The Fracture Toughness Enhancement of Micro-ceramic

Micro- and nano-architected ceramics offer exceptional stiffness-to-weight ratios, thermal stability, and multifunctionality, yet their widespread application remains limited by intrinsic brittleness and flaw sensitivity at small length scales. As the characteristic dimensions of ceramic components approach the micron and sub-micron regime, fracture behavior becomes increasingly governed by surface condition, residual stress, and interface architecture rather than bulk material properties alone. This thesis investigates physically grounded surface- and interface-engineering strategies to enhance fracture resistance and control deformation behavior in micro-scale ceramic systems. The thesis begins by establishing a reliable intrinsic mechanical baseline for sinterless silica fabricated via two-photon polymerization and low-temperature pyrolysis. Using nanoindentation and micropillar splitting, the elastic modulus, hardness, and fracture toughness of printed silica are quantitatively benchmarked against conventionally fabricated silica, demonstrating mechanical equivalence despite drastically reduced processing temperatures and enabling confident use of this material platform for microscale architectures. Building upon this baseline, the thesis next explores fracture toughness enhancement of micro silica through atomic layer deposition (ALD) stress engineering. By conformally coating silica micropillars with thin amorphous Al2O3 and ZnO films of controlled thickness and intrinsic stress state, the interaction between film-induced residual stress and microscale crack systems is systematically examined. The significant improvement of fracture toughness (165%) reveals that thin-film stress can be deliberately leveraged as an active design parameter to modify crack driving forces and enhance apparent fracture toughness in brittle micro-ceramics. Finally, the deformation and fracture behavior of optical ceramic nanomultilayers fabricated by physical vapor deposition (PVD) is investigated, with a particular focus on the role of aperiodicity and interface architecture. By comparing optically optimized and non-optimized multilayers composed of crystalline and amorphous ceramic constituents, this work elucidates how interface density, stress redistribution, and layer sequence govern crack propagation pathways and mechanical reliability. Together, these studies demonstrate that surface and interface engineering, through residual stress control and multilayer interface design, provides powerful, complementary strategies for overcoming the intrinsic brittleness of micro-ceramics. The insights developed in this thesis establish a mechanistic foundation for the future design of robust, coated ceramic metamaterials with tunable mechanical performance.