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Closed Projects

This project was a joint collaboration between Tata Steel and the SN department with the aim of performing quantitative characterisation of multi-phase precipitates in grain oriented electrical steel (GOES) using high-resolution chemical composition mapping by means of Energy-Filtering Transmission Electron Microscopy (EF-TEM). [more]
Nb-based intermetallic alloys consisting of Nb solid solution and high-melting, strengthening intermetallic phases are of considerable interest for structural applications at very high temperatures. [more]
Current engineering materials are designed to exhibit superior mechanical properties by carefully balancing their chemical composition and microstructure. However, once the material is produced, the material properties and behavior tend to remain same under the certain boundary conditions. [more]
TiAl-based alloys currently mature into application. Sufficient strength at high temperatures and ductility at ambient temperatures are crucial issues for these novel light-weight materials. By generation of two-phase lamellar TiAl + Ti3Al microstructures, these issues can be successfully solved. Because oxidation resistance at high temperatures is still a problem which could be improved by increasing the Al content, Al-rich TiAl alloys have recently come into focus. [more]
The goal of this project is to study the deformation mechanism, mechanical properties of silicon (Si) single crystal under nanotribological loading conditions by using ex situ scanning electron microscopy (SEM) and in situ transmission electron microscopy (TEM). The quantitative correlation between the mechanical properties linked with real time observations of deformation processes will provide a fundamental understanding of the tribological behavior of Si at the nanoscale. [more]
Deviations from the ideal, stoichiometric composition of tcp (tetrahedrally close-packed) intermetallic phases as, e.g., Laves phases can be partially compensated by point defects like antisite atoms or vacancies, but also planar defects may offer an opportunity to accommodate excess atoms. [more]
The Ni- and Co-based γ/γ’ superalloys are famous for their excellent high-temperature mechanical properties that result from their fine-scaled coherent microstructure of L12-ordered precipitates (γ’ phase) in an fcc solid solution matrix (γ phase). The only binary Co-based system showing this special type of microstructure is the Co-Ti system, where the Co solid solution is the γ phase and TiCo3 the L12-ordered γ’ phase. [more]
The elasto-plastic fracture mechanics is well established at the micron scale. However, can test protocols be easily downscaled to the micrometer length scale? [more]
A novel design with independent tip and sample heating is developed to characterize materials at high temperatures. This design is realized by modifying a displacement controlled room temperature micro straining rig with addition of two miniature hot stages. [more]
The objectives of this project is to understand the strengthening mechanisms of high entropy alloys (HEAs) from a dislocation plasticity point of view. The effects of microstructure and local composition, down to the atomic scale, on the plastic deformation are also investigated to establish a fundamental structure-property relationship of HEAs. [more]
The thorough, mechanism-based, quantitative understanding of dislocation-grain boundary interactions is a central aim of the Nano- and Micromechanics group of the MPIE [1-8]. For this purpose, we isolate a single defined grain boundary in micron-sized sample. Subsequently, we measure and compare the uniaxial compression properties with respect to single crystalline samples, using in situ micromechanical techniques. Two specific boundaries are targeted in this project:
While several methods are well-suited for studying dislocation transmission through grain boundaries, a quantitative approach understanding dislocation source activation in grain boundaries is currently lacking. [more]
This project focused on the interface between dielectric materials and different metals. [more]
The local accumulation of fatigue damage is not understood for micron sized materials possessing grain and phase boundaries. This is primarily due to the lack of a characterization technique measuring the decisive material parameters (e.g. local strains, dislocation densities, grain boundary character, etc.) non-destructively with high spatial resolution (<1μm). [more]
Focus: Microcantilever fracture tests were carried out on various metallic glass thin films systems to evaluate their fracture strength and fracture toughness as a function of Poisson’s ratio. [more]
Nano- and Micromechanical experiments are nowadays widely explored to investigate site specific mechanical properties of materials and material systems which were not previously accessible in bulk dimensions [1]. Currently, the testing protocols for materials at non-ambient conditions, like high temperature or chemical non-inert atmospheres, are developed worldwide for micro/nanoscale testing (e.g. [2-4]). [more]
The mostly unknown influence of Ag as solute segregate at copper grain boundaries on mechanical properties is studied by aberration-corrected STEM from an atomistic structural point of view and by in-situ TEM nanocompression experiments to visualize dislocation-grain boundary interactions. [more]
