Study on optimum thickness of interlayer in ceramic/metal joints

摘要

A major problem in ceramic/metal joint is thermal expansion coefficient mismatch between ceramics and metal. This thermal expansion coefficient mismatch causes serious residual stresses at the interface of the ceramic/metal joint, which generated during joint-cooling process. Then, an interlayer, which is ductile metal such as copper, nickel and so on, is inserted between ceramics and metal because of relaxing the residual stress. It should be considered that thickness of interlayer have significant influence on the joint strength with considering the residual stress. In this study, it paid attention to the thickness of interlayer, and the optimum thickness of interlayer was discussed from a viewpoint of the stresses based on simulation model analysis as well as 4 point bending tests, considering the residual stresses, which were analyzed using three-dimensional plasto-elastic finite element method. As a result of the analysis, residual stress increased with decreasing of the interlayer thickness. The superposing stress of the applied bending stress and the residual stress showed minimum value in the case of the interlayer thickness of 0.2mm. On the other hand, paying notice to the result of the bending test as well as the analysis, the joint specimen showed the highest bending strength in the case of the interlayer thickness of 0.2mm. Furthermore, the scatter of joint strength is apparently small in this thickness compared with in the other thickness.