Salvador Bueno

Flaw Tolerant Ceramic Laminates with Negligible Residual Stresses between Layers

Ceramic laminates can be designed to combine high strength with flaw tolerance. In this paper, the designing approach based on the mechanical response of residual stresses free biological layered structures is revised. The main design tools are analysed and different ceramic-ceramic systems combining stiffness, high strength and flaw tolerance with thermo-mechanical stability are described. Two main approaches have been used depending on the relative toughness of the layers and the interfaces between them. Laminates constituted by layers separated by weak interfaces, to originate crack deflection and delamination along the interface, show high thermal shock resistance but limited resistance to shear stresses and, thus, to wear. Laminates with strong interfaces that combine stiff and high strength external layers with flaw tolerant internal ones are appropriate for wear applications. In this group of materials, the combination of layers with the same phase composition and different microstructures avoids residual stresses due to thermal expansion mismatch, but the attainment of such microstructural differences implies the co-sintering of layers with large differences in the green state. The generation “in situ” during sintering of the desired microstructural differences represents an interesting alternative in terms of processing for this group of materials.

Colloidal Processing of Laminates in the System Alumina – Titania

Alumina-aluminium titanate composites present R-curve behaviour due to crack bridging. In general this behaviour is associated with very low strength due to microcracking. Laminates in which the R-curve material is located between high strength layers are one way to overcome this problem. In this work, the processing parameters to obtain laminates based on alumina-aluminium titanate from aqueous alumina and titania mixtures are described.