Science

Unraveling the secrets of interfaces and grain boundaries

Date: 

Monday, 17 September, 2018 -
10:00 to 10:45

Where: 

Tyree Energy Technology Building, K-H6-LG07

Hosts: 

School of Materials Science and Engineering

Type of event: 

Seminar

Correlating atom probe tomography with aberration-corrected scanning transmission electron microscopy is a powerful tool for interface characterization at ultimate resolution. Quantitative analysis of e.g. strain state and coherency of an interface can be directly obtained from atom probe needles using aberration-corrected STEM prior to the field evaporation. Such measurements were performed at austenitic steel samples where nanometer-sized kappa-carbide precipitates were present [1]. The interface between the carbides and the matrix was found to be fully coherent. To achieve this, the matrix channels were tetragonal distorted, an unexpected results which can be explained with the help of density functional theory calculations and the chemical composition analyzed by atom probe tomography (APT). The investigations revealed that the interface is atomically sharp with chemical fluctuations occurring within less than 1 nm [1]. Surprising results were also obtained for facetted Si grain boundaries where correlative APT and aberration-corrected STEM measurements revealed a topological segregation behavior of impurities [2]. Again, the strain state at the grain boundary played an important role and determined where segregation takes places. Line segregation occurred only at an asymmetric facet junction core with a specific strain state [2].

[1] C. H. Liebscher, M. Yao, P. Dey, M. Lipińska-Chwalek, B. Berkels, B. Gault, T. Hickel, M. Herbig, J. Mayer, J. Neugebauer, D. Raabe, G. Dehm, and C. Scheu, Physical Review Materials 2, (023804) (2018)

[2] C. H. Liebscher, A. Stoffers, M. Alam, L. Lymperakis, O. Cojocaru-Miredin, B. Gault, J. Neugebauer, G. Dehm, C. Scheu, and D. Raabe, Physical Review Letters 121 (015702), (2018)

 

Biography: 

Christina Scheu holds a joint position as a full professor at the RWTH Aachen University, and as an independent research group leader at the Max-Planck-Institut für Eisenforschung GmbH (MPIE) in Düsseldorf Germany. From 2008 to 2014 she was a full professor at the Ludwig-Maximilians-University (Munich, Germany). Christina received a diploma degree in physics and did her doctorate at the Max Planck Institut für Metallforschung in Stuttgart (Germany) in the field of material science. From 1996 to 1998 she was a Minerva Fellow at the Technion - Israel Institute of Technology – in Haifa, Israel

Christina’s expertise is the analysis of functional and structural materials with ex-situ and in-situ scanning transmission electron microscopy and electron energy loss spectroscopy with a focus on interface phenomena and nanostructures. The studies are complemented by 3D atom probe tomography to get further inside in the elemental distribution and the presences of impurities.