In-situ high temperature micromechanical testing of ultrafine grained yttria-stabilized zirconia processed by spark plasma sintering

Yttria-stabilized zirconia (YSZ) exhibits both enhanced strength and fracture toughness attributed to transformation-induced plasticity. Recent studies show that miniaturization of YSZ to the microscale enhances the effectiveness of stress-induced phase transformation by reducing mismatch stress among incommensurate grains. However, the fundamental understandings on the high temperature micromechanical behaviors of ultrafine grained YSZ remain limited. Here, we report on the high temperature (up to 670 °C) in-situ micromechanical testing of spark plasma sintered YSZ. The mechanical behaviors of YSZ tested below 400 °C are highlighted by large inelastic strain (∼7%) due primarily to phase transformation toughening. Beyond 400 °C, martensitic transformation toughening is gradually superseded by grain boundary sliding triggered by ultrafine grains. The micropillars tested at 670 °C exhibit significantly enhanced plastic flow, arising mainly from dislocation activity along with grain boundary sliding.