Mechanical behaviour of directionally solidified alumina/aluminium titanate ceramics

Directionally solidified eutectic ceramics of the alumina–titania system have been developed. Compositions from the alumina-rich part of the phase diagram were included in the study. The challenge was to produce materials that combine strength and flaw tolerance. A eutectic with 44 mol% TiO2 and two off-eutectics consisting of 12 and 26 mol% TiO2 were chosen for the study. The specimens exhibited a highly oriented microstructure that was aligned with the growth axis. The material with eutectic composition consisted of Al6Ti2O13/Al2TiO5 lamellae arranged in rods separated by longitudinal cracks. The materials with off-eutectic compositions consisted of alumina dendrites separated by Al6Ti2O13 matrix. Three-point bending tests and fractographic analyses revealed the high strains before failure. The eutectic rods and the alumina dendrites ensured a load-bearing capability. Cracks were arrested by the longitudinal pre-existing cracks in the eutectic composition material and were deflected at the alumina/aluminium titanate interfaces in the off-eutectic samples. This crack–crack interaction and associated change in load transfer conditions produced non-linear load–displacement curves, high failure strains and non-planar fracture surfaces.