Compressive deformation behaviour of superplastic Y-TZP-based ceramics: Role of grain boundary phases

The compressive deformation behaviour of Y-TZP-based ceramics was investigated for its dependence on temperature, applied stress, grain size and the grain boundary phases of the materials. The deformation behaviour of the materials depends strongly on the grain boundary phase and the testing temperature. At 1250°C and above, the presence of LAS glass at boundaries in Y-TZP leads to much promoted deformation rates; while at temperatures lower than 7250°C, the LAS added composites show apparent retarded deformation. The activation energy for the compressive deformation was calculated to increase from 410 k J/mol for pure Y-TZP to 784 kJ/mol for the composite with 5 vol% LAS glass addition from 1150 to 1350°C. Strain hardening effect is limited for testing at 100°C below sintering temperatures, and the grains retained their equiaxed shape after deformation. The deformation of Y-TZP/Al₂O₃ composite shows a mixed effect of alumina particles and the very small amount of glass phase at triple points in the bulk. Some small cavities were found at triple points for single-phase Y-TZP but no cavities can be identified in the materials containing some glass phase. The mechanism of the superplastic flow of the material is believed to be grain boundary sliding.