Fractography and Fracture Analysis on Ceramics/Metal Joint.

Four point bending tests for Si3N4/steel joints were conducted and their fracture surfaces were examined by advanced fractographic method. Based on these results, the fracture mechanism was discussed by the fracture mechanics approach.The crack initiates at the ceramics/adhesive interface. A part of crack front is arrested at the microcrack in the ceramics side of the interface. Another part of the crack front grows along the interface. Then, the stress intensity factor, K, at the arrested crack front increases as the profile of the whole crack front becomes like a Chevron notch. The unstable fracture occurs when K at the arrested crack front reaches KIC for ceramics.