Strain energy distribution in ceramic-to-metal joints

This work introduces a framework for evaluating the strength characteristics of ceramic-to-metal joints with multiple interlayers. Strain energy in the ceramic is used as a strength metric instead of maximum tensile stress. Based on the FEM analysis and order of magnitude scaling (OMS), simple analytical formulations between the strain energy and material properties are developed, which provide a guideline in designing multiple interlayers. Our analysis reveals the important role of multiple interlayers, which reduce the strain energy in the ceramic, increasing the strength of the joint. Based on the proposed design rule, Si₃N₄ to Inconel 718 joints have been brazed with single, double and triple interlayers and the joint strength was evaluated using a shear test. The experimental results support the design rules and confirm that strain energy is a good strength metric.