Plastic deformation in impure nanocrystalline ceramics

Plastic deformation behavior of impure nanocrystalline ceramics (NCC) was modeled using the percolative composite model in conjunction with models for plastic deformation by grain boundary sliding. The "glass transition temperature" concept was used to determine the threshold strain rate criterion below which the impure nanocrystalline ceramic would deform plastically. Threshold strain rate is stress independent. It increases with the temperature increase and with the grain size decrease. Using the dissolution-precipitation model, dependence of the strain rate on temperature, stress, and grain size in the nanometer regime for impure NCCs was calculated. As an example, the critical conditions for plasticity in impure yttria-tetragonal zirconia polycrystals (Y-TZP) were evaluated. At 600 degrees C, strain rates as high as 10(-4) s(-1) were expected in 10 nm impure Y-TZF. Comparison of the published data extrapolated into the nanometer range to the calculated threshold level showed that increase in the applied stress is associated with increase in the grain size and strain rate onsets for plastic deformation.