Abstract
Strengthening of alumina ceramics and porcelain bodies by dip-coating of zirconia without a stabilizer was investigated. Five-μm-thick zirconia coating on alumina could be made dense by sintering and the particle size of zirconia depended on the thickness of the sintered coating. Although tetragonal-monoclinic phase transformation occurred upon cooling, no cracks were observed in the surface layer. Zirconia coating caused an increase in the bending strength of alumina from 564MPa to 633MPa, and the Weibull modulus increased from 10 to 17. Zirconia particles which were coated on porcelain dispersed into glass phase and sintered together. This formed a smooth surface and resulted in a strength increase from 137MPa to 186MPa. The total thermal expansion of zirconia without a stabilizer from room temperature to 1500°C is less than that of alumina or porcelain bodies when a monoclinic-tetragonal transformation is taken into account. The thermal expansion difference introduced an effective compressive stress in zirconia coating and strengthened the alumina and porcelain bodies.
