Nano-indentation was performed on the cleaved surface of a CaF2 single crystal

and the dislocation structure was investigated via the etch pit technique using

atomic force microscopy. The deformation during indentation was first purely

elastic until dislocations were created observable in a pop-in in the load

displacement data, as well as in a dislocation rosette around the indentation. After

pop-in a relatively high hardness was observed, which gradually decreased until, at

3μm, a nearly constant hardness was found. By using sequential polishing, etching

and imaging, the dislocation structure underneath indentations with indentation

depths of 300nm and 110nm (load: 5mN, 1mN) was quantified. The dislocation

density and radial distribution of dislocation density depend on the indentation

depth, where a smaller indentation depth leads to a higher dislocation density,

which was in qualitative agreement with the observed increase in hardness.

Study on the Indentation Size Effect in CaF2: Dislocation Structure and Hardness.

P.Sadrabadi, K.Durst, M.Göken: Acta Materialia, 2009, 57[4], 1281-9