Relationship between Grain Boundary Segregation Phenomena and Phase Transformation in Zirconia Ceramics

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The mixed powders of ZrO_2-3mol% Y_2O_3 (partially stabilized zirconia) and Al_2O_3 are pressed and sintered at various temperatures ranging 1673 to 1973 K.Sintered bodies are investigated mainly by X-ray diffraction technique, TEM observations and estimation of mechanical properties. The resultso btained are as follows :(1) Bending strength and fracture toughness increase with the addition of alumina.(2) The tetragonal to monoclinic phase transformation takes place isothermally. With the addition of alumina, overall trans-formation rate decreases ; i.e., the nucleation rate of martensite lath decreases drastically but the growth stage is not affected, irrespective of alumina addition.(3) In grain boundaries of PSZ containing alumina, amorphous phase enriched with alumina, silica, zirconia is formed. Its thickness increases with sintering temperature.(4) The suppression of phase transformation and improvement of mechanical properties are attributed tothe formation of grain boundary amorphous phase. Silica plays an important role for theformation of grain boundary phase.