Flexure Strength, Fracture Toughness, and Slow Crack Growth of YSZ/Alumina Composites at High Temperatures

Flexure strength and fracture toughness of zirconia–alumina composites, fabricated by hot pressing 10 mol% yttria‐stabilized zirconia (10‐YSZ) reinforced with 0–30 mol% alumina particulates or platelets, were determined as a function of alumina content at 1000°C in air. Both strength and fracture toughness of the two composite systems increased with increasing alumina content. For a given alumina content, flexure strength of the particulate composites was greater than that of the platelet composites at higher alumina contents (≥20 mol%); whereas, fracture toughness of the platelet composites was greater than that of the particulate counterparts, regardless of the alumina content. The susceptibility to slow crack growth (SCG), determined at 1000°C via constant stress‐rate testing, was greatest for 30 mol% particulate composite with SCG parameter n =5–8 and was least for 30 mol% platelet composite with n =33. Elastic modulus of both composite systems decreased below 400°C and then remained almost unchanged up to 1000°C, forming a unique transition around 400°C, irrespective of alumina content.