Bimaterial Composites via Colloidal Rolling Techniques: II, Sintering Behavior and Thermal Stresses

Shrinkage behavior and crack formation during firing have been investigated for Al2O3/Ce-TZP composites that have been fabricated by colloidal rolling and folding. These composites show improved sinterability and sinter isotropically after repeated rolling. Interface instability in rolling creates corrugated interfaces with large layer waviness; therefore, rolling can substantially alleviate the in-plane sintering constraints, which leads to improved sinterability. A loss of sintering anisotropy also is observed and is directly correlated to the microstructure instability, which is coincident with the laminate–cellular transition. Sintering cracks during heating and thermal cracks during cooling both are limited to the thick Ce-TZP layers in the composites. The critical layer thickness and the normalized crack spacing of the thermal cracks follow the predicted behavior of elasticity theory. Thus, crack-free, high-density Al2O3/Ce-TZP composites with either a laminate or cellular microstructure can be obtained, with a layer thickness of 4–60 μm, via pressureless sintering.