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2.11.2016
Spoštovani raziskovalci,

Vabljeni na predavanja prof. Stefana Zaeffererja iz Max-Planck Instituta z naslovom:

Electron channelling contrast imaging (ECCI): an amazing tool for observations of crystal lattice defects in bulk samples

Predavanje bo v petek, 4. 11. 2016, ob 10:00 v sejni sobi na IMT (Inštitut za kovinske materiale in tehnologije, Lepi pot 11, Lj.).

Vljudno vabljeni.

Electron channelling contrast imaging (ECCI): an amazing tool for observations of crystal lattice defects in bulk samples

 

Stefan Zaefferer

 

Max-Planck-Institut für Eisenforschung, Max-Planck-Str. 1, 40237 Düsseldorf, Germany

*E-mail: s.zaefferer@mpie.de

 

Electron channelling is a contrast mechanism in scanning electron microscopy (SEM) which allows, using backscattered electrons, direct observation of crystal lattice defects like dislocations, stacking faults, strain fields and others in a volume close to the surface of a bulk sample. Although the technique is long-time known it is only with the advent of suitable microscopes that it can be fully exploited. In particular it is important that the instrument, like a scanning transmission electron microscope (STEM), delivers a beam with very small beam convergence, high brightness and small spot size. Furthermore, the backscatter detector must be large and quick.

Using ECCI it is possible to observe lattice defects in a number of different materials, including all kinds of metals, ceramics and even some minerals. Since the samples are observed in bulk form and not as thin foils, the defects are potentially seen in a more natural arrangement because no stress release occurs during sample preparation. Furthermore, the bulk nature of the samples allows performing straining or heating experiments more easily as with TEM samples.

We will present a short overview on the theory of ECCI [1], followed by some examples indicating the practice of the technique [1]. Finally we will show some advanced applications like Burgers vector determination in conjunction with hydrogen embrittlement of superalloys and 3D ECCI on creep dislocation structures in a single crystal Ni-base superalloy [2].

 

[1] S. Zaefferer, N.-N. Elhami, (2014) Theory and application of electron channelling contrast

imaging under controlled diffraction conditions, Acta Materialia 75, 20–50.

[2] F. Ram, Z. Li, S. Zaefferer, M. Hafez Haghighat, Z. Zhu, D. Raabe, R. C. Reed.(2016), On

the origin of creep dislocations in a Ni-base, single-crystal superalloy: an ECCI, EBSD, and

Dislocation Dynamics-based study, Acta Materialia 109, 151-161