Crack healing, reopening and thermal expansion behavior of Al2TiO5 ceramics at high temperature

Thermal expansion behavior and its correlation with microstructure of ZAT (ZrTiO4–Al2TiO5) composites were investigated. Thermal expansion coefficient increased from 0.05 [mm/(mm°C) × 106] at room temperature to 1.6 [mm/(mm°C) × 106] at 1100 °C. The low thermal expansion of Al2TiO5 ceramics is apparently due to a combination of grain boundary micro-cracking caused by the large thermal expansion anisotropy of the crystal axes of the Al2TiO5 phase. During the reheating run, the individual crystallites expanded at low temperature; thus, the solid volume of the specimen expanded into the micro-cracks, whereas the macroscopic dimensions remained almost unchanged. As a result, the material expanded very little up to 1000 °C. The micro-cracks closed at higher temperatures. This result is closely related to relatively steeper thermal expansion curves.