Surface damage of structural ceramics: Implications for wear modeling

Abstract

The reason for the failure of the fracture toughness approach to wear modeling for ceramics is that the assumed linking of the radial and lateral cracks does not often occur. There is indeed wear in sliding but this is due to the fracture and fragmentation of material nearer the surface than the radial and lateral cracks. This scale of fracture is of the order of grain sizes whereas the radial and lateral cracks are of the order of the size of indentations and are usually below the indentation.These conclusions were reached by observing the damage to four commercial ceramic materials, after indentation and after sliding. The four ceramic materials were hot-pressed Si3N4, hot-pressed SiC, sintered Al2O3 and sintered ZrO2. Tests were done in air, water, aqueous acid and aqueous base. The surfaces of the specimens were "finished" by four different abrasive operations before the test, thereby providing four different states of surface roughness and stress state.All of the materials showed both large scale (macro) and small scale (micro) damage. There were major differences in micro-damage but only minor or negligible differences in macro-damage. The latter provide the information from which hardness and fracture toughness are calculated.