Plastic deformation in impure nanocrystalline ceramics

Plastic deformation behavior of impure nanocrystalline ceramics (NCC) was m odeled using the percolative composite model in conjunction with models for plastic deformation by grain boundary sliding. The "glass transition tempe rature" concept was used to determine the threshold strain rate criterion b elow which the impure nanocrystalline ceramic would deform plastically. Thr eshold strain rate is stress independent. It increases with the temperature increase and with the grain size decrease. Using the dissolution-precipita tion 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 zircon ia polycrystals (Y-TZP) were evaluated. At 600 degrees C, strain rates as h igh 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 thre shold level showed that increase in the applied stress is associated with i ncrease in the grain size and strain rate onsets for plastic deformation.