Design of alumina-zirconia composites with spatially tailored strength and toughness

Composites of Al₂O₃-5vol.% t-ZrO₂ (ATZ) and Al₂O₃-30vol.% m-ZrO₂ (AMZ) layers were designed with 3-1 connectivity to explore the effect of spatially-dependent residual stress and layer distribution on mechanical behavior. ATZ composites with 'shallow' and 'deep' regions of AMZ, defined relative to the distance from the surface, were fabricated. Four-point bending tests on indented 3-1 composites showed crack arrest in the first compressive AMZ layer and a fracture strength nearly independent of indent size (i.e. minimum strength); the failure occurring in the region with thicker outer ATZ layers ('deep' region). Region dependent crack growth resistance was measured on SEVNB specimens and compared to theoretical predictions using a fracture mechanics model. Spatially tailored constant strengths were obtained, ranging between 148MPa and 470MPa; the maximum value corresponding to a 'shallow' region with a relatively thicker AMZ compressive layer embedded close to the tensile ATZ surface. The 3-1 design concept allows the fabrication of 'deep' and 'shallow' embedded regions within a unique composite architecture, thus providing a preferential path for crack propagation, opening new possibilities for design of composite structures with spatially-tailored crack growth resistance.