Design and processing of a ceramic laminate with high toughness and strong interfaces

Abstract

An alumina–aluminium titanate laminate designed to combine high crack deflection capability with strong interfaces is proposed. It is constituted by relatively stiff and brittle external layers with microcracked internal layers to produce multiple crack deflection at the microstructural scale. The most important difference of the laminated structure proposed here and that of other laminates with high capability for crack deflection is that the crack deflection process occurs at local level, thus, delamination lengths are limited and delamination does not lead to the lost of structural integrity. A symmetric structure formed by five layers has been design to minimise residual stresses taking into account the strain on cooling and the Young’s modulus of monolithic materials of the same compositions as those of the layers and fabricated using the same processing procedure as that of the laminate. Special care was given to adjust the processing variables that permitted the fabrication of the designed laminated by sequential slip casting and sintering. Mechanical characterisation has been done in terms of strength (4-points bending), dynamic Young’s modulus, work of fracture and apparent toughness. The two latter parameters have been determined by 3-points bending of Single-Edge-V-Notch-Beams (SEVNB) and fractographic analysis has been performed on the tested samples. The apparent toughness value at the point of failure (12 MPa m 1/2) was comparable to values reported for the stationary state of transformation-toughened ceramics. Work of fracture (62 ± 3 Jm −2) was significantly higher (≈26%) than that obtained by calculation from the values corresponding to monolithic materials of the same composition as that of the layers, revealing the synergic effect of the laminated structure on the mechanical behaviour of the material.