Fe single crystals exhibit substantial strain rate sensitivity. Previous studies by Huang et.al [1] reported the strain rate sensitivity of (100) 𝛼-iron using micropillar compression tests in the quasi-static strain rate regime. However, the strain rate sensitivities of single crystal bcc materials are yet to be explored at higher strain rates using nanoindentation and micropillar compression due to nanoindentation traditionally being limited to quasi-strain rate testing regime. At higher strain rates, the resonance of the nanoindenter components (load frame, load sensor, etc.) inhibit reliable measurements.

We recently reported the reliable extraction of nanoindentation hardness, modulus, and strain rate sensitivities of SU-8 polymer up to 1000 s ^-1 strain rates [2] using Oliver-Pharr method [3]. This was accomplished using a special piezoelectric load sensor and stiff load frame design of an in situ nanoindenter [4]. We extend these studies to Fe single crystals to study any possible changes in strain rate sensitivities at higher strain rates. We will report both nanoindentation and micropillar compression on two orientations of Fe single crystals - (100) and (111). The hardness, modulus and strain rate sensitivities will be compared between the two orientations and strain rates (10 ^-3 to 10 ⁴ s ^-1 ). Additionally, transmission electron microscopy studies of the deformation sub-structure in both micropillar compression and nanoindentation will be presented as a function of both strain rates and crystal orientation. This talk will present the first comprehensive study on high-rate deformation of Fe single crystals studied using nanoindentation and micropillar compression over seven orders of strain rates.

References

[1] R. Huang, Q.-J. Li, Z.-J. Wang, L. Huang, J. Li, E. Ma, Z.-W. Shan, Flow Stress in Submicron BCC Iron Single Crystals: Sample-size-dependent Strain-rate Sensitivity and Rate-dependent Size Strengthening, Mater. Res. Lett. 3 (2015).

[2] R. Cherukuri, A. Lambai, L. Sukki, J. Väliaho, P. Kallio, E. Sarlin, R. Ramachandramoorthy, M. Kanerva, G. Mohanty, In-situ SEM micropillar compression and nanoindentation testing of SU -8 polymer up to 1000 s ^-1 strain rate, Mater. Lett. 358 (2023).

[3] WC Oliver, GM Pharr, Measurement of hardness and elastic modulus by instrumented indentation: Advances in understanding and refinements to methodology, J. Mater. Res. 19 (2004).

[4] G. Guillonneau, M. Mieszala, J. Wehrs, J. Schwiedrzik, S. Grop, D. Frey, L. Philippe, J.-M. Breguet, J. Michler, JM Wheeler, Nanomechanical testing at high strain rates: New instrumentation for nanoindentation and microcompression, Mater. Of. 148 (2018).