Applications of In-Situ SEM Micro-Pillar Compression Tests

The mechanical response of low material volumes along one axis can be measured using in-situ SEM micro-pillar compression tests. These tests also allow stress-strain data to be correlated with individual deformations.

In-situ SEM micro-pillar compression tests can be used for research into size effects, e.g. involving strengthening and deformation mechanisms, or for the quantification of specific particles and phases. High displacement and load resolutions are necessary components of any measurement system used to isolate and study individual deformations.

When running an experiment SEM and EBSD should first be used to determine a suitable location for measurement in terms of the sample’s crystal orientation or microstructure. Following this, micro-pillars are produced using a focused-ion beam (FIB) to carry out top-down milling. Once the structure has been machined a lower ion current is used to polish the final structure, with the lower current preventing damage from the FIB.

During the compression protocol, a period of linear elasticity is seen first, during the loading stage, which is then followed by periods of yielding and plasticity. During the plastic regime dislocation slip events are observed as serrated plastic flow behavior with sudden stress drops followed by reloading periods.

A correlation can be found between the stress drops, shown in the stress-strain data, and the formation of shear-bands, as seen through the SEM, with a) elastic loading, b) nucleation of the first slip event, c) intersection with the top surface and d) multiplication of slip events.

It is important to note that many load-controlled testing systems can display strain bursts in their stress-strain curves. These are distinct from stress drops and their presence can prevent accurate quantitative measurements. For this reason, an instrument that has true displacement control, such as the FT-NMT04, should be used.

The FT-NMT04 also has an extremely low noise floor, allowing small magnitude stress drops to be detected and analyzed. These capabilities provide researchers with novel insights into the mechanisms and interactions between lattice defects and dislocations.

This information has been sourced, reviewed and adapted from materials provided by FemtoTools AG.

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