Processing optimisation and fracture behaviour of layered ceramic composites with highly compressive layers

Multilayer ceramics with five thick layers of alumina-YTZP and four thin layers of alumina-pure zirconia have been fabricated by slip casting and mechanically characterized in order to evaluate the influence of residual stresses on the fracture behaviour. In doing so, processing parameters are optimised in terms of suspension stabilization and well-dispersion of the zirconia particles within the alumina layers. Two different compressive residual stress values are attained through sequential slip casting of specimens with thick/thin layer thickness ratios of 5.4 and 9.5, by controlling the stability and casting time of aqueous slurries. Flexural tests conducted on indented monoliths and multilayered materials show a stepwise failure in the laminates associated with the bifurcation of the impinging crack when interacting with the internal layers, this phenomenon being evidenced even for the case of laminates with very thin compressive layers where edge cracking is not observed.