Scientific Events

Room: Large Conference Room No. 203 Location: Max-Planck-Institut für Eisenforschung GmbH

New in-situ and operando techniques for correlative microscopy and chemical imaging : Case studies in mapping hydrogen and other low-Z elements in energy materials

Development of innovative characterization tools is of paramount importance to advance the frontiers of science and technology in nearly all areas of research. In order to overcome the limitations of individual techniques, correlative microscopy has been recognized as a powerful approach to obtain complementary information about the investigated materials. High-resolution imaging techniques such as Transmission Electron Microscopy (TEM) or Helium Ion Microscopy (HIM) offer excellent spatial resolution. However, the analytical techniques associated with TEM such as Energy Dispersive X-ray spectroscopy (EDX) or Electron Energy-Loss Spectroscopy (EELS) are inadequate for the analysis of (i) isotopes, (ii) trace concentrations (< 0.1 at. % or < 1000 ppm) and (iii) light elements (H, Li, B). Secondary Ion Mass Spectrometry (SIMS), on the other hand, has several advantages such as the possibility to analyse elements and isotopes of all elements of the periodic table while also providing high-sensitivity to detect even trace concentrations. However, the main drawbacks of SIMS are (i) difficulty in quantification and (ii) lateral resolution of SIMS imaging is fundamentally limited by ion-solid interaction volume to ~10 nm. Owing to the complementary strengths of SIMS imaging, we developed new in-situ and operando instrumentations for correlative microscopy combining electron microscopy and SIMS imaging. In this presentation, we will discuss the instrumentation development aspects of correlative microscopy techniques based on SIMS imaging. With a range of examples from energy materials, we will show the powerful correlative microscopy possibilities that emerge due to these new in-situ and operando methods and compare with ex-situ correlation. Our recent work in the application of these methods in hydrogen containing materials and Li ion batteries will be reviewed. [more]

Mesoscale simulation of grain boundaries

The mechanical behavior of most metals in engineering applications is dominated by the grain size. Physics-based models of the interaction between dislocations and the grain boundary are important to correctly predict the plastic deformation behavior of polycrystalline materials. Dislocation-grain boundary interaction is complex and a challenge to model. In this talk, I will present a short history, opportunities, and challenges for modeling grain boundaries at the mesoscale using discrete dislocation dynamics. This includes an effective model and a novel model for physical transmission of dislocations through grain boundaries with a residual grain boundary dislocation. In addition, I will provide an outlook how these models can and should be calibrated using micromechanical experiments on bicrystals. [more]

Structure and spectroscopy at the atomic scale: advanced electron microscopy for improved design of functional materials

Many of the functional materials we hope to leverage for next-generation technological applications — such as computing, energy harvesting and storage, or communication devices — draw their unique and sometimes exotic properties from a suite of interactions between the atoms, spins, and charges in a crystalline lattice. With direct, real-space access to these order parameters down to the atomic scale, the scanning transmission electron microscope (STEM) is a powerful tool to probe the fundamental framework of such compounds and their properties. As an example of this, I will show how advanced STEM techniques can elucidate key questions about the landscape of superconductivity in recently discovered nickelates. But many of these functional systems are most useful (and therefore interesting) away from the ambient conditions of most typical high-resolution STEM experiments, for instance at cryogenic or elevated temperatures or under an external bias. It is therefore imperative to expand the environmental compatibility of these methods through the parallel development of both hardware and data processing tools, key examples of which will be highlighted here. [more]

Atomistic Dynamics of Deformation, Fracture and GB Migration in Oxides

In order to clarify the deformation and fracture mechanism in oxides such as Al2O3 and STO, TEM in situ nanoindentation experiments were conducted for their single crystals and bicrystals. We successfully observed the dynamic behavior of twin formation, twin-GB interaction, pile-up dislocation, jog and kink formation and jog drag dynamics and so on. The mechanism of each dynamic behavior will be discussed in detail in this presentation. GB migration plays an important role in considering the high temperature mechanical properties. Recently, we have found that GB migration behavior in Al2O3 can be precisely controlled by the aid of the high-energy electron beam irradiation. This technique was applied to directly visualize the atomistic GB migration. It was revealed that the GB migration is processed by a cooperative shuffling of atoms in GB ledges along specific routes. References [1] S. Kondo, T. Mitsuma, N. Shibata, Y. Ikuhara, Sci. Adv., 2[11], e1501926(2016). [2] S. Kondo, A. Ishihara, E. Tochigi, N. Shibata, and Y. Ikuhara, Nat. Commun., 10, 2112 (2019). [3] J.Wei, B.Feng, R.Ishikawa, T.Yokoi, K.Matsunaga, N.Shibata and Y.Ikuhara, Nat. Mater.,20 (7), 951 [4] J.Wei, B.Feng, E.Tochigi, N.Shibata and Y.Ikuhara, Nat. Commun., 13(1), 1455, (2022) [more]

Local Phase Transformations: A New Creep Strengthening Mechanism in Ni-Base Superalloys

Polycrystalline Ni-based superalloys are vital materials for disks in the hot section of aerospace and land-based turbine engines due to their exceptional microstructural stability and strength at high temperatures. In order to increase operating temperatures and hold times in these engines, hence increasing engine efficiency and reduction of carbon emissions, creep properties of these alloys becomes increasingly important. Microtwinning and stacking fault shearing through the strengthening g’ precipitates are important operative mechanisms in the critical 600-800°C temperature range. Atomic-scale chemical and structural analyses indicate that local phase transformations (LPT) occur commonly during creep of superalloys. Furthermore, the important deformation modes can be modulated by LPT formation, enabling a new path for improving high temperature properties. [more]

High-resolution micro-plasticity in advanced high-strength steels

The persistent demand for green, strong and ductile advanced high strength steels, with a reduced climate footprint, calls for novel and improved multi-phase microstructures. The development of these new steels requires an in-depth understanding of the governing plasticity mechanisms at the micron scale. In order to address this challenge, novel numerical-experimental methods are called for that account for the discreteness, statistics and the intrinsic role of interfaces. This lecture sheds light on recent and innovative developments unravelling metal plasticity at the micron scale. Multi-phase through-thickness samples allow for a full characterization of the underlying microstructure. Using computational crystallographic insights, a slip system based local identification method has been developed, which provides full-field crystallographic slip system activity maps. The resulting deformation maps are directly used to assess the model predictions. Heterogeneous spatial variations are introduced by sampling the slip system properties of individual atomic slip planes from a probability density function. This allows to recover naturally localized slip patterns with a high resolution. It is demonstrated that this discrete slip plane model adequately replicates the diversity of active slip systems in the corresponding experiment, which cannot be achieved with standard crystal plasticity models. Recent experimental observations on dual-phase steels demonstrate substructure boundary sliding parallel to the habit plane in lath martensite, for which a habit-plane slip enriched laminate model is developed. This model adequately captures the role of the substructure boundary sliding on the deformation of the martensite aggregate. [more]

Effect of droplets on inhibitor performance for steel and galvanized steel

Effect of droplets on inhibitor performance for steel and galvanized steel
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