The geometry of fractures caused by cleavage of α‐Al 2 O 3 single crystals

Abstract The possibibity of the existence of cleavage in α‐Al 2 O 3 single crystals has been estimated by elementary structural considerations and has been shown that the {10 1 } and {11 2 0} planes are the more probable cleavage planes. The values of the fracture surface energy measured by Wiederhorn and the estimates of the surface energy made by Hartman confirm this conclusion. In crystals with small numbers of blocks and dislocations and low residual stress we really found a perfect cleavage along the {10 1 1} and {11 2 0} planes. Therefore the existence of the cleavage is defined by the crystal imperfection. It has been shown in what way the orientation of crystals can be visually determined from the direction of cleavage steps.