Diffusional Creep and Kinetic Demixing in Yttria‐Stabilized Zirconia

The creep behavior of fine‐grained yttria‐stabilized zirconia with 25 mol% Y 2 O 3 has been characterized as part of an investigation of kinetic demixing in solid‐solution oxides which are subjected to a nonhydrostatic state of stress. At temperatures between 1400° and 1600°C, the steady‐state strain rate of (Zr 0.6 Y 0.4 )O 1.8 samples with average grain sizes between 2.5 and 14.5 μm can be summarized by the flow law ɛ= 6.5 × 10 −7 σ 1.2 exp[−550 (kJ/mol)/ RT ] d −2.2 (s −1 ) for stresses in the range 8 to 60 MPa, where σ is in pascals and d is in meters. This flow law indicates that deformation occurs by a Nabarro‐Herring creep mechanism in which the creep rate is limited by cation lattice diffusion. Kinetic demixing was not observed in deformed polycrystalline samples even though diffusional creep was rate limited by cation lattice diffusion. This result can be explained if the cation diffusivities are approximately equal or if extensive grain rotation occurs during diffusional creep.