Investigation of ammonium perchlorate by nanoindentation

Abstract

The near surface of cleaved {210} planes of ammonium perchlorate (AP) was studied by nanoindentation. The crystals were etched to determine the {210} surface and the resulting etch pits were investigated with atomic force microscopy (AFM). The sides and bottom of the etch pits had a terraced structure. Nanoindentation was used to measure hardness and elastic modulus over the contact depth range of 30–130 nm. The hardness exhibited the indentation size effect, that is, the hardness increased with decreasing depth. The measured hardness of the near surface was higher than that previously reported for deeper Vickers indentations where cracking was observed. The elastic modulus of the near surface was consistent with the low end of values reported in the literature. Multiple pop-in events were observed for all indentations. Indenting with high loads (>1 mN) using either a Berkovich indenter or spherical indenter resulted in significant asymmetric pile-up, slip traces on the surface and cracks. Cracking was observed in the 〈120〉 direction and a step on the surface was observed in then 〈001〉 direction.