Double-tough and ultra-strong ceramics: leveraging multiscale toughening mechanisms through Bayesian Optimization

We present an optimization-driven approach to creating a double-tough ceramic material with a brick-and-mortar microstructure, where the mortar is itself transformation-toughened, engineered with the goal of simultaneously achieving high strength and fracture toughness levels. Specifically, we design a material where high-strength alumina bricks are interconnected via a ceria-stabilized zirconia mortar. As the design of such a material, driven by multiscale toughening mechanisms, requires a laborious trial-and-error approach, we propose a Bayesian optimization framework as an integral part of our methodology to streamline and accelerate the design process. We use a Gaussian process to emulate the material's mechanical response and implement a cost-aware batch Bayesian optimization to efficiently identify optimal design process parameters, accounting for the cost of experimentally varying them. This approach expedites the optimization of the material's mechanical properties. As a result, we develop a bio-inspired all-ceramic composite that exhibits an exceptional balance between bending strength (704 MPa), and fracture toughness (13.6 MPa m^0.5).