Vickers microindentation deformation of different cleavage faces of potassium bichromate single crystals: Anisotropy in microhardness and crack formation

Abstract Experimental results of an investigation of anisotropy in microhardness measurements and crack formation on the {001}, {010} and {100} cleavage faces of potassium bichromate (KBC) single crystals by Vickers indentation deformation are presented and discussed. It was found that: (1) the experimental hardness HV data measured at indentation loads P up to 0.6 N reveal two or three regions of indentation diagonal d characterized by load-independent, normal or reverse indentation size effect (ISE), (2) in the range of measurement of the different d regions the ISE behavior is associated with the competition between factors related to the material deformation and the crack formation during indentation, (3) the value of intrinsic hardness Hin of KBC crystal, independent of applied load, indenter orientation and plane used for hardness measurement in the region of normal ISE, is 0.764 GPa, (4) the values of fracture toughness Kc depend on the crystallographic orientation of the investigated cleavage face as well as on the orientation of the indenter on it, and (5) the anisotropy in the arrangement of indentation cracks on the cleavage faces is a consequence of anisotropic distribution of indentation stress due to the triclinic structure of KBC crystals.