THE ASSESSMENT OF SURFACE FATIGUE EFFECTS IN TOUGHENED ZIRCONIA USING A NEW POINT CONTACT METHOD

Abstract

Abstract—The effects of repeated point contact loading of a toughened ceria‐stabilised zirconia ceramic, CeTZP, by softer metallic cones, have been investigated. All tests were conducted on a purpose‐designed and built computer‐controlled apparatus. The results clearly indicate that zirconia is susceptible to cyclic loading. The evolution of the cyclic deformation and cracking processes have been analysed in terms of contact pressures, applied loading conditions and number of cycles. The ground tips of both quenched, and quenched and tempered, silver steel cones are plastically deformed during the initial loading cycle to produce a conforming planar surface approximately 50‐100 μm in diameter. In all cases, plastic deformation in the CeTZP was observed within, and adjacent to, the contact zones. The degree of plastic deformation increased as the number of cycles increased. The expansion associated with the tetragonal‐to‐martensitic phase transformation in the zirconia caused granular lifting from the surface, at the edge of the contact zone. This resulted in localised spalling at the peripheries of the contact zones, where the tensile stresses are the highest, followed by a radial expansion at higher cycle numbers. This investigation has identified that the rate of evolution of the fatigue damage, in decreasing order of significance, was controlled by: (a) cone hardness, (b) cyclic load amplitude and (c) mean load.