Fracture toughness control of gradient layered ZrC–Al2O3 ceramic composites

Fracture toughness of ZrC-Al₂O₃ composites with gradient layered structure have been studied. The outer layers were represented purely by ZrC and Al₂O₃, and the intermediate layers were represented by their composites. It is shown that a crack nucleated in the ZrC experiences deflections and bifurcations under the action of residual compressive stresses. In the case of crack nucleation in Al₂O₃ tensile microstresses create favorable conditions for its development. It was found that increasing the number of intermediate layers leads to equalization of residual microstresses, reducing the fracture toughness. Thus, there is a compromise when creating gradient composites based on components with a noticeable difference in the coefficient of thermal expansion values: increasing the number of layers provide a gradient transition from one phase to another, reduces the risk of structure defects formation. Reducing the number of layers carries the risk of delamination, but is more efficient in dissipation of crack energy.