Elevated temperature, strain rate jump microcompression of nanocrystalline nickel

Abstract

Nanocrystalline and ultrafine-grained materials show enhanced strain rate sensitivity (SRS) in comparison to their coarse grained counterparts. Majority of SRS measurements on nanocrystalline thin films reported in literature have focused on nanoindentation-based approaches. In this paper, micropillar strain rate jump tests were demonstrated on an electrodeposited nanocrystalline nickel film from 25 to 100 °C. SRS exponent, m, and activation volume, V, values were determined as a function of temperature. The measured values were found to be in good agreement with previously reported literature on bulk and nanoindentation measurements. Apparent activation energy for deformation was found to be about 100 kJ/mol, which is close to that for grain boundary diffusion in nickel. Grain boundary sliding was observed in the deformed pillars from scanning electron microscopy images.

Keywords:

• strain rate jump microcompression
• strain rate sensitivity
• nanocrystalline nickel

Acknowledgements

The authors would like to thank Damian Frey for performing the GDOES measurements and S. Hostettler of Synton-MDP AG for help with the joint development of the heated indenter tips used in this work. Gaurav Mohanty would like to acknowledge funding from EMPA Postdoc program cofunded by FP7: Marie Curie Actions.