A STUDY OF THE BRITTLE-FRACTURE CHARACTERISTICS OF COSI2 USING LASER-BEAM REFLECTIONS

The room temperature brittle fracture characteristics of oriented CoSi2 single crystals with edge notches, subjected to three-point bending experiments, have been investigated. A rather uncommon but powerful method has been used: fractured surfaces reflect incident laser beams; the reflected beam pictures correspond to distributions of local surface normals that allow surface elements to be readily characterized. CoSi2 specimens fail according to two distinct mechanisms. The first one corresponds to the fracture of the specimen parallel to a unique crystallographic plane (the notch plane approximately). The directions of fracture propagation are always different from [110]. Various cleavage planes are associated with it such as (101), (111) and some other planes with higher indices close to (212) and (412). The second mechanism corresponds to the simultaneous activation (about the notch) of various non-parallel local cleavage planes [such as (101), (212), (111)...] which have the [10 $$($) over bar 1] zone axis that corresponds to the direction of fracture propagation. The local cleavage planes have normals located in the (10 $$($) over bar 1) plane between [111]-[101] or [101]-[1 $($) over bar$$ 11] or both.