The atomic structure and transitions of grain boundaries in copper

Grain boundaries (GBs) are one of the most important features in metals regarding strength, microstructural stability or corrosion resistance. GB engineering has an enormous potential to improve material’s properties by controlling their microstructure. Structural transformations of GBs have been already suggested to affect the diffusivity or grain growth in a material. Nevertheless, few experimental studies explore the atomic structure of GBs, their transitions and draw correlations to materials properties.

Recently, it has been shown that textured copper (Cu) films are ideally suited to study pure tilt GBs, which can be lifted out by focused ion beam (FIB) preparation and then analyzed by aberration-corrected (scanning) transmission electron microscopy ((S)TEM). In previous studies, the atomic structure of symmetric and asymmetric Σ19b [11-1] tilt GBs and their correlated segregation effects were investigated in these Cu films.

A part of this project is to investigate the relationship between GB misorientation and atomic structure with GB migration by ex situ and in situ heating experiments. Furthermore, different pure tilt GBs will be investigated by aberration-corrected (S)TEM. Figure 1 shows an example high-resolution TEM image of a faceted Σ37c [11-1] tilt GB. The aim is to resolve differences and similarities in the atomic structure of GBs for different misorientation angles, GB habit planes or and their temperature induced changes. Last but not least, in order to directly observe GB phase transitions, in situ heating experiments in a STEM will be conducted. By comparing the observed structures with simulations, GB properties such as GB energy or excess volume can be resolved. The obtained results will help to understand GBs, their migration behavior and their correlated properties. These insights will pave the way to develop novel materials with improved properties such as elevated strength and fracture toughness.

Fig.1. High resolution TEM image of a faceted Σ37c [11-1] tilt grain boundary.

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