The dislocation – grain boundary interactions are shown to depend strongly on the type of grain boundaries, for example in micropillar compression tests on bicrystalline copper [1]. The coherent Σ3/{111} twin is shown to be a weak obstacle for dislocation motion where perfect slip transfer can take place across the grain boundary [2]. However, a large number of CTBs in nanotwinned metals lead to increase in yield strength [3]. Within this project we aim for extending the work on micropillar compression of bicrystals with a single CTB to those with multiple CTBs to investigate the critical role of microstructure constraints on slip transfer. [more]
Copper structures in microelectronic devices have to fulfill two important requirements, a high electrical and thermal conductivity. However, the lifetime is determined by the static and dynamic mechanical properties of the Cu structures. [more]
The project in the scope of research activities of the Advanced Transmission Electron Microscopy group has two main objectives: (i) epitaxial thin film deposition and (ii) in-situ TEM tensile experiments. [more]
Understanding the mechanical behavior and microstructure correlation of copper-chromium films is of paramount importance both from scientific and technological perspectives. [more]
Here, we study strain und temperature induced phase transformation pathways in high entropy alloys (HEA) by aberration-corrected and in situ scanning transmission electron microscopy (S/TEM). The bidirectional phase transformation (face-centered cubic (FCC) → hexagonal close packed (HCP) → FCC) in a transformation-induced plasticity (TRIP)-assisted high-entropy alloy (HEA) is explored by a combination of atomic resolution imaging and in situ tensile straining. In a similar HEA, the temperature induced transformation from HCP to nanotwinned FCC and associated formation of nanocarbides at the nanotwin boundaries are investigated at atomic resolution by in situ heating. We aim to reveal the atomic scale origins of phase transformations to guide the design of advanced HEAs with a unique combination of strength, ductility and thermal stability. [more]
Fusion is one of the most promising safe, emissionless and limitless sources of energy. The extreme conditions in a fusion reactor, require the development of novel materials to withstand high temperature ion irradiation and at the same time provide sufficient mechanical stability. [more]
Peritectoid transformations are a comparatively rare type of invariant reaction where in the solid state of a material, a phase A decomposes on heating into a mixture of two other phases B and C [more]
The fracture toughness of AuXSnY intermetallic compounds is measured as it is crucial for the reliability of electronic chips in industrial applications. [more]
The mechanical response of miniaturized material systems strongly depends on the sample size. Macroscopically well documented material properties like the yield stress or the hardening rate are changing when the smallest sample dimension reaches the micrometer range. [more]
Nanotribology mechanisms, i.e. friction and wear, gain greater importance as the size of technological devices shrinks to the micro- and nanoscale. This project focuses on tribological experiments at the micro- and nanoscale of iron alloy microstructures. [more]
The research focused on the mechanical behaviour of nanostructured materials and the deformation mechanisms underlying the outstanding mechanical properties with respect to their microstructure. [more]
A structural hierarchy due to chemical ordering, dimensionality and spatial arrangement of the constituent phases was obtained in a precipitation strengthened ferritic alloy. Nearest-neighbor ordered B2-NiAl precipitates were coherently embedded in the disordered bcc-Fe matrix. Throughout the solid-state aging heat treatment a coherent substructure of the next-nearest-neighbor ordered L21-Ni2TiAl phase formed only within the primary B2-NiAl precipitates. [more]
The objective of this large-scale collaborative research project is the development of intermetallic materials for application in large diesel ship engines. [more]
The segregation of impurities to grain boundaries (GBs) has a significant influence on the cohesive properties, atomic arrangements and properties of such interfaces. The segregation strongly depends on the structural units of the GB as well as on the impurity atom itself. Aberration–corrected (S)TEM techniques in combination with atomistic simulations are applied to unravel the connection of grain boundary structure and chemistry at atomic resolution. [more]
Focus: The research focused on testing the reliability of various novel fracture toughness test geometries at the small length scales using in-situ fracture tests in the SEM. [more]
Ferritic superalloys are an attractive alternative to Cr-rich martensitic steels or Ni-based superalloys for high-temperature applications in thermal power plants due to their excellent mechanical properties, oxidation resistance and low density. Strengthening of the Fe-matrix by coherent B2-NiAl precipitates leads to an increase in creep resistance up to temperatures of 700 ºC and stresses of 100 MPa. [more]
A novel design with independent tip and sample heating is developed to characterize materials at high temperatures. This design is realized by modifying a displacement controlled room temperature micro straining rig with addition of two miniature hot stages. [more]
