POLYCRYSTALLINE T'-ZRO2(LN2O3) FORMED BY DISPLACIVE TRANSFORMATIONS

ZrO2 (3 mol % Y2O3) tetragonal and t'-ceramics (displacively formed ce ramics) were compared with ZrO2 ceramics (3 mol % Ln2O3, where Ln = La , Pr, Nd, Sm, Gd, Tb, Dy, Er, or Yb) processed in an identical manner. Sintering at 1 500-degrees-C for 2 h produced mainly tetragonal polyt ypes for the dopants with smaller ionic radii than Dy(i.e., Er, Y and Yb) but when ZrO2 was reaction sintered with dopants with larger ionic radii excessive monoclinic phase transformation and associated microc racking resulted. High-temperature annealing in the cubic stability re gime and rapid cooling through the tetragonal stability regime was use d to fabricate t'-composites of ZrO2 doped with Y, Yb, Er or Dy. Room- temperature fracture toughness and strength values are explained on th e basis of a ferroelastic-cubic-to-tetragonal transformation. The doma in structure was viewed by transmission optical microscopy (TOM) or tr ansmission electron microscopy (TEM).