Fracture behavior of centrifugally cast multilayer alumina/alumina composites

Abstract

Increased fracture toughness in brittle materials can be achieved by incorporating weak (porous) interfaces (1,2). These improvements have been attributed to energy absorption through crack deflection and frictional bridging along the weaker interfaces (1). While improved fracture properties are attractive for thermal and structure ceramic components, difficulties in producing a specific degree of interfacial porosity for a wide range of ceramics have limited application of this approach. Studies investigating the influence of weak interlayers in brittle composites (1–10) have examined systems ranging from tape cast multilayered composites of alternating fully dense and porous interlayers (7) to brittle plates bonded with weaker thermoplastic adhesives (8–9). During flexural loading, cracks typically deflect along the weaker interfaces, giving rise to a step-wise drop in the loaddisplacement behavior rather than a catastrophic failure typical of non-deflecting brittle materials. Residual stress distributions within layered ceramic composites can also produce similar fracture behavior, where alternating layers of tensile and compressive stress states due to thermal expansion mismatch can promote crack bifurcation (10). Advances in centrifugal consolidation of colloidal suspensions (11–14) have made the technique an attractive alternative for producing layered composites. Tailored microstructures can be achieved by incorporating suspensions that are either flocculated (11) to inhibit particle segregation or dispersed (12–14) to allow segregation due to differences in particle size and density. This paper summarizes the initial results on the fracture behavior of alumina and alumina/agglomerated alumina multilayered composites produced by centrifugal consolidation.