Strain mapping by scanning low energy electron microscopy

abstract

English

Various techniques exist which are capable of studying the material microstructure, the scanning electron microscopy (SEM), (scanning) transmission microscopy ((S)TEM) and focused ion beam (FIB) microscopy being perhaps the most known. A specific way to visualizing the microstructure of polycrystalline materials at high spatial resolution, to achieve a high contrast between grains in polycrystals and very fast data acquisition, is to use the cathode lens (CL) mode in SEM. The CL mode in the SEM enables us to observe specimens at arbitrary landing energies of the primary electrons and to detect slow but not only slow, high angle scattered electrons that carry mainly crystallographic contrast based on the electron channelling, mostly in the Mott scattering angular range. The material under investigation was a commercial purity copper prepared by equal channel angular pressing (ECAP) method using 8 passes, route Bc, namely in the as-pressed state and after annealing (in argon atmosphere, 180 C, 6 minutes). Ultra-fine grained materials (UFG) prepared by severe plastic deformation are characterized by a very high density of (sub)grain boundaries. Grain boundary dislocations and their assemblies can be regarded as the source of elastic stress fields. These stresses result in significant distortions and dilatations of the crystal lattice near the grain boundaries. It is known that UFG materials are often rather non-stable and their grain growth occurs already at temperatures near 0.4 T (T as the melting temperature) or even lower. Annealing of these materials leads first to partial annihilation of defects at grain boundaries and inside grains and relaxation of internal elastic stresses, later to migration of non-equilibrium grain boundaries and abnormal grain growth.

scanning low energy electron microscopy (SLEEM), contrast of crystal orientation, microscopic strain

MIKMEKOVÁ, Š.; MAN, O.; PANTĚLEJEV, L.; HOVORKA, M.; MÜLLEROVÁ, I.; FRANK, L.; KOUŘIL, M.

28. 6. 2010

VUTIUM Brno

Brno

978-80-214-4112-5

6th International Conference on Materials Structure & Micromechanics of Fracture

MSMF

6

177

177

1