Strain-dependent transition of time-dependent deformation mechanism in single-crystal ZnO evaluated by spherical nanoindentation

Abstract

We have systematically explored the time-dependent plasticity of (0 0 0 1)-oriented ZnO single crystal through spherical indentation tests. Constant load indentation creep tests were performed in elastic strain and elastic–plastic strain regimes. In both regimes, creep indeed occurred at ambient temperature. With the observed quasi-steady-static strain rate, the stress exponent was found as ~1.361 for elastic contact regime and ~3.077 for elastic–plastic regime, suggesting predominant creep mechanism of diffusion and dislocation, respectively. This strain-dependent transition of creep mechanism is discussed in terms of possible factors affecting the creep in each regime.

Keywords:

• nanoindentation
• ZnO
• creep

Funding

This research was supported in part by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) [grant number 2013R1A1A2A10058551], and in part by the Human Resources Development program of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government (MOTIE) [grant number 20134030200360].