Probing the stochastic behavior of the onset of plasticity for potassium dihydrogen phosphate single crystal by grating spherical nanoindentation

Abstract

To support high-throughput instrumental nanoindentation testing, the statistical dataset of incipient plasticity via first pop-in event was acquired in potassium dihydrogen phosphate (KDP) single crystal. The onset of plastic deformation occurred stochastically over a wide range of critical stresses. The corresponding maximum shear stress below the indenter could approach the theoretical shear stress for the activating of a single dislocation. The result of the experiment shows that the threshold stress for the onset of plasticity could be well represented by the Gaussian distribution law and its average value obviously depends on the crystal orientation. Moreover, the activation volume of dislocation nucleation was experimentally characterized on the length scale of the atomic vacancy (28 ± 3.5 Å3) and independent of the crystalline orientation. This suggests that the point defects caused by breakage of the atomic bond on the cleavage surface are the activation source for the dislocation nucleation.