Temperature Dependence of Fatigue Behavior of Aluminum Titanate Ceramics

Aluminum titanate (Al2TiO5: AT) ceramics have been recently applied as refractories in Al alloy casting systems, because they have excellent thermal shock resistance and corrosion resistance to molten Al alloys. The AT ceramics contain many microcracks at grain boundaries as a result of the large thermal expansion anisotropy during cooling after sintering. In this study, cyclic and static fatigue of the AT ceramics was investigated at actual casting operating temperatures (R. T. -700°C) and the fatigue life related to the morphological change of the microcracks. At R. T., the microcracks around the main crack tip are thought to propagate according to crack resisting-reactivating and wedging-microcracking mechanisms. When the microcracks were closed at 300°C due to the thermal expansion of each AT grain, grain bridging degradation occurs predominantly instead of above mechanisms. In contrast, at the temperature of 700°C that AT grains are bonded together via glassy phase added as a sintered aid, microcracks underwent repeated initiation and self-healing via a glassy phase segregated at the grain boundaries.