Cyclic loading for the characterisation of strain hardening during in situ microcompression experiments

Abstract

Various parameters from fabrication and testing are known to influence the behaviour for microcompression experiments, especially the work-hardening behaviour. In this regard, the most important factor is found to be the availability of unconstrained slip planes. The second-most important factor is the lateral constraint acting on the sample, which usually arises from friction between indenter and pillar in a combination with a laterally stiff indenter setup, which can generate significant grain rotation and deviation from ideal single slip behaviour. The effect of lateral constraints on the strain-hardening rate is demonstrated on single crystals of gold and a novel solution by cyclic loading conditions is suggested, which could provide comparable conditions for different types of indenter hardware. In this work, the cyclic loading method is shown to minimise the influence of lateral constraints and provide more accurate measurements of strain-hardening behaviour than commonly applied microcompression methods by preventing grain rotation due to frictional constraint.

Keywords:

• Microcompression
• scanning electron microscopy (SEM)
• strain hardening
• in situ
• nanomechanics

Acknowledgements

The authors would like to thank S. Pathak of Empa, Thun (now University of Nevada, Reno) for providing the bulk sample and assistance with initial experiments together with M. Schamel and C. Niederberger. The authors would like to thank P. Gasser and K. Kunze (ScopeM, ETH Zurich) for their help in the sample preparation using FIB, HRTEM, and EBSD characterisation.