Point contact surface fatigue in zirconia ceramics

Abstract

The surface deformation and fragmentation behaviour of three zirconia ceramics have been studied by using unlubricated metallic repeated point contact loading at room temperature to investigate the possibilities of cyclic fatigue effects. All tests were conducted on a purpose built computer-controlled apparatus. The zirconias studied were ceria stabilized tetragonal polycrystalline, magnesia partially stabilized, and single crystal calcia stabilized. 120° steel cones were cyclically loaded against the flat, polished zirconia counterfaces, and the damage was observed and analysed as a function of the number of cycles, up to a total of 5 × 10 5 cycles, for loads of 19.6 ± 9.8 N. The ground tips of the cones plastically deformed during the initial loading cycle to produce a flattened end which conformed with the zirconia counterface. The contact pressures were in the range 4 to 10 GPa. In all cases plastic deformation was observed in the zirconias within, and adjacent to, the contact areas. The degree of plastic deformation increased with increasing number of cycles. After approximately 1 × 10 4 cycles, localized cracking was induced at the peripheries of the contact zones, which gradually increased in extent until after 5 × 10 5 cycles there was extensive fragmentation. No material transfer, i.e. metal onto ceramic, or vice versa, was generally observed until after the surface had become rough as a result of the fracturing.