Effect of HIPping, stress and surface finish on the environmental degradation of Y-TZP ceramics

Hot isostatically pressed (HIPped) and hot pressed (designated unHIPped) bar samples of yttria stabilized tetragonal zirconia polycrystalline ceramic (3Y-TZP) were subjected to three point bend testing in water at 90 degreesC. HIPped femoral heads with three different surface finishes were also aged in 90 degreesC water. The early stages of the environment induced tetragonal to monoclinic transformation was monitored as a function of time by X-ray diffraction, white light interferometry and scanning electron microscopy. HIPped samples were found to transform less readily than unHIPped samples and have a longer incubation period prior to transformation. There was an increase in the amount of monoclinic phase detected following the application of stress, particularly on the compression surface. Microcraters, believed to result from the expulsion of transformed grains when stress was applied, were observed on tension surfaces, particularly of unHIPped samples. There was no effect of surface roughness on the environment induced transformation for the range of surface finishes investigated. (C) 2001 Kluwer Academic Publishers.