Surface fatigue in ceria-stabilized polycrystalline tetragonal zirconia between room temperature and 1073 K

Abstract

An investigation has been conducted to study the fatigue deformation and fracture induced by pressing 120° hardened silver steel conical tips against a flat, polished CeTZP counterface between 293 and 1073 K with cyclic loads of 19.6±9.8 N, for up to 475 000 cycles. The ground tips of the cones plastically deformed during the initial loading cycle to produce a flattened end which conformed with the substrate. This test format has been devised to be comparable to the service conditions that these types of ceramics are likely to experience. At temperatures up to, and including, 673 K, the sequence of events is that a tetragonal to monoclinic transformed zone is formed around the contact zone. This expands as the number of cycles is increased. Much later in the fatigue process, grain lifting occurs at the periphery of the contact zone. This subsequently causes intergranular pitting to progress around the edge of the contact zone followed by extension both away from and into the contact region. At 673 K and above, a small number (3–5) of radial intergranular cracks are formed after a few cycles (≤10) which propagate a substantial distance away from the contact zone.