of pure Cu bicrystals to that of Ag segregated Cu bicrystals. more

Influence of Chemical and Structural Complexity on Dislocation Processes

Project A02 of the SFB1394 studies dislocations in crystallographic complex phases and investigates the effect of segregation on the structure and properties of defects in the Mg-Al-Ca System. more

Fundamental Dislocation Processes in Superalloys

Project C3 of the SFB/TR103 investigates high-temperature dislocation-dislocation and dislocation-precipitate interactions in the gamma/gamma-prime microstructure of Ni-base superalloys. more

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