A nanoindentation study on the room‐temperature plasticity in titanium dioxide bicrystals

Abstract The increasing demand for manufacturing, processing, and utilizing ceramic materials necessitates a deeper understanding of their mechanical properties, particularly plasticity. In this study, the nanoindentation responses of rutile titanium dioxide (TiO 2 ) were investigated using bicrystal samples. Two types of TiO 2 bicrystals with symmetric 10° tilt grain boundaries were fabricated by diffusion bonding: one with a (001) tilt grain boundary around the [110] rotation axis, and the other with a (010) tilt grain boundary around the [001] rotation axis. High‐resolution transmission electron microscopy observations showed that both bicrystals contained a low‐angle grain boundary composed of periodic dislocations. Nanoindentation experiments were conducted in the single‐crystal regions to characterize the mechanical properties of rutile TiO 2 , as well as near the grain boundary to evaluate its influence on hardness. Nanoindentation results from the single‐crystal regions showed that the (001) plane exhibited significantly higher hardness and elastic modulus than the {110} and (100) planes, indicating the anisotropic mechanical behavior of TiO 2 . The (010) and (100) planes are two equivalent crystallographic planes in rutile TiO 2 , but the (001) plane differs from them. Scanning probe microscopy revealed clear slip traces near the indents without accompanying cracks, indicating that nanoindentation at 5 mN achieved dislocation‐mediated plasticity in rutile TiO 2 at room temperature. For nanoindentations on the {110} and (001) planes, plastic deformation was governed by the {101}<10> slip system, while the (100)[010] slip system dominated the plasticity for nanoindentations on the (100) plane. Nanoindentation experiments near grain boundaries revealed a pronounced hardness peak at the (001) grain boundary, whereas a minor hardening effect was observed at the (010) grain boundary. These findings provide new insights into the room‐temperature plasticity, mechanical anisotropy, and grain boundary hardening effects in rutile crystals.