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Virag Raut1 Tom Glen2 Hang Yu3 Steven Boles1

1, Electrical Engineering, Hong Kong Polytechnic University, Kowloon, , Hong Kong
2, University of Edinburgh, Edinburgh, Scotland, United Kingdom
3, Materials Science and Engineering, Virginia Tech, Blacksburg, Virginia, United States

The multiplicity of phases (cubic, tetragonal, monoclinic, etc.) in zirconia-based systems has produced many opportunities for new applications and research directions. Interestingly, zirconia doped with ceria in certain compositions gives rise to a shape memory effect (SME) and superelasticity when exposed to applied stress and/or temperature. In this work, we have investigated SME behaviour in 12% ceria-doped zirconia (Ce0.12Zr0.88O2, CZ). CZ undergoes a martensitic transformation upon application of an applied stress which is marked by a phase change between tetragonal (T) and monoclinic (M) phases. The monoclinic content (MC) generated from the applied stress can subsequently undergo a thermally induced reverse phase transformation from M to T. The findings from our experiment suggest that the shape and morphology of CZ powder influences the MC generated during stress-induced transformation. A higher MC in pellets is produced after stress-induced transformation despite of a reduced MC i.e. fewer nucleation sites after annealing the CZ powder. The behaviour is split into two regimes: for lower temperature treatments, the morphology give rise to stress concentrations and contribute to a higher growth in MC; for higher temperature treatments, sintering and grain growth seemingly dominate the morphology and applied stress has a limited ability to increase MC. These results suggest conventional processing steps for bulk ceramics may be challenging. To avoid deleterious thermal treatments, a slurry based additive manufacturing approach is employed to produce porous ceramic structures. Infiltrating porous CZ with polymer materials using architected topologies and new design methods may lead to optimization of SME properties for meta-materials research and applications.

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