Nanoindentation pop‐in in oxides at room temperature: Dislocation activation or crack formation?

Abstract

AbstractMost oxide ceramics are known to be brittle macroscopically at room temperature with little or no dislocation‐based plasticity prior to crack propagation. Here, we demonstrate the size‐dependent brittle to ductile transition in SrTiO3 at room temperature using nanoindentation pop‐in events visible as a sudden increase in displacement at nominally constant load. We identify that the indentation pop‐in event in SrTiO3 at room temperature, below a critical indenter tip radius, is dominated by dislocation‐mediated plasticity. When the tip radius increases to a critical size, concurrent dislocation activation and crack formation, with the latter being the dominating process, occur during the pop‐in event. Beyond the experimental examination and theoretical justification presented on SrTiO3 as a model system, further validation on α‐Al2O3, BaTiO3, and TiO2 are briefly presented and discussed. A new indentation size effect, mainly for brittle ceramics, is suggested by the competition between the dislocation‐based plasticity and crack formation at small scale. Our finding complements the deformation mechanism in the nano‐/microscale deformation regime involving plasticity and cracking in ceramics at room temperature to pave the road for dislocation‐based mechanics and functionalities study in these materials.