Evaluating a Critical Resolved Shear Stress Criterion for Domain Nucleation in Ferroelastic Ceramics

The mechanical behavior of single crystal, ferroelastic, tetragonal, ceria-titania-stabilized zirconia is evaluated through uniaxial micro-scale compression experiments. The deformed single crystal micropillars exhibit characteristics of several deformation modes, including twinning (ferroelastic domain nucleation), dislocation plasticity, and microcracking. Following earlier work that revealed how the onset of twinning obeys a critical resolved shear-stress law, much akin to Schmid's law, we test this model and show that it does not hold for the data presented herein. We ascribe this discrepancy to the fact that multiple deformation mechanisms can be active in different micropillars and even in the same micropillars at room temperature, which is revealed by transmission electron microscopy. Whilst little is known about the potential interactions between these mechanisms at such low homologuous temperatures, their coexistence implies that crystal orientation alone is not sufficient to predict ferroelastic domain nucleation behavior in small-scale single crystals.