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 micro mechanical behaviors of ultrafine grained YSZ remain limited. Here, we report on the high temperature (up to 670 degrees C) in-situ micromechanical testing of spark plasma sintered YSZ. The mechanical behaviors of YSZ tested below 400 degrees C are highlighted by large inelastic strain (similar to 7%) due primarily to phase transformation toughening. Beyond 400 degrees C, martensitic transformation toughening is gradually superseded by grain boundary sliding triggered by ultrafine grains. The micropillars tested at 670 degrees C exhibit significantly enhanced plastic flow, arising mainly from dislocation activity along with grain boundary sliding. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.