Investigation of pop-in events and indentation size effect on the (001) and (100) faces of KDP crystals by nanoindentation deformation

Results of an investigation of the nature of load-displacement curves, pop-in events and indentation size effect of the (001) and (100) faces of KDP crystals by nanoindentation deformation under Berkovich indenter at different loads are presented and discussed. It was found that: (1) load-displacement curves reveal numerous pop-in events but these pop-in events occur less frequently on the (100) face than on the (001) face, (2) different segments of individual load-displacement curves are explained by plastic deformation under the indenter, (3) the value of indentation displacement excursion d of pop-in events lies between 3 and 20 nm, (4) nanohardness H lies between 2.2 and 3.3 GPa and between 1.6 and 3.2 GPa for the (001) and (100) faces, respectively, and is comparable with that reported before, whereas penetration independent hardness H0 obtained from analysis of the H(h) data is 2.04 and 1.41 GPa for the (001) and (100) faces, respectively.