The effect of oxide impurities on the microstructure and properties of Y-T.Z.P.

An investigation has been carried out into the effects of three common oxide impurities, TiO2, A12O3, and SiO2/ on the properties and behaviour of Y-T.Z.P. These impurities are present in varying amounts in almost all commercially available Y-T.Z.P. materials, and substantial costs are incurred in removing them in the purest systems.However, the effects of these impurities, both individually and in combination have received relatively little study in the published literature, and it has not been made clear to what degree these impurities influence the properties and behaviour of the material.To carry out the investigation it has been necessary to develop a novel technique for introducing the impurities as dopants into a high purity, commercially available Y-T.Z.P., whilst retaining a high degree of chemical homogeneity in the material. The technique developed uses a variant on the alkoxide sol-gel process to coat the individual powder particles with a thin layer of dopant atoms and offers a number of advantadges over other doping techniques. The process could be exploited to solve a variety of ceramic processing problems. The results obtained from impurity doped materials showed that alumina and silica reduced the sintering temperature and promoted enhanced densification at lower sintering temperatures, whilst titania impaired the sintering at lower temperatures. Alumina additions resulted in pronounced grain growth and associated destabilisation of the tetragonal phase of zirconia, particularly for higher sintering temperatures. A factorial experiment was carried out to obtain additional, and previously unreported information. This showed that there were significant interactions occurring between all of the additives investigated some of which appeared to be beneficial.An investigation into the effect of the additives on the mechanical properties (hardness and fracture toughness) was carried out for a range of sintering temperatures.The results of these experiments suggested that the impurities had very limited direct effects on the transformation toughening mechanism, although there were differences in properties associated with the effects of the impurity additions on the microstructures of the sintered materials.