Focus: Role of the interface in the deformation and fracture behavior of nanolaminate metallic systems have been studied in-situ in the SEM. [more]
Wear and abrasion occur during sliding friction of metallic body and counter-body. Surface roughness is purposefully introduced into the metal to reduce wear and abrasion and to increase the lubricant flow. [more]
The local accumulation of fatigue damage is not understood for materials possessing grain and phase boundaries. This is primarily due to the lack of a characterization technique measuring the decisive material parameters (e.g. local strains, dislocation densities, grain boundary character, etc.) nondestructively with high spatial resolution (<1μm). [more]
Carbon(C)-containing martensitic steels are ideal candidates for high-strength applications, e.g. in automotive and aerospace applications, due to their excellent mechanical properties and low cost. Carbon can even redistribute at room temperature leading to the formation of nanoscale carbides that can significantly influence the mechanical properties. [more]
The focus lies on the analysis of the mechanical behavior and their underlying deformation mechanisms in new ductile solid solution Mg alloys by performing micromechanical experiments with electron microscopy analyses. [more]
Driven by increasing reliability requirements in automotive microelectronics and severe restrictions on lead-containing solders, recent research is focused on the examination of failure mechanisms in lead-free solder joints. [more]
The mechanical properties of bulk CrFeCoNi compositionally complex alloys (CCA) or high entropy alloys (HEA) are widely studied in literature [1]. Notably, these alloys show mechanical properties similar to the well studied quinary CrMnFeCoNi [2] . Nevertheless, little is known about the deformation mechanisms and the thermal behavior of these alloys in thin film form. The current project aims to investigate these properties within the framework of a joint  DFG/ANR project involving the collaboration of Prof. Alfred Ludwig (Ruhr-Universität Bochum, Germany), Dr. Dominique Chatain (CINaM, Marseille, France) and Dr. Natalie Bozzolo (CEMEF, Sophia Antipolis, France). [more]
The production of reliable flexible electronic devices are believed to be a future key-technology. The material systems thereby suffer from various loading conditions (e.g. temperature variation, monotone and cyclic strains,…). The pronounced differences in mechanical behavior between metal and polymer makes film/substrate systems prone to failure. [more]
Experimental studies of the interfacial adhesion and interfacial fracture strength (energy release rate) are crucial to pave the way for mechanically and thermo-mechanically robust and reliable electronic devices. Our research mission is to examine the adhesion and fracture strength of interfaces between dissimilar materials. [more]
The development of nanostructured metals and alloys with superior mechanical properties is of paramount importance for both, a fundamental scientific understanding of the structure property relationship of materials and future technological applications in modern micro- and nanotechnologies. [more]
The TRR 188 aims for a thorough understanding and quantitative control of damage in advanced materials. As a subpart of TRR188, this project aims at microscopically studying the initiation of damage on dual phase steel DP800. [more]
By combining advanced characterization and mechanical testing of microsized, single-phase intermetallic samples through in situ micromechanical experiments inside an SEM or TEM, the mechanical response can be measured while simultaneously observing the microstructural changes. From these experiments, it is expected to get a much deeper insight in the complicated deformation mechanism of intermetallic phases, which is very much different from that in pure metals. [more]
Today there is an increasing economic and ecological need for the development of new structural materials for applications at high temperatures. Possible candidates for such materials are metallic alloys containing high-melting intermetallic phases which retain high strengths at high temperatures. [more]
Even though most structural materials are polycrystalline, the dislocation grain boundary interaction is not thoroughly understood. [more]
The next generation of Advanced Ultra Supercritical Coal-fired power plants (A-USC) aim at operating temperatures of approx. 700 °C and pressures of approx. 320 bars. Under these conditions, conventional ferritic steels are no longer usable. [more]
Fe-Al alloys in the composition range up to 50 at.% Al with disordered A2 or ordered B2 or D03 crystal structure are intensively discussed in the literature as potential materials for structural applications at elevated and high temperatures especially due to their excellent corrosion resistance and low density compared to conventional steels. [more]
Substitution of so-called strategic elements such as Co, Nb, Ta or W becomes increasingly important to avoid political and economic dependencies. A possible replacement for alloys containing large amounts of strategic elements such as Cr-Ni steels or Ni- and Co-based alloys are Fe-Al-based alloys. Parts constructed out of Fe-Al-based alloys can be operated under high loads at high temperatures in aggressive environments. [more]
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