AMORPHOUS STATE FORMATION AND STRUCTURAL-CHANGES IN ALPHA-ALUMINA BY REPEATED RUBBING

Sintered alpha alumina was repeatedly rubbed in a dry condition. Observations under a scanning electron microscope revealed that, in many cases, the configuration of the friction surface on the entering side of the slider (for the most part, adhesion of flattened debris) is different from that on the emergent side (for the most part, cleavage at grain boundaries), Observations of the friction surface and near vicinity under a transmission electron microscope revealed the formation of extremely fine grains (about 30 nm). The transmission electron microscopy diffraction pattern from this area suggests the formation of an amorphous state and a structure ordered almost only in one direction. These transformations can be considered to be one of the mechanisms of plastic deformation during the rubbing.