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

Hot isostatically pressed (HIPped) and hot pressed (designated unHIPped) ba r 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 tetragon al to monoclinic transformation was monitored as a function of time by X-ra y 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 i ncrease in the amount of monoclinic phase detected following the applicatio n of stress, particularly on the compression surface. Microcraters, believe d to result from the expulsion of transformed grains when stress was applie d, were observed on tension surfaces, particularly of unHIPped samples. The re was no effect of surface roughness on the environment induced transforma tion for the range of surface finishes investigated. (C) 2001 Kluwer Academ ic Publishers.