Size and plasticity effects in zirconia micropillars compression

Abstract

The micropillar compression technique has shown the potential for activating the brittle-to-ductile transition in ceramic monocrystals when testing reduced volumes. In this work, the role of size is studied by comparing the mechanical response of polycrystalline tetragonal zirconia micropillars and macroscopic specimens under compression. In micropillars, the absence of the natural defect population typical of bulk zirconia increases considerably the strength, allowing the activation of plastic deformation mechanisms and their study, showing in this way that the brittle-to-ductile transition is not limited to ceramic monocrystals only. The main mechanism of plastic deformation is transformation-induced plasticity, which is shown to be size dependent. The deformation behavior is studied in detail by loading-unloading tests at constant and increasing peak stresses, while the microstructure evolution is revealed by FIB cross-sections, TEM and STEM observations performed on lamellas extracted from pillars retrieved before failure. Finally, a failure mechanism is proposed, based on the damage induced by phase transformation.