Toughening of TiO ₂ via Femtosecond Laser Shock Peening

ABSTRACT Most ceramics have low fracture toughness (<5 MPa ) at room temperature. This work explores the feasibility of toughening TiO 2 via femtosecond laser shock peening (fs‐LSP). Transmission electron microscopy (TEM) analyses reveal LSP‐induced the creation of high‐density stacking faults, dislocation structures, and twin boundaries in the LSP‐treated surface layer (∼55 µm thick) of single‐crystal rutile TiO 2 . Meanwhile, oxygen vacancies were introduced into TiO 2 via the LSP treatment, as evidenced by X‐ray photoelectron spectroscopy (XPS) results and the red peak shifts in Raman spectra. In addition, X‐ray diffraction scans show in‐plane compressive residual stress (−61 to −306 MPa) built in LSP‐processed TiO 2. The indentation fracture resistance ( K IFR ) of TiO 2 is enhanced from 2.8 to 6.8–8.2 . The role of compressive residual stress, oxygen vacancy, dislocations, stacking faults, and twins are discussed using atomistic simulations, semiquantitative and qualitative analyses. This study demonstrates the remarkable synergistic effects of defect networks and residual compressive stress in toughening TiO 2 and possibly other ceramic materials. Our work also qualifies the fs‐LSP as an effective and scalable method to toughen ceramic materials.