Nanoindentation size effect on stochastic behavior of incipient plasticity in a LiTaO3 single crystal

Abstract

We investigated the characteristic of first pop-in event under spherical nanoindentation in the typical orientation (0 1 1¯ 2), i.e., Y-42° plane of a LiTaO3 single crystal. Three spherical tips with different radii were adopted to probe yield stress and its stochastic behavior as the incipient plasticity occurred. The values of yield stress were 10.75 ± 0.78, 6.3 ± 0.44 and 5.36 ± 0.4 GPa, which were equivalent to E/14, E/30 and E/36 under spherical tips with radii of 0.76, 2.95 and 9.8 μm, respectively. The occurrence of incipient plasticity exhibited a uniform and scattering distribution in a wide range under all the tips. The activation volumes of plastic unit were computed based on the statistical distribution of yield stress, which were 6, 12 and 12 Å3 for 0.76, 2.95 and 9.8 μm tips. A strong indentation size effect was revealed on the threshold stress for evoking incipient plasticity and the critical volume for plastic unit activation. Furthermore, incipient plasticity of LiTaO3 single crystal was confirmed to be loading history-independent. The obtained yield stress and its statistic distribution were similar within the range of loading rate from 0.125 to 2 mN/s.