Microstructural Evolution of a ZrO 2 ‐SiO 2 Nanocrystalline‐Amorphous Dual‐Phase Ceramic Under Highly Localized Stress Induced by Nanoindentation

Ceramics in miniaturized devices are susceptible to high localized stresses, which can drive microstructural evolution. However, conventional mechanical testing techniques lack the spatial resolution and stress concentration capability required to replicate these conditions. Owing to the highly localized stress field it generates, nanoindentation provides an excellent platform for investigating microstructural evolution of materials under high‐stress conditions. In this study, we investigate the microstructural evolution of a ZrO 2 –SiO 2 nanocrystalline‐amorphous dual‐phase ceramic (NADC) using nanoindentation coupled with scanning transmission electron microscopy (STEM). The studied ceramic consists of monocrystalline ZrO 2 nanograins (NGs) embedded in an amorphous SiO 2 matrix. The presence of ∼43 vol.% ZrO 2 NGs in the NADC does not impair the intrinsic deformation capacity of the amorphous SiO 2 matrix. Nanoindentation induces multiscale microstructural alterations: at the micrometer scale, densification and plastic flow of the amorphous SiO 2 matrix jointly contribute to the irreversible deformation of the ceramic, while simultaneously increasing the local packing density of ZrO 2 NGs; at the nanometer scale, subgrain formation, crystal‐to‐amorphous transitions within ZrO 2 NGs, and stress‐induced tetragonal‐to‐monoclinic phase transformation accommodate high localized stresses and strains; and at the atomic scale, dislocation activation and lattice distortion within ZrO 2 NGs further facilitate stress relaxation and energy dissipation. These mechanistic insights provide a foundation for understanding the microstructure evolution of dual‐phase ceramics containing both crystalline and amorphous phases under high stress.