Investigation of Deformation Mechanisms in BCC Chromium by Macro- and Small-scale Testing Techniques

Investigation of size effects and deformation kinetics on small-scale samples became very popular over the last years, since they allow to determine the temperature dependent mechanical behaviour of thin films or small components.
Deformation mechanisms can be differentiated by the strain rate sensitivity (SRS) of the flow stress and the related activation volume. Moreover, it is known that the deformation behaviour is influenced significantly by the present microstructure and the critical temperature of the respective material.
In this work, we concentrate on the deformation behaviour of chromium, which exhibits a strong contribution of the thermal stress component to the flow stress. Focused ion beam milling was used to fabricate single crystalline (sx) and ultrafine-grained (ufg) pillars in a size range between 200 nm and 4 µm. Subsequently, the pillars were compressed in-situ in a scanning electron microscope at room temperature to extract SRS data from calculated stress-strain curves. This data was compared to results acquired by nanoindentation and macroscopic compression tests, carried out at different temperatures.
Finally, the stress-strain behaviour of macro- and small-scale ufg samples were compared and related to single crystalline chromium, where the well-known sample size effect was observed.
We conclude, that small-scale samples can be used to determine rate dependent deformation behaviour as for macro-scaled samples, as long as the sample size effect is properly taken into account.