THE OPTIMAL SELECTION OF INSERT METALS IN CERAMIC-METAL BONDING

In ceramic-metal joints, how to select the interlayer materials is a very important problem. Two main conditions should be satisfied for an optimal insert metal: high diffusivity and reactivity to ceramic to get enough strength of interface, and the reduction of residual stresses resulting from the thermal expansion dismatch. In this paper, thermal elastic-plastic FEM is used to analyze the residual stress in Si3N4-1Cr18Ni9Ti diffusion bonding. The research shows the effects of the joints' type, property and thickness of insert metals on the reduction of residual stresses. It can be concluded that the maximum tensile stress in ceramic usually occurs just on the cylindrical surface near the interface, which is the fatal damage to ceramics. Two kinds of interlayers, the soft metal and low expansion metal with certain thickness, can be employed to reduce the maximum stress. Calculation shows the composite interlayer by both above metals is the proper insert material, the maximum tensile stress in ceramics can be reduced to minimum, and the bending test demonstrates that the strength of Si3N4-lCrl8Ni9Ti joint with the optimal composite interlayer is over 260 MPa.