Tribological induced microstructural changes in subsurface layers of Si sub 3 N sub 4 -based materials

The microstructure of tribo-oxidation layers on sintered Si sub 3 N sub 4 and a Si sub 3 N sub 4 /TiN composite stressed at 800 deg C were investigated in the analytical TEM after preparation of appropriate cross sections. In both materials 200-400 nm thick layers of nanocrystalline oxide particles associated with amorphous silicon oxide were observed in the low wear regime. Whereas the soft layer, which had formed on the composite, provided very good wear resistance, the harder one on sintered Si sub 3 N sub 4 could not absolutely prevent microcracking and debris formation.