Ferroelastic and plastic behaviors in pseudo-single crystal micropillars of nontransformable tetragonal zirconia

The orientation-dependent micromechanical properties of nontransformable tetragonal (t') zirconia, which underwent a diffusionless transformation from the fluorite cubic phase and does not exhibit a stress-induced phase transformation, were characterized via pseudo-single crystal micropillar compression and electron microscopy. The t' zirconia sample was obtained via atmospheric plasma spraying of 4.5 mol% yttria-stabilized zirconia (YSZ) powders into liquid nitrogen and consolidated into a bulk state via hot pressing at 1100 degrees C. Dense and cylindrical micropillars were fabricated using a focused ion beam from pseudo-single crystalline regions, which exhibited a nanodomain microstructure of three t' variants partitioned by [1 0 1), twin boundaries with 90 symmetry. These micropillars were compressed using a flat-end diamond indenter. Near-< 0 0 1 >, compressions were attributed to ferroelastic domain switching and subsequent [1 0 1), and/or [1 1 1), hard slips. In ferroelastic deformation, a certain t' variant diminished, and a binary domain microstructure developed with c axes perpendicular to the compressive direction. Near-< 1 1 1 >, compressions were governed by [0 0 1), soft slips accompanied by strain hardening with negligible ferroelasticity, which resulted in buckling deformation with rotational kinking. In both the hard- and soft-slip orientations, ferroelastic toughening was observed with certain t' variants awaken around the crack tips. Contrarily, cleavage fractures subsequent to yielding were observed in near-< 1 0 1 >, compressions. In the cubic counterpart with a domain-free microstructure (8.0 mol% YSZ), ferroelastic toughening was not observed. Hence, it is viewed as the origin of enhanced toughness in t' zirconia. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd.

Automated summary

The micro mechanical properties of nontransformable tetragonal zirconia were characterized through compression experiments, revealing different deformation mechanisms in different strain directions. The study also investigated the reasons behind the enhanced toughness of t' zirconia.