Mechanical behaviors of Si3N4-SiC/Si3N4-Si3N4 layered composites

The present study involves the fabrication of three-layered ceramics with an interior layer of SiC/Si3N4 which has a greater thermal expansion coefficient than the two enter surface layers formed of monolithic Si3N4. Surface compressive stress develops upon cooling owing to the higher thermal expansion coefficient of the inner layer. The bending strength and toughness of layered Si3N4 composites are substantially greater than those of monolithic Si3N4 because of the surface compressive stress on the outer layer and crack deflection by the interfaces. The residual stress increases with the addition of SiC in the inner layer and with the inner layer thickness. Crack behavior in layered samples is affected by the residual stresses, interfaces and free sample surfaces. Theoretical stress calculated based on beam theory is compared with the experimentally determined residual stress.