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Indentation contact deformation of superplastic and non-superplastic 3Y-TZP at elevated temperatures

The contact deformation mechanisms of superplastic (SP) and non-superplastic (NSP) 3Y-TZP (3 mol.% yttria-partially stabilized tetragonal zirconia polycrystals) are examined in indentation creep tests at elevated temperatures. A large discrepancy between SP-TZP and NSP-TZP in their indentation contact behaviours is observed. The indentation creep curves of SP-TZP exhibit a hardening behaviour, i.e. the creeping rate decreases as the penetration depth and/or the creep time increases. In contrast, the indentation creep curves of NSP-TZP shows a steady-state viscous flow in its long-time creeping. The surface profiles of indentation impression after creep deformation suggest that the deformation mechanisms of indentation creep of SP-TZP and NSP-TZP are quite different. A well-defined piling-up impression profile is observed in SP-TZP, while it is sinking-in for NSP-TZP. This fact implies that the rearrangements of individual grains through grain-boundary sliding take place beneath the pyramidal indenter in SP-TZP, whereas the viscoelastic deformations and flows through bulk/grain-boundary diffusion processes dominate the indentation creep in SP-TZP.