IMPURITY AND YTTRIUM SEGREGATION IN YTTRIA-TETRAGONAL ZIRCONIA

X-ray photoelectron spectroscopy, scanning electron microscopy and impedance dispersion spectroscopy have been used to study the segregation behaviour of yttrium and impurities in yttria-tetragonal zirconia polycrystals (Y-TZP). Sintered and polished specimens of two Y-TZP's with different levels of impurities were annealed at temperatures between 800 and 1500-degrees-C. On annealing, significant amounts of impurity silicates and yttrium incorporated into the silicate, segregated to the external surface of specimens, even at low annealing temperatures. The segregation layer increased with increasing annealing temperature. Impedance spectroscopy indicated that grain boundary cleaning accompanied redistribution of the silicate phase to the external surface. The segregation of silicate phases at the external surface led to yttrium redistribution in the surface grains and enhanced grain growth.