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 degrees 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 degrees 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 degrees C and then remained almost unchanged up to 1000 degrees C, forming a unique transition around 400 degrees C, irrespective of alumina content.