Determination of Residual Stresses in Ceramic-Metal Brazed Joint using Finite Element Analysis (FEA) and Experimental Validation of the Results

Abstract

Ceramic vacuum feedthroughs are an inevitable requirement for any vacuum system which requires electrical feedlines to be inserted into the vacuum environment. These feedthroughs consist of metal-ceramic-metal transition and, therefore, require the brazing process as a joining technique. This process allows joining two base materials, i.e., Alumina and Kovar, for this case, which manifests different thermo-mechanical response. The difference between the coefficient of thermal expansion (CTE) of these materials causes the development of residual stresses during the cooling phase of the brazing process. Such residual stresses, if not addressed properly, can lead to the failure in the brazed joint even before the design limits. The purpose of this study is to assess these stresses by performing the thermo-mechanical analysis of the brazing process of ceramic-metal assembly through finite element analysis (FEA) technique. This study includes the assessment of non-linear behavior (due to temperature-dependent material properties) of Alumina and Kovar assembly. Further, X-ray diffraction (XRD) based residual stress measurement technique has been utilized to validate the FEA results. The paper shall present the FEA methodology (model, boundary condition, and results) followed by the experimental results and their comparison.