Temperature dependence of flexural strength and residual stress of Al2O3 reinforced by kyanite coating

A pre-stressing design has been developed for strengthening Al2O3 components by using low-shrinkage kyanite as the coating on green body. Immersions followed by pressureless sintering were employed to fabricate the kyanite-Al2O3 pre-stressed ceramics (marked as KcAs) successfully. Temperature dependence of the flexural strength and residual stress of KcAs were investigated. Experimental results show that the flexural strength and the thermal shock resistance of KcAs were greatly enhanced at room temperature. In the range from room temperature to 1000 degrees C, the residual stress and the strength difference between coated and uncoated Al2O3 ceramics decreased with the increasing temperature. As the testing temperature reached and exceed 1000 degrees C, the pre-stressed Al2O3 and the common Al2O3 possessed approximately equal flexural strength, because the residual stress vanished entirely. Therefore, a zero-stress temperature (T-zero) was defined at which the residual stress in the coating is near zero, and it is 1000 degrees C for pre-stressed Al2O3 ceramics in this work.