Residual stress profile in ceramic laminates

Abstract. Tape casting followed by high temperature compaction and sintering can be used for the production of ceramic laminates with a very high fracture toughness compared to their bulk counterpart. These enhanced properties can be obtained by suitable choice of the layers to be co-sintered in order to obtain a particular residual stress profile in the final com-ponent. The stress profile can be accurately measured by means of synchrotron radiation diffraction in energy-dispersive fixed-gauge-volume setup. The data for a set of alu-mina/zirconia/mullite laminates of ca. 1mm thickness, made of layers as thin as ca. 40μm are here presented and the results compared with theoretical predictions. In addition to the aver-age stress profile, diffraction allowed to establish the stress in each of the different phases constituting the layers, thus showing coupling between the grains present therein. Introduction Traditional ceramic materials usually show brittle behaviour and low toughness. Strength values are highly scattered, as they strongly depend on the presence of defects such as cracks and scratches, introduced by the manufacturing process. Therefore, as the characteristics of such defects are heavily dependent on the conditions the material has undergone, the material has very low reliability because the fracture point is far from being clearly definite [1,2]. In order to enhance the strength of such materials, a possibility is to inhibit, limit or suitably guide crack propagation. Several techniques have been proposed to achieve this goal [3,4]. The simplest one is to create a low-energy path for crack advancement by adding soft or porous layers. There is no actual increase in strength but elongation and toughness increase significantly. Also, the material shows clear signals of imminent rupture before this happens. A smarter solution is to exploit a designed residual stress profile in the material [5,6]. If a compressive residual stress is introduced near the surface, then cracks must overcome the stored elastic energy barrier in order to propagate: the same principle is used to enhance the resistance properties of glass components (tempered glass). To achieve this, the traditional material is transformed into a