One of the obstacles preventing the extensive application of ceramics is their limited ductility and toughness, which stems from the conventional trade-off between strength and ductility observed in numerous difficult-to-deform materials. However, it was discovered in 1975 that doping zirconia could induce a stress-induced martensitic transformation from a tetragonal to a monoclinic phase. This phase transformation becomes the source of transformation induced toughening [1].

In this context, ceria-stabilized tetragonal zirconia (CSTZ) is advantageous when compared to the better-known yttria (Y2O3)-stabilized zirconia. Stabilization with ceria reduces the critical stress required for phase transformation, enabling to initiate transformation before cracks propagate. Thus, CSTZ ceramics can exhibit plasticity induced by phase transformation (TRIP for "Transformation-Induced Plasticity"), with a plastic deformation capacity of the order of 1% before fracture [2]. However, even though the TRIP effect has been studied on a macroscopic scale [3], small-scale characterizations are needed for a thorough understanding.

In that regard, the objective of this work (ANR-21-CE08-0019 NANOTRIP) is to unveil the mechanisms that control the TRIP effect, focusing on the crystallographic and mechanical aspects, as well as on the transformation propagation from one grain to another. For that, single and bi-crystalline micropillars were in situ compressed concurrently with Laue microdiffraction at the BM32 beamline the European Synchrotron ESRF. Correlative analyses such as in situ micro-compression tests in a scanning electron microscope (SEM), post-mortem transmission electron microscopy (TEM) of transformed micropillars, and the theory of martensitic transformation were used in parallel. Information about critical stresses, plasticity by dislocations (glide planes …), and the TRIP effect were obtained, as well as information about the crystallography of the transformation (variants, habit planes…). Combining these results with the crystallographic theory of martensitic transformation and finite-element method (FEM) simulations allows drawing a full picture of the microscopic phase transformation mechanism.

References
[1] Garvie et al., Nature, 1975, 258, 703.
[2] Chevalier et al., J. Am. Cer. Soc. 2019, 103, 1482.
[3] Liens et al., Acta Materialia, 2020, 183, 